New Square-Pyramidal Oxovanadium (IV) Complexes Derived from Polydentate Ligand (L¹)

New series of oxovanadium (IV) complexes isolated from 2,4,6-tris-(2-pyridyl)-1,3,5-triazine (L ¹) are incorporated and portrayed using spectroscopic (IR, UV-Vis, ESR, mass spectrometric), magnetic moment, thermal and cyclic voltammetry measurements. The results demonstrate that L ¹ acts in various styles of chelation with [V ₃O ₃(L ¹)(SO ₄) ₃(EtOH) _1/2(H ₂O) _3/2] 1), [VO(L ¹)(2,4-pentadionate)]·Cl·4HCl 2), [V ₂O ₂(L ¹)(SO ₄) ₂(EtOH) _5/2] 3), [V ₂O ₂(L ¹)(SO ₄) ₂(EtOH) _3/2(H ₂O) _1/2] 4), [VO(L ¹)SO ₄ (H ₂O) _3/2]·2.5H ₂O 5) and [V ₂O ₂(L ¹)(SO ₄) ₂(H ₂O)]·H ₂O 6). The values of magnetic moments and spectral studies suggest a square-pyramidal geometry around the V (IV) ion for all complexes. The molar conductance values suggest that the complexes are non-electrolyte, except the [VO(L ¹) (2,4-pentadionate)] Cl·4HCl. Molecular modeling calculates the bond length, bond angle, chemical reactivity, energy components (Kcal/mol) and binding energy (Kcal/mol) for the isolated complexes. The in vitro antibacterial studies of these complexes screened against pathogenic bacteria prove them as growth inhibiting agents. Antitumor activity is carried out in vitro on human mammary gland (breast) MCF-7 and cervical cancer cell-HeLa has shown that [VO(L ¹)SO ₄(H ₂O) _3/2]·2.5 H ₂O and [VO(L ¹)(2,4-pentadionate)] Cl·4HCl complexes display the highest powerful activity between all of the investigated complexes.

• Oxovanadium (IV) Complexes
• Antimicrobial Activity
• Cytotoxic Activity
• Breast Cancer

1. Introduction

Vanadium complexes have various biological activities, for example, an insulin-like activity [1] - [2] and the decrease of hyperlipidemia and hypertension. Vanadium has a decent therapeutic potential, moreover, dietary organization restrains synthetically actuated mammary carcinogenesis [3] . Likewise, it is found that concentrations of vanadium, evaluated by X-ray energy fluorescence are observed to be fundamentally higher in malignant bosom tissue contrasted with typical bosom tissue [4] . The complexes of L¹ are utilized in various applications like luminescent materials [5] , electrocatalytical [6] , photocatalytic reactions, biocatalytic activity as antitumor agents [7] and as a catalyst [8] [9] . Additionally, they have been utilized for the formation of coordination polymers and networks [9] . Metal complexes have risen as viable alternatives to organic molecules as therapeutic agents in the course of recent decades [10] - [13] . Our goal in this paper is to synthesize and characterize six V⁴⁺ complexes by (IR, UV-vis, mass and ESR), magnetic and thermal measurements. The outcomes propose that L¹ coordinates in different ways in all complexes through one nitrogen of triazine and nitrogen atoms of pyridine. The DFT outcomes are discussed and the biological studies of the V⁴⁺ complexes show promising affect against breast and ovarian cancer.

2. Experimental

2.1. Materials and Methods

All materials and solvents were purchased from BDH and Aldrich quality and used without purification. VOSO₄・3H₂O was of Aldrich quality and used without purification. Carbon, hydrogen, nitrogen, sulphate and chloride were determined by the standard methods [14] .

2.2. Instruments

IR spectra (400 - 4000 cm⁻¹) using KBr discs and/or Nujolmull were recorded with a Mattson 5000 FTIR spectrophotometer. Electronic spectra were recorded using Unicam UV-visible UV2 and V-100 spectrophotometers. The magnetic measurements were carried out at room temperature (25˚C) using a Sherwood magnetic balance. Diamagnetic corrections were calculated using Pascal’s constants [15] . The mass spectra of the complexes were recorded using a direct inlet unit (DI-50) of a Shimadzu GC/MS-QP5050A mass spectrometer at the Regional Center for Mycology and Biotechnology at Al-Azhar University. Thermogravimetric analysis (TGA) was carried out in the range 20˚C - 1000˚C with a Shimadzu TGA-50 analyser at a heating rate of 15˚C min⁻¹ and nitrogen flow rate of 20 mL・min⁻¹. A powder ESR spectrum was obtained in a 2 mm quartz capillary at room temperature with a Bruker EMX spectrometer working in the X-band (9.43 GHz) with 100 KHz modulation frequency. The results were analyzed after compensating the residual current at the corresponding condition. The electrochemical cell used as conventional three electrode type saturated calomel electrode (SCE) as a reference electrode and Pt wire and glass carbon as auxiliary and working electrode. 0.1 M tetrabutylammonium perchlorate (TBAP) as electrolyte. A scan rate of 50 mV・s⁻¹ was employed.

2.3. Synthesis of Metal Complexes

2.3.1. Synthesis of [V 3 O 3 (L 1 )(SO 4 ) 3 (EtOH) 1/2 (H 2 O) 3/2 ] (1)

The complex was prepared by adding 1 mmol, 0.31 g of 2,4,6-tri-(2-pyridyl)-1,3,5-triazine (L¹); dissolved in a mixture of dist. H₂O and hot EtOH (9:1) to VOSO₄・3H₂O (2 mmol, 0.44 g) dissolved in 100 ml H₂O. The reaction mixture was refluxed on a hot plate for 2 hrs. The complex was isolated in the pH range 5 - 6. The complex was filtered off, washed successfully with EtOH and diethyl ether, respectively and finally dried in a desiccator over CaCl₂. The isolated product is in color. The chemical formula of the green V (IV) complex, [V₃O₃(L¹) (SO₄)₃(EtOH)_1/2(H₂O)_3/2], is Anal. Found: C, 29.6; H, 2.9; N, 10.2%. Calcd: for C₁₉H₁₈N₆S₃O₁₇V₃: C, 26.8; H, 2.1; N, 9.9%; m.p.; >300˚C; Yield: 60%. The powder IR (KBr, cm⁻¹): 3222 - 3447(OH), 3081 (CH) aromatic, 1486 - 1228 (C-N+C-C), 1550, 1575, 1604, 1651 (C=C+C=N) coordinated, 1685 (C=N+C=N) uncoordinated, 768 (C-H) deformation, 424 (V-N) py, 452 (V-N) triaz, 515 (V-O). MS (70 eV) m/z (%): 852 (M, 1.12), 312 (5), 234 (16), 180 (64), 104 (68), 91 (16), 77 (45), 67 (41), 51(100).

2.3.2. Synthesis of [VO(L 1 )(2,4-Pentadionate)]・Cl・4HCl (2)

The complex was prepared by adding anEtOH solution of L¹; 1 mmol, 0.31 g), and V (IV) oxide bis (2,4-pen- tanedionate) (1 mmol, 0.27 g) dissolved in hot EtOH. The reaction mixtures were refluxed on a hot plate for 2 hrs. The pH of the solution was 5 - 6. On adding few drops of conc. HCl the complex was precipitated in the pH range 2 - 3. The isolated product is brick red in color. Yield 80%; m.p. >300˚C. IR (KBr, cm⁻¹): 3433 - 3478 (OH), 3077 (CH) aromatic, 1485-1223 (C-N+C-C), 1555, 1576 (C=C+C=N) coordinated, 1671 (C=N+C=N) uncoordinated, 787 (C-H) deformation, 424 (V-N)py, 442 (V-N)triaz, 550 (V-O). MS (70 eV) m/z (%): 659 (M, 1.2), 517 (68), 447 (18), 432 (19), 392 (70), 312 (100), 104 (45), 78 (26), (64) (25), (52) (26). Anal. Calcd for C₂₃H₂₃N₆O₃Cl₅V (659.7): C: 41.9; H: 3.5; Cl: 26.9%. Found: C: 42.6; H: 2.9; Cl: 26.4%.

2.3.3. Synthesis of [V 2 O 2 (L 1 )(SO 4 ) 2 (EtOH) 5/2 ] (3) and [V 2 O 2 (L 1 )(SO 4 ) 2 (EtOH) 3/2 (H 2 O) 1/2 ] (4)

The complex was synthesized by adding 1 mmol, (0.31 g) of L¹ dissolved in dist. water and hot EtOH with ratio (1:9) to VOSO₄ solution (2 mmol, 0.44 g) dissolved in 100 ml redistilled water H₂O. The reaction mixture was refluxed on a hot plate for 2 h. The complex was isolated in the pH range 5 - 6. Yield 50%; green powder; m.p. >300˚C. IR (KBr, cm⁻¹): 3403 - 3445 (OH), 3078 (CH) aromatic, 1478 - 1262 (C-N+C-C), 1603, 1575, 1562, 1542 (C=C+C=N) coordinated, 1686, 1653 (C=N+C=N) uncoordinated, 767 (C-H) deformation, 425, 445 (V-N) pyr, 474, 489 (V-N) triaz, 547, 577 (V-O). MS (70 eV) m/z (%): 753.6 (M, 8.6), 682 (13), 604 (11), 417 (10), 363 (8), 315 (6), 234 (20), 185 (14), 155 (13), 104 (14), 91 (9), 78 (35), 64 (17), 53 (100). Anal. Calcd for C₂₃H₂₇N₆O_25/2S₂V₂ (753.5): C: 36.7; H: 3.6; N: 11.1%. Found: C: 37.7; H: 2.6; N: 10.2 % and µ_eff (3.01 BM). [V₂O₂(L¹)(SO₄)₂(EtOH)_3/2(H₂O)_1/2] (4) was obtained from the filtrate after cooling. Yield 50%; green powder; m.p. >300˚C. IR (KBr, cm⁻¹): 3269 - 3449 (OH), 3042 (CH) aromatic, 1401 - 1249 (C-N+C-C), 1653, 1588 (C=C+C=N) coordinated, 1683 (C=N+C=N) uncoordinated, 767 (C-H) deformation, 427 (V-N) pyr, 453 (V-N) triaz, 514 (V-O). MS (70 eV) m/z (%): 714 (M-2H, 7.9), 622 (13), 311 (6), 232 (8), 183 (29), 155 (18), 104 (71), 91 (93), 77 (81), 51 (100). Anal. Calcd for C₂₁H₂₂N₆O₁₂S₂V₂(716.44): C: 35.2; H: 3.1; N: 11.7 %. Found: C: 34.8; H: 3; N: 11.2% and µ_eff (2.66 BM).

2.3.4. Synthesis of [VO(L 1 )SO 4 (H 2 O) 3/2 ]・2.5H 2 O (5) and [V 2 O 2 (L 1 )(SO 4 ) 2 (H 2 O)]・H 2 O (6)

[VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O (5) and [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O(6) were synthesized with different molar ratios 1:1 and 2:1 (M:L), respectively. A hot EtOH solution of L¹ (0.312 g; 1.0 mmol) was added to VOSO₄・3H₂O dissolved in hot EtOH (0.22 g, 0.44 g; 1.0 mmol and 2.0 mmol for 1:1 and 2:1, respectively). The reaction mixtures were refluxed on a hot plate for 2 h. All complexes were filtered off, washed several times with hot EtOH, dried in an oven at 120˚C for 0.5 h and finally kept in a desiccator over CaCl₂. [VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O (5): yield 58%; color brown powder; m.p. >300˚C. IR (KBr, cm⁻¹): 3387(OH), 3069 (CH) aromatic, 1489 - 1215 (C-N+C-C), 1642 (C=C+C=N) coordinated, 1548 (C=N+C=N) uncoordinated, 775 (C-H) deformation, 434 (V-N)pyr, 486 (V-N)triaz, 528 (V-O). MS (70 eV) m/z (%): 547.6 (M, 4.6), 461 (1.83), 360 (5.7), 312 (62), 156 (7), 104 (73), 78 (53), 52 (100). Anal. Calcd for C₁₈H₂₀N₆SO₉V (547.39): C: 39.5; H: 3.7; N: 15.35; SO₄: 17.6 %. Found: C: 39.1; H: 3.1; N: 15.02; SO₄: 17.8 % and µ_eff (2.7 BM). [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O (6): yield 51%; color brown powder; m.p. >300˚C. IR (KBr, cm⁻¹): 3384(OH), 3071 (CH) aromatic, 1489 - 1216 (C-N+C-C), 1642 (C=N+C=N) coordinated, 1548 (C=N+C=N) uncoordinated, 777 (C-H) deformation, 441 (V-N)pyr, 485 (V-N)triaz, 606 (V-O). MS (70 eV) m/z (%): 672.35 (-2M, 3), 651 (4), 414 (5), 360 (4), 312 (97), 156 (5), 130 (6), 105 (100), 78 (32), 52 (28). Anal. Calcd. for C₁₈H₁₆N₆S₂O₁₂V₂ (674.36): C: 32.1; H: 2.4; N: 12.5; SO₄: 28.5%. Found: C: 32.5; H: 2.8; N: 12.4; SO₄: 29.3% and µ_eff (2.8 BM).

2.4. Biological Activity

2.4.1. In Vitro Anticancer Activity

The antitumor assays were performed utilizing the accompanying two cell lines: MCF-7 (Michigan Cancer Foundation-7) and Epitheliod carcinoma cervix cancer (Hela). The cell line of MCF-7 was acquired from the American Type Culture Collection (ATCC, Rockville, MD). The cells were developed onRPMI-1640 medium supplemented with 10% inactivated fetal calf serum and 50 mg/ml gentamycin. The cells were kept up at 37˚C in humidified atmosphere with 5% CO₂ and were sub-refined a few times each week.

The antitumor activity was assessed on carcinoma cell lines at the Regional center for Mycology and Biotechnology at Al-Azhar University, Egypt. Quickly, the cell lines were developed as monolayers in growth medium supplemented with 10% inactivated fetal calf serum and 50 mg/ml gentamycin. The monolayers of 10.000 cells followed at the bottom of the wells in a 96-well microtiter plate (Falcon. NJ. USA) brooded for 24 h at 37˚C in a humidified incubator with 5% CO₂. The monolayers were then washed with sterile phosphate buffered saline (0.01 M pH 7.2) and at the same time the cells were treated with 100 mL from various dilutions of tested compound in fresh maintenance medium and brooded at 37˚C. A control of untreated cells was made without the tried compound. Three wells were utilized for every concentration of the test sample. The observation under the inverted microscope was made each 24 h. The staining so as to survive quantity cells was controlled the cells with precious stone violet took after by cell lysing utilizing 33% glacial acetic acid and read the absorbance at 590 nm utilizing ELISA reader after well mixing. The absorbance values from untreated cells were considered as 100% expansion and the rate of feasibility was ascertained as [1-(ODt/ODc)] × 100% where ODt is the mean optical density of wells treated with the tried compounds and ODc is the mean optical density of untreated cells [16] - [18] .

The cell line of Epitheliod carcinoma cervix cancer (Hela) was gotten from ATCC via Holding company for biological products and vaccines (VACSERA), Cairo, Egypt. 5-fluorouracil was utilized as a standard anticancer drug for comparison. The cell line was utilized to focus the inhibitory impacts of compounds on cell development utilizing the MTT assay. The colorimetric assay is basically depending on the transformation of the yellow tetrazolium bromide (MTT) to a purple form azan derivative by mitochondrial succinate dehydrogenase in various cells. Hela cells were cultured in RPMI-1640 medium with 10% fetal bovine serum. Antibiotics added were 100 units/ml penicillin and 100 µg/ml streptomycin at 37˚C in a 5% CO₂ incubator. The cell line was seeds in a 96-well plate at a density of 1.0 × 10⁴ cells/well at 37˚C for 48 h under 5% CO₂. After brooding the cells were tested with different concentration of compounds and incubated for 24 h. After 24 h of drug treatment, 20 µl of MTT solution at 5 mg/ml was added and incubated for 4 h. DMSO in volume of 100 µL is added into each well to dissolve the purple formazan formed. The colorimetric assay is measured and recorded at absorbance of 570 nm utilizing a plate reader (EXL 800). The relative cell viability in percentage was computed as (A570 of treated samples/A570 of untreated sample) X 100 [16] [19] - [20] .

2.4.2. Antibacterial Activities

The in vitro assessment of antibacterial activity was researched against three bacterial strains, Gram-positive (Staphylococcus aureus), Gram-negative (Escherichia coli) bacterial and Candida Albicans. The bacterial species were developed in nutrient broth at 37˚C for 24 hrs [21] .

Chemical compounds were individually tried against a panel of Gram-positive (Staphylococcus aureus), Gram-negative (Escherichia coli) bacteria and Candida albicans. Every of the compounds was dissolved in DMSO and solution of the concentration 1 mg/ml were prepared separately paper discs of whatman filter paper were prepared with standard size (5 cm) were cut and sterilized in an autoclave. The paper discs soaked in the desired concentration of the complex solution were places aseptically in the Petri dishes containing nutrient agar media (peptone 5 g + agar 20 g + beef extract 3 g) seeded with Staphylococcus aureus, E. coli and Candida albicans. The Petri dishes were incubated at 36˚C and the inhibition zones were recorded after 24 hrs of incubation. Every treatment was replicated three times. The antibacterial activity of a common standard Antifungal Colitrimazole and antibiotic ampicillin was also recorded utilizing the same procedure as above at the same solvents and concentration.

2.5. Solution Studies

Stock solutions (1 × 10⁻² M) of L¹ and VOSO₄・3H₂O were prepared by dissolving the calculated accurate weights of L¹ and VOSO₄・3H₂O in absolute EtOH and dist. H₂O, respectively then completed to the mark (50 ml). In continuous variation (CV) study, a series of 10 ml solutions was prepared by mixing solutions of V⁴⁺ and L¹ solutions in different ratios keeping the total molar concentration constant as 6 × 10⁻³ M and the absorbance at 604 nm was recorded. For molar ratio method (MR), series of 10 ml solutions was prepared in which the V⁴⁺ ion concentration was kept constant at 2.5 × 10⁻³ M while that of L¹ was regularly varied. The absorption spectra were recorded and the absorbance at 604 nm.

3. Results and Discussion

3.1. Physical Properties and Elemental Analyses

L¹ coordinates to the V⁴⁺ ions in different styles like mononuclear (1:1), binuclear (2:1) and tri-nuclear (3:1) (M:L) in bidentate and tridentate manner. The metal complexes are non-hygroscopic (stable at room temperature) and are in the form of amorphous solids, except [VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O and [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O, but unfortunately crystals suitable for X-ray measurements were not available. Complex (2) is soluble in water and common organic solvents as DMF, DMSO and water. The structures of the complexes are established by elemental analyses and confirmed by weight loss determination. The values of molar conductivity of all complexes indicate that [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2], [V₂O₂(L¹)(SO₄)₂(EtOH)_5/2], [V₂O₂(L¹)(SO₄)₂(EtOH)_3/2 (H₂O)_1/2], [VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O and [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O are non-electrolytic nature, while [VO (L¹)(2,4-pentadionate)] Cl・4HCl has electrolytic nature [22] .

3.2. Infrared Spectra

The comparative IR spectra of the ligand and oxovanadium (IV) complexes indicate about the binding behavior of the ligand with metal ion. So, in comparing the IR of the L¹ (Figure S1) with its complexes (Figure S2-S6), we find that the IR spectrum of the [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2](Figure 1) shows four bands at 1550, 1575, 1601 and 1651 cm⁻¹ which are shifted to lower wave numbers and are attributed to the coordinated ѵ(C=N + C=C) [23] [24] , which indicate that L¹ coordinates as bidentate via all the active group in pyridine and triazine rings with three vanadium atoms. The square pyramidal geometry around V⁴⁺ is completed by water, EtOH and sulphate which have characteristics bands appeared in the spectrum. The spectrum also shows broad bands in the 3222 - 3447 cm⁻¹ region together with a band at 1604 cm⁻¹ region assigned to ѵ(OH) and ∂(OH) vibrations of H₂O molecule, respectively. Existence of strong band at 976 cm⁻¹ is strong evidence for the coordination of vanadium ion with L¹ as it is characterized for V=O vibration in VO²⁺ [25] . In addition, new bands are observed at 424 and 452 cm⁻¹ which are assigned to V-N bonds of pyridine and triazine, respectively, and at 515 and 592 cm⁻¹ which are assigned to V-O bond [26] . Also, new bands at 424, 625, 978, 1033 cm⁻¹ are assigned to coordinated group and the position of these bands indicates the participation of the in a unidentatemanner as a result, the complex is nonelectrolyte.

The IR spectrum of the [VO(L¹)(2,4-pentadionate)] Cl・4HCl (Figure S2) estimates bands, which are shifted to lower wave numbers and are observed at 1634 and 1576 cm⁻¹ and are referred to the bands of the coordinated ѵ(C=N +C=C) for triazine and pyridine, respectively indicating the involvement of C=N in coordination to the metal ion [23] [24] as well as new bands at 424 and 442 cm⁻¹ which are assigned to V-N bonds of pyridine and triazine, respectively, and a band at 550 cm⁻¹ which is assigned to V-O vibration [26] .

IR spectrum of [V₂O₂(L¹)(SO₄)₂(EtOH)_5/2] (Figure S3) shows bands at 1603, 1575, 1562 and 1542 cm⁻¹ are referred to the bands of the coordinated ѵ(C=N + C=C) [23] [24] , in addition, a broad band in the 3403 - 3445 cm⁻¹ region together with a band at 1603 cm⁻¹ region assigns to ѵ(OH) and ∂(OH) vibrations of coordinated EtOH molecules, respectively and coincides with the results of the thermal analyses which suggest that EtOH molecules reside inside the coordination sphere. Moreover, the band in the 3031 - 3078 cm⁻¹ region is assigned to the aromatic ѵ(C-H) vibration of L¹ in the complex. The bands observed in the 1478 - 1262 cm⁻¹ region are assigned to (C-N+C-C) while the band at 767 cm⁻¹ is assigned to the aromatic C-H deformation vibration. A vanadyl complex shows a band at 978 cm⁻¹ which may be attributed to the ѵ(V=O) vibration of VO²⁺ [25] . New bands are

Figure 1

IR spectrum of the [V 3 O 3 (L 1 )(SO 4 ) 3 (EtOH) 1/2 (H 2 O) 3/2 ] complex

observed at 425, 445 (V-N)pyr, 474, 489 (V-N) triaz, 547, 577 (V-O) cm⁻¹ [26] . Also, new bands are observed at 425, 629, 956 and 1032 cm⁻¹ which are assigned to coordinated group and the position of bands are assigned to that group bonded as unidentate ligand which is in agreement with the conductivity measurements.

IR spectrum of the [V₂O₂(L¹)(SO₄)₂(EtOH)_3/2(H₂O)_1/2] (Figure S4) shows bands at 1653 and 1588 cm⁻¹ arecharacterized to coordinated ѵ(C=N+C=C) [23] [24] . Presence of H₂O and EtOH is proved by existence ofa broad band in the 3305 - 3449 cm⁻¹ region together with a band at 1610 cm⁻¹ region assigned to ѵ(OH) and ∂(OH) vibrations of H₂O molecule, respectively. Peaks revealing the presence of L¹ in the complex centered at 3042 cm⁻¹ (aromatic C-H stretching vibration). New bands are observed at 427 (V-N)py, 453 (V-N)triaz, 514 (V-O) cm⁻¹ [26] . Additionally, thevanadyl complex shows a strong band at 984 cm⁻¹ which may be attributed to the ѵ(V=O)vibration of VO²⁺ [25] . Also, the bands at 427, 653, 978, 1033 cm⁻¹ are assigned to coordinated group and the position of bands assigned to that group bonded as unidentate ligand.

The IR spectrum of [VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O (Figure S5) shows bands at 1642 and 1548 cm⁻¹ are referred to the bands of the coordinated ѵ(C=N+C=C) and the uncoordinated (C=N+C=C) band, respectively [23] [24] . Appearance of a broad band in the 3387 cm⁻¹ region together with a band at 1621 cm⁻¹ region assigned to ѵ(OH) and ∂(OH) vibrations of H₂O molecule, respectively, which suggest existence of H₂O molecules inside and outside the coordination sphere. The H₂O molecules inside the sphere is bonded with nitrogen atom by hydrogen bond so it proves the high shift of the band at 3387 cm⁻¹ and the remain molecules are solvation outside the sphere. The results of thermal analyses confirmed this observation. New bands are observed at 434 and 486 cm⁻¹ assigned to V-N bonds of pyridine and triazine, respectively. The band at 528 cm⁻¹ assigned to V-O vibration [26] . The oxovanadium complex shows a strong band at 971 cm⁻¹ attributed to the high π-band order of vanadium to oxygen link of VO²⁺ [25] . The bands are observed at 434, 613, 971, 1032 cm⁻¹ are assigned to the coordinated group and the position of bands assigned to that group bonded inunidentatemanner. The conductivity measurements supported this observation where the complex is nonelectrolyte.

The IR spectrum of [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O (Figure S6) shows two bands at 1642 and 1548 cm⁻¹ assigned to the coordinated (C=N+C=C) [23] [24] . Also, it shows a broad band at 3384 cm⁻¹ together with a band at 1619 cm⁻¹ assigned to ѵ(OH) and ∂(OH) vibrations of H₂O molecule, respectively which present inside and outside the coordination sphere. Moreover, the band at 3071 cm⁻¹ is assigned to the aromatic ѵ(C-H) vibrations of L¹. The bands observed in the 1489 - 1216 cm⁻¹ region are assigned to (C-N+C-C) while the band at 777 cm⁻¹ region is attributed to the aromatic C-H deformation vibrations. New bands are observed at 441 and 485 cm⁻¹ which, are assigned to V-N bonds of pyridine and triazine, respectively, and at 606 cm⁻¹ which, is assigned to V-O bond [26] . Appearance of strong band at 976 cm⁻¹ is characterized for V=O vibration in VO²⁺ [25] . New bands appear at 441, 606, 971, 1033 cm⁻¹ are assigned to coordinated group and the position of bands assigned to that group bonded as unidentate ligand and it matches with the conductivity measurement as the complex is nonelectrolyte.

3.3. Mass Spectra

Mass spectra of the complexes have molecular ion peaks that are in agreement with their formulae. As we observed in all the complexes, there are two pathways. Depending on the thermodynamic basics, the pathway must be till the thermodynamically butadiene radical [27] .

The mass spectrum of [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2], shows a fragmentation pattern corresponding to the successive degradation of the complex, shows the molecular ion peak [m/z] at 852.3 with abundance 1.47% and coincides with the theoretical value (851.4) as shown in Figure 2. This suggests that the proposed structure for the complex is correct and has the chemical formula; C₁₉H₁₈N₆S₃O₁₇V₃. The fragmentation pattern of the V⁴⁺ complex (1:3) is shown in Scheme 1. The mass spectrum of [VO(L¹)(2,4-pentadionate)] Cl・4HCl, shows the molecular ion peak [m/z] at 659.2 with abundance 1.16% and coincides with the theoretical value (659.7) as shown in (Figure S7). The fragmentation pattern of the complex is shown in (Figure S8). This suggests that the proposed structure for the complex is correct and has the chemical formula, C₂₃H₂₂N₆O₃Cl₅V. The mass spectrum of [V₂O₂(L¹)(SO₄)₂(EtOH)_5/2], shows the molecular ion peak [m/z] at 753.6 with abundance 8.6% and coincides with the theoretical value (753.501) as shown in (Figure S9). The fragmentation pattern of the complex is shown in (Figure S10). This suggests that the proposed structure for the complex is correct and has the chemical formula, C₂₃H₂₇N₆O_25/2S₂V₂. The mass spectrum of [V₂O₂(L¹)(SO₄)₂(EtOH)_3/2(H₂O)_1/2], shows the molecular ion peak [m/z] at 714 with abundance 7.9% and coincides with the theoretical value (716.44) as

Figure 2

Mass spectrum of [V 3 O 3 (L 1 )(SO 4 ) 3 (EtOH) 1/2 (H 2 O) 3/2 ] complex

Scheme 1. Fragmentation pattern of [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2] complex.

shown in (Figure S11). The fragmentation pattern of the complex is shown in (Figure S12). This suggests that the proposed structure for the complex is correct and has the chemical formula, C₂₁H₂₂N₆O₁₂S₂V₂. The mass spectrum of the V⁴⁺ complex (1:1), [VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O, at 120˚C shows the molecular ion peak [m/z] at 547.6 and coincides with the theoretical value (547.39) as shown in (Figure S13). This suggests that the proposed structure for the complex is correct and has the chemical formula; C₁₈H₂₀N₆SO₉V. The fragmentation pattern of the V⁴⁺ complex (1:1) is shown in (Figure S14). The mass spectrum of the V⁴⁺ complex (1:2), [V₂O₂(L¹) (SO₄)₂(H₂O)]・H₂O, shows the molecular ion peak [m/z] at 672.35 and coincides with the theoretical value (674.36) as shown in (Figure S15). The fragmentation pattern of the V⁴⁺ complex (1:2) is shown in (Figure S16). This suggests that the proposed structure for the complex is correct and has the chemical formula, C₁₈H₁₆N₆S₂O₁₂V₂. Also, the results of elemental analyses and thermal analyses are taken as evidences for the proposed structures.

3.4. Thermal Analysis

The steps of decomposition, temperature extent and decomposition products and also the weight loss percentages of V⁴⁺ complexes are reported in Table 1. Figure 3 and (Figure S17-S20) show the TGA/DTG curves of the five metal complexes. The experimental weight loss values are in good agreement with the calculated values. In the TGA curve of the [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2] (3:1; M:L) (Figure 3) shows four decomposition stages. The first stage was in 27˚C - 263˚C range with a loss corresponding to 1.5 coordinate H₂O molecules and 1.5 EtOH molecule and N₂ fragment (Found: 9.2%; Calcd.: 9.3%). The second step lies in the range 263˚C - 329˚C corresponds to the loss of NO₂ and 2H₂ fragment (Found: 5.9%; Calcd.: 6.0%). The third step corresponds to

Table 1

Decomposition steps with the temperature range and weight loss for V 4+ complexes

Compound	Decomposition Step	Temperature Range (˚C)	Removes Species	Wt. Loss
				% (Cacld.)	% Found
[V3O3(L1)(SO4)3(EtOH)1/2(H2O)3/2] (C19H18N6S3O17V3)	1st	27 - 263	1.5 H2O+1/2EtOH+N2	9.2	9.3
	2rd	263 - 329	NO2+2H2	5.9	6.0
	3rd	329 - 449	2SO4+C3H3+CO	30.4	30.0
	4th	449 - 598	SO4+C9H5	24.6	24.7
	Residue	598 - 800	V3N3C5	30.0	30.0
[VO(L1)(2,4-pentadionate)] Cl・4HCl (C23H23N6O3Cl5V)	1st	27 - 211	2HCl	11.1	11.4
	2nd	211 - 398	Cl+2HCl+2N2+O2+CO	34.01	33.9
	3rd	398 - 563	C17H9N	34.45	34.7
	Residue	563 - 800	C5H10NV	20.5	20.0
[V2O2(L1)(SO4)2(EtOH)5/2] (C23H27N6O25/2S2V2)	1st	28 - 207	1/2 EtOH+C	4.7	4.8
	2rd	208 - 343	2EtOH+O2+N2+C2H4	23.9	23.9
	3rd	343 - 422	SO4+CH4	14.9	14.8
	4th	422 - 565	SO4+N2+2H2	17	17.3
	Residue	565 - 800	V2N2C14	39.6	39.2
[VO(L1)SO4(H2O)3/2]・2.5H2O (C18H20N6SO9V)	1st	18 - 216	2.5 H2O	8.23	8.5
	2rd	216 - 443	3/2 H2O+SO4+C5H5	34.4	34.5
	3rd	443 - 574	C9H5N5O	36.4	35.9
	Residue	574 - 1000	C4H2NV	21	20.8
[V2O2(L1)(SO4)2(H2O)]・H2O (C18H16N6S2O12V2)	1st + 2nd	19 - 395	2 H2O+SO4	19.6	20.9
	3rd	395 - 448	SO4+CH	16.2	15.8
	4th	448 - 525	C14H5N4O2	38.7	38.2
	Residue	525 - 1000	C3H6N2V2	25.5	25.1

Figure 3

The TGA curve of the [V 3 O 3 (L 1 )(SO 4 ) 3 (EtOH) 1/2 (H 2 O) 3/2 ]

2SO₄ and C₃H₃ and CO fragments are (Found: 30.4%; Calcd.: 30.0%) in range 329˚C - 449˚C. The fourth step attributes (Found: 24.7%; Calcd.: (24.7%) refers to SO₄ and C₉H₅ fragment. The residual part (Found: 30.0%; Calcd.: 30.0%) refers to V₃N₃C₅. Secondly, the TGA curve of [VO(L¹)(2,4-pentadionate)]Cl・4HCl (Figure S17) shows the first step in 27˚C - 211˚C range with a loss corresponding to 2HCl fragment (Found: 11.1%; Calcd.: 11.4%). The second step lies in the range 211˚C - 398˚C corresponds to the loss of Cl, 2HCl, 2N₂, O₂ and CO fragments (Found: 34.01%; Calcd.: 33.9%). The mass loss corresponds to the main skeleton of complex C₁₇H₉N are (Found: 34.5%; Calcd.: 34.7%) in the 398˚C - 563˚C range. The residual part (Found: 20.5%; Calcd.: 20.0%) refers to C₅H₁₀VN fragment. Also, the TGA of [V₂O₂(L¹)(SO₄)₂(EtOH)_5/2] (Figure S18) shows the first step in 28˚C - 207˚C range with a loss corresponding to 1/2 EtOH and carbon fragment (Found: 4.7%; Calcd.: 4.8%). The second step lies in the range 208˚C - 343˚C corresponds to the loss of 2EtOH, O₂, N₂ and C₂H₄ fragments (Found: 23.9%; Calcd.: 23.9%). The third step lies in the range 343˚C - 422˚C corresponds to the loss of SO₄ and CH₄ fragments (Found: 14.9%; Calcd.: 14.8%). The fourth step corresponds to loss of SO₄, N₂ and 2H₂ (Found: 17%; Calcd.: 17.3%) in the 422˚C - 565˚C range. The residual part (Found: 39.6%; Calcd.: 39.2%) refers to C₁₄V₂N₂ fragment. Additionally The TGA curve of [VO(L¹)(SO₄₎(H₂O)_3/2]・2.5H₂O (1:1; M:L) (Figure S19) shows three stages of decomposition within the temperature range 18˚C - 1000˚C. The first stage in 18˚C - 216˚C range corresponded to the loss of 2.5 lattice water molecules (Found: 8.5%; Calcd.: 8.23%). The second step lies in the range 216˚C - 443˚C corresponds to the loss of 1.5 coordinated water molecules (hydrogen bond), SO₄ group and C₅H₅ fragment (Found: 34.5%; Calcd.: 34.4%). In the third stage, the mass loss attributes to C₉H₅N₅O are (Found: 35.9%; Calcd.: 36.4%) in range 443˚C - 574˚C. The residual part (Found: 20.8%; Calcd.: 21%) refers to VN and C₄H₂ fragment. Finally, the TGA curve of [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O (2:1; M:L) (Figure S20) shows four stages of decomposition within the temperature range 25˚C - 1000˚C. The first and second steps in 19˚C - 395˚C range correspond to one lattice H₂O molecule, one coordinated H₂O molecule and coordinated SO₄ group (Found: 20.9%; Calcd.: 19.6%). The third step lies in the range 395˚C - 448˚C corresponds to the loss of other coordinated SO₄ group and CH fragment (Found: 15.8%; Calcd.: 16.2%). The mass loss corresponds to the main skeleton of complex C₁₄H₅N₄O₂ are (Found: 38.2%; Calcd.: 38.7%) in the 448˚C - 525˚C range. The residual part (Found: 25.1%; Calcd.: 25.5%) refers to V₂N₂ and C₃H₆ fragments.

3.5. Electron Spin Resonance

The ESR spectra of the researched complexes show just an intense and broad signal without hyperfine splitting. The nonappearance of vanadium hyperfine coupling is regular in solid state [28] and is credited to the simultaneous flipping of neighbouring electron spins [29] [30] or because of strong exchange interactions, which average out the collaboration with the nuclei. The solid ESR spectra of V(IV) complexes, [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2 (H₂O)_3/2], [VO(L¹)(2,4-pentadionate)] Cl・4HCl and [VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O, are shown in Figure 4 and (Figure S21-S22), respectively,. The shape of the spectra is predictable with square-pyramidal environment around V(IV) ion and the lower g value for the investigated complexes, when contrasted with that of free electron

Figure 4

X-band ESR spectrum of [V 3 O 3 (L 1 )(SO 4 ) 3 (EtOH) 1/2 (H 2 O) 3/2 ]

(g = 2.0023) uncovering a considerable covalency of metal ligand bonding with d_x2-y2 as the ground-statenormal for square pyramidal stereochemistry as appeared in Table 2. The decrease of the g value than that of the free-electron value (2.0023) is an estimated measure of the ligand field strength; the stronger the ligand field the littler the reduction in the g value and the other way around. The |g|, g_┴ and |A| values are measured from the spectra, which are in good agreement for a square-pyramidal structure. The high value of α² for the [VO(L¹)(2,4-pentadionate)] Cl・4HCl (0.621) suggests the ionic nature of this complex. On the other hand the low values of α² for [V₃O₃(L¹) (SO₄)₃(EtOH)_1/2・(H₂O)_3/2] (0.2499) and [VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O (0.2079) indicate the covalent nature of these complexes.

3.6. Stoichiometry of the Metal Complexes

The stoichiometry of V⁴⁺-L¹ complex was resolved utilizing continuous variation (CV) and molar ratio methods (MR). In continuous variation method the absorbance of the prepared solutions of V⁴⁺ and L¹ with total molar concentration constant 6 × 10⁻³ M and at 604 nm were recorded. The plot of absorbance as a function of the mole fraction of L¹ estimated that the complex has a maximum absorbance at 0.5 mol fraction providing evidence for 1:1 (M:L) complex (Figure 5). In molar ratio method, the absorbance of prepared solutions with constant metal ion concentration was recorded at 604 nm and plotted versus the molar ratio [L]/[M] (Figure 6). The curve consists of two linear portions crossing at 1:1 M:L species. The stability constant of the formed complex was computed from only one method (CV) by evaluating the degree of complex formation was determined by applying the accompanying formula [31] [32] :

where A, A_m, n and C are the absorbance of the partially formed complex, the fully formed complex, stoichiometry ratio and concentration of metal utilized, respectively. The K_f, Log β and ∆G˚ values obtained from the continuous variation method are 1492.11, −3.17 and −18105.96, respectively.

3.7. Electronic and Magnetic Measurements

The electronic spectra of the complexes were recorded in Nujol mull and DMSO. The electronic spectrum of [VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O (Figure 7) shows six bands. The first three bands at 32,679, 25,773 and 22,935 cm⁻¹ are attributed to charge-transfer of the type L → M. The last three bands at 16,611, 19,230 and 20,576 cm⁻¹ are assigned to d-d transition ²B₂ (d_xy → d_xz, d_yz) → ²E, ²B₂ (d_xy → d_x2-y2) → ²B₁ and ²B₂ (d_xy → d_z²) → ²A₁ transitions, respectively [33] . The data of IR spectra gathering with electronic spectra suggest a square-pyramidal geometry around the V⁴⁺ ion [34] . But, the value of the magnetic moment of the complex is 2.7 B.M which is higher than the proposed for d¹-system; recommending an orbital contribution [35] .

The electronic spectrum of [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O (Figure S23) estimates three bands at 166,666, 19,157 and 23,809 cm⁻¹ assigned to d-d transition ²B₂ (d_xy → d_xz, d_yz) → ²E, ²B₂ (d_xy → d_x2-y2) → ²B₁ and ²B₂

Figure 5

Continuous variation method of V 4+ -L 1

Figure 6

Molar ratio method of V 4+ -L 1

Figure 7

Electronic spectrum of [VO(L 1 )SO 4 (H 2 O) 3/2 ]・2.5H 2 O

Table 2

Magnetic measurements of V(IV) complexes

No.	Compound	g┴	g||	gav	A11	α2	β2
1	[VO(L1)(2,4-pentadionate)] Cl・4HCl	1.98	2.011	1.99	0.02118	0.621	----
2	[V3O3(L1)(SO4)3(EtOH)1/2(H2O)3/2]	1.97	1.99	1.98	8.5 × 10−3	0.2499	0.7909
3	[VO(L1)SO4(H2O)3/2]・2.5H2O	1.96	1.98	1.97	7.5 × 10−3	0.2079	----

(d_xy → d_z²) → ²A₁ transitions, respectively [33] , in a square-pyramidal geometry around the V⁴⁺ ion [34] . Also, the bands at 34,965, 31,847 and 25,641 cm⁻¹ are attributed to charge-transfer of the type L → M. Moreover, the value of the corrected magnetic moment (µ_eff = 2.8 BM) is evaluated per each V⁴⁺ ion [36] . The electronic spectrum of [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2] Figure S24) reveals five bands at 35,971, 33,333, 24,509, 17,361 and 12,987 cm⁻¹. The first two bands are attributed to charge-transfer of the type L → M while the last three bands are assigned to d-d transitions of a square-pyramidal geometry around the V⁴⁺ ion [33] . The trinuclear complex shows subnormal magnetic susceptibility value (µ_eff = 2.8 B.M) at room temperature. It might be ascribed to that the unpaired electron in the d_xy orbital of the adjacent vanadium atoms, so this interaction prompts subnormal magnetic moment at room temperature [37] . The electronic spectrum of [VO(L¹)(2,4-pentadionate)] Cl・4HCl complex (Figure S25) reveals two bands at 32,258, 29,240 cm⁻¹ are characterized for charge-transfer of the type L → M. Also, three bands at 12,594, 14,535 and 20,747 cm⁻¹ are for ²B₂ (d_xy → d_xz, d_yz) → ²E, ²B₂ (d_xy → d_x2-y2) → ²B₁ and ²B₂ (d_xy → d_z²) → ²A₁ transitions respectively, in a square-pyramidal geometry around the V⁴⁺ ion [33] . The electronic spectrum of [V₂O₂(L¹)(SO₄)₂(EtOH)_5/2] complex (Figure S26) shows five bands. The bands at 36,232 and 33,557 cm⁻¹ are attributed to charge-transfer of the type L → M, in addition tothe bands at 12,500, 16,891 and 27,624 cm⁻¹ are assigned to d-d transition ²B₂ (d_xy → d_xz, d_yz) → ²E, ²B₂ (d_xy → d_x2-y2) → ²B₁ and ²B₂ (d_xy → d_z²) → ²A₁ transitions respectively, in a square-pyramidal geometry around the V⁴⁺ ion [33] . Moreover, the value of the corrected magnetic moment (µ_eff = 3.01 BM) per each V⁴⁺ ion is taken an evidence for existence of two vanadium atoms [36] .

3.8. Computational Studies

We performed cluster calculations utilizing DMOL³ program [38] in Materials Studio package [39] , which is intended for the realization of vast scale density functional theory (DFT) calculations. DFT semi-core pseudopods (dspp) calculations were performed with the twofold numerical basis in addition to plus polarization functional (DNP). The DNP basis sets are of comparable quality to 6-31G Gaussian basis sets [40] . The molecular structure alongside atom numbering of the ligand metal complexes is appeared in Figure 8 and (Figure S27-S32). Analysis of the data (Tables S1-S12) involving the bond lengths and bond angles proposes the accompanying remarks.

Vanadium complexes have a square-pyramidal structure. All the active groups participating in coordination where have bonds longer than that as of now exist in the ligand (like C=N) because of M-N bond formation which makes the C-N and C=N bond weaker likewise, The bond angles in the complexes are very close to a square-pyramidal geometry. In the event of

1) [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2] complex (Figure 8), L¹ acts as a bidentate style coordinating via N(8)triaz, N(10)triaz, N(12)triaz, N(12)py, N(19)py, N(24)triaz atoms. The SO₄ groups, EtOH and H₂O molecules finish the square-pyramidal structure around the three vanadium atoms. There is an expansive variety in C(11)-N(12)triaz, N(10)triaz-C(11), C(9)-N(10)triaz, N(8)triaz-C(9), N(12)triaz-C(7) and C(7)-N(8)triaz, N(2) py-C(3), N(24)py-C(14) and N(19)py-C(13)bond lengths. The bond angles of the L¹ moiety are modified upon coordination; the biggest change influences C(23)-N(24)py-C(14), C(18)-N(19)py-C(13), C(11)-N(12)triaz-C(7), N(12)triaz-C(11)-N(10)triaz, C(11)-N(10)triaz-C(9), N(10)triaz-C(9)-N(8)triaz, C(9)-N(8)triaz-C(7), N(12)py- C(7)-N(8)triaz and C(3)-N(2)py-C(1) which are lessened or expanded on complex formation as a result of bonding.

2) In[VO(L¹)(2,4-pentadionate)]Cl・4HCl complex (Figure S28), L¹ serves in a bidentate manner coordinating by means of N(8)triaz and N(2)py atoms. There is a vast variety in N(8)triaz-C(9), C(7)-N(8)triaz, C(3)-C(7), N(2) py-C(3) and C(1)-N(2)py bond lengths. The bond angles of L¹ moiety are modified to some degree upon coordination; the biggest change impacts C(7)-C(3)-N(2)py, C(3)-N(2)py-C(1), N(8)triaz-C(7)-C(3), and C(9)-N(8) triaz-C(7) which are diminished or expanded on complex development as an outcome of bonding.

3) Also, [V₂O₂(L¹)(SO₄)₂(EtOH)_5/2] (Figure S29), L¹ is a bi-dentate ligand coordinating via N(8)triaz, N(12)triaz, N(2)py and N(19)py atoms. There is a vast variety in C(18)-N(19)py, N(19)py-C(14), C(11)-C(14), C(11)-N(12)triaz, N(8)triaz-C(9), C(7)-N(8)triaz, C(3)-C(7), N(2)py-C(3), C(1)-N(2)py and N(12)triaz-C(7) bond lengths. The bond angles of the TPTZ moiety are modified to some degree upon coordination; the biggest change influences C(18)-N(19)py-C(14), C(11)-N(12)triaz-C(7), C(14)-C(11)-N(12)triaz, N(12)triaz-C(11)- N(10)triaz, C(9)-N(8)triaz-C(7), C(7)-C(3)-N(2)py, C(3)-N(2)py-C(1) and N(8)triaz-C(7)-C(3)which are lessened or expanded on complex arrangement as a result of holding.

4) L¹ in [V₂O₂(L¹)(SO₄)₂(EtOH)_3/2(H₂O)_1/2] (Figure S30), serves in a bidentate manner coordinating by means of N(8) triaz, N(12)triaz, N(4)py and N(15)py atoms. There is an expansive variety in C(13)-N(15)py, C(9)-C(13), N(8) triaz-C(9), C(7)-N(8)triaz, N(4)py-C(5), C(3)-C(7) and C(3)-N(4)py bond lengths. The bond angles of L¹ moiety are modified to some degree upon coordination; the biggest change impacts N(15)py-C(13)-C(9), C(5)- N(4)py-C(3), C(7)-C(3)-N(4)py, C(9)-N(8)triaz-C(7), N(12)triaz-C(7)-C(3) and C(13)-C(9)-N(8)triaz which are lessened or expanded on complex formation as a result of bonding.

5) L¹ in [VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O (Figure S31), acts as a tridentate style coordinating by mean of N(5)triaz, N(19)py and N(20)py atoms. The ions O(26) in axial positions and O(27) finish the square-pyramidal structure. There is a vast varietyin C(18)-N(19)py, C(21)-C(22), N(20)py-C(21), N(19)py-C(8), C(6)-C(7), N(5)triaz-C(6), C(4)-C(8), C(7)-N(20)py and C(4)-N(5)triaz bond lengths. The bond angles of the L¹ moiety are modified to some degree upon coordination; the biggest change influences C(21)-N(20)py-C(7), C(18)-N(19)py-C(8), N(19)py-C(8)-C(4), N(20)py-C(7)-C(6), C(7)-C(6)-N(5)triaz, C(6)-N(5)triaz-C(4) and C(8)-C(4)-N(5)triaz which are lessened or expanded on complex formation as a result of bonding.

6) [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O (Figure S32) has a square-pyramidal structure. L¹ acts as a tridentate manner coordinating via N(5) triaz, N(10)py and N(19)py atoms, also coordinates as a bidentate style coordinating via N(1) triaz and N(20)py atoms. In case of the tridentate fashion the atoms O(31) and O(26) finish the square-py- ramidal structure and dwell, while in case of a bidentate fashion the atoms O(33), O(35) of sulphate group and O(34) of water molecule finish the square-pyramidal structure. There is a vast varietyin N(20)py-C(21), C(18)- N(19)py, N(10)py-C(11), C(9)-N(20)py, N(19)py-C(8), C(7)-N(10)py, C(6)-C(7), N(5)triaz-C(6), C(4)-C(8), C(4)-N(5) triaz, C(2)-C(9), C(6)-N(1)triaz and N(1)triaz-C(2) bond lengths. The bond angles in [V₂O₂(TPTZ) (SO₄)₂ (H₂O)]・H₂O complex are very close tosquare-pyramidal geometry where the bond angles of atoms around the V⁴⁺ atoms in the square-pyramidal structure are N(20)py-V(32)-N(1)triaz, N(19)py-V(25)-N(10)py, N(19)py-V(25)-N(5)triaz, N(10)py-V(25)-N(5)triaz, C(21)-N(20)py-C(9), C(18)-N(19)py-C(8), C(11)-N(10) py-C(7), N(20)py-C(9)-C(2), N(19)py-C(8)-C(4), N(10)py-C(7)-C(6), C(7)-C(6)-N(5)triaz, C(6)-N(5)triaz-C(4), C(8)- C(4)-N(5)triaz, C(9)-C(2)-N(1)triaz and C(6)-N(1)triaz-C(2). The bond angles of the TPTZ moiety are modified somewhat upon coordination; the largest change influences C(11)-N(10)py-C(7), C(6)-N(5)triaz-C(4), C(8)-C(4)-N(5)triaz, C(9)-C(2)-N(1)triaz, N(20)py-C(9)-C(2), which are decreased or increased on complex formation as a result of bonding.

3.8.1. Chemical Reactivity

Global Reactivity Descriptors

The determination of energies of the HOMO (π-donor) and LUMO (π-acceptor) are essential parameters in quantum chemical computations. The HOMO is the orbital that fundamentally goes about as an electron donor and the LUMO is the orbital that largely to a great extent go about as the electron acceptor. These molecular orbitals are additionally called the frontier molecular orbitals (FMOs).

i) The E_HOMO and E_LUMO and their neighboring orbitals are all negative (Table 3), which appear that the investigated molecules are steady [41] .

Table 3

Calculated E HOMO , E LUMO , energy band gap (E H -E L ), chemical potential (μ), electronegativity (χ), global hardness (η), global softness (S) and global electrophilicity index (ω) for L 1 and its complexes

Compound	EH eV	EL eV	(EH-EL) eV	Χ eV	µ eV	η eV	S eV−1	ω eV	Ϭ eV
L1	−3.814	−2.479	−1.335	3.1465	−3.1465	0.6675	0.749064	7.416077	1.498127
[V3O3(L1)(SO4)3(EtOH)1/2(H2O)3/2]	−5.897	−5.875	−0.022	5.886	−5.886	0.011	45.45455	1574.773	90.90909
[VO(L1)(2,4-pentadionate)] Cl・4HCl	−6.027	−3.614	−2.413	4.8205	−4.8205	1.2065	0.414422	9.630013	0.828844
[V2O2(L1)(SO4)2(EtOH)5/2]	−6.579	−4.08	−2.499	5.3295	−5.3295	1.2495	0.40016	11.36597	0.80032
[V2O2(L1)(SO4)2(EtOH)3/2(H2O)1/2]	−5.248	−4.758	−0.49	5.003	−5.003	0.245	2.040816	51.08165	4.081633
[VO(L1)SO4(H2O)3/2]・2.5H2O	−4.373	−4.297	−0.076	4.335	−4.335	0.038	13.15789	247.2661	26.31579
[V2O2(L1)(SO4)2(H2O)]・H2O	−5.053	−5.041	−0.012	5.047	−5.047	0.006	83.33333	2122.684	166.6667

H = HOMO, L = LUMO.

ii) The FMOs theory predicts positions of coordination (electrophilic attack) on aromatic compounds. An introductory assumption is that the reaction happens with most extreme overlap between the HOMO on one molecule and the LUMO on the other. The overlap between the HOMO and the LUMO is a governing factor in many reactions. The aim of the calculations is the scanning for the biggest estimations of molecular orbital coefficients. In this way, orbitals of L¹ with the biggest estimation of molecular orbital coefficients may be considered as the locales of coordination. This conclusion is affirmed by the data acquired from the calculations which can demonstrate that the nitrogen of the CN group has the largest values of molecular orbital coefficients.

iii) Gutmann’s variation rules, “the bond strength increases as the adjacent bonds become weaker” such as found by Linert et al. [42] . This elucidation concurs well with the resultant as the increment of the E_HOMO is joined by a shortcoming (lengthening) of the metal-ligand bonds, which prompts a reinforcing (shortness) of the destinations nearby the metal ligand centers.

iv) The HOMO level is for the most part confined on the Natom (Figure 8 and Figure S27-S31) indicating that this atom is the favored nucleophile positions at the central metal ion. This implies that these moieties, with high coefficients of HOMO density, are oriented toward the metal ions.

v) The energy gap (E_HOMO-E_LUMO) is a critical stability index serves to investigate the chemical reactivity and kinetic stability of the molecule [43] . The gap (E_HOMO-E_LUMO) is applied to improve a theoretical model for clarifying the structure and conformation barriers in many molecular systems, which impacts the biological activity of the molecule. A molecule with a little gap is more polarized and is called soft molecule. Soft molecules are more reactive than hard ones due to their easily offer electrons to an acceptor. The energy gap is little in L¹ estimating that charge-transfer easily happen in it, which impacts the biological activity of the molecule. Low value of energy gap is additionally referred to the groups that go into conjugation [44] .

Figure 8

Molecular modeling of (a)[V 3 O 3 (L 1 )(SO 4 ) 3 (EtOH) 1/2 (H 2 O) 3/2 ], (b) electron den- sity, (c) HOMO and (d) LUMO.

(b)(c) (d)

vi) The lower HOMO energy estimations demonstrate that molecules donating electron ability is the weaker. On opposite, the higher HOMO energy suggests that the molecule is a good electron donor. LUMO energy displays s the ability of a molecule receiving electron [43] .

DFT method concept can suggest the chemical reactivity and position selectivity of the molecular systems. The energies of frontier molecular orbitals (E_HOMO + E_LUMO), energy band gap (E_HOMO-E_LUMO) which shows the eventual charge-transfer interaction within the molecule, electronegativity (χ), chemical potential (µ), global hardness (η), global softness (S) and global electrophilicity index (ω) [45] - [46] are appeared in Table 3.

The inverse value of the global hardness is designed as the softness σ as follow:

Electrophilicity index is one of the most vital quantum chemical descriptors in explaining toxicity of different pollutants in terms of their reactivity and position selectivity [47] . Also, the electrophilicity properly quantifies the biological activity of drug receptor collaboration. This novel reactivity index calculates the stabilization in energy when the system acquires an extra electronic charge from the environment. So, the importance of η and σ is to calculate the molecular stability and reactivity. In a complex formation system, L¹ serves as a Lewis base while the V⁴⁺ acts as a Lewis acid.

3.8.2. Molecular Electrostatic Potential (MEP)

The MEP is a plot of electrostatic potential mapped onto the steady electron density surface. It is additionally exceptionally helpful in exploration of molecular structure with its physiochemical property relationship and also hydrogen bonding interactions [48] - [50] . The electrostatic potential V(r) at a given point r (x, y, z) is the interaction energy between the electrical charge produced from the molecule electrons, nuclei and proton located at r [51] [52] . In the present study, 3D plots of molecular electrostatic potential (MEP) of L¹ (Figure 9) have been drew. The maximum negative, region which favored local for electrophilic attack, is shown by a red color, the maximum positive region which favored position for nucleophilic attack indicated as blue color. Potential

Figure 9

MEP plot by using DFT method forL 1

increases in the order red < green < blue, where blue represents the strongest attraction and red reveals the strongest repulsion. Regions having the negative potential are over the electronegative atoms while the regions having the positive potential are over the hydrogen atoms.

3.8.3. Dipole Moment and other Molecular Properties

The calculations of the binding energy uncovered that the increment of the value of the calculated binding energy of V⁴⁺ complexes contrasted with L¹ indicates that the formed V⁴⁺ complexes are more stable than L¹. Also, energy components were evaluated by DFT method listed in Table 4.

3.9. Biological Activity

3.9.1. Antibacterial Activity

Depending on data obtained for diameter of inhibition zone (Figure 10 and Table 5), it was found that the complexes were active on both sorts of bacterial strains. A look of data shows that:

i) [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2], [VO(L¹)(2,4-pentadionate)] Cl・4HCl,[V₂O₂(L¹)(SO₄)₂(EtOH)_3/2(H₂O)_1/2] and [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O complexes exhibited aexceptional antibacterial activity against all organisms.

ii) [VO(L¹)(2,4-pentadionate)] Cl・4HCl revealed a potent antibacterial activity against Escherichia coli and Candida albicans bacterial strain (Gram-ve) more than [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2] then [V₂O₂(L¹) (SO₄)₂(H₂O)]・H₂O and [V₂O₂(L¹)(SO₄)₂(EtOH)_3/2(H₂O)_1/2].

iii) [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2] had a potent antibacterial activity against Staphylococcus aureus bacterial strain (Gram + ve) more than [VO(L¹)(2,4-pentadionate)] Cl・4HCl and [V₂O₂(L¹)(SO₄)₂(EtOH)_3/2(H₂O)_1/2] and [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O have the lower and equal an anti-bacterial activity.

The outcomes can be can be ascribed either to the failure of the complexes to diffuse through the cell wall of

Figure 10

Antimicrobial activity of V 4+ -complexes

Table 4

Some of energetic properties of L 1 and complexes calculated by DMOL 3 using DFT-method

No.	Compound	HOMO (eV)	LUMO (eV)	Binding energy (Kcal/mol)	Total energy (Kcal/mol)	Dipole moment (D)
1	L1 C18H12N6	−3.814	−2.479	−4430.410	−6.413 × 105	3.2814
2	[V3O3(L1)(SO4)3(EtOH)1/2(H2O)3/2]	−5.897	−5.875	−8363.258	−2.455 × 106	11.1456
3	[VO(L1)(2,4-pentadionate)]Cl・4HCl	−6.027	−3.614	−6297.314	−9.60 × 105	4.3354
4	[V2O2(L1)(SO4)2(EtOH)5/2]	−6.579	−4.080	−8174.541	−1.917 × 106	12.2852
5	[V2O2(L1)(SO4)2(EtOH)3/2(H2O)1/2]	−5.248	−4.758	−7179.095	−1.867 × 106	14.278
6	[VO(L1)SO4(H2O)3/2]・2.5H2O	−4.373	−4.297	−5679.432	−1.277 × 106	10.7288
7	[V2O2(L1)(SO4)2(H2O)]・H2O	−5.053	−5.041	−5664.384	−1.769 × 106	9.4451

Table 5

Antimicrobial activities of the isolated complexes

No.	Compound	E. coli (mg/ml)		S. aureus (mg/ml)		C. Albicans (mg/ml)
		Diameter of inhibition zone (in mm)	% Activity index	Diameter of inhibition zone (in mm)	% Activity index	Diameter of inhibition zone (in mm)	% Activity index
1	[V3O3(L1)(SO4)3(EtOH)1/2(H2O)3/2]	18	78.3	19	90.5	18	69.2
2	[VO(L1)(2,4-pentadionate)] Cl・4HCl	19	82.6	14	66.7	22	84.6
4	[V2O2(L1)(SO4)2(EtOH)3/2(H2O)1/2]	11	47.8	10	47.6	7	26.9
5	[VO(L1)SO4(H2O)3/2]・2.5H2O	-	NA	-	NA	-	NA
6	[V2O2(L1)(SO4)2(H2O)]・H2O	13	56.5	10	47.6	14	53.8
	Ampicillin	23	100	21	100	-	NA
	Colitrimazole	-	NA	-	NA	26	100

the bacterium and henceforth not able to meddle with its biological activity or they can diffuse and inactivated by unknown cellular mechanism i.e. bacterial enzymes. The reason for high antimicrobial activity of vanadium complexes can be clarified regarding the impact of vanadium metal ion on the normal cell process. The complexation reaction decreases the polarity of the metal ion by the partial participating of metal ion positive charge with donor groups and electron delocalization over the chelate ring. Hence, the lipophilic character of the central metal atom is improved which brings about a higher capacity to penetrate the microorganisms through the lipid layer of the cell membrane. In addition, all metal complexes under the investigation estimate a large value of binding energy than L¹ that enhances the steadiness of these complexes [53] . Additionally, electrophilicity of all complexes is bigger than that of L¹ and that could be another target behind some complexes to exhibit the biggest strong antimicrobial activity than the ligand. Likewise, it is observed from these studies that the vast majority of the metal chelates have a higher movement than the free ligand and that can be explained on the premise of chelation hypothesis. The chelation goes about as all the more able and strong fungicidal and bactericidal agents, subsequently murdering more fungi and bacteria than the ligand. In the complex the positive charge of the metal is somewhat imparted to the donor atoms present in the ligands, and there may be π-electron delocalization over the all chelating system [54] . The variety in the activity of different complexes against various microorganisms depend either on cells impermeability of the microbes or contrasts in ribosomes in microbial cells [55] . The negative results can be credited either to the powerlessness of the complexes to diffuse through the cell wall of the bacterium and henceforth not able to interfere with its biological activity or they can diffuse and inactivated by obscure cellular mechanism i.e. bacterial enzymes.

3.9.2. In Vitro Anticancer Activity

In vitro cytotoxicity tests were conducted utilizing all the prepared compounds against human tumor cell lines MCF-7 and Hela normal cell line by means of a colorimetric assay (MTT assay) that is a measurement for mitochondrial dehydrogenase activity as an indication of cell viability. The activities corresponding to viability of cancer cell growth. In parallel, the impact of widely utilized anticancer drug, 5-fluorouracil has been also assayed as standard. The IC₅₀ values were computed from the graph plotted between % cell viability and concentration. The outcomes of IC₅₀ of five complexes for both cell lines covered a large range of activity with ranging from 5.7 to 50.4 µg/ml as appeared in Figure 11, indicating that the five complexes exhibited antitumor activity against the cell lines without damaging the normal cells. [VO(L¹)SO₄(H₂O)_3/2]・2.5H₂O and [VO(L¹)(2,4-penta- dionate)] Cl・4HCl complexes revealed potential activity than [V₃O₃(L¹)(SO₄)₃(EtOH)_1/2(H₂O)_3/2] complex than [V₂O₂(L¹)(SO₄)₂(H₂O)]・H₂O then [V₂O₂(L¹)(SO₄)₂(EtOH)_3/2(H₂O)_1/2], respectively. It means that the chemical structure of compounds is important to explain the complex biological activity and it can be essential in designing and synthesizing novel anticancer drugs. There is obviously direct correlation between strong interaction of V(IV) complex with DNA and antiproliferative activity of V(IV) complex. These observations suggests that DNA may be the targeting molecules of V(IV) complex’s anti-carcinogenic action, and V(IV) ion coordination and bind significantly enhances the Schiff base drugs anticancer activity. So, It is unmistakably watched that complexation with metal has a synergistic impact on the cytotoxicity.

Figure 11

Scavenging capacities (IC50) of V 4+ complexes (5-fluorouracil- standardantitumor)

Figure 12

Cyclic voltammogram in DMSO solution with 0.1 M tetrabuty- lammonium perchlorate (TBAP), scan rate 50 mVs −1 for 10 −3 M of [V IV O (L 1 )(2,4-pentadionate)] Cl・4HCl

3.10. Voltammetric Studies

The voltammogram reveals two reduction peaks for the complex [V^IVO(L¹)(2,4-pentadionate)]Cl・4HCl, centered at −0.75 V and −0.43 V which correspond to V^IV/V^II and V^IV/V^III, respectively as appeared in (Figure 12) [56] .

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