Preparation, Crystal Structure and Spectroscopy Characterization of Vanadium(V) Complex, 2-Amino-4-Picolinium, 2-Methylimidazolium Decavanadate Hydrate (C₄N₂H7)₄(C₆N₂H₁₀)V₁₀O₂₈·2H₂O

A new decavanadate, (C ₄ N ₂ H ₇ ) ₄ (C ₆ N ₂ H ₁₀ )V ₁₀ O ₂₈ ·2H ₂ O, was synthesized by slow evaporation at room temperature and characterized by single crystal X-ray diffraction, IR and UV-Vis spectroscopies. The compound crystallizes in the triclinic system, P-1 space group with the cell parameters: a = 11.200(5) Å, b = 12.056(9) Å, c = 20.511(7) Å, α = 73.40(4), β = 84.67(3), γ = 63.51(5), Z = 2 and volume V = 2373.7(1) ų. The formula unit is composed of one decavanadate [V₁₀O₂₈]^6- anion, four 2-methylimidazolium (C₄N₂H₇)⁺ cations, one 2-amino-4-picolinium (C₆N₂H₁₀)²⁺ cation and two water molecules. In the cr y stal, the layers of decavanadate groups, organic cations and water molecules stack up parallel to the (011) plane. The cohesion is provided by N-H···O, O-H···O hydrogen bonds and Van der Waals interactions leads to a three-dimensional structure. The absorbance spectrum measurement shows an optical band gap of 3.27 eV which allows us to conclude that this compound is a semiconductor material.

• Decavanadate
• Synthesis
• X-Ray Analysis
• Crystal Structure
• Semiconductor Material

1. Introduction

Polyoxometalates (POMs) are a kind of inorganic clusters, which can be combined with organic ligands and metal ions to form supramolecular compounds. These groups have been extensively studied due to their potential applications in various fields such as catalysis [1] and materials science [2] . The size and the structure are two important criteria among others that determine the properties and hence the applications of these species.

Among the various types of POMs, decavanadate represents an important part of the group which has been studied extensively in the past decades because of their excellent catalysis properties [3] [4] and versatile bioactivities [5] [6] [7] [8] . In addition, the decavanadate anion [V₁₀O₂₈]⁶⁻ has been characterized by numerous cations for antibacterial, antidiabetes and catalytic activities [9] - [17] . Recently, organic decavanadates have been synthesized with the aim to understand their biological [18] , magnetic [19] , and optical properties [20] .

Several decavanadate compounds containing organic cations have been synthesized such us: (C₅H₁₂N)₉[HV₁₀O₂₈](NO₃)₄ [21] , (C₇H₁₀N)₄[H₂V₁₀O₂₈]∙2H₂O [22] , (C₁₂H₁₂N₂)₃(V₁₀O₂₈)∙2H₂O [23] , [C₈NH₂₀]₉[H₂V₁₀O₂₈][HV₁₀O₂₈]∙2∙13H₂O [24] .

In a continuation of these studies, a new decavanadate compound containing organic cations has been prepared.

In this paper, we report the synthesis, crystal structure, IR and UV-Vis spectroscopies of the novel decavanadate (C₄N₂H₇)₄(C₆N₂H₁₀)V₁₀O₂₈∙2H₂O.

2. Experimental

2.1. Synthesis and Crystallization of 2-Amino-4-Picolinium, 2-Methylimidazolium Decavanadate Hydrate: (C 4 N 2 H 7 ) 4 (C 6 N 2 H 10 )V 10 O 28 ∙2H 2 O (1)

The compound (C₄N₂H₇)₄(C₆N₂H₁₀)V₁₀O₂₈∙2H₂O was prepared from a mixture of 0.321 g of vanadium oxide V₂O₅, 0.091 g of 2-methylimidazole (C₄H₆N₂) and 0.057 g of 2-amino-4-picoline (C₆H₈N₂) in water. The mixture obtained was stirred and heated for about 3 hours. Finally, the solution was allowed to stand at room temperature and after a week, single orange crystals suitable for ray diffraction analysis were obtained.

2.2. X-Ray Diffraction Study

The collect of diffracted intensities was performed using an Enraf-Nonius CAD4 four-circle diffractometer with K_α radiation of molybdenum (λ = 0.71067 Å). The structure was solved by direct method using the SHELXS-97 program [25] and refined by the full-matrix least squares method on all F² data using the program SHELXL-2014 [26] .

Anisotropic thermal parameters were used to refine all the non-hydrogen.

B atoms and the positions of the hydrogen atoms were calculated using the HFIX instruction.

Crystal data and details on data collection and refinement are summarized in Table 1.

DIAMOND [27] package was used for molecular graphics. CIF file containing complete information about the structure of (1) was deposited with the Cambridge Crystallographic Data Center (CCDC 1908881). The file is freely available upon request from the following web site: https://www.ccdc.cam.ac.uk/data_request/cif.

2.3. X-Ray Powder Diffraction Study of Compound (1)

The purity of phase (I) were checked by comparing, using the Origin software [28] , the experimental diffractogram (λ_Cu (Kα1) = 1.5406 Å) with the calculated diffractogram from single-crystal X-ray diffraction data, obtained using the VESTA program [29] . The superposition of the two diffractograms (Figure 1) confirms the purity of the sythesized phase.

Table 2 groups the different peaks, their indications and their intensities.

2.4. IR Spectra of Compound (1)

In Figure 2, we present the IR spectrum of the compound (1) (Pellets with KBr, mg: analyte 2, KBr 250; Perkin-Elmer spectrometer) cm^–1: 585, 608, 745, 830 ν(VO₆), 970 ν(V=O), 1310 ν(C=C) and cycle vibrations, 1430 ν(C=N), 1610 δ(O-H), 1830, 1930, 2690 ν(C-H), ν(C-N), ν(N-H) and ν(C-C), 2905 hydrogen bonds, 3095, 3145, 3365 ν(O-H).

2.5. UV-Vis Spectra of Compound (1)

The UV-Vis spectra were recorded on a T70/T70 + UV-V is spectrophotometer in the range 200 - 700 nm (Figure 3). The UV-Vis spectrum of 1 displays two intense absorption bands. The band observed at 300 nm can be assigned to charge-transfer (CT) transitions of the type π(O) → d(V) and the band at 494.64 nm can be explained the color (orange) of crystals of the title compound. The band gap is estimated by extrapolation of the linear part. The absorbance spectrum measurement shows an optical band gap of 3.27 eV which allows us to conclude that this compound is a semiconductor material (the gap energy is less than 4 eV).

3. Results and Discussion

The formula unit is composed of one decavanadate [V₁₀O₂₈]⁶⁻ anion, four 2-methylimidazolium (C₄N₂H₇)⁺ cations, one 2-amino-4-picolinium (C₆N₂H₁₀)²⁺ cation and two water molecules (Figure 4).

Each decavanadate cluster is composed by ten distorted edge-sharing VO₆ octahedra. In fact, the distortion indexes vary between 7.6% and 9.9% [30] (Table 3). The vanadium is in the +5 oxidation. This result was confirmed by the bond valence sums calculations (Table 3) according to Brown [31] [32] (S = Σsi = Σexp[(R₀ − R_i)/B]. The V-O_terminal bond distances range between 1.593(4) and 1.621(4) Å. The V-O_2b bonds are in the range of 1.678(4) and 2.071(4) Å. The

Table 1

Crystallographic characteristics, the X-ray data collection and structure-refinement parameters for (C 4 N 2 H 7 ) 4 (C 6 N 2 H 10 )V 10 O 28 ∙2H 2 O

System, sp. gr., Z	Triclinic, P-1, 2
a, b, c, Å	11.200(5), 12.056(9), 20.511(7)
α, β, γ deg	73.40(4), 84.67(3), 63.51(5)
V, Å3	2373.58(1)
Dx, g∙cm−3	2.01
Radiation, λ, Å	MoKα, 0.71073
μ, mm−1	1.976
T, K	298(2)
Sample size, mm	0.25 × 0.19 × 0.15
Diffractometer	ENRAF-NONIUS CAD4
Scan mode	ω/2θ
Absorption correction	Psi-scan
Tmin, Tmax	0.8027,0.9979
θmax, deg	26.984
h, k, l ranges	–14 ≤ h ≤ 1, –15 ≤ k ≤ 14, –26 ≤ l ≤ 26
Number of reflections: measured/unique Rint Number of reflections with I > 2σ (I)	11024/10252 (N1) 0.029 5525 (N2)
Number of refined parameters	662
R1/wR2 relative to N1	0.084/0.181
R1/wR2 relative to N2	0.059/0.162
S	1.021
∆ρmax/∆ρmin, e∙Å−3	1.325/-0.923
Programs	SHELXS-97 [25] , SHELXL-2014 [26] , DIAMOND [27]

Table 2

Indexation of DRX diffractogram of compound (1)

h	k	l	2θ (˚)	I/I0	h	k	l	2θ (˚)	I/I0
0	1	1	8.46927	100*	0	2	1	16.41792	1.53332
1	0	0	8.82155	50.96973	1	0	3	16.45854	3.72334
0	0	2	8.99789	40.19615	2	1	−1	17.01392	7.9014
1	1	1	9.31284	40.05874	2	1	2	17.4696	1.52741
1	0	1	10.06554	3.55709	0	1	−3	17.87741	2.06015
0	1	−1	10.6696	24.81571	1	1	−3	17.93931	2.45911
1	1	−1	11.06584	20.26129	2	0	−1	18.08847	1.99497
1	1	2	11.39276	3.35978	2	0	v2	19.55503	1.80471
1	0	−2	12.3561	9.39765	2	0	2	20.20981	3.97823
1	0	2	12.86607	10.83167	1	0	4	20.44567	1.96777
1	2	0	15.38431	1.95101	2	1	4	22.8685	1.89693
1	2	2	15.49405	3.86325	2	3	1	23.18129	8.72159
1	−1	−2	15.81212	3.41893	1	3	−1	24.91429	5.91526
1	0	−3	15.8584	5.8791

*Only the most significant peaks are considered.

V-O_3b bond distances range from 1.929(4) and 2.059(4) Å. The V-O_6b bond lengths are within 2.061(4) and 2.374(4) Å. The V-V distances are in the range 3.051(1) to 3.120(1) Å.

The 2-methylimidazolium (C₄N₂H₇)⁺ and 2-amino-4-picolinium (C₆N₂H₁₀)²⁺ cations forming two different alternating layers. The first layer is composed by 2-amino-4-picolinium (C₆N₂H₁₀)²⁺ and 2-methylimidazolium (C₄N₂H₇)⁺ cations. The second layer is formed by 2-methylimidazolium (C₄N₂H₇)⁺ cations (Figure 5). The bond lengths of C-C and C-N are from 1.353(1) to 1.502(1) Å and from

Table 3

Distortion, indexes ID and BVS calculations for (C 4 N 2 H 7 ) 4 (C 6 N 2 H 10 )V 10 O 28 ∙2H 2 O

Octahedra	V1O6	V2O6	V3O6	V4O6	V5O6
BVS ID	Σsi = 4.95 ID = 7.6%	Σsi = 4.95 ID = 9.2%	Σsi = 4.99 ID = 9.1%	Σsi = 4.94 ID = 9.1%	Σsi = 5.00 ID = 9.1%
Octahedra	V6O6	V7O6	V8O6	V9O6	V10O6
BVS ID	Σsi = 4.94 ID = 7.9%	Σsi = 5.00 ID = 8.8%	Σsi = 4.90 ID = 9.9%	Σsi = 4.96 ID = 8.7%	Σsi = 5.00 ID = 9.1%

1.292(1) to 1.511(1) Å, respectively. These bond lengths are in agreement with those reported in literature [33] [34] .

Decavanadate groups, organic cations and water molecules form infinite zigzag chains viewed along the c axis as shown in Figure 6. The cohesion of these layers by N-H···O, O-H···O hydrogen bonds and Van der Waals interactions leads to a three-dimensional structure.

The decavanadate groups form hydrogen bonds on the one hand with the water molecules and on the other hand with the organic molecules. Similarly organic cations form hydrogen bonds with oxygen atoms of V 10 O 28 6 − groups and

water molecules (Figure 7). In this structure, five hydrogen bonds are strong with a range of D---A bond lengths from 2.677 to 2.876 Å and the other five are weak with the D---A bond lengths vary from 3.112 to 3.350 Å according to Brown [35] (Table 4).

Table 4

Hydrogen bonds in crystal of (1)

D-H…A	D-H (Å)	H…A (Å)	D…A (Å)	D-H…A (˚)
OW1-H27....O2	0.958	1.919	2.860	166.78
OW1-H28….O23i	0.959	2.047	2.772	131.02
OW1-H28 ....O25i	0.959	2.500	3.269	137.19
OW2-H30....O15	0.930	1.984	2.854	155.13
N1-H5….O3	0.860	1.875	2.677	154.52
N2-H6A….O6ii	0.890	2.506	3.186	133.60
N2-H6A….O10iii	0.890	2.506	3.186	133.60
N2-H6B….O12	0.890	2.441	2.876	110.55
N5-H16….O9IVi	0.860	2.384	3.112	142.69
N8-H21….O9Vi	0.860	2.428	3.230	155.52

Symmetry codes: (i) –x + 1, −y + 1, −z; (ii) −x, −y + 1, −z + 1; (iii) x − 1, y, z; (ivi) –x + 1, −y + 1, −z + 1; (vi) x−1, y, z.

4. Conclusion and Perspectives

A novel decavanadate has been synthesized and characterized by single crystal X-ray diffraction, IR and UV-Vis spectroscopies. The decavanadates anions, organic cations and the water molecules are connected through N-H···O, O-H···O hydrogen bonds and Van der Waals interactions to form a three-dimensional structure. In perspective, biological analyzes will be carried out, as part of a project with the Institute of Pasteur of Tunis, to better understand the mode of action of vanadium crystals developed and therefore evaluate their effect on the germination of spores. Germination tests are also very useful for evaluating the mechanism of action of the antifungal compounds.

Acknowledgements and Funding Information

Financial support from the Ministry of Higher Education and Scientific Research of Tunisia is gratefully acknowledged.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

References

1. Bregeault, J.M., Vennat, M., Salles, L., Piquemal, J.Y., Mahha, Y., Briot, E., Bakala, P.C., Atlamsani, A. and Thouvenot, R. (2006) From Polyoxometalates to Polyoxoperoxometalates and Back Again; Potential Applications. Journal of Molecular Catalysis A, 250, 177-181. https://doi.org/10.1016/j.molcata.2006.01.027

2. Coronado, E. and Day, P. (2004) Magnetic Molecular Conductors. Chemical Reviews, 104, 5419-5448. https://doi.org/10.1021/cr030641n

3. Huang, X., Li, J., Shen, G., Xin, N., Lin, Z., Chi, Y., Dou, J., Li, D. and Hu, C. (2017) Three Pd-Decavanadates with a Controllable Molar Ratio of Pd to Decavanadate and Their Heterogeneous Aerobic Oxidation of Benzylic C-H Bonds. Dalton Transactions, 47, 726-733. https://doi.org/10.1039/C7DT03898D

4. Wang, C., Chen, Z., Yao, X., Chao, Y., Xun, S., Xiong, J., Fan, L., Zhu, W. and Li, H. (2018) Decavanadates Anchored into Micropores of Graphene-Like Boron Nitride: Efficient Heterogeneous Catalysts for Aerobic Oxidative Desulfurization. Fuel, 230, 104-112. https://doi.org/10.1016/j.fuel.2018.04.153

5. Aureliano, M. (2014) Decavanadate Contribution to Vanadium Biochemistry: In Vitro and in Vivo Studies. Inorganica Chimica Acta, 420, 4-7. https://doi.org/10.1016/j.ica.2013.10.010

6. Aureliano, M. and Ohlin, C.A. (2014) Decavanadate in Vitro and in Vivo Effects: Facts and Opinions. Journal of Inorganic Biochemistry, 137, 123-130. https://doi.org/10.1016/j.jinorgbio.2014.05.002

7. Galani, A., Tsitsias, V., Stellas, D., Psycharis, V., Raptopoulou, C.P. and Karaliota, A. (2015) Two Novel Compounds of Vanadium and Molybdenum with Carnitine Exhibiting Potential Pharmacological Use. Journal of Inorganic Biochemistry, 142, 109-117. https://doi.org/10.1016/j.jinorgbio.2014.10.004

8. Trevino, S., Sánchez-Lara, E., Sarmiento-Ortega, V., Sánchez-Lombardo, I., Flores-Hernández, J., Pérez-Benítez, A., Brambila-Colombres, E. and González-Vergara, E. (2015) Hypoglycemic, Lipid-Lowering and Metabolic Regulation Activities of Metforminium Decavanadate (H2Metf)3[V10O28]·8H2O Using Hypercaloric-Induced Carbohydrate and Lipid Deregulation in Wistar Rats as Biological Model. Journal of Inorganic Biochemistry, 147, 85-92. https://doi.org/10.1016/j.jinorgbio.2015.04.002

9. Choi, H., Chang, Y.Y., Kwon, Y.U. and Han, O.H. (2003) Incorporation of Decavanadate Ions into Silica Gels and Mesostructured Silica Walls. Chemistry of Materials, 15, 3261-3267. https://doi.org/10.1021/cm034061i

10. Martín-Caballero, J., Wéry, A.S.J., Reinoso, S., Artetxe, B., Felices, L.S., Bakkali, B.E., Trautwein, G., Alcaniz-Monge, J., Vilas, J.L. and Gutiérrez-Zorrilla, J.M. (2016) A Robust Open Framework Formed by Decavanadate Clusters and Copper(II) Complexes of Macrocyclic Polyamines: Permanent Microporosity and Catalytic Oxidation of Cycloalkanes. Inorganic Chemistry, 55, 4970-4979. https://doi.org/10.1021/acs.inorgchem.6b00505

11. Baruah, B., Roden, J.M., Sedgwick, M., Correa, N.M., Crans, D.C. and Levinger, N.E. (2006) When Is Water Not Water? Exploring Water Confined in Large Reverse Micelles Using a Highly Charged Inorganic Molecular Probe. Journal of the American Chemical Society, 128, 12758-12765. https://doi.org/10.1021/ja0624319

12. Nomiya, K., Torii, H., Hasegawa, T., Nemoto, Y., Nomura, K., Hashino, K., Uchida, M., Kato, Y., Shimizu, K. and Oda, M. (2001) Insulin Mimetic Effect of a Tungstate Cluster. Effect of Oral Administration of Homo-Polyoxotungstates and Vanadium-Substituted Polyoxotungstates on Blood Glucose Level of STZ Mice. Journal of Inorganic Biochemistry, 86, 657-667. https://doi.org/10.1016/S0162-0134(01)00233-1

13. Wang, M., Sun, W., Pang, H., Ma, H., Yu, J., Zhang, Z., Niu, Y. and Yin, M. (2016) Tuning the Microstructures of Decavanadate-Based Supramolecular Hybrids via Regularly Changing the Spacers of Bis(triazole) Ligands. Journal of Solid State Chemistry, 235, 175-182. https://doi.org/10.1016/j.jssc.2015.12.033

14. Ma, H., Meng, X., Sha, J., Pang, H. and Wu, L. (2011) Synthesis, Crystal Structure and Properties of a New Bi-Dentate Decavanadate [Cu(en)2H2O]2[H2V10O28]·12H2O. Solid State Sciences, 13, 850-854. https://doi.org/10.1016/j.solidstatesciences.2011.03.007

15. Li, S., Sun, W., Wang, K., Ma, H., Pang, H., Liu, H. and Zhang, J. (2014) Turn Helical Motifs from Pair to Single Entangled Double Helixes in a Cobalt-Vanadate System via Introduction of a V-Shaped Ligand. Inorganic Chemistry, 53, 4541-4547. https://doi.org/10.1021/ic500224m

16. Klistincová, L., Rakovsky, E. and Schwendt, P. (2008) Decavanadate Ion as Bridging Ligand. Synthesis and Crystal Structure of (NH4)2[Cu2(NH3CH2CH2COO)4- (V10O28)]·10H2O. Inorganic Chemistry Communications, 11, 1140-1142.

17. Putrevu, N.R., Doedens, R.J. and Khan, M.I. (2013) Decavanadate with a Novel Coordination Complex: Synthesis and Characterization of (NH4)2[Ni(H2O)5(NH3)]2- (V10O28)·4H2O. Inorganic Chemistry Communications, 38, 5-7.

18. Chatkon, A., Barres, A., Samart, N., Boyle, S.E., Haller, K.J. and Crans, D.C. (2014) Guanylurea Metformium Double Salt of Decavanadate, (HGU+)4(HMet+)2(V10O286-)·2H2O. Inorganica Chimica Acta, 420, 85-95. https://doi.org/10.1016/j.ica.2013.12.031

19. Truflandier, L.A., Boucher, F., Payen, C., Hajjar, R., Millot, Y., Bonhomme, C. and Steunon, N. (2010) DFT-NMR Investigation and 51V 3QMAS Experiments for Probing Surface OH Ligands and the Hydrogen-Bond Network in a Polyoxovanadate Cluster: The Case of Cs4[H2V10O28]·4H2O. Journal of the American Chemical Society, 132, 4653-4668. https://doi.org/10.1021/ja908973y

20. Kodama, S., Taya, N. and Ishii, Y. (2014) A Novel Octanuclear Vanadium(V) Oxide Cluster Complex Having an Unprecedented Neutral V8O20 Core Functionalized with 4,4’-Di-tert-butyl-2,2’-bipyridine. Inorganic Chemistry, 53, 2754-2756. https://doi.org/10.1021/ic4031393

21. Graia, M., Ksiksi, R. and Driss, A. (2009) Nonapiperidinium Monohydrogen Deca-Vanadate Tetra-Nitrate. Acta Crystallographica E, 65, m953-m954. https://doi.org/10.1107/S1600536809026555

22. Rakovsky, E. and Krivosudsky, L. (2014) Tetrakis(2,6-di-methyl-pyridinium) Di- Hydrogen Deca-Vanadate Dehydrate. Acta Crystallographica E, 70, m225-m226. https://doi.org/10.1107/S1600536814011118

23. Fernadez de Luis, R., Urtiaga, M.K., Mesa, J.L. and Arriortua, M.I. (2010) Tris[4,4’- (ethene-1,2-di-yl)dipyridinium] Deca-Vanadate Dehydrate. Acta Crystallographica E, 66, m323-m324. https://doi.org/10.1107/S1600536810006215

24. Omri, I., Mhiri, T. and Graia, M. (2016) A New Monohydrogendecavanadate (V)-Dihydrogendecavanadate (V) with Dibutylammonium Cations [C8NH20]9- [H2V10O28][HV10O28].2.13H2O: Synthesis, Crystal Structure, Vibrational and Optical Properties. Journal of Molecular Structure, 1108, 334-340.

25. Sheldrick, G.M. (2008) A Short History of SHELX. Acta Crystallographica A, 64, 112-122. https://doi.org/10.1107/S0108767307043930

26. Sheldrick, G.M. (2015) Crystal Structure Refinement with SHELXL. Acta Crystallographica C, 71, 3-8. https://doi.org/10.1107/S2053229614024218

27. Brandenburg, K. (2001) DIAMOND Version 2.1e Crystal Impact GbR Bonn Germany.

28. Microcal Origin Version 8.0 (1991-2009). Microcal Software Inc. One, Northampton.

29. Momma, K. and Izumi, F. (2011) VESTA 3 for Three-Dimensional Visualization of Crystal, Volumetric and Morphology Data. Journal of Applied Crystallography, 44, 1272-1276. https://doi.org/10.1107/S0021889811038970

30. Baur, W.H. (1974) The Geometry of Polyhedral Distortions. Predictive Relationships for the Phosphate Group. Acta Crystallographica B, 30, 1195-1215. https://doi.org/10.1107/S0567740874004560

31. Brown, I.D. (1992) Chemical and Steric Constraints in Inorganic Solids. Acta Crystallographica B, 48, 553-572. https://doi.org/10.1107/S0108768192002453

32. Bresse, N.E. and O’Keeffe, M. (1991) Bond-Valence Parameters for Solids. Acta Crystallographica B, 47, 192-197. https://doi.org/10.1107/S0108768190011041

33. Siddiqi, Z.A., Sharma, P.K., Shahid, M., Kalid, M., Siddique, A. and Kumar, S. (2012) Novel Decavanadate Cluster Complexes [H2V10O28][LH]4·nH2O (L = Imidazole, n = 2 or 2-Methylimidazole, n = 0): Preparation, Characterization and Genotoxic Studies. Journal of Molecular Structure, 1029, 86-91. https://doi.org/10.1016/j.molstruc.2012.06.035

34. Yan, J., Zhao, H., Li, Z., Xing, Y., Zeng, X., Ge, M. and Niu, S. (2009) A Self-Assembled 3D Hydrogen Bonded Network Constructed from Polyoxovanadate and Protonated Organic Substrate with a Solvent Hydrolysis Reaction. Journal of Cluster Science, 20, 717-724. https://doi.org/10.1007/s10876-009-0274-1

35. Brown, I.D. (1976) On the Geometry of O-H...O Hydrogen Bonds. Acta Crystallographica A, 32, 24-31. https://doi.org/10.1107/S0567739476000041