Stabilization of tetrameric metavanadate ion by tris(1,10-phenanthroline)cobalt(III): Synthesis, spectroscopic and X-ray structural study of [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O

Abstract

A new complex salt of composition [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O (phen = 1,10-phenanthroline and [V₄O₁₂]^4- = tetrameric dodecaoxotetravanadate ion) was synthesized by reacting appropriate salts in aqueous medium. The complex salt has been characterized by elemental analyses, thermogravimetric analysis (TGA), cyclic voltammetry (CV), FT-IR and UV/Vis spectroscopies, solubility product and conductance measurements. Single crystal X-ray structure determination revealed ionic structure consisting of three complex cations, [Co(phen)₃]³⁺, two [V₄O₁₂]^4- anions, one chloride and twenty seven lattice waters. Detailed structural and spectroscopic analyses of [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O show that the large anion is stabilized by the large cationic metal complex as there is preferred shape compatibility that leads to a large number of lattice stabilizing non-covalent interactions.

1. Introduction

Anions are essential to life with roles in biological processes, industry and agriculture [1-9]. Some anionic species exit only in solution but cannot be isolated as solid salts due to solvent stabilization or lattice inhibition. This lattice inhibition can be removed by selection of suitable counter ions. According to D.H. McDaniel, the counter ion affects the formation of complex in a number of ways like lattice dominating, lattice energy limiting, insulating effects, polarization effect, shape and size [10]. Solid metal complexes are stabilized by large counter ions, preferably ions of the same but opposite charge. The importance of shape and size of cation in precipitating the desired complexes is well illustrated by halocuprate and iodoplatinate(II) salts [10, 11]. Counter ions which can have non-covalent interactions with anions in addition to the electrostatic interaction are useful in synthesis of new and unusual anionic species like [Hg₂(SCN)₇]^3- and [HgBr₅]^3- [12, 13]. In these complexes, in addition to the large counter anion, non-covalent interaction like N-H…X play crucial roles in lattice stabilization.

Anionic species containing polyoxotransition metals have been studied extensively due to their varied geometries and oxidation states. Vanadium, in the form of organic–inorganic metal hybrid vanadium oxides or complexes with polyoxovanadate have shown ability to adopt a variety of coordination geometries and oxidation states [14] with potential utilization in catalysis and materials. These vanadates are good electron acceptors, electron relay stations [15] and some are used in photolytic water splitting [16, 17]. The formation of polyoxovanadates depends upon coordination preferences of the transition metal used and geometrical constraints of the polydentate ligands. Anhydrous alkali metal metavanadates are composed of infinite chains of corner sharing VO₄ tetrahedra in MVO₃ (M = NH₄, K, Rb, Cs); KVO₃·H₂O and Ca(VO₃)₂ [18] contain chains of edge-linked VO₅ units while forming M₂V₂O₆ with metals like Mg, Zn, Pb, Cd and Cu [19-23]. For transition metals with large organic ligands, oxovanadates V₄O₁₂^4- have been reported, [Co₄O₄(dpaH)₄(CH₃COO)₂]₂·V₄O₁₂·5H₂O [24] and [M^II(phen)₃]₂V₄O₁₂·phen·22H₂O (M^II = Co, Ni) [25]. The majority of complexes containing polyoxovanadates reported have been prepared under isothermal conditions except a few like Ni(C₈H₂₂N₄)](VO₃)₂ and [M^II(phen)₃]₂V₄O₁₂·phen·22H₂O (M^II = Co, Ni). In the present study we have utilized cationic tris(1,10-phenanthroline)cobalt(III) complex for isolation of peroxovanadate (V₄O₁₂)^4- as there is no report in the literature of stabilization of [V₄O₁₂]^4- by trivalent or complexed metal ion. It is also envisaged that oxygens bonded to vanadium(V) will form hydrogen bonds (through second sphere interactions) with C-H groups originating from 1,10-phenanthroline coordinated to cobalt(III) to generate an intricate network that would stabilize the crystal lattice. This study reports synthesis, spectroscopic and X-ray structural study of [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O, the first report of a stabilization of rare [V₄O₁₂]^4- by [Co(phen)₃]³⁺.

2. Experimental

2.1. Materials

Analytical grade reagents were used without purification. [Co(phen)₃]Cl₃ was prepared by reacting [Co(NH₃)₅Cl]Cl₂ and 1,10-phenanthroline monohydrate according to the method described in the literature [26].

2.2. Instruments and measurements

C, H and N were estimated microanalytically by automatic PERKIN ELMER 2400 CHN elemental analyzer. Cobalt was estimated by volumetric method [27]. UV/Visible spectra were recorded in water using a HITACHI 330 spectrophotometer. Infrared spectrum was recorded using a PERKIN ELMER spectrum RX FT-IR system using a KBr pellet. Conductance measurements were performed on a Pico Conductivity Meter (Model CNO4091201, Lab India) in aqueous medium at 25 °C using doubly-distilled water.

Thermogravimetric analysis (TGA) was conducted with a Mettler Toledo TGA/SDTA 851 instrument calibrated using high purity indium and high purity zinc standards. The experiment was conducted under nitrogen flow between 308 and 873 K and under air flow between 873 and 1173 K. The flow was maintained at 70 ml min^-1. The specimen, about 10 mg, contained in a 70 μl alumina pan was carried from 308 to 1173 K at variable heating rate: the heating rate was 1 K min^-1 when the weight loss was higher than 2 μg s^-1, and 20 K min^-1 when the weight loss was less than 1 μg s^-1.

Electrochemical measurements were conducted on a potentiostat (CH Instuments 440a) with a glass encased 3-mm diameter glassy carbon electrode (Cypress Systems), Pt wire, and Ag/AgCl (3 M KCl) as the working, auxiliary, and reference electrodes, respectively. The working electrode was polished on a polishing pad with 0.05 μm alumina powder, rinsed and sonicated prior to use. All solutions were bubbled with N₂ for 5 min to remove O₂ prior to scanning.

2.3. Synthesis of [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O

Tris(1,10-phenanthroline)cobalt(III) chloride (0.5 g, 0.7 mmol) was dissolved in water (10 mL) and in another beaker (0.248 g, 2.1 mmol) ammonium metavanadate was dissolved in water (30 mL). Upon mixing the two solutions, no color change or precipitation occurred. When it was allowed to evaporate slowly at room temperature, yellow single crystals appearing after a few hours were allowed to grow. The crystals were separated and dried in air. The yield was 0.487 g (66.25%). The composition was established by elemental analyses. [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O Found (%): C, 41.57; H, 4.02; N, 8.05; Co, 5.67; Cl, 1.09; Calculated (%): C, 41.67; H, 4.05; N, 8.10; Co, 5.70; Cl, 1.14.

2.4. X-ray structure determination

Single crystal X-ray diffraction data for the complex salt were collected on a Nonius Kappa CCD diffractometer using graphite-monochromated MoKα radiation (λ = 0.71069 Ǻ). All intensities were corrected for Lorentz, polarization and adsorption [28]. The structure was solved by direct methods with the SIR97 program [29] and refined by block matrix least squares (four blocks) using the SHELXL-97 program [30]. Non-hydrogen atoms were refined anisotropically. Hydrogens of phenanthroline were given calculated positions, while those belonging to water were not included in the refinement. All other calculations were performed using WinGX [31] and PARST [32]. Final R-values together with selected refinement details are given in table 1.

Table 1.

Crystal data and refinement parameters of [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O

Chemical formula	3(CoC36H24N6)·2(V4O12)·Cl·27(H2O)
Mr	3112.03
Cell setting, space group	Triclinic, P-1
Temperature (K)	295
a, b, c (Å)	15.4063(2), 18.8746(3), 25.1206(4)
α, β, γ (°)	97.7540(8), 103.5560(7), 101.4310(7)
V (Å3)	6833.14(18)
Z	2
Dx (Mg m−3)	1.746
Radiation type	Mo Kα
μ (mm−1)	0.99
Crystal form, color	Prismatic, orange
Crystal size (mm)	0.29 × 0.14 × 0.09
No. of measured, independent and observed reflections	42624, 28163, 10204
Criterion for observed reflections	I > 2σ(I)
θmax (°)	27.0
Refinement on	F2
R[F2 > 2σ(F2)], wR(F2), S	0.101, 0.361, 0.98
No. of reflections / No. of parameters	28163 / 1776
Weighting scheme	Calculated w = 1/[σ2(Fo2) + (0.1928P)2], where P = (Fo2 + 2Fc2)/3
Δρmax, Δρmin (e Å−3)	0.99, -0.69

3. Results and discussion

3.1. Synthesis

The complex salt, [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O was obtained by reaction of tris(1,10-phenanthroline)cobalt(III) chloride and ammonium metavanadate in water in 1:3 molar ratio (scheme 1); metavanadate tetramerizes to form [V₄O₁₂]^4- in the presence of [Co(phen)₃]³⁺.

Scheme 1.

Schematic representation of chemical reaction.

The newly formed complex salt has been characterized by elemental analyses, TGA, cyclic voltammetry studies, spectroscopies (UV/Visible and FT-IR) and conductance measurements. The presence of one chloride ion was confirmed by its gravimetric analysis using AgNO₃ solution. The complex salt is sparingly soluble in water and other common solvents. The crystal structure has been unambiguously established by single crystal X-ray crystallography.

3.2. Thermogravimetric analysis

Thermogravimetric analysis of the complex salt showed five weight loss steps. The first and second steps in the TGA curve correspond to weight loss of 12.8% and 2.8% at 363 K and 411 K, respectively (Supplementary Material), which can be ascribed to loss of free water (calculated weight loss was 15.62% and observed weight loss was 15.60% in the first two steps). The third and fourth weight loss of 5.3 and 4.3%, respectively, take place between 425 and 873 K, corresponding to pyrolysis of organic matter. The fifth weight loss (41.3%) corresponds to oxidation of combustible material at 873 K, when the atmosphere changed from nitrogen to air. In the pan, at the end of analysis, 33.5% of ash remains.

3.3. Cyclic voltammetry studies

The electrochemical properties of [Co(phen)₃]³⁺ have been studied [33], with CV reported to have an E_pc and E_pa of 0.114 and 0.179 V vs. Ag/AgCl, respectively. CV of [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O showed a similar CV response at a glassy carbon electrode in 0.1 M KCl aqueous solution with a scan rate of 100 mV/s. A CV of the chloride salt showed similar behavior. [Co(phen)₃]³⁺ undergoes a one-electron reduction to the 2+ form with a peak potential (E_pc) of 0.143 V vs. Ag/AgCl as shown in Supplementary Material. On the reverse scan, Co(phen)₃²⁺ is reoxidized at E_pa of 0.215 V. The peak potential separation (ΔE) of 72 mV indicates that this is the reversible one electron couple mentioned earlier. No electro-activity was seen for V⁵⁺ species in the potential range studied (0.6 to -0.9 V), even though the standard reduction potential (E⁰) of VO²⁺ to V³⁺ species is 0.115 V vs. Ag/AgCl. The ratio of I_pa/I_pc was close to 1 (0.988), further indicating that only the reversible couple contributes to I_pc as the irreversible reduction of V⁴⁺ species would be expected to contribute to I_pc.

3.4. Measurement of solubility product

The solubility product (Ksp) of the complex salt determined in water at 25 °C was 8.08 × 10^-22 as compared to that of [Co(phen)₃]Cl₃ (2.7 × 10^-3), showing affinity of the complex cation is greater for metavanadate than chloride. This increase in affinity may be due to the increased interactions between cations and anions.

3.5. Molar conductance measurements

Molar conductance of complex salt was measured in water in the concentration range 0-100 × 10^-4 M at 25 °C. The limiting molar conductance at infinite dilution (Λ_o) was obtained by plotting the square root of concentration versus molar conductance, when extrapolated to zero. The Λ_o obtained is 882 Scm²mol^-1. The high value of molar conductance revealed that the complex salt consists of a large number of ions and unusual composition of complex salt.

3.6. Spectroscopic characterization

Vibrational spectrum of newly synthesized complex has been recorded in the region 400-4000 cm^-1. The peak assignments have been made in consultation with literature values [34-36]. IR spectral bands at 1634-1582, 3340 and 488 cm^-1 were assigned to ν(C=C)/ν(C=N), ν(O-H) of H₂O and ν(Co-N). These peaks are characteristic for 1,10-phenanthroline attached to cobalt(III) and water of crystallization. The IR spectrum of individual polyoxovanadate is characteristic due to the relatively rigid structure of V₄O₁₂^4- ion. IR bands at 942 and 905 cm^-1 were assigned to symmetrical and asymmetric vibrations of V-O_t (terminal oxygens) while bands at 815 and 640 cm^-1 were assigned to asymmetrical and symmetric vibrations of the bridging V-O_b-V. Similar IR bands have been reported for [Co(phen)₃]₂V₄O₁₂·phen·22H₂O and [Ni(phen)₃]₂V₄O₁₂·phen·22H₂O [25]. For [Co₄O₄(dpaH)₄(CH₃COO)₂]₂V₄O₁₂·5H₂O [24] bands due to V-O, V-O-V were reported at 950-770 cm^-1.

For Co(III) low spin complexes, it is possible to observe d-d transitions in the visible region because transitions corresponding to t_2g⁶ → t_2g⁵ e_g¹ with promoted electron maintaining its spin are possible. Therefore, two electronic transitions ¹A_1g → ¹T_1g and ¹A_1g → ¹T_2g are reported for familiar orange–yellow color for coordination compounds containing Co(III) which were observed around 340 and 470 nm. 1,10-Phenanthroline is also coordinated to Co(III) and transitions around 224, 264, 290 nm arise from phen [34, 37, 38]. The electronic spectrum of the title complex salt in water show absorption maxima (λ_max) at 219, 273, 280, 349 and 456 nm, close to reported values.

3.7. Description of the structure

3.7.1. Coordination geometry and bonding

The asymmetric unit is large, being constituted by three [Co(phen)₃]³⁺, two dodecaoxotetravanadates, one chloride and 27 co-crystallized waters. The high water content is confirmed by TGA analysis, as reported above. The chloride is disordered over two equivalent positions, as well as a number of co-crystallized solvent molecules. A selection of relevant bond distances and angles is reported in table 2. The geometry around the three cobalts is slightly distorted octahedral with N-Co-N angles involving nitrogen of the same 1,10-phenanthroline being < 90°. The Co-N distances are consistent with those found in recently reviewed Co(III)-1,10-phenanthroline complexes [17-21]. The oxidation states of Co have been checked in the frame of the bond valence sum method [39] using the Co-N parameters reported in the byparm2009.cif table [40]. The calculated values are 3.5, 3.6 and 3.4 for Co1, Co2 and Co3, respectively. V-O distances are similar to the mean bond lengths obtained from a CSD search on compounds containing the oxovanadate anion, 1.779(6) and 1.632(6) Å for exocyclic and endocyclic bonds, respectively (values calculated on 16 hits). The eight-membered vanadate rings are almost planar, as shown by the total puckering amplitude index 0.16(9), according to Cremer & Pople [41]) and by values of the endocyclic torsion angles, ranging from 0.7 to 38°. ORTEPIII [42] views of one cobalt complex and one oxovanadate are shown in figure 1.

Table 2.

Selected bond lengths and angles (Å and °) for [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O.

Co1-N1	1.931(8)	Co2-N10	1.950(9)
Co1-N2	1.936(8)	Co2-N11	1.938(9)
Co1-N3	1.952(8)	Co2-N12	1.922(8)
Co1-N4	1.960(9)	Co3-N13	1.951(9)
Co1-N5	1.959(9)	Co3-N14	1.955(9)
Co1-N6	1.935(8)	Co3-N15	1.937(9)
Co2-N7	1.932(9)	Co3-N16	1.961(9)
Co2-N8	1.954(9)	Co3-N17	1.955(9)
Co2-N9	1.930(8)	Co3-N18	1.971(9)
V1-O1	1.642(10)	V4-O12	1.604(7)
V1-O2	1.769(8)	V5-O13	1.623(8)
V1-O3	1.767(10)	V5-O14	1.628(10)
V1-O4	1.600(9)	V5-O15	1.774(8)
V2-O2	1.774(9)	V5-O16	1.786(11)
V2-O5	1.630(10)	V6-O16	1.762(11)
V2-O6	1.773(10)	V6-O17	1.643(9)
V2-O7	1.616(7)	V6-O18	1.624(8)
V4-O3	1.765(11)	V10-O19	1.599(12)
V3-O6	1.773(11)	V10-O20	1.773(10)
V3-O8	1.651(10)	V10-O21	1.731(1)
V3-O9	1.758(8)	V10-O24	1.619(12)
V3-O10	1.630(9)	V11-O20	1.758(10)
V4-O9	1.786(8)	V11-O22	1.628(12)
V4-O11	1.622(10)	V11-O23	1.595(11)
N1-Co1-N2	84.6(3)	N8-Co2-N12	87.9(4)
N1-Co1-N3	94.9(3)	N9-Co2-N10	84.2(4)
N1-Co1-N5	94.2(4)	N9-Co2-N11	91.5(4)
N1-Co1-N6	87.8(3)	N10-Co2-N11	88.9(4)
N2-Co1-N3	89.7(3)	N10-Co2-N12	93.7(4)
N2-Co1-N4	93.1(3)	N11-Co2-N12	85.1(4)
N2-Co1-N6	93.6(4)	N13-Co3-N14	84.1(3)
N3-Co1-N4	84.8(4)	N13-Co3-N16	92.5(4)
N3-Co1-N5	92.1(4)	N13-Co3-N17	94.4(3)
N4-Co1-N5	88.0(4)	N13-Co3-N18	89.7(3)
N4-Co1-N6	92.7(4)	N14-Co3-N15	92.6(4)
N5-Co1-N6	84.6(4)	N14-Co3-N16	88.9(4)
N7-Co2-N8	85.1(4)	N14-Co3-N18	93.6(4)
N7-Co2-N9	89.2(4)	N15-Co3-N16	83.9(4)
N7-Co2-N10	93.5(4)	N15-Co3-N17	89.1(4)
N7-Co2-N12	94.5(4)	N15-Co3-N18	94.0(4)
N8-Co2-N9	94.2(4)	N16-Co3-N17	94.1(4)
N8-Co2-N11	92.8(4)	N17-Co3-N18	83.4(4)

Figure 1.

ORTEPIII view of one cobalt complex cation, one polyoxovanadate anion and one chloride. Ellipsoids are drawn at 40% probability. For the sake of clarity, the other ions and all lattice water molecules constituting the asymmetric unit are omitted.

3.7.2. Packing

The crystal packing, due to the high number of water molecules involved, is quite complicated. Table 3 reports short O⋯O contacts inside the crystal lattice, ranging from 2.55(3) to 2.98(3) Å, which are typical for hydrogen bonding of medium strength. In addition, phen C–H groups were involved in C–H⋯O/Cl type interactions [43-46] (as many as thirty two significant hydrogen bonds have been observed which are given in table 4) defining the second-sphere coordination around the three cobalt complex cations. Three complex cations with C-H…O contacts are shown in figure 2. These C-H…O interactions (H…A distance ranging from 2.33-2.69 Å and angles A…H-D ranging from 132-160°) are of comparable strength to commonly employed N-H…O interaction (H…A distance ranging from 2.08-2.76 Å angles A…H-D ranging from 130-179°) [47] in anion binding studies. These C-H…O interactions play a crucial role in binding [V₄O₁₂]^4- as nineteen C-H…O interactions are between oxygens originating from [V₄O₁₂]^4- and C-H of 1,10-phenanthroline. No significant π-π interactions have been found, since the centroids of the stacked phenanthroline moieties are located more than 3.8 Å apart. The packing diagram of the complex salt is shown in figure 3.

Table 3.

Short O⋯O/Cl contacts (Å) for [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O.

O14…O19W	2.768(17)	O8W…O22W	2.824(23)
O17…O5W	2.900(13)	O9W…O16W	2.755(16)
O17…O10W	2.775(15)	O9W…O17W	2.798(20)
O18…O27W	2.679(21)	O9W…O21W	2.844(21)
O24…O31W	2.818(22)	O10W…O16W	2.940(18)
O1W…O15W	2.892(16)	O16W…O27W	2.730(28)
O2W…O4W	2.777(15)	O18W…O20W	2.799(16)
O2W…O6W	2.868(16)	O18W…O32W	2.870(32)
O2W…O14W	2.787(20)	O19W…O20W	2.822(22)
O3W…O5W	2.698(13)	O26W…O29W	2.821(33)
O5W…O19W	2.780(19)	O26W…O31W	2.785(35)
O6W…O18W	2.816(17)	O27W…O34W	2.912(37)
O8W…O21W	2.897(18)
O4…O24Wi	2.737(18)	O33W…O22Wiv	2.554(27)
O23W…O23i	2.728(26)	O3W…O22v	2.693(15)
O1W…O11ii	2.735(12)	O28W…O30Wvi	2.778(40)
O8W…O8ii	2.776(14)	O23W…O11vi	2.810(23)
O15W…O10ii	2.690(16)	O25W…O32Wvi	2.732(34)
O16W…O8ii	2.747(17)	O14W…O5vii	2.748(17)
O22W…O5ii	2.742(20)	O28W…O23viii	2.693(20)
O1W…O24iii	2.738(16)	O32W…O25Wix	2.732(34)
O6W…Cl1iii	2.781(13)	O1…O4Wx	2.782(15)
O15W…O26Wiii	2.801(23)	O4W…O24Wxi	2.815(23)
O17W…O14iii	2.790(14)	O29W…O18Wxi	2.989(25)
O25W…O22Wiv	2.984(26)	O30W…O19xi	2.841(28)

⁽ⁱ⁾Symmetry codes: 1-x,-y,-z;

⁽ⁱⁱ⁾x,y+1,z+1;

⁽ⁱⁱⁱ⁾1-x,-y,1-z;

^(iv)x+1,y,z;

^(v)x,y,1+z;

^(vi)x,y+1,z;

^(vii)x+1,y,z+1;

^(viii)x+1,y+1,z+1;

^(ix)x,y-1,z;

^(x)1-x,-y-1,1-z;

^(xi)2-x,-y,1-z

Table 4.

Hydrogen bonding parameters for C–H…O/Cl contacts (Å and °).

D–H …A	D–H	D…A	H…A	D–H…A
C11-H7…O21	0.930	3.55(1)	2.67	158
C22-H14…Cl1	0.930	3.54(2)	2.66	156
C43-H29…O7	0.930	3.23(2)	2.55	130
C73-H49…O15	0.930	3.15(1)	2.45	133
C85-H57…O33W	0.930	3.24(3)	2.51	136
C102-H68…O18	0.930	3.38(2)	2.69	132
C51-H35…O3i	0.930	3.24(1)	2.39	151
C54-H36…O12i	0.930	3.51(1)	2.63	158
C1-H1…O2i	0.930	3.03(1)	2.33	132
C30-H20…O10i	0.930	3.36(1)	2.60	139
C7-H5…O12ii	0.930	3.20(1)	2.45	138
C12-H8…O22iii	0.930	3.28(1)	2.51	141
C13-H9…O24Wiii	0.930	3.36(2)	2.67	131
C63-H43…O5Wiv	0.930	3.50(2)	2.67	149
C49-H33…O2Wiv	0.930	3.26(2)	2.47	143
C25-H17…Cl1v	0.930	3.30(1)	2.54	138
C31-H21…O13vi	0.930	3.41(1)	2.57	150
C36-H24…Cl2vi	0.930	3.28(1)	2.49	144
C34-H22…O16vi	0.930	3.25(1)	2.48	139
C97-H65…O5Wvi	0.930	3.26(1)	2.51	136
C62-H42…O22vii	0.930	3.20(2)	2.38	147
C37-H25…O9vii	0.930	3.19(1)	2.47	134
C55-H37…O4vii	0.930	3.38(2)	2.66	135
C57-H38…O4vii	0.930	3.40(2)	2.68	135
C59-H40…O8Wviii	0.930	3.40(1)	2.65	139
C79-H53…O13ix	0.930	3.25(2)	2.52	136
C91-H61…O28Wx	0.930	3.42(3)	2.58	149
C84-H56…O25Wx	0.930	3.39(2)	2.61	142
C87-H59…O8Wxi	0.930	3.28(2)	2.39	158
C106-H70…O6xii	0.930	3.30(1)	2.41	160
C103-H69…O7xii	0.930	3.46(1)	2.58	158
C108-H72…O9Wxiii	0.930	3.29(2)	2.54	138

⁽ⁱ⁾Symmetry codes : -x,-y-1,-z;

⁽ⁱⁱ⁾1-x,-y-1,-z;

⁽ⁱⁱⁱ⁾1-x,-y,-z;

^(iv)x-1,y,z-1;

^(v)-x,-y,-z;

^(vi)1-x,-y,1-z;

^(vii)x-1,y,z;

^(viii)x-1,y-1,z-1;

^(ix)2-x,-y,1-z;

^(x)2-x,1-y,1-z;

^(xi)1-x,1-y,1-z;

^(xii)x+1,y+1,z+1;

^(xiii)x+1,y,z

Figure 2.

C-H…O interactions between complex cations and hydrogen bond acceptor groups from anions and lattice waters.

Figure 3.

Packing diagram of the complex salt (viewed along a).

All related structures reported are characterized by high content of co-crystallized solvent with the number of waters ranging from 5 to 22. In particular, the structure of the Co(II) salt contains, besides 22 water molecules, a free co-crystallized phenanthroline. A possible explanation is that two cumbersome objects (the cation and the anion), very different in shape, when put together in the crystal lattice leaves large empty spaces that have to be occupied by the solvent of crystallization to assure efficient packing and thereby increasing stability of crystal lattice. Thus, O⋯O/Cl short contacts and C-H⋯O/Cl hydrogen bonds are driving forces for stabilization of the crystal lattice and formation of the complex salt.

4. Conclusions

A new complex salt [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O has been synthesized and characterized by physico-chemical, spectroscopic and X-ray structural studies. Single crystal X-ray structure determination revealed an ionic structure consisting of three complex cations, two V₄O₁₂^4- anions, one chloride and twenty seven lattice waters. The crystal lattice is stabilized by hydrogen bonding, C-H⋯O/Cl non-covalent interactions in addition to the electrostatic forces. Detailed structural and spectroscopic analyses of [Co(phen)₃]₃(V₄O₁₂)₂Cl·27H₂O show the large anion [V₄O₁₂]^4- was stabilized by the large [Co(phen)₃]³⁺.