supplementary materials


wm2477 scheme

Acta Cryst. (2011). E67, m626-m627    [ doi:10.1107/S1600536811014280 ]

Aquachloridobis(diphenylglyoximato-[kappa]2N,N')cobalt(III) dihydrate

P. Meera, M. A. Selvi and A. Dayalan

Abstract top

The asymmetric unit of the title complex, [Co(C14H11N2O2)2Cl(H2O)]·2H2O or [Co(dpgH)2Cl(H2O)]·2H2O, where dpgH- is diphenyl glyoximate, consists of one-half of a [Co(dpgH)2Cl(H2O)] complex and one solvent water molecule. The complex is completed through inversion symmetry, with the CoIII atom situated at the centre of symmetry. The coordination geometry around the CoIII atom is distorted octahedral with the four N atoms of the two dpgH- ligands forming an approximate square plane with N-Co-N bite angles of 81.13 (14) and 98.87 (14)°. The Cl- ligand and the water molecule are disordered in a 1:1 ratio and are in the axial positions, almost perpendicular to the plane of the glyoximate ligands [O-Co-Cl = 175.3 (10)°]. The two glyoximate ligands are linked by strong intramolecular O-H...O hydrogen bonds. In addition, O-H...O interactions involving the solvent water molecules and O-H...N hydrogen-bonding interactions are also observed. The solvent water molecule is disordered over five positions with different occupancies.

Comment top

The dioxime complexes of cobalt(III), known as cobaloximes, and their derivatives have been found to mimic vitamin-B12 coenzyme. The studies on steric and electronic effects of cobaloximes helped in the successful design of novel derivatives with desired properties (Gupta et al., 2003; Randaccio, 1999; Brown & Satyanarayana, 1992; Gilaberte et al., 1988). Among the stereoisomeric benzildioximes (syn, amphi, anti), only the anti isomer shows chelation properties towards transition metal ions (Varhelyi et al., 1999).

In the structure of the title compound, [Co(C14H11N2O2)2Cl(H2O)].2H2O, or [Co(dpgH)2Cl(H2O)].2H2O, where dpgH- = diphenyl glyoximate, two halves of the complex molecule are related through inversion symmetry with CoIII situated at the centre of symmetry. The coordination geometry around CoIII is a slightly distorted octahedron (Fig. 1) with the four N atoms of the dpgH- ligand forming an approximate square plane. The bite angles N1—Co—N2 of the equatorial ligands are 81.13 (14) and 98.87 (14)°, respectively. The Cl- ligand and the water molecule are in axial positions and are disordered in a 1:1 ratio. They are almost perpendicular to the plane containing the equatorial dpgH- ligand (O3—Co1—Cl1 = 175.3 (10)°). The two glyoximate ligands are linked by strong intramolecular O—H···O hydrogen bonds. In addition, O1—H1···N2 hydrogen bonding interaction is also observed (Fig. 2). A similar interaction was observed for a related complex (Meera et al., 2009). The lattice water molecule (O4) is disordered over five positions with different occupancies. Although the H positions of the disordered water molecules could not be located, close O···O interactions suggest likewise an involvement in hydrogen bonding (Table 2).

Related literature top

For related complexes, see: Gupta et al. (2003); Randaccio (1999); Brown & Satyanarayana (1992); Gilaberte et al. (1988). For the nature of equatorial ligands, see: Varhelyi et al. (1999). For similar structures, see: Meera et al. (2009). For details of the synthesis, see: Toscano et al. (1983); Gupta et al. (2001). For spectroscopic studies related to the complex, see: Gupta et al. (2004); Lopez et al. (1992); Silverstein & Bassler (1984); Mandal & Gupta (2005).

Experimental top

Cobalt(II) chloride hexahydrate was thoroughly ground and mixed with diphenylglyoxime in a 1:2 molar ratio in an aqueous solution of acetone. The reaction mixture was stirred for five hours at an elevated temperature (Toscano et al., 1983; Gupta et al., 2001). The resulting brown mass was filtered, washed with acetone, ether and dried in a desiccator. Brown coloured crystals appeared in two to three days on slow evaporation of the saturated solution of the complex in ethanol. Elemental analysis, obtained by analytical method, agreed well with the theoretical data expected for the formula of the complex, C28H28N4O7ClCo. Anal., % (calc., %): C 53.97 (53.58); H 4.94 (4.47); N 9.05 (8.93). The CN stretching vibration of oxime in its complex was observed at 1385 cm-1 and the intramolecular hydrogen bonded –OH around 3140 cm-1. A moderate peak around 1090 cm-1 may be assigned to the C=N—O stretching of the oxime. The band around 540 cm-1 could be attributed to cobalt(III)-nitrogen stretching. The 1H NMR spectrum of the complex in acetone-d6 shows three different signals corresponding to the three different aromatic protons of the diphenylglyoximate (Gupta et al., 2004; Lopez et al., 1992). The H atoms in the second and the sixth position of the benzene ring of the diphenylglyoximate show a doublet at 7.2 p.p.m., while the third and fifth H atoms show a triplet at 7.4 p.p.m.. Similarly, the fourth one gives a triplet at 7.3 p.p.m..The oxime –OH protons resonate at 9.1 p.p.m.. A singlet around 8.5 p.p.m. represents the protons of the –OH group of the aqua ligand (Silverstein & Bassler, 1984; Mandal & Gupta, 2005).

Refinement top

The O atom of the solvent water molecule in the lattice is disordered over five positions O4A, O4B, O4C, O4D, O4E with different site occupancy factor. The refinement of occupancy by means of free variable in each case is 0.302, 0.250, 0.131, 0.198 and 0.119 for O4A, O4B, O4C, O4D and O4E, respectively. The O atoms of water were refined anisotropically with equal anisotropic displacement parameters. The disordered chloride (Cl1) and oxygen (O3) atom sharing the axial position were refined with equal site occupancies of 1:1. The H atoms bound to aromatic carbon were constrained to ride on their parent atom with d(C—H) = 0.93Å and Uiso(H) =1.2Uequ(C). The position of the H atom bound to the hydroxyl group was identified from the difference in the electron density map and constrained to a distance of d(O2—H2) = 0.92 (1) Å. H positions of the positionally disordered lattice water molecules could not be found from difference maps and were eventually omitted from refinement.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2008); software used to prepare material for publication: PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. ORTEP representation of the complex drawn at the 30% probability level with the atom labelling scheme. [Symmetry Code: (i) 1-x, -y, -z].
[Figure 2] Fig. 2. Packing of the complex in the unit cell with the disordered water occupying the intermolecular voids. The hydrogen atoms bound to aromatic carbons have been omitted for clarity.
Aquachloridobis(diphenylglyoximato-κ2N,N')cobalt(III) dihydrate top
Crystal data top
[Co(C14H11N2O2)2Cl(H2O)]·2H2OF(000) = 648
Mr = 626.92Dx = 1.363 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 2441 reflections
a = 12.0709 (4) Åθ = 2.8–25.0°
b = 5.9689 (2) ŵ = 0.70 mm1
c = 21.9224 (5) ÅT = 293 K
β = 104.770 (1)°Block, brown
V = 1527.32 (8) Å30.30 × 0.20 × 0.20 mm
Z = 2
Data collection top
Bruker APEXII CCD
diffractometer
2682 independent reflections
Radiation source: fine-focus sealed tube2431 reflections with I > 2σ(I)
graphiteRint = 0.030
ω and φ scanθmax = 25.0°, θmin = 1.8°
Absorption correction: multi-scan
(SADABS; Bruker, 1999)
h = 1414
Tmin = 0.761, Tmax = 0.861k = 77
13610 measured reflectionsl = 2526
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.062H-atom parameters constrained
wR(F2) = 0.199 w = 1/[σ2(Fo2) + (0.1021P)2 + 2.2574P]
where P = (Fo2 + 2Fc2)/3
S = 1.25(Δ/σ)max < 0.001
2682 reflectionsΔρmax = 0.92 e Å3
215 parametersΔρmin = 0.53 e Å3
1 restraintExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.025 (3)
Crystal data top
[Co(C14H11N2O2)2Cl(H2O)]·2H2OV = 1527.32 (8) Å3
Mr = 626.92Z = 2
Monoclinic, P21/nMo Kα radiation
a = 12.0709 (4) ŵ = 0.70 mm1
b = 5.9689 (2) ÅT = 293 K
c = 21.9224 (5) Å0.30 × 0.20 × 0.20 mm
β = 104.770 (1)°
Data collection top
Bruker APEXII CCD
diffractometer
2682 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 1999)
2431 reflections with I > 2σ(I)
Tmin = 0.761, Tmax = 0.861Rint = 0.030
13610 measured reflectionsθmax = 25.0°
Refinement top
R[F2 > 2σ(F2)] = 0.062H-atom parameters constrained
wR(F2) = 0.199Δρmax = 0.92 e Å3
S = 1.25Δρmin = 0.53 e Å3
2682 reflectionsAbsolute structure: ?
215 parametersFlack parameter: ?
1 restraintRogers parameter: ?
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
C10.3917 (4)0.0079 (7)0.0955 (2)0.0349 (9)
C20.5064 (3)0.0989 (7)0.12232 (19)0.0342 (9)
C30.3003 (4)0.0027 (8)0.1290 (2)0.0404 (11)
C40.2296 (4)0.1819 (9)0.1254 (2)0.0519 (12)
H40.24230.30920.10370.062*
C50.1405 (5)0.1770 (12)0.1539 (3)0.0668 (16)
H50.09270.30090.15080.080*
C60.1215 (5)0.0054 (12)0.1864 (3)0.0677 (18)
H60.06100.00620.20550.081*
C70.1911 (5)0.1880 (11)0.1913 (3)0.0619 (15)
H70.17840.31310.21390.074*
C80.2809 (4)0.1867 (9)0.1625 (2)0.0482 (11)
H80.32840.31120.16600.058*
C90.5534 (3)0.1512 (8)0.19009 (18)0.0353 (9)
C100.5471 (4)0.0079 (8)0.2349 (2)0.0457 (11)
H100.50780.14120.22270.055*
C110.5994 (5)0.0313 (11)0.2977 (2)0.0576 (14)
H110.59690.07670.32790.069*
C120.6550 (4)0.2299 (11)0.3153 (2)0.0604 (16)
H120.69000.25590.35760.073*
C130.6600 (4)0.3909 (10)0.2718 (2)0.0519 (13)
H130.69720.52590.28440.062*
C140.6092 (4)0.3513 (8)0.2090 (2)0.0432 (11)
H140.61250.45990.17910.052*
N10.3780 (3)0.0578 (6)0.03761 (16)0.0335 (8)
N20.5663 (3)0.1165 (6)0.08134 (15)0.0325 (8)
O10.2790 (2)0.1374 (6)0.00398 (14)0.0455 (8)
O20.6748 (2)0.1866 (6)0.09899 (14)0.0416 (8)
H2A0.70250.18490.06850.10 (3)*
Co10.50000.00000.00000.0294 (3)
Cl10.5813 (10)0.3227 (16)0.0360 (5)0.0429 (13)0.50
O30.564 (2)0.296 (4)0.0254 (12)0.044 (7)0.50
O4A0.7645 (12)0.624 (3)0.0072 (7)0.084 (3)0.302 (9)
O4B0.9669 (16)0.417 (4)0.0424 (9)0.084 (3)0.250 (10)
O4C0.875 (3)0.618 (7)0.0176 (17)0.084 (3)0.131 (9)
O4D1.023 (2)0.437 (5)0.0007 (13)0.084 (3)0.198 (9)
O4E1.002 (3)0.295 (9)0.028 (2)0.084 (3)0.119 (10)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.033 (2)0.038 (2)0.034 (2)0.0038 (17)0.0086 (17)0.0021 (16)
C20.031 (2)0.037 (2)0.034 (2)0.0015 (17)0.0082 (17)0.0000 (17)
C30.033 (2)0.054 (3)0.033 (2)0.0056 (19)0.0075 (18)0.0005 (18)
C40.054 (3)0.059 (3)0.046 (3)0.016 (2)0.019 (2)0.004 (2)
C50.054 (3)0.087 (4)0.064 (3)0.030 (3)0.023 (3)0.003 (3)
C60.045 (3)0.109 (5)0.057 (3)0.008 (3)0.027 (3)0.003 (3)
C70.049 (3)0.083 (4)0.058 (3)0.010 (3)0.022 (2)0.009 (3)
C80.039 (2)0.058 (3)0.050 (3)0.002 (2)0.015 (2)0.005 (2)
C90.0275 (19)0.046 (2)0.033 (2)0.0019 (18)0.0090 (16)0.0058 (18)
C100.041 (3)0.057 (3)0.041 (2)0.002 (2)0.013 (2)0.001 (2)
C110.053 (3)0.083 (4)0.036 (3)0.013 (3)0.011 (2)0.009 (2)
C120.038 (3)0.104 (5)0.035 (2)0.008 (3)0.002 (2)0.020 (3)
C130.038 (2)0.067 (3)0.050 (3)0.003 (2)0.011 (2)0.023 (3)
C140.035 (2)0.053 (3)0.043 (2)0.005 (2)0.0112 (18)0.008 (2)
N10.0282 (17)0.0370 (18)0.0344 (18)0.0050 (14)0.0061 (14)0.0023 (15)
N20.0278 (17)0.0378 (19)0.0312 (16)0.0044 (14)0.0061 (13)0.0015 (14)
O10.0311 (15)0.065 (2)0.0411 (16)0.0167 (15)0.0101 (13)0.0096 (15)
O20.0272 (15)0.060 (2)0.0369 (15)0.0128 (14)0.0064 (12)0.0088 (14)
Co10.0256 (5)0.0331 (5)0.0286 (5)0.0046 (3)0.0054 (3)0.0011 (3)
Cl10.044 (3)0.0374 (18)0.041 (3)0.0015 (18)0.001 (3)0.004 (2)
O30.027 (8)0.064 (12)0.031 (8)0.003 (7)0.012 (5)0.016 (5)
O4A0.062 (6)0.103 (9)0.087 (7)0.019 (6)0.021 (5)0.004 (6)
O4B0.062 (6)0.103 (9)0.087 (7)0.019 (6)0.021 (5)0.004 (6)
O4C0.062 (6)0.103 (9)0.087 (7)0.019 (6)0.021 (5)0.004 (6)
O4D0.062 (6)0.103 (9)0.087 (7)0.019 (6)0.021 (5)0.004 (6)
O4E0.062 (6)0.103 (9)0.087 (7)0.019 (6)0.021 (5)0.004 (6)
Geometric parameters (Å, °) top
C1—N11.298 (6)C11—C121.368 (9)
C1—C21.463 (6)C11—H110.9300
C1—C31.473 (6)C12—C131.366 (8)
C2—N21.294 (5)C12—H120.9300
C2—C91.482 (6)C13—C141.377 (6)
C3—C81.375 (7)C13—H130.9300
C3—C41.383 (7)C14—H140.9300
C4—C51.375 (7)N1—O11.323 (4)
C4—H40.9300N1—Co11.894 (3)
C5—C61.353 (9)N2—O21.334 (4)
C5—H50.9300N2—Co11.891 (3)
C6—C71.363 (9)O2—H2A0.8200
C6—H60.9300Co1—N2i1.891 (3)
C7—C81.386 (7)Co1—N1i1.894 (3)
C7—H70.9300Co1—O31.95 (3)
C8—H80.9300Co1—O3i1.95 (3)
C9—C141.382 (6)Co1—Cl12.214 (11)
C9—C101.382 (6)Co1—Cl1i2.214 (11)
C10—C111.381 (7)O4D—O4Dii0.94 (4)
C10—H100.9300
O4A···O3iii2.592 (4)O4A···CL1iii2.470 (2)
O4A···O1i2.951 (2)
N1—C1—C2112.1 (4)C13—C14—C9120.5 (5)
N1—C1—C3123.8 (4)C13—C14—H14119.8
C2—C1—C3124.0 (4)C9—C14—H14119.8
N2—C2—C1113.0 (4)C1—N1—O1121.7 (3)
N2—C2—C9122.6 (4)C1—N1—Co1116.8 (3)
C1—C2—C9124.2 (4)O1—N1—Co1121.0 (3)
C8—C3—C4118.7 (4)C2—N2—O2120.4 (3)
C8—C3—C1120.1 (4)C2—N2—Co1116.6 (3)
C4—C3—C1121.2 (4)O2—N2—Co1122.5 (2)
C5—C4—C3120.0 (5)N2—O2—H2A109.5
C5—C4—H4120.0N2—Co1—N2i179.998 (1)
C3—C4—H4120.0N2—Co1—N181.13 (14)
C6—C5—C4120.9 (5)N2i—Co1—N198.87 (14)
C6—C5—H5119.5N2—Co1—N1i98.87 (14)
C4—C5—H5119.5N2i—Co1—N1i81.13 (14)
C5—C6—C7120.1 (5)N1—Co1—N1i180.00 (17)
C5—C6—H6120.0N2—Co1—O391.3 (7)
C7—C6—H6120.0N2i—Co1—O388.7 (7)
C6—C7—C8119.8 (5)N1—Co1—O390.4 (9)
C6—C7—H7120.1N1i—Co1—O389.6 (9)
C8—C7—H7120.1N2—Co1—O3i88.7 (7)
C3—C8—C7120.5 (5)N2i—Co1—O3i91.3 (7)
C3—C8—H8119.7N1—Co1—O3i89.6 (9)
C7—C8—H8119.7N1i—Co1—O3i90.4 (9)
C14—C9—C10119.5 (4)O3—Co1—O3i179.999 (2)
C14—C9—C2121.0 (4)N2—Co1—Cl186.6 (3)
C10—C9—C2119.4 (4)N2i—Co1—Cl193.4 (3)
C11—C10—C9119.9 (5)N1—Co1—Cl190.6 (3)
C11—C10—H10120.1N1i—Co1—Cl189.4 (3)
C9—C10—H10120.1O3—Co1—Cl14.7 (10)
C12—C11—C10119.6 (5)O3i—Co1—Cl1175.3 (10)
C12—C11—H11120.2N2—Co1—Cl1i93.4 (3)
C10—C11—H11120.2N2i—Co1—Cl1i86.6 (3)
C13—C12—C11121.3 (4)N1—Co1—Cl1i89.4 (3)
C13—C12—H12119.4N1i—Co1—Cl1i90.6 (3)
C11—C12—H12119.4O3—Co1—Cl1i175.3 (10)
C12—C13—C14119.3 (5)O3i—Co1—Cl1i4.7 (10)
C12—C13—H13120.3Cl1—Co1—Cl1i179.999 (1)
C14—C13—H13120.3
N1—C1—C2—N26.6 (5)C1—C2—N2—O2176.8 (3)
C3—C1—C2—N2170.3 (4)C9—C2—N2—O20.8 (6)
N1—C1—C2—C9169.3 (4)C1—C2—N2—Co15.3 (5)
C3—C1—C2—C913.8 (7)C9—C2—N2—Co1170.7 (3)
N1—C1—C3—C8132.9 (5)C2—N2—Co1—N2i164 (6)
C2—C1—C3—C843.6 (6)O2—N2—Co1—N2i25 (6)
N1—C1—C3—C444.5 (7)C2—N2—Co1—N12.1 (3)
C2—C1—C3—C4139.0 (5)O2—N2—Co1—N1173.5 (3)
C8—C3—C4—C51.4 (7)C2—N2—Co1—N1i177.9 (3)
C1—C3—C4—C5176.0 (5)O2—N2—Co1—N1i6.5 (3)
C3—C4—C5—C60.9 (8)C2—N2—Co1—O388.1 (10)
C4—C5—C6—C70.0 (9)O2—N2—Co1—O383.2 (10)
C5—C6—C7—C80.4 (9)C2—N2—Co1—O3i91.9 (10)
C4—C3—C8—C71.0 (7)O2—N2—Co1—O3i96.8 (10)
C1—C3—C8—C7176.4 (4)C2—N2—Co1—Cl189.0 (4)
C6—C7—C8—C30.1 (8)O2—N2—Co1—Cl182.4 (4)
N2—C2—C9—C1450.7 (6)C2—N2—Co1—Cl1i91.0 (4)
C1—C2—C9—C14133.8 (4)O2—N2—Co1—Cl1i97.6 (4)
N2—C2—C9—C10125.5 (5)C1—N1—Co1—N22.0 (3)
C1—C2—C9—C1050.0 (6)O1—N1—Co1—N2174.3 (3)
C14—C9—C10—C111.9 (7)C1—N1—Co1—N2i178.0 (3)
C2—C9—C10—C11174.4 (4)O1—N1—Co1—N2i5.7 (3)
C9—C10—C11—C121.4 (7)C1—N1—Co1—N1i133 (100)
C10—C11—C12—C130.1 (8)O1—N1—Co1—N1i39 (100)
C11—C12—C13—C140.8 (7)C1—N1—Co1—O393.2 (8)
C12—C13—C14—C90.2 (7)O1—N1—Co1—O394.5 (8)
C10—C9—C14—C131.1 (6)C1—N1—Co1—O3i86.8 (8)
C2—C9—C14—C13175.1 (4)O1—N1—Co1—O3i85.5 (8)
C2—C1—N1—O1177.4 (4)C1—N1—Co1—Cl188.4 (4)
C3—C1—N1—O10.5 (6)O1—N1—Co1—Cl199.2 (4)
C2—C1—N1—Co15.1 (5)C1—N1—Co1—Cl1i91.6 (4)
C3—C1—N1—Co1171.8 (3)O1—N1—Co1—Cl1i80.8 (4)
Symmetry codes: (i) −x+1, −y, −z; (ii) −x+2, −y+1, −z; (iii) x, y+1, z.
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O2—H2A···O1i0.821.682.477 (4)162
O2—H2A···N1i0.822.402.999 (4)130
O4A—···.O3iii..2.592 (4).
Symmetry codes: (i) −x+1, −y, −z; (iii) x, y+1, z.
Table 1
Selected geometric parameters (Å)
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Co1—N2i1.891 (3)Co1—O31.95 (3)
Co1—N1i1.894 (3)Co1—Cl12.214 (11)
Symmetry codes: (i) −x+1, −y, −z.
Table 2
Hydrogen-bond geometry (Å, °)
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D—H···AD—HH···AD···AD—H···A
O2—H2A···O1i0.821.682.477 (4)162
O2—H2A···N1i0.822.402.999 (4)130
O4A—···.O3ii..2.592 (4).
Symmetry codes: (i) −x+1, −y, −z; (ii) x, y+1, z.
Acknowledgements top

The authors are thankful to Rev. Dr B. Jeyaraj, S. J., Principal, Loyola College (Autonomous), Chennai 34, India, for providing the necessary facilities, the Head, SAIF, CDRI, Lucknow, India, for supplying elemental data, and the Head, SAIF, IIT Madras, Chennai 36, India, for recording NMR spectra and for X-ray data collection.

references
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