cis-Tetrachloridobis(1H-imidazole-κN 3)platinum(IV)

In the title complex, cis-[PtCl4(C3H4N2)2], the PtIV ion lies on a twofold rotation axis and is coordinated in a slightly distorted octahedral geometry. The dihedral angle between the imidazole rings is 69.9 (2)°. In the crystal, molecules are linked by N—H⋯Cl hydrogen bonds, forming a three-dimensional network.

In (I) the Pt IV ion is in a slightly distorted octahedral coordination geometry formed by two N and four Cl atoms. Two imidazole ligands are in a cis orientation. The Pt-Cl bond distances are similar, within 3σ, to other Pt-Cl bond lengths [2.323 (38) Å] in platinum(IV) complexes (Orpen et al., 1989). The Pt-N distances are usual for platinum complexes bearing two cis-coordinated N-bonded heterocycles, e.g. 2.044 (3)-2.055 (5) Å in platinum(IV) complexes (Khripun et al., 2007;Khripun et al., 2006).
The title compound (1) represents the first example of the structurally characterized platinum complex having the neutral unsubstituted imidazole ligand and the second example of an imidazole Pt(IV) complex (Kuduk-Jaworska et al., 1988). The dihedral angle between the imidazole rings is 69.9 (2)°. The bond distances and angles in the heterocyclic ligands are in good agreement with those previously observed for imidazole ligands at platinum (Korte et al., 1981;Kuduk-Jaworska et al., 1988;Bayon et al., 1987;Yip et al., 1993) and other transition metal centers (for recent examples see Huo et al., 2004;Chen et al., 2006;Garcia et al., 2000;Hao et al., 2007;Gao et al., 2004). In the crystal, molecules are linked bt N-H···.Cl hydrogen bonds to form a three-dimensional network (Table 2).

Experimental
Complex (1) was synthesized by the reaction of cis-[PtCl 4 (EtCN) 2 ] with 2 equivs of imidazole in CH 2 Cl 2 solution at room temperature. The crystals suitable for X-ray crystallography were obtained from an acetone/toluene solution by a slow evaporation of the solvent at room temperature.

Refinement
The NH hydrogen was initially located in difference Fourier maps but was included in a calculated position as riding with U iso = 1.5 U eq (N). Other H atoms were positioned geometrically and also allowed to ride on their parent atoms, with C-H = 0.95 Å, and U iso = 1.2 U eq (C). The highest peak is located 0.85 Å from atom Pt1 and the deepest hole is located 0.89 Å from atom Pt1.

Figure 1
The molecular structure of (I), with displacement ellipsoids drawn at the 40% probability level. Unlabled atoms are related by the symmetry operator (-x, y, -z+1/2).

cis-Tetrachloridobis(1H-imidazole-κN 3 )platinum(IV)
Crystal data [PtCl 4 (C 3  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.