cis-trans Isomers of PtX4L2 (X = halogen and L = neutral ligand): trans-bis(dimethyl sulfide)tetra-iodidoplatinum(IV)

The octahedral title complex, [PtI4(C2H6S)2] or trans-PtI4(dms)2 (dms is dimethyl sulfide), crystallizes in the monoclinic space group P21/n (Z = 2), with molecular symmetry Ci, which is the most frequently occurring point group for trans-PtX4L2 {56%, 28 structures in the Cambridge Structural Database (CSD) [Allen (2002). Acta Cryst. B58, 380-388]}, followed by C1 (22%, 11 structures). The complexes form a puckered pseudo-hexagonal layer in the (101) plane, and the layers are stacked with an interplanar distance of 7.10 A. Density functional theory (DFT) calculations on an isolated complex with the observed parameters as a starting structure converged to C2h. Constraints to Ci on the observed geometry give 3-4 kJ mol-1 higher energy compared with C2h. DFT calculations on [PtCl4(PzH)2] (PzH is pyrazole), reported in the CSD in both the cis and trans forms, show an energy difference of 21 kJ mol-1 in favour of the trans complex. A CSD search for PtX4L2-type complexes, where X is a halogen and L is a ligand with a donor atom from group 14, 15 or 16, indicated a preferred trans geometrical arrangement, with a total fraction of 68%. The dominating crystal packing operators for the trans complexes are an inversion centre combined with a screw axis/glide plane (48%), followed by an inversion centre alone (28%).