Isomerism in [MCl2(ERR′)2] (M = Pd, Pt; E = S, Se; R, R′ = Me, Ph)

A series of thioether and selenoether complexes [MCl2(EPh2)(2)] and [MCl2(SMePh)(2)] (M = Pt, Pd; E = S, Se) have been prepared and characterized to explore the isomerism of the complexes in solution and in the solid state. The NMR spectroscopic information indicates that only one isomer is present in solution in case of the palladium complexes, while two isomers are formed in the case of most platinum complexes. Single-crystal X-ray structures of trans-[PdCl2(SPh2)(2)] (1t), trans-[PdCl2(SePh2)(2)] (2t), cis-[PtCl2(SePh2)(2)] (4c), trans-[PdCl2(SMePh)(2)] ( 5t), and trans-[PtCl2(SMePh)(2)] ( 7t) are reported and have been used as starting points for the X-ray powder diffraction structure determinations using simulated annealing method together with Rietveld refinement of the powder diffraction data. The presence of only trans- isomers in the solid phases was deduced in the case of [PdCl2(SPh2)(2)] and [PdCl2(SePh2)(2)] (1t and 2t, respectively). By contrast, the Rietveld refinement of the powder X-ray diffraction diagrams of [PtCl2(SPh2)(2)] and [PtCl2(SePh2)(2)] indicated the presence of both trans- and cis-isomers (3t, 3c and 4t, 4c, respectively) with mixing ratios that are consistent with NMR spectroscopic information in solution. The density functional theory calculations using [MCl2(EMe2)(2)] as model complexes indicated that while the trans- isomers of the palladium complexes lie at significantly lower energy than the cis-isomers do, in the case of the platinum complexes the energy difference is smaller and decreases, as the chalcogen atom of the chalcogenoether ligand becomes heavier.