A series of thioether and selenoether complexes [MCl 2 (EPh 2 ) 2 ] and [MCl 2 (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- 5t), and trans-[PtCl 2 (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 [PdCl 2 (SPh 2 ) 2 ] and [PdCl 2 (SePh 2 ) 2 ] (1t and 2t, respectively). By contrast, the Rietveld refinement of the powder X-ray diffraction diagrams of [PtCl 2 (SPh 2 ) 2 ] and [PtCl 2 (SePh 2 ) 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 [MCl 2 (EMe 2 ) 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.
Key indicators: single-crystal X-ray study; T = 120 K; mean (C-C) = 0.009 Å; R factor = 0.052; wR factor = 0.160; data-to-parameter ratio = 15.1.In the title compound, (CH 2 ) 2 (PPh 2 ) 2 Se 2 or C 26 H 24 P 2 Se 2 , there are two half-molecules in the asymmetric unit, both molecules having inversion symmetry. The P-Se bond lengths suggest weak double-bond character. Weak C-HÁ Á ÁSe hydrogen bonds help to assemble the molecules into a three-dimensional network.
CommentThe crystals of the title compound, (I), (CH 2 ) 2 (PPh 2 ) 2 Se 2 , were isolated as a side product during the synthesis (Risto et al., 2007) of [Pd(SeC 4 H 4 S) 2 (dppe)] (dppe = diphenylphosphine) from [PdCl 2 (dppe)] and LiSeC 4 H 4 S (prepared from thiophene, n-butyllithium, and an excess of elemental selenium). The asymmetric unit of (I) consists of two independent half-molecules, both molecular environments being completed by crystallographic inversion symmetry (Fig. 1). The two independent P-Se bond lengths are 2.104 (2) and 2.109 (2) Å indicating a slight double bond character [the sum of the covalent radii of phosphorus and selenium is 2.22 Å (Emsley 1998)]. The other bonds show normal single bond lengths. The molecules are assembled into a three-dimensional network by weak C-H···Se interactions (Table 2, Fig. 2).
ExperimentalThe crystals of the title compound were isolated in synthesis of [Pd(SeC 4 H 4 S) 2 (dppe)] from [PdCl 2 (dppe)] (0.387 g, 0.673 mmol, in 15 ml dichloromethane) and lithium 2-thienylselenolate (1.474 mmol in 4.1 ml tetrahydrofuran, prepared from thiophene, n-butyllithium, and an excess of elemental selenium; used in situ). Colourless plates of (I) were obtained from the reaction mixture.
RefinementThe H atoms were positioned geometrically (C-H = 0.95-0.98 Å) and refined as riding with U iso (H) = 1.2 U eq (C).
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