trans influence on bond distances. Structures of trans-diiodobis(tetrahydrothiophene)palladium(II) and trans-diiodobis(tetrahydrothiophene)platinum(II)

Crystals of trans-diiodobis(tetrahydrothiophene)-palladium(II) and trans-diiodobis(tetrahydrothiophene)platinum(II) were prepared by dissolving the appropriate metal iodide in tetrahydrothiophene at 353 K and cooling to room temperature. Crystal data at room temperature (Mo K-alpha, lambda = 0.7107-angstrom) are: [PdI2(C4H8S)2], M(r) = 536.54, triclinic, P1BAR, a = 8.4920 (8), b = 8.8248 (1), c = 9.4580 (11) angstrom, alpha = 97.595 (9), beta = 91.963 (9), gamma = 99.482 (9)-degrees, V = 691.8 (1) angstrom-3, Z = 2, D(x) = 2.576 Mg m-3, mu = 5.997 mm-1, F(000) = 496, R = 0.028 for 2090 unique reflections with I > 3-sigma-(I); [PtI2(C4H8S)2], M(r) = 625.24, triclinic, P1BAR, a = 7.889 (2), b = 8.676 (1), c = 10.616 (2) angstrom, alpha = 103.75 (1), beta = 90.36 (1), gamma = 94.70 (2)-degrees, V = 703.2 (2) angstrom-3, Z = 2, D(x) = 2.953 Mg m-3, mu = 14.67 mm-1, F(000) = 560, R = 0.024 for 3988 reflections with I > 3-sigma-(I). Both compounds consist of van-der-Waals-packed mononuclear trans-[MI2(C4H8S)2] complexes. There are two centrosymmetric metal complexes in the asymmetric unit of the Pt compound but only one pseudoplanar complex in the Pd compound. The acceptor-donor distances are Pd-I 2.603 (1), 2.625 (1); Pd-S 2.316 (2), 2.329 (2); Pt-I 2.606 (1), 2.616 (1); and Pt-S 2.309 (1), 2.310 (1) angstrom. A literature survey of compounds in which ligand-I or -S (in thioethers) atoms are trans to themselves shows average M-I and M-S distances of Pd-I 2.605 (20), Pd-S 2.324 (15), Pt-I 2.609 (9) and Pt-S 2.313 (13) angstrom. The spread of the M-I and M-S distances is significantly increased if complexes are included where I or S are not trans to themselves, indicating that for some donor atoms the trans influence dominates over other factors such as the cis influence and packing forces.