Solvent Effects in Dithiocarbamate Complexes

The crystal and molecular structures of the title complexes were solved by single-crystal x-ray diffraction using computer techniques. Crystal data: Fe(S2CNC4H8)3·0.5C 6H6 space group P21/n, Z = 4, a = 16.356 (3) Å, b = 14.933 (2) Å, c = 10.191 (2) Å, β = 90.3 (1)°, V = 2489 Å, R = 4.5%, 3276 reflections; Cr(S2CNC4H8)3·0.5C6H 6, space group P21/n, Z = 4, a = 16.490 (5) Å, b = 15.071 (7) Å, c = 9.909 (6) Å, β = 91.01 (3)°, V = 2462 Å3, R = 4.4%, 1599 reflections; Ir(S2CNC4H8)3·0.5C 6H6, space group P21/n, Z = 4, a = 16.72 (1) Å, b = 15.272 (5) Å, c = 9.602 (2) Å, β = 91.54 (3)°, V = 2451 Å3, R = 6.4%, 1646 reflections. The complex molecules are monomeric and well separated, but the solvating benzene molecule lies on a center of symmetry. The benzene-solvated Fe complex has a slightly greater (0.03 Å) average metal-ligand bond length than the previously studied, unsolvated, complex. This is unexpected, since the former compound exhibits a high-spin-low-spin equilibrium at low temperatures, while the latter is purely high spin. Qualitatively only, this complex conforms with the expectation that increased population of the high-spin state in a series of complexes with slight structural differences corresponds to increased metal-ligand bond length. The Ir complex is closest to having an octahedral ligand environment, but all are trigonally distorted from octahedral symmetry. The average metal-ligand distance increases with increasing number of unpaired electrons, and this effect overrides that of increasing atomic number vertically downward in the periodic table: 〈Fe-S〉 = 2.434 Å (t23e2), 〈Cr-S〉 = 2.404 A (t23), 〈Ir-S〉 = 2.38 Å (t26)