METAL THIOLATE BONDING PROPERTIES - SINGLE-CRYSTAL ESR, SUSCEPTIBILITY, AND POLARIZED ABSORPTION EVIDENCE FOR A STRONG PI-INTERACTION IN TETRAKIS(THIOPHENOLATO)COBALTATE(II)

The single-crystal ESR, magnetic susceptibility, and polarized absorption results of (Ph4P)2[CoII(SPh)4] are presented. This complex is known to possess a molecular geometry of approximate D2d symmetry. From the single-crystal ESR results, the principal values of the apparent g tensor (g') have been determined to be g'x < 0.6, g'y < 1.5, and g'z = 7.75 +/- 0.10 with the molecular z axis coincident with the approximate D2d geometry. The single-crystal susceptibilities in a temperature range of 1.6-100 K exhibit a remarkably large anisotropy indicative of a large zero-field splitting. Combination of the ESR and susceptibility results leads to the following estimate for the spin Hamiltonian parameters (S = 3/2): D = -70 +/- 10 cm-1, \E/D\ < 0.09, g perpendicular-to = 2.2 +/- 0.1, and g parallel-to = 2.60 +/- 0.05. The anomalous character of the complex, where the tetrahedral Co(II) ion exhibits such a large zero-field splitting and a significant g anisotropy, should be noticed. The single-crystal polarized absorption results are analyzed with a view to characterizing the tetragonal ligand field. The one-electron d-orbital splitting thus obtained reveals a very large splitting between d(z)2 and d(x)2-y2 with d(z)2 situated lower (mu = 4140 cm-1) and a rather small splitting between d(xy) and d(yz,zx) with d(xy) lower (delta = 1710 cm-1). This splitting pattern shows that a strong pi-interaction is incorporated in the cobalt(II)-thiolate bonding. This situation is described in a more quantitative fashion by use of the angular overlap model. The present findings are contrasted with the literature ones concerning iron(II)- and iron(III)-thiolate bondings.