Abstract:
The magnetic susceptibility (1.7-300 K) and low-temperature (1.7-30 K) magnetization (1-4 T) of the bis(tetrathiometalato)iron trianion in polycrystalline [EtN][Fe(MoS)] have been measured. The temperature and field dependence of the magnetization have been analyzed in terms of an S = 3/2 orbital singlet ground state with a substantial zero-field splitting, g = 1.985 and D = +4.4 cm. Spin-restricted scattered wave-SCF-Xα calculations of the electronic structure of the [Fe(MoS)] anion (D symmetry) suggest that this spin state arises from occupancy of the iron d orbitals by seven electrons leading to a ground-state electron configuration (z)(xy)(x - y)(xz,yz) with the three unpaired electrons occupying the b and e orbitals of the iron atom. This leads to the formulation of [Fe(MoS)] as an iron(I) complex coordinated by two MoS anions. Even though a d configuration is favored, the resulting charge distribution is close to that of analogous d iron(II) [Fe(MoS)(SH)] complexes. The extra charge in the trianion is principally delocalized over the tetrathiomolybdate anions. Spin-polarized calculations lead to similar conclusions concerning the charge distribution with a change in the nature of the LUMO from an iron (xz,yz)e to a [(x - y)]b orbital. Calculations of the Mössbauer quadrupole splitting agree well with the experimentally reported value. Contributions to the electric field gradient from both iron p and d electrons are found to be of similar magnitude. Similar calculations on the analogous tungsten complex suggest an explanation for why the isomer shifts of [Fe(WS)] are almost identical, but their quadrupole splittings are markedly different. © 1987 American Chemical Society.
