Mott-hubbard state in one-dimensional iodo-bridged binuclear metal dithioacetato complexes, M₂(dta)₄I (M=Pt and Ni)

Polarized reflection, electrical conductivity, magnetic susceptibility measurements and X-ray crystal structure redetermination have been carried out on one — dimensional iodo-bridged binuclear metal dithioacetato complexes, M₂(dta)₄| (M=Pt and Ni; dta=CH₃CS₂⁻) in order to elucidate their electronic property. The chain structure consists of -M^2.5+-M^2.5+-|-M^2.5+-M^2.5+ - with no Peierls distortion, and two metal atoms in binuclear moieties are bridged by four dithioacetato ligands to give a cage structure. The magnetic behavior of these compounds revealed very strong antiferromagnetic coupling between electronic spins (S=1/2) localized on the M-M dimers. They show semiconducting behavior with high conductivities and small activation energies compared with those of the MX compounds. From these results, it may be concluded that the compounds are one-dimensional Mott-Hubbard insulators, in contrast to Peierls insulators of R₄[Pt₂(pop)₄X].nH₂0 complexes (…M²⁺-M²⁺…X-M³⁺-M³⁺-X.).