The magnetochemical characterisation of the bonding features in ternary chalcogenides of manganese, iron and cobalt with low dimensional structural units

The alkali metal-transition metal chalcogenides A(x)M(y)X(z) crystallise in structures which, dependent upon the stoichiometry, contain isolated groups, dimers or chains comparable with those in the silicate structures, where the anionic building units M(y)X(z)(x-) are formed by linkage of [MX(4)] tetrahedra via their edges. The magnetic properties of the transition metal ions can be used as an indication of the change in bonding properties at the transition from molecular units to collective framework structures. In the case of the ternary iron(III) chalcogenides, susceptibility measurements and neutron scattering experiments show an unusual reduction in the magnetic moments with increasing degree of linkage in the anionic framework. For the corresponding manganese(II) and cobalt(II) compounds, a comparable reduction is not observed.