THE ANTIFERROMAGNETIC STRUCTURES OF KFES2, RBFES2, KFESE2, AND RBFESE2 AND THE CORRELATION BETWEEN MAGNETIC-MOMENTS AND CRYSTAL-FIELD CALCULATIONS

The ternary compounds KFeS//2, RbFeS//2, KFeSe//2, and RbFeSe//2 were prepared and their crystal structures were determined from single-crystal diffractometer data. The atomic arrangement in the isotypic compounds (space group C2/c) is characterized by tetrahedra of chalcogen atoms. Those tetrahedra are centered by iron ions and linked by edges, thus forming chains of **1// infinity left bracket FeX** minus //4/////2 right bracket frameworks. Susceptibility measurements are reported. Calculations based on a simple point charge model are discussed to correlate the magnetic moments and crystal field splittings.