ISOLATED AND CONDENSED M2CO2 CLUSTERS (M = NB, TA) IN THE LAYERED TELLURIDES NB2CO2TE4 AND TACO2TE2

The new ternary layer compounds Nb2Co2Te4 and TaCo2Te2 have been prepared by reaction of the elements at high temperature; isolated and condensed M2Co2 (M = Nb or Ta) clusters are the structural key features of these unusual layer compounds, tight-binding band structure calculations indicate the importance of Nb-Co(Ta-Co) and Nb-Nb(Ta-Ta) interactions for the electronic stability of the structures.