Hypervalent Tellurium in One-Dimensional Extended Structures Containing Te5n- Units

The electronic structure of three one-dimensional chains containing square-planar Te₅^n- units is presented, with employment of both molecular and band calculations. Two chains containing only Te₅^2- in different conformations and one in which they are modulated by Sn are treated. The Rb₂Te₅ or Cs₂Te₅ and K₂SnTe₅ structures are thus modeled. A three-center, four-electron model can be used to understand the elongation of the Te-Te bands within the Te₅ unit, whose inherent instability is overcome by the formation of the chains. It is suggested how oxidation of the chain, for instance, by suitable choice of synthetic conditions, would alter the geometric physical properties of these polymers.