Unusual As–As and Sb–Sb Bonding in Thermoelectric Materials H. Kleinke, Department of Chemistry, University of Waterloo, Waterloo, ON N2L 3G1 Many thermoelectric materials are based on tellurides or antimonides. The antimonides all exhibit unusual Sb–Sb interactions, e.g. linear chains in b-Zn4Sb3, linear Sb37– ions in Yb14MnSb11 or planar Sb4 rectangles in the filled skutterudites. In Mo3Sb5Te2, the squares are interconnected to form empty cubes, where the edges correspond to weak so-called half ("hypervalent" one-electron) bonds. Our efforts during the past year afforded two new materials, Hf3Cu2Ge4–xSb1+x and Ba2Cu4–xTe5. The former contains an undistorted planar Ge/Sb atom layer with half bonds, and the latter uniquely distorted Te atom chains with various bonds. 2.69 Å Te chains in Ba2Cu4–xTe5 3.12 Å 3.45 Å 3.53 Å 3.02 Å Planar Ge/Sb layer in Hf3Cu2Ge4–xSb1+x 3.67 Å 2.87 Å