Metal-metal vs Tellurium-tellurium bonding in WTe2 and its ternary variants TaIrTe4 and NbIrTe4

Article abstract of DOI:10.1021/ja00049a029

The new ternary transition-metal tellurides TaIrTe₄ and NbIrTe₂ are ordered variants of the WTe₂ structure, which in turn is based on a distortion of the CdI₂-type layered structure. The layers in WTe₂ consist of buckled sheets of Te atoms, with the metal atoms residing in distorted octahedral sites. Through single- crystal X-ray diffraction methods, the structure of TaIrTe₄ has been determined and that of WTe₂ has been redetermined. The compounds TaIrTe₄ and WTe₂ belong to space group C₂₀⁷Pmn2₁ of the orthorhombic system with four formula units in cells of dimensions a = 3.770 (1), b= 12.421 (6), and c = 13.184 (6) ? and a = 3.477 (2), b = 6.249 (4), and c = 14.018 (9) ?, respectively, at 113 K. While metal-metal bonding is a structural feature common to all three compounds, Te-Te bonding is observed only in the ternary compounds. The trends of increasing metal-metal and decreasing Te-Te distances on progressing from WTe₂ to TaIrTe₄ and NbIrTe₄ have been rationalized by electronic band (extended Hückel) calculations. These trends are related to the creation of Te-Te bonds, ensuring the stability of the WTe₂ structure type even when addition of more d electrons leads to a weakening of metal-metal bonds. This concept is generalized to an entire series of compounds MM′Te₄ (M = Nb, Ta; M′ = Ru, Os, Rh, Ir).