Calculations on indium and thallium cyclopentadienyls. Metal–metal interactions and possible new species

Abstract

The possibility of an attractive interaction between two closed-shell molecules containing In(I) or Tl(I) was studied using relativistic pseudopotentials and correlated abinitio methods ranging from MP2 to CCSD(T). The results for the simple test system (TlH)₂ qualitatively agree with earlier ones by Schwerdtfeger (Inorg. Chem., 1991, 30, 1660). The calculated dimerization energy is -20 kJ mol^-1. The results for the more realistic [M(η⁵-Cp)]₂ model (M=In, Tl; Cp=cyclopentadiene, C₅H₅) yield a weaker attraction of about - 12 and - 16 kJ mol^-1, respectively. The M–M secondary bond lengths are somewhat longer and the M–M–Cp angles more acute than in the dimers found in solids. This is attributed to the crystal effects. The calculated structures for [M(η⁵-Cp)₂]^- anions agree with experimental ones for the known M=Tl case. Predicted structures are given for the [M(η⁵-Cp₂)]⁺ cations and for a hypothetical M(η⁵-Cp)₃.