Structure and bonding of [E-Cp-E′]⁺ complexes (E and E′ = B-Tl; Cp = cyclopentadienyl)

The geometries and metal-ligand bond dissociation energies of [E-Cp-E′]⁺ complexes (E, E′ = group 13 element; Cp = cyclopentadienyl) have been calculated within the density functional theory framework. The geometries of the title complexes were optimized at the BP86 level with the TZ2P valence basis set. The nature of the metal-ligand bonding has been studied using the energy decomposition analysis (EDA). The calculated bond strengths for the homoleptic complexes [E-Cp-E]⁺ with respect to loss of a neutral or charged group 13 atom are Ga > Al > In > Tl ≫ B. While the energetically most favorable pathway for the boron complex [B-Cp-B]⁺ is the loss of a neutral boron atom, heavier homologues [E-Cp-E]⁺ (E = Al-Tl) dissociate via loss of the charged atom E ⁺. The heteroleptic species [E-Cp-E′]⁺ are less stable than the homoleptic complexes [E-Cp-E]⁺. The lowest energy pathway for dissociation is the loss of the positively charged heavier atom E′⁺. The B-Cp interactions in the boron complexes have a larger (covalent) orbital character than the E-Cp bonding in the heavier homologues. The energy decomposition analysis of [E-Cp-E′]⁺, using Cp ^- and (E⋯E′]²⁺ as ligands, suggests that the a₁(σ) bonding has nearly the same strength as the e ₁(π) bonding.