A comparative DFT study of stacking interactions between adjacent metal atoms in linear chains of Ir and Rh acetylacetonato complexes

Abstract

A computational chemistry study using DFT explains why the electrical conductivity along the metal axis in adjacent [Rh(acetylacetonato)(CO)2] molecules was found to be four to five orders of magnitude smaller than along the metal axis of adjacent [Ir(acetylacetonato)(CO)2] molecules. Computational chemistry results, obtained by a variety of different techniques, showed that strong interaction exists between iridium atoms in neighbouring [Ir(acetylacetonato)(CO)2] molecules. Bonds between the neighbouring iridium atoms were identified by quantum theory of atoms in molecules (QTAIM) calculations. A natural bond orbital (NBO) analysis showed that LP(Ir) donor – LP*(Ir) acceptor interactions between the two adjacent iridium centres in [Ir(acetylacetonato)(CO)2]2, are more than twice the value of the LP(Rh) donor – LP*(Rh) acceptor interactions obtained for adjacent rhodium centres in [Rh(acetylacetonato)(CO)2]2. The stacking of [Ir(acetylacetonato)(CO)2] molecules in the solid state is further stabilised by additional four weak BD(COcarbonyl) donor – BD*(CHmethyl) acceptor interactions, as well as four weak BD(COcarbonyl) donor – BD*(COacac) acceptor interactions between adjacent [Ir(acetylacetonato)(CO)2] molecules, which were not obtained by the NBO analysis of [Rh(acetylacetonato)(CO)2]2. A fragment analysis of the frontier molecular orbitals of [Ir(acetylacetonato)(CO)2]2 showed that the intermolecular iridium-iridium bonding energy in dimolecular [Ir(acetylacetonato)(CO)2]2 is about six times higher than the intermolecular rhodium-rhodium bonding energy in [Rh(acetylacetonato)(CO)2]2.