Relevance of Orbital Interactions and Pauli Repulsion in the Metal–Metal Bond of Coinage Metals

Abstract

The importance of relativity and dispersion in metallophilicity has been discussed in numerous studies. The existence of hybridization in the bonding between closed shell d10–d10 metal atoms has also been speculated, but the presence of attractive MO interaction in the metal–metal bond is still a matter of an ongoing debate. In this comparative study, a quantitative molecular orbital analysis and energy decomposition is carried out on the metallophilic interaction in atomic dimers (M+···M+) and molecular perpendicular [H3P–M–X]2 (where M = Cu, Ag, and Au; X = F, Cl, Br, and I). Our computational studies prove that besides the commonly accepted dispersive interactions, orbital interactions and Pauli repulsion also play a crucial role in the strength and length of the metal–metal bond. Although for M+···M+ the orbital interaction is larger than the Pauli repulsion, leading to a net attractive MO interaction, the bonding mechanism in perpendicular [H3P–M–X] dimers is different due to the larger separation between the donor and acceptor orbitals. Thus, Pauli repulsion is much larger, and two-orbital, four-electron repulsion is dominant.

Structural and Luminescent Properties of Homoleptic Silver(I), Gold(I), and Palladium(II) Complexes with nNHC-tzNHC Heteroditopic Carbene Ligands

“…64,65 This level of theory gave reliable results in recent studies on gold complexes. 66−68 TD-DFT calculations were performed on the optimized geometries of 5(f s ) and 6(t) in the gas phase using all-electron TZ2P basis sets for all of the atoms. SAOP, which is an appropriate exchange-correlation potential with the statistical averaging of (model) orbitals, was chosen to calculate the excitation energies 69,70 because it reliably describes the excited states of organometallic compounds.…”

The Energetic Significance of Metallophilic Interactions

“…Similarly, QCISD and CCSDT approaches also contradict the suggestion from MP2 calculations that metallophilic interactions become more favorable on descending group 11 . Most recently, molecular orbital analysis and energy decomposition analysis have suggested that the dimerization of metal complexes arises from a combination of favorable electrostatic interactions and weakly covalent metal⋅⋅⋅metal orbital interactions, which are counterbalanced by Pauli repulsion …”

The Energetic Significance of Metallophilic Interactions

“…[13] Most recently, molecular orbital analysis and energy decomposition analysis has suggested that the dimerization of metal complexes arises from a combination of favorable electrostatic interactions and weakly covalent metal•••metal orbital interactions, which are counterbalanced by Pauli repulsion. [14] The theoretical inconsistencies regarding the nature of metallophilic interactions also extend to estimates of their strength; calculated gas-phase energies range from negligible at one extreme, [8b, 8c] to being comparable to hydrogen bonding at the other (i.e. 0 to 60 kJ mol −1 ).…”