Regium bonds formed by MX (M═Cu, Ag, Au; X═F, Cl, Br) with phosphine-oxide/phosphinous acid: comparisons between oxygen-shared and phosphine-shared complexes

Abstract

ABSTRACTRegium bonds interaction between phosphine oxide (H3PO), the trans phosphinuous acid (T-PH2OH), the cis phosphinuous acid (C-PH2OH) and MX (M═Cu, Ag, Au; X═F, Cl, Br) complexes were investigated by means of ab initio MP2/aug-cc-pVTZ method. For phosphinuous acid and MX complexes, two types of regium bonded interaction (trans and cis complexes) are observed and the two types of structures are very easily transformed from one type to another due to a low energy barrier. The molecular interaction energies are in the order of Au > Cu > Ag, F > Cl > Br and increase with the decrease of intermolecular distance Rint. Two resonance-type structures of P:M-X (ωI) ↔ P–M:X (ωII), O:M-X (ωI) ↔ O–M:X (ωII) are recognised by the natural resonance theory (NRT) and the natural bond orbitals (NBOs) analysis. The competition between ωI ↔ ωII resonance structures mainly arises from hyperconjugation interactions, in all phosphor-shared complexes, P–M:X resonance accounts for a larger proportion which leads to the covalent characters. All of complexes have been described in terms of their electron density properties.