Experimental proof for σ and π-hole driven dual pnicogen bonding in phosphoryl chloride-nitromethane heterodimers: A combined matrix isolation infrared and ab initio computational studies

Abstract

Relative to phosphorus of POCl3, establishing its status as an electron-accepting pnicogen experimentally, some time ago, nitrogen in nitromethane (CH3NO2), began capturing the attention of the scientific community as a possible electron acceptor only recently. The POCl3-CH3NO2 dimer stabilized by dual pnicogen bonding involving both phosphorus of POCl3 and nitrogen of CH3NO2 in combination with hydrogen bonding, forms an interesting example. The present work furnishes the first spectroscopic evidence for the prevalence of this dual pnicogen bonding in coexistence with hydrogen bonding. The heterodimers stabilized by dual - P…O (phosphorus as a pnicogen, σ-hole driven) and N…O (nitrogen as a pnicogen, π-hole driven) - pnicogen bonding were generated within N2 and Ar matrixes at 12 K as confirmed by infrared spectroscopy and ab initio computational methodologies. The occurrence of dual pnicogen bonding was affirmed using electrostatic potential mapping, quantum theory of atoms in molecules, natural bond orbital, energy decomposition and non-covalent interaction analyses. POCl3 and CH3NO2, both act as electron donors (conventional Lewis bases) and electron acceptors (novel and unique pnicogens), simultaneously, facilitating a highly specific geometry of enhanced stability.