Structures and Infrared Spectroscopy of Metal Cation-Borazine Complexes

Borazine (B3N3H6) is known as ‘inorganic benzene’ because of a planar B3N3 ring with equivalent B-N distance. The lone pair from N in the ring delocalize to the adjacent p-orbital of B which leads to a conjugated system. Even though metal-benzene complexes have been studied extensively as models for cationπ interactions and organometallic bonding, similar systems with borazine is relatively scarce. Here, we present a density functional study on metal cation-borazine complexes focusing on geometric and electronic structures and their effects on infrared spectra. We have chosen Al, V, Mn, and Zn cations with various d-configurations which provide models for study donor-acceptor complexes. Among these four metal complexes, Al and Mn prefer to bind to π-cloud on top of the borazine ring. On the other hand, V and Zn bind to B and N, respectively. Infrared spectra of these complexes show four major bands: N-H-, B-H stretches and B-N-B ring and scissoring modes. Interactions of Al and Mn barely shift these band positions in the respective complexes as compared to those in isolated borazine, because of less cation-π interactions. On the other hand, V and Zn significantly perturb the borazine ring resulting shifts in infrared bands in these systems.