An insight into the structure of acebutolol tetraphenylborate: crystal structure and quantum chemical calculations

Reaction between Acebutolol hydrochloride and sodium tetraphenylborate in water afforded an Acebutolol-tetraphenyl-borate complex. This ion-pair was characterized by a variety of analytical and spectroscopic tools including X-ray crystallographic analysis. Comprehensive theoretical studies including ground-state geometry optimization, Mulliken atomic charges, and vibrational analysis were executed to get an insight into the nature of the charge transfer between the donor and acceptor ions. The crystal structure demonstrated that three inter- and intramolecular hydrogen-bonds stabilize the molecular packing in the solid state. Natural bond orbital analysis confirmed the presence of many interactions between B(Ph)₄ ^- and particular Acebutolol functional groups, such as NH and OH groups. The positive Mulliken atomic charges of the acidic protons of the NH and OH groups of Acebutolol were increased upon the formation of the ion-pair. This has been experimentally confirmed by IR and NMR spectroscopies. Through the use of frontier molecular orbital models, time-dependent density functional theory calculations have provided more insight into the existence of two electronic transitions, beginning at B(Ph)₄ ^- and terminating at the π* system of mono-protonated Acebutolol ions.