Unusual molecular structure of the 1:2.5:2 complex of DABCO di-betaine (1,4-diacetate-1,4-diazoniumbicyclo[2.2.2]octane) with p-hydroxybenzoic acid and water

The molecular structure of the 1:2.5:2 complex of DABCO di-betaine, p-hydroxybenzoic acid (HBA) and water (1) has been characterized by single-crystal X-ray diffraction, infrared spectroscopy and DFT calculations. The crystals 1 are triclinic, space group P (1) over bar. The carboxylate groups of DABCO di-betaine are engaged in the COO center dot center dot center dot HOOC and COO center dot center dot center dot HO hydrogen bonds with two HBA molecules of 2.750(2) and 2.621(2) angstrom, respectively. Two water molecules and one HBA, disordered over the inversion center in two orientations with half occupancies, play a role of the bridge between the DABCO di-betaine.(HBA)2 complexes. Three structures of DABCO di-betaine with HBA and water of different stoichiometry (2-4) have been optimized at the B3LYP/6-31G(d,p) level of theory. The nu C=O and nu asCOO vibrations are distinguished in the solid-state FTIR spectrum of 1 and confirmed by the second-derivative spectrum of 1 and the calculated spectrum of 2 by the B3LYP/6-31G(d,p) approach. (C) 2011 Elsevier B.V. All rights reserved.