Unusual 2:3:2 complex of DABCO mono-betaine with HCl and H2O studied by X-ray diffraction, DFT calculations and spectroscopic methods

DABCO mono-betaine (1,4-diazabicyclo[2,2 2]octane-1-acetate) forms a complex with HCl and water in the ratio 2:3.2. The crystals are triclinic, space group P (1) over bar Two non-equivalent molecules of protonated DABCO mono-betaines form a homoconjugated cation through the short and asymmetric O H O hydrogen bond of 2 470(3) angstrom. Two chloride anions are involved in the N-H Cl hydrogen bonds of 3 049(2) and 3.023(3) angstrom. The third chloride anion is solvated by the water molecules. The molecules of bis(1,4-diazoniumbicyclo[2 2,2]octane-1-acetate) trihydrochloride dihydrate are linked into comb-like chains by the hydrogen bond formed between water molecules of the neighboring complexes. the O(W)-H O(W) distance is 2 920(5) angstrom FTIR spectrum shows several broad bands attributed to the vO-H, vN-H and vO H O vibrations. The structure of three bis(1,4)-diazoniumbicyclo[2,2 2]octane-1-acetate) hydrochlorides are optimized at the B3LYP/6-31G(d,p) level of theory and a theoretical IR spectrum is calculated The values of pK(a) of DABCO. DABCO mono- and di-betaines are determined by the potentiometric titration of their hydrohalides. (C) 2009 Elsevier B.V All rights reserved