Crystal structure of bis(N-methylmorpholine betaine) hydrochloride, FTIR and NMR studies of 1:1 and 2:1 complexes of N-methylmorpholine betaine with mineral acids

Several 1:1 and 2:1 complexes of N-methylmorpholine betaine (MMB, N-(carboxymethyl)- N-methylmorpholinium inner salt) with HCl, HBr, HNO3' HBF4, HI and HClO4 were synthesized and their FTIR, H-1 and C-13 NMR spectra were investigated. In the 1: 1 complexes, MMB-HX, a proton is transferred from the acid to the betaine molecule and both the nuOH and vC=O frequencies vary with the proton acceptor properties of the anion. The spectra of the 2:1 complexes, (MMB)(2)H.X, show a broad and intense nuOHO stretching absorption in the 1500-400 cm(-1) range which is slightly affected by the anion and are similar to that for the type A acid salts of carboxylic acids. The crystal structure of bis(N-methylmorpholine betaine) hydrochloride [(MMB)(2)H.Cl] was solved by X-ray diffraction as monoclinic, space group C2/c, a = 23.113(2) Angstrom, b = 6.9404(6) Angstrom, c = 10.800(1) Angstrom, beta = 94.450(7)degrees, Z = 4. The carboxylate groups of a pair of MMB are bridged by a hydrogen atom to form a dimeric cation [(MMB)(2)H](+) with a very strong, linear and symmetrical O...H...O hydrogen bond of the length 2.435(2) Angstrom. The centers of cations and anions are located in special positions, in the inversion centers and on twofold axes, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.