Molecular structure and spectroscopic properties of N-methylmorpholine betaine complex with 4-hydroxybenzoic acid

Crystal structure of the 1:1 complex of N-methylmorpholine betaine (MMB) with 4-hydroxybenzoic acid (4-HBA) has been determined by X-ray diffraction. Crystals are orthorhombic, space group Pna2(1) with a = 7.933(2), b = 15.336(3), and c = 12.007(2) Angstrom, Z = 4, R = 0.033. The acid molecule forms two O-(HO)-O-... hydrogen bonds with two betaine molecules. The COOH group of the acid forms shorter hydrogen bond with betaine (2.587(2) Angstrom), than the hydroxyl group (2.677(2) Angstrom). The carbonyl oxygen atom of the acid also interacts with the methylene hydrogen atom of the betaine through C-H...O hydrogen bond (3.256(2) Angstrom). Thus formed infinite chains parallel to the z axis are connected by other C-H...O hydrogen bonds into layers perpendicular to the x axis. The morpholine ring has a chair conformation with the methyl group in the equatorial position and CH2COO- group in the axial one. The powder FTIR and Raman spectra and semiempirical calculations of the isolated molecule confirm the structure of the complex investigated, The H-1 and C-13 spectra indicate that in DMSO-d(6) solution, protons are not transferred from the acid to the betaine molecules. (C) 2003 Elsevier Science B.V. All rights reserved.