Molecular structure of 1-piperidinium acid a perchlorate studied by X-ray diffraction and FTIR spectroscopy

Crystalline complex of I-piperidineacetic acid with perchloric acid, PAAH.ClO4, has been prepared and characterised by X-ray diffraction method at 100 K and refined to the R = 0.022 (I > 2sigma(I)). The crystals are orthorhombic, space group P2(1)2(1)2(1), with a = 6.607(1), b = 8.171(2), c = 18.651(4) Angstrom, Z = 4, V = 1006.9(4) Angstrom(3). The N-H proton is in an axial position and the CH2COOH substituent in an equatorial one. The COOH group is involved in two hydrogen bonds; one with the ClO4- anion, O(2)-H(2)O-...(1') = 2.664(1) Angstrom, and the second with the N+-H proton of a neighbouring molecule, related by the twofold screw axis parallel to x; O(1)H-...(11)-N(1) = 2.957(1) Angstrom. The N+-H proton forms a trifurcated (four-centre) hydrogen bond. The two contacts of the N+-H hydrogen atom, an intermolecular with the ClO4- anion and an intramolecular with the O=C group are formed. Each ClO4- anion is surrounded by five 1-piperidiniumacetic acid molecules and each oxygen atom interacts electrostatically with three positively charged nitrogen atoms. Powdered spectra of PAAH.ClO4 and its deuterated analogue were measured and assignment of the observed bands to vibrations of the hydrogen bonds and internal vibrations are proposed. The (NHO)-O-... and (OHO)-O-... hydrogen bonds are manifested by superimposition of a broad and smooth absorption in the 3300-2800 cm(-1) region with a maximum at 3120 cm(-1). (C) 2002 Elsevier Science B.V. All rights reserved.