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

Abstract

Crystalline complex of 1-piperidineacetic acid with perchloric acid, PAAH·ClO 4, has been prepared and characterised by X-ray diffraction method at 100 K and refined to the R=0.022 ( I>2 σ( I)). The crystals are orthorhombic, space group P2 12 12 1, with a=6.607(1), b=8.171(2), c=18.651(4) A ̊ , Z=4, V=1006.9(4) A ̊ 3. The N–H proton is in an axial position and the CH 2COOH substituent in an equatorial one. The COOH group is involved in two hydrogen bonds; one with the ClO 4 − anion, O(2)–H(2)⋯O(1′)=2.664(1) Å, 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) Å. The N +–H proton forms a trifurcated (four-centre) hydrogen bond. The two contacts of the N +–H hydrogen atom, an intermolecular with the ClO 4 − anion and an intramolecular with the OC group are formed. Each ClO 4 − 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·ClO 4 and its deuterated analogue were measured and assignment of the observed bands to vibrations of the hydrogen bonds and internal vibrations are proposed. The NH⋯O and OH⋯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.