Crystal and molecular structure of the 2:1 complex of 1-piperidineacetic acid with perchloric acid

The 2:1 complex of 1-piperidineacetic acid with perchloric acid, (PAA)2H·ClO4, has been prepared and characterized by X-ray diffraction at 130 K and refined to the R ¼ 0:041 ðI . 2sðIÞÞ: The crystals are monoclinic, space group C2=c; a ¼ 11:663ð2Þ; b ¼ 12:844ð3Þ; c ¼ 12:512ð3Þ A ° , b ¼ 103:35ð3Þ8; V ¼ 1823:6ð7Þ A ° 3, Z ¼ 4: An asymmetric unit comprises one 1-piperidiniumacetate zwitterion and a half of the perchlorate anion. Two such species are related by the two-fold axes and the zwitterions form a homoconjugated cation through a short and probably symmetrical hydrogen bond with the O· · ·H· · ·O distance of 2.441(3) A ° . These homoconjugated cations related by the symmetry centre are connected by N–H· · ·O hydrogen bonds (2.766(2) A ° ). In the structure of complex (PAA)2H·ClO4 optimized by the PM3 and SAM1 methods one molecule of the 1-piperidineacetic acid exists as a zwitterion, whereas the other is in cationic form. In the powder FTIR spectrum of (PAA)2H·ClO4 the N–H· · ·O and O· · ·H· · ·O hydrogen bonds are manifested by two well separated broad absorption bands in the 3030–2690 cm21 and 1500–400 cm21 regions, respectively. q 2003 Elsevier B.V. All rights reserved