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)(2)H.ClO4, has been prepared and characterized by X-ray diffraction at 130 K and refined to the R = 0.041 (I>2sigma(I)). The crystals are monoclinic, space group C2/c, a = 11.663(2), b = 12.844(3), c = 12.512(3) A, 0 = 103.35(3)', V = 1823.6(7) Z = 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 (OHO)-H-...-O-... distance of 2.441(3) Angstrom. These homoconjugated cations related by the symmetry centre are connected by N-(HO)-O-... hydrogen bonds (2.766(2) Angstrom). In the structure of complex (PAA)(2)H.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)(2)H.ClO4 the N-(HO)-O-... and (OHO)-H-...-O-... hydrogen bonds are manifested by two well separated broad absorption bands in the 3030-2690 cm(-1) and 1500-400 cm(-1) regions, respectively. (C) 2003 Elsevier B.V. All rights reserved.