Molecular structure of the unusual complex of 1-piperidineacetic acid with 2,4,6-trinitrophenol studied by X-ray, FTIR and 1H, 13C and 13C CP MAS NMR

Crystals containing three kinds of molecules 1-piperidiniumacetate (II), 1-piperidiniumacetic acid (III) and 2,4,6-trinitrophenolate (picrate, TNP2), belong to the monoclinic system, space group P21/c and Z ¼ 4; a ¼ 12.831(3), b ¼ 26.093(5), c ¼ 7.157(1) A ° , b ¼ 101.18(3)8, R ¼ 0.0758. The zwitterion molecule (II) is a double acceptor of protons from two molecules of 1-piperidiniumacetic acid (III) (N–H· · ·O, 2.735(5) A ° and O–H· · ·O, 2.472(5) A ° ), and a donor of proton to the picrate molecule (N–H· · ·O, 2.747(5) A ° ). These three molecules, which have three donor centers and several acceptor groups, form hydrogen-bonded chains parallel to the z axis. The oxygen atoms inactive in these hydrogen bonds, are engaged in the C–H· · ·O short contacts, which can be treated as weak hydrogen bonds, and join the chains into a three-dimensional network. The presence of protonated 1-piperidineacetic acid (III) and its zwitterion (II) in the crystal has been confirmed by 13C CP MAS NMR and solid state FTIR spectra. q 2004 Elsevier B.V. All rights reserved.