4-Carboxypiperidinium 1-carboxycyclobutane-1-carboxylate.

ABSTRACT

The title salt, C(6)H(12)NO(2)(+)·C(6)H(7)O(4)(-) or ISO(+)·CBDC(-), is an ionic ensemble assisted by hydrogen bonds. The amino acid moiety (ISO or piperidine-4-carboxylic acid) has a protonated ring N atom (ISO(+) or 4-carboxypiperidinium), while the semi-protonated acid (CBDC(-) or 1-carboxycyclobutane-1-carboxylate) has the negative charge residing on one carboxylate group, leaving the other as a neutral -COOH group. The -(+)NH(2)- state of protonation allows the formation of a two-dimensional crystal packing consisting of zigzag layers stacked along a separated by van der Waals distances. The layers extend in the bc plane connected by a complex network of N-H···O and O-H···O hydrogen bonds. Wave-like ribbons, constructed from ISO(+) and CBDC(-) units and described by the graph-set symbols C(3)(3)(10) and R(3)(3)(14), run alternately in opposite directions along c. Intercalated between the ribbons are ISO(+) cations linked by hydrogen bonds, forming rings described by the graph-set symbols R(6)(6)(30) and R(4)(2)(18). A detailed analysis of the structures of the individual components and the intricate hydrogen-bond network of the crystal structure is given.