Anhydrous 1:1 proton-transfer compounds of isonipecotamide with picric acid and 3,5-dinitrosalicylic acid: 4-carbamoylpiperidinium 2,4,6-trinitrophenolate and two polymorphs of 4-carbamoylpiperidinium 2-carboxy-4,6-dinitrophenolate

Abstract

The structures of the anhydrous 1:1 proton-transfer compounds of isonipecotamide (4-carbamoylpiperidine) with picric acid and 3,5-dinitrosalicylic acid, namely 4-carbamoylpiperidinium 2,4,6-trinitrophenolate, C6H13N2O8 + C6H2N3O7 - (I) and 4-carbamoylpiperidinium 2-carboxy-4,6-dinitrophenolate, C6H13N2O8 + C7H3N2O7 -: two forms, the monoclinic a-polymorph (II) and the triclinic ߭polymorph (III) have been determined at 200 K. All compounds form hydrogen-bonded structures, one-dimensional in (II), two-dimensional in (I) and threedimensional in (III). In (I), the cations form centrosymmetric cyclic head-to-tail hydrogen-bonded homodimers [graph set R2 2(14)] through lateral duplex piperidinium N-H緷Oamide interactions. These dimers are extended into a two-dimensional network structure through further interactions with anion phenolate-O and nitro-O acceptors, including a direct symmetric piperidinium N-H緷Ophenol,Onitro cation-anion association [graph set R2 1(6)]. The monoclinic polymorph (II) has a similar R2 1(6) cation-anion hydrogen-bonding interaction to (I) but with an additional conjoint symmetrical R1 2(4) interaction as well as head-to-tail piperidinium N-H緷Oamide O hydrogen bonds and amide N-H緷Ocarboxyl hydrogen bonds, give a network structure which include large R3 4(20) rings. The hydrogen bonding in the triclinic polymorph (III) is markedly different from that of monoclinic (II). The asymmetric unit contains two independent cation-anion pairs which associate through cyclic piperidinium N-H緷O,O'carboxyl interactions [graph set R2 1(4)]. The cations also show the zig-zag head-to-tail piperidinium N-H緷Oamidehydrogen-bonded chain substructures found in (II) but in addition feature amide N- H緷Onitro and Ophenolate and amide N-H緷Onitro associations. As well there is a centrosymmetric double-amide N -H緷Ocarboxyl bridged bis(cation-anion) ring system [graph set R2 4(8)] in the three-dimensional framework. The structures reported here demonstrate the utility of the isonipecotamide cation as a synthon with previously unrecognized potential for structure assembly applications. Furthermore, the structures of the two polymorphic 3,5-dinitrosalicylic acid salts show an unusual dissimilarity in hydrogen-bonding characteristics, considering that both were obtained from identical solvent systems.