rac-4-Carbamoylpiperidinium cis-2-carboxycyclohexane-1-carboxylate

In the title racemic salt, C6H13N2O+·C8H11O4 −, formed from the reaction of cis-cyclohexane-1,2-dicarboxylic anhydride with isonipecotamide, the cations are linked into duplex chain substructures through both centrosymmetric cyclic head-to-head ‘amide motif’ hydrogen-bonding associations [graph set R 2 2(8)] and ‘side-by-side’ R 2 2(14) associations. The anions are incorporated into the chains through cyclic R 4 3(10) interactions involving amide and piperidinium N—H⋯Ocarboxyl hydrogen bonds which, together with inter-anion carboxylic acid O—H⋯Ocarboxyl hydrogen bonds, give a two-dimensional layered structure extending along (011).

Both of these associations have been found in the structures of Lewis base salts of isonipecotamide (Smith & Wermuth, 2010). In the present structure, the monoanions are incorporated into the ribbons through cyclic R 3 4 (10) amide and piperidinium N-H···O carboxyl associations and together with inter-anion carboxylic acid O-H···O carboxyl hydrogen bonds down c (Fig. 3), give a two-dimensional layered structure extending along (011).

Experimental
The title compound was synthesized by heating together under reflux for 15 min, 1 mmol quantities of cyclohexane-1,2dicarboxylic anhydride and piperidine-4-carboxamide (isonipecotamide) in 50 ml of methanol. After volume reduction to 30 ml, the hot-filtered solution was allowed evaporate to dryness at room temperature, giving a white amorphous powder.
Minor colourless crystal plates were obtained in the residual viscous residue after evaporation of a solution of the compound in 80% propane-2-ol-water.

Refinement
H atoms potentially involved in hydrogen-bonding associations were located in a difference Fourier analysis and their positional and isotropic displacement parameters were refined. Other H atoms were included in the refinement at calculated positions [C-H = 0.97-0.98 Å] with U iso (H) = 1.2U eq (C), using a riding-model approximation.   The hydrogen-bonded ribbon substructure in the title salt showing the isonipicotamide cation R 2 2 (8) and R 2 2 (14) cyclic associations and the R 3 4 (10) incorporation of the monoanion. For symmetry codes, see Table 1.

rac-4-Carbamoylpiperidinium cis-2-carboxycyclohexane-1-carboxylate
Crystal data Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.