Study of short hydrogen bonds. I: Structures of 4-methylpiperidinium hydrogen bis(p-methylbenzoate) and piperidinium hydrogen bis(p-methylbenzoate)

The crystal structures of 4-methylpiperidinium hydrogen bis(p-methylbenzoate) 1 and piperidinium hydrogen bis(p-methylbenzoate) 2 have been determined by X-ray diffraction method. Crystal data: 1, monoclinic, P21⁄n (No. 14), a=19.260(2), b=8.0061(5), c=14.065(1) A, β=94.391(7)°, V=2162.5(3) A3, Z=4, Dx=1.141 g cm−3; 2, orthorhombic, Pcan (No. 60), a=10.292(1), b=25.248(4), c=7.763(2) A, V=2017.2(5) A3, Z=4, Dx=1.177 g cm−3. Final R values for 1 and 2 are 0.088 and 0.065 for 3446 and 1510 unique reflections, respectively. In both crystals the piperidinium cations and the hydrogen bis(benzoate) anions are held together by two kinds of N–H···O hydrogen bonds. The structure of 2 is disordered around a two-fold axis. Two benzoate residues in the anions are linked by the very short O–H···O hydrogen bonds; in 1 asymmetric [O···O 2.505(3), O–H 1.07(5), H···O 1.48(5) A, O–H···O 158(5)°]; in 2 crystallographically symmetric [O···O related by the two-fold axis 2.473(4), O···H 1.25(5) A, O···H···O 163(5)°]. The short...