Crystal structure of a salt of the pyridinium-pyridine ion by X-ray and neutron diffraction

The crystal structure of (C₅H₅N)₂H]⁺ZnBr_3/2Cl_3/2(C₅H₅N)]^– has been determined and refined by full-matrix least-squares methods using X-ray (R, on ¦F _o¦, = 0.045 with 2291 reflections) and neutron (¯R, on ¦F _o¦, = 0.035 with 2030 reflections) diffraction data. The crystals of the compound are monoclinic, space groupP2₁/c witha = 12.728(1),b = 11.600(1),c = 13.354(1) Å, = 107.38(1) °,Z = 4,D _x = 1.68, andD _m(flotation) = 1.69 g cm^–3. The X-ray and neutron intensities were measured by the counter -2 scan technique with CuK X-rays ( = 1.5418 Å) and neutrons with = 1.109 Å, respectively. An intramolecular N--H hydrogen bond holds pairs of pyridine molecules together in the lattice N N, 2.737(3) Å]. The hydrogen atom is very asymmetrically disposed with N-H distances of 1.086(7) Å and 1.658(6) Å. The coordination about the zinc atom is tetrahedral with the nitrogen atom of the pyridine molecule in one tetrahedral position and different mixtures of the two halogen atoms in the other three positions. The important average bond distances from the neutron study are Zn-N 2.073(3) Å], Zn-Cl 2.251(2) Å], Zn-Br 2.394(3) Å], N-C 1.334(5) Å], C-C 1.378(5) Å], and C-H 1.075(7) Å].