CRYSTAL AND MOLECULAR STRUCTURE OF N-METHYL-1,4-DIAZABICYCLO[2.2.2]OCTONIUM TRICHLOROAQUONICKELATE(II). A HIGH-SPIN 5-COORDINATE COMPLEX OF NICKEL(II) WITH MONODENTATE LIGANDS

N-MethyI-1,4-diazabicyclo[2.2.2]octonium trichloroaquonickelate(II), C7H15N2(H2O)NiCl3, has been characterized by a three-dimensional X-ray diffractometer study. Refinement was carried out using full-matrix least-squares techniques on 1246 observed reflections to a final R value of 7.2%. The molecule crystallizes in the monoclinic space group P21/m with unit cell dimensions a = 8.173 (4), b = 9.393 (5), c - 7.769 (4) Å; β = 96° 40 (2)′; Z = 2; pca|cd = 1.74, pobsd = 1.73 g/cm3. The complex is monomeric with the N-methyl-1,4-diazabicyclo[2.2.2]octonium ion, NCh2CH2)3N+CH3, coordinated to the nickel atom through the unquaternized nitrogen. The resulting zwitterion has crystallographic symmetry m-Cs, and is best described as a distorted trigonal bipyramid with equatorial chlorine atoms. Distortions are observed in the form of nonequivalent Ni-Cl bond lengths (one of 2.282 ± 0.002 Å and two of 2.339 ± 0.002 Å) and an axial N-Ni-O bond angle of 171°. These result chiefly from steric repulsions between the chlorine atoms and the cation ligand (causing all N-Ni-Cl bond angles to be greater than 90°) combined with intermolecular hydrogen bonding. The observed crystal stability is attributed to the presence of infinite chains formed by the latter interaction. © 1969, American Chemical Society. All rights reserved.