CRYSTAL AND MOLECULAR-STRUCTURE, SPECTROSCOPY, AND MAGNETISM OF DIAQUOBIS(IMIDAZOLE)-CATENA-MU-(SQUARATO-1,3)-NICKEL(II) - ONE-DIMENSIONAL POLYMER

The crystal and molecular structure of diaquobis(imidazole)-catena-μ-(squarato-1, 3)-nickel(II), NiC4O4(C3N2H4)2(H2O)2, has been determined by a single-crystal X-ray analysis using three-dimensional diffractometer data. The compound crystallizes in the monoclinic system, with two formula units in a centrosymmetric unit cell, with space group P21/c and lattice parameters a=7.478 (1) Å, b=11.539 (2) Å, c=8.101 (2) Å, and β=109.27 (2)°. The structure was solved with a direct method. A refinement by full-matrix least-squares procedures converged to RF=0.023 and RWF=0.032 for 1576 independent observed reflections. The Ni(II) ions are octahedrally surrounded by four oxygens of two water molecules and two squarato anions and two nitrogens of the imidazole ligands. The crystal structure contains chains of (squarato-1, 3)-bridged Ni(II) ions. These chains are held together by strong hydrogen bonds between the noncoordinating oxygens of the squarato anions and the water molecules, forming a two-dimensional sheet of Ni(II) ions. These sheets are held together by weaker hydrogen bonds between the imidazole hydrogens and coordinating squarato oxygens. The Ni-N bond length (2.076 (1) Å) and Ni-Ow bond length (2.069 (1) Å) are normal. The Ni-Os bond length (2.121 (1) Å) is rather long compared with that of similar compounds. Infrared, far-infrared, Raman, and ligand-field spectroscopies all agree with the observed crystal structure. The magnetic susceptibility data in the temperature region 1.2-100 K could best be described by neglecting the influence of the exchange coupling, yielding a zero-field splitting parameter D and ḡ value of +5.8 (2) cm-1 and 2.28 (3), respectively. Fitting of the data with the available theory for Heisenberg one-dimensional coupled S=1 ions, with both D and J ≠ 0, yielded poor results. © 1979, American Chemical Society. All rights reserved.