The Ni(II) and Co(II) hippurates, M(hipp)2(H2O)3-2H2O, have been studied at 298 K by single-crystal X-ray diffraction and UV-visible spectroscopy, and magnetic susceptibility measurements down to 2.2 K have been obtained. The compounds are essentially isostructural and crystallize as linear chains with canted metal octahedra bridged by the oxygen atom of a water molecule. The space group is C2/c with four formula weights per unit cell. The structural properties of the Ni(II) and Co(II) hippurates, respectively, are (1) for Ni, a = 40.833 (10)Å,, b = 6.928 (1)Å,, c = 7.884 (2)Å, β = 91.92 (1)°, R = 0.130 for 392 reflections; for Co, a = 40.823 (7)Å,b = 6.903 (1)Å, c = 7.992 (2)Å, 0 = 91.88 (1), R = 0.090 for 715 reflections; (2) the intrachain M-M1 distances (3.942Å, Ni; 3.966Å, Co); (3) the interchain M-M* distances along the b axis (6.928Å, Ni; 6.903Å, Co); (4) along the a axis, the M-M* distance is about 20 A in both compounds; (5) the M-02 (bridging water molecule) distances (2.12Å, Ni; 2.22Å, Co); (6) the M-02-M' angle (137.2°, Ni; 128.3°, Co); (7) the canting angle, 6, made by the canted octahedra with the crystallographic axis (21.4°, Ni; 25.9°, Co). The Ni(II) hippurate complex exhibits a visible spectrum typical of high-spin octahedral Ni(II) complexes; however, the splitting in the visible spectrum of the Co(II) hippurate complex is indicative of the lower site symmetry (C2h) of these compounds. Magnetic susceptibility studies show the Ni(II) hippurate to be an antiferromagnet with TcC ≃ 34 K and J = -12.9 cm-1B; the Co(II) hippurate is a metamagnet with Tcb ≃ 15 K and TcC ≃ 3.1 K. The crystallographic and magnetic susceptibility data indicate that an anisotropic superexchange occurs along the chain (c axis) and that interchain exchange is restricted to dipolar interactions along the b axis. Thus, the nickel and cobalt hippurates constitute pseudo-one-dimensional materials characterized by layers of chains being separated by about 20 Å along the a axis. Since magnetic ordering is not expected between these layers, the nickel and cobalt hippurates represent the first examples of psuedo-one-dimensional magnetic materials in which three-dimensional magnetic ordering is not predicted to occur until T → 0K. © 1979, American Chemical Society. All rights reserved.
