Preparation and Structural Characterization of Nickel(II) Catecholates

The early literature of catecholate complexes of Ni(II) is explained with regard to both high-spin octahedral and low-spin square-planar complexes. The former contain coordinated solvent, while the latter do not. The syntheses of the paramagnetic (S = 1; &mgr;(eff) = 2.93 &mgr;(B) at 300 K) octahedral Ni(II) complex Na(2)[trans-(H(2)O)(2)(cat)(2)Ni(II)].12H(2)O (1a) and the diamagnetic square-planar Ni(II) complex Na(2)[(cat)(2)Ni(II)].2DMF (2) are described. The physical and chemical properties of these Ni catecholates and their X-ray crystal structures are presented. In aqueous solution at low temperature the centrosymmetric octahedral complex is formed, which has average Ni-O distances of 2.044(3) Å (catecholate) and 2.162(3) Å (water). At higher temperature or under more weakly solvating conditions the square-planar complex is formed; the complex 2 is centrosymmetric with an average Ni-O(catecholate) distance of 1.863(3) Å. The crystals of 1a conform to space group C2/c, with unit cell dimensions a = 26.0287(8) Å, b= 9.0016(3) Å, c = 10.6992(3) Å, beta = 101.809(1) degrees, V = 2453.8(1) Å(3), and Z = 4. Those of 2 conform to space group P2(1)/m, with unit cell dimensions a = 6.0906(5) Å, b = 13.208(1) Å, c = 12.826(1) Å, beta = 95.711(1) degrees, V = 1026.7(1) Å(3), and Z = 2.