The early literature of catecholate complexes of Ni(IT) 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; mu(eff) = 2.93 mu(B) at 300 K) octahedral Ni(II) complex Na-2[trans-(H2O)(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) Angstrom (catecholate) and 2.162(3) Angstrom (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) Angstrom. The crystals of In conform to space group C2/c, with unit cell dimensions a = 26.0287(8) Angstrom, b = 9.0016(3) , c 10.6992(3) Angstrom, beta = 101.809(1)degrees, V = 2453.8(1) Angstrom(3), and Z = 4. Those of 2 conform to space group P2(1)/m, with unit cell dimensions a = 6.0906(5) Angstrom, b = 13.208(1) Angstrom, c 12.826(1) Angstrom, beta = 95.711(1)degrees, V = 1026.7(1) Angstrom(3), and Z = 2.