CRYSTAL-STRUCTURE OF A DIMERIC NICKEL(II) COMPLEX WITH 3-IMIDAZOLINE NITROXIDE RADICAL

The crystal structure of an unusual dimeric Ni(II) complex with 3-imid azoline nitroxide LH = C9H14N2O2 of the formula Ni2(LH)4 has been dete rmined. The structure is molecular, space group P2(1)/c, with a = 12.1 50(3) angstrom, b = 11.229(3) angstrom, c = 15.780(4) angstrom, beta = 101.59(3)-degrees and d(calc) = 1.54 g/cm3, for Z = 2; V = 2109(1) an gstrom3, R = 0.059. In the centrosymmetric dimer, the Ni .. Ni distanc e is 3.254(2) angstrom; the coordination polyhedron of Ni is a square pyramid (the coordination number is 5) formed by the donor O and N ato ms of LH ligands ''ting as the bidentate-cyclic and bidentate bridged- cyclic structures. The Ni - O and Ni - N distances are 1.989(7) and 2- 032(8) angstrom, respectively (for the atoms forming the pyramid base) , and 2.000(8) angstrom to the apical N atom. The Ni atom is displaced from the base to the apex of the pyramid by 0.35 angstrom. The intera tomic distances and the bond angles in the ligands agree with those fo r the previously studied M(LR)2 complexes. The distances between the N i(II) ions and the [GRAPHICS] N - O O atoms inside the Ni(LH)2 fragmen ts are 5.39(1) and 5.45(1) angstrom, the intermolecular Ni ... 0 - dis tances exceed 6 angstrom, and the - O ... O - distances are as long as 4.73(1) angstrom.