Study of zero-field splitting in Ni(II) complexes with near octahedral geometry

Four novel Ni(II) complexes, [Ni(dppm(O,O))(2)(NCS)(2)](1), [Ni(dppm(O,O))(3)][NiCl4](2), [Ni(dmbpy)(H2O)(2)Br-2] 3 and [Ni (dppm(O,O))(3)][NiCl4]center dot[Ni(dppm)Cl-2] 4 (dppm = bis(diphenylphosphino)methane, dppm(O,O) = bis(diphenylphosphanoxido)methane, dmbpy = 4,4'-dimethyl-2,2'-bipyridine), have been synthesized and structurally and magnetically characterized. Complexes 1 and 3 are routinely pseudooctahedral, while 2 and 4 are unique due to the existence of hexa(-)or tetracoordination in two/three independent Ni(II) atoms. For hexacoordinated systems the magnetic data confirm small magnetic anisotropy expressed through the axial zero-field splitting parameter D/hc = -4.5 to + 4.4 cm(-1). For [NiCl4](2-) tetrahedral units (in complexes 2 and 4) the magnetic anisotropy is substantially larger. Experimental findings have been confirmed by ab initio calculations and forwarded to magnetostructural D-correlations.