Crystal structures of cobalt(II), nickel(II) and zinc(II) dichloro complexes bearing 2-pyridyl-substituted nitronyl nitroxide (NIT2py)

The X-ray analysis of Co(II), Ni(II) and Zn(II) dichloro complexes containing 2-(2-pyridyl)-4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide (NIT2py) demonstrated that the Co(II) complex containing two dichloromethane solvate molecules, [CoCl2(NIT2py)2]·2CH2Cl2 (1), crystallizes in a space group P21/c isomorphous to the corresponding Mn(II), Ni(II) (2) and Cu(II) complexes, and that the molecular structure of the complex having Ci symmetry in 1 is isostructural to the above Mn(II), Ni(II) and Cu(II) complexes. A new Ni(II) complex having only one dichloromethane solvate molecule, [NiCl2(NIT2py)2]·CH2Cl2 (2′), could be crystallized from a mixture of dichloromethane, methanol and n-heptane. The (OC-6-12)-[trans(Cl)-trans(py)] geometrical structure of the Ni(II) complex in 2′ is identical to that in 2, but the puckered six-membered chelate rings formed via pyridyl-N and nitroxide-O atoms of NIT2py take the different conformations; i.e. the molecular symmetry is C2 (racemate) with the λ, λ or δ, δ conformations in 2′ and Ci (meso) with the δ, λ conformations in 2. In the case of Zn(II), a reaction of ZnCl2 with NIT2py afforded purple crystals consisting of octahedral bis(NIT2py) and tetrahedral mono(NIT2py) complexes with hydration: [ZnCl2(NIT2py)2]·2[ZnCl2(NIT2py)]·2/3H2O (3). The geometrical structure of the octahedral Zn(II) complex in 3 was found to be (OC-6-22)-[cis(Cl)-trans(py)].