Racemic nickel(II) pyridine-2-aldoximate complexes capped by 2,2′-bipyridine and 1,10-phenanthroline: syntheses, structures and magnetic properties

Two Ni(II) pyridine-2-aldoximate complexes, Ni(pao)2(bpy) (1) and Ni(pao)2(phen) (2) (pao−=pyridine-2-aldoximate, bpy=2,2′-bipyridine, phen=1,10-phenanthroline), were synthesized via the deprotonation of NiCl2(Hpao)2 in methanol followed by the addition of bidentate ligands of 2,2′-bipyridine and 1,10-phenanthroline. Crystallization in CHCl3 gave block-type crystals of 1 and 2 in high yields. The mononuclear structure surrounded by three bidentate ligands, i.e., two pao− and one bpy or phen, was revealed by X-ray crystallography: 1 crystallizes in monoclinic space group P21/c with cell dimensions of a=13.457(3) Å, b=14.493(3) Å, c=19.104(4) Å, β=108.681(3)°, Z=4, and 2 crystallizes in monoclinic space group P21/n with cell dimensions of a=14.235(5) Å, b=12.018(4) Å, c=20.696(7) Å, β=110.304(4)°, Z=4. 1 and 2 each have two oximate groups (pao−), with an NO-trans arrangement around the NiII ion. Complexes 1 and 2 are racemic, namely, each molecule has a chiral center of Δ or Λ, thereby forming NO-trans-Δ and -Λ geometries in the solid state. Magnetic measurements revealed a paramagnetic S=1 spin state with a positive zero-field splitting parameter.