Nickel(II) and iron(II) mononuclear complexes with 1-methylimidazole-2-aldoximate: New building units for molecule-assembled magnetic materials

A new class of mononuclear metal complexes with 1-methylimidazole-2-aldoximate (miao) has been synthesized and characterized: trans-NiII(Cl)2(Hmiao)2 (1), trans-NiII(miao)2(py)2 (2), NO-trans-NiII(miao)2(phen) (3), and NO-trans-FeII(miao)2(phen) (4). The crystal structures of 2, 3, and 4 have been determined by single-crystal X-ray crystallography. Compound 1 having the protonated miao ligand (i.e., Hmiao) is a precursor for synthesizing 2 and 3. Compound 2 is an octahedral NiII complex surrounded by two miao bidentate ligands and two monodentate ligands of pyridine in a trans-arrangement. Compound 3 is a cis-type octahedral NiII complex with two miao ligands and a bidentate ligand of 1,10-phenanthroline, in which the ligand arrangement around NiII center is found in an NO-trans form. Compound 4 is an isostructural FeII derivative of 3. Compounds 1, 2, and 3 exhibit paramagnetic nature with an S = 1 spin and a positive zero-field splitting, among which it for 3 is overlapped with intermolecular ferromagnetic interaction (zJ/kB = +0.16 K). Compound 4 is diamagnetic due to the existence of low-spin FeII ion.