Reactions of 3d-metal nitrates with N, N'-bis(2-pyridyl)urea (LH_2): preparation, X-ray crystal structures and spectroscopic studies of the products trans-[M(II)(ONO_2)_2(LH_2)_2] (M = Mn, Fe, Co, Ni, Cu, Zn) and mer-[Co(III) (LH)_2] (NO_3)·MeOH

摘要

The reactions of M(NO_3)_2·4H_2O (M = Mn, Zn), M(NO_3)_2·6H_2O (M = Co, Ni), Cu(NO_3)_2·3H_2O and Fe(NO_3)_3·9H_2O with the di-substituted urea ligand N, N'-bis(2-pyridyl)urea (LH_2) were studied in methanol. The new complexes trans-[M(II)(ONO_2)_2(LH_2)_2], where M = Mn (1), Fe (2), Co(4), Ni (6), Cu (7) and Zn (8), mer-[Co(III)(LH)_2](NO_3)·MeOH (5) and [Fe_2(III, III)O(NO_3)_4(LH_2)_2(MeOH)_2] (3) have been isolated. Of remarkable chemical interest is the reduction of iron(III) under aerobic conditions to give complex 2 and the presence of the deprotonated ligands in the cobalt(III) complex 5. Complexes 1, 2 and 4-8 have been structurally characterized by single-crystal X-ray studies. The structures of 1, 2, 4 and 6-8 consist of centrosymmetric octahedral molecules; the ligand LH_2 behaves as a bidentate chelate with the ligated atoms being the urea (amide) oxygen and one of the 2-pyridyl nitrogens, while the coordination sphere of the metal ion is completed by two monodentate nitrato groups. The coordination geometry around low-spin Co(III) in 5 is distorted octahedral; LH~- chelates as a tridentate through both pyridyl nitrogen atoms and the deprotonated urea nitrogen atom forming one six- and one four-membered chelate ring. The new complexes were characterized by elemental analyses, thermal decomposition data, magnetic susceptibilities at room temperature and spectroscopic (IR, far-IR, Raman, UV-Vis, ~(57)Fe-Mossbauer, ~1H NMR) techniques. An oxo-bridged dinuclear structure with six-coordinate Fe(III) atoms is proposed for 3. All data are discussed in terms of the nature of bonding and known or assigned structures.