Reactions of 3d-metal nitrates with N,N′-bis(2-pyridyl)urea (LH2):: preparation, X-ray crystal structures and spectroscopic studies of the products trans-[M(II)(ONO2)2(LH2)2] (M = Mn, Fe, Co, Ni, Cu, Zn) and mer-[Co(III)(LH)2](NO3)•MeOH

The reactions of M(NO3)(2). 4H(2)O (M = Mn, Zn), M(NO3)(2). 6H(2)O (M = Co, Ni), Cu(NO3)(2). 3H(2)O and Fe(NO3)(3). 9H(2)O with the di-substituted urea ligand N,N ' -bis(2-pyridyl)urea (LH2) were studied in methanol. The new complexes trans-[M(II)(ONO2)(2)(LH2)(2)], where M = Mn (1), Fe (2), Co (4), Ni (6), Cu (7) and Zn (8), mer-[Co(III)(LH)(2)](NO3). MeOH (5) and [Fe-2(III,III)O(NO3)(4)(LH2)(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 characterised by single-crystal X-ray studies. The structures of 1, 2, 4 and 6-8 consist of centrosymmetric octahedral molecules; the ligand LH2 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 characterised by elemental analyses, thermal decomposition data, magnetic susceptibilities at room temperature and spectroscopic (IR, far-IR, Raman, UV-Vis, Fe-57-Mossbauer, H-1 NMR) techniques. An oxo-bridged dinuclear structure with six-coordinate Fc(III) atoms is proposed for 3. All data are discussed in terms of the nature of bonding and known or assigned structures. (C) 2001 Elsevier Science Ltd. All rights reserved.