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)center dot 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 ure a 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(I II,III)O(NO3)(4)(LH2)(2)(MeOH)(2)] (3) have been isolated. Of remarkable ch emical interest is the reduction of iron(III) under aerobic conditions to g ive complex 2 and the presence of the deprotonated. ligands in the cobalt(I II) 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 bident ate 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 aro und low-spin Co(III) in 5 is distorted octahedral; LH- chelates as a triden tate through both pyridyl nitrogen atoms and the deprotonated urea nitrogen atom forming one six- and one four-membered chelate ring. The new complexe s were characterised by elemental analyses, thermal decomposition data, mag netic susceptibilities at room temperature and spectroscopic (IR, far-IR, R aman, UV-Vis, Fe-57-Mossbauer, H-1 NMR) techniques. An oxo-bridged dinuclea r structure with six-coordinate Fc(III) atoms is proposed for 3. All data a re discussed in terms of the nature of bonding and known or assigned struct ures. (C) 2001 Elsevier Science Ltd. All rights reserved.