Synthesis, structure, and properties of μ-oxo-bridged FeIII2 and heterometallic azide-bridged FeIII2CuII complexes of a picolinamide in-plane ligand

A new mu-oxodiiron(III) complex [{Fe-III(bpc)(H2O)}(2)O] (1) with the bis(picolinamide) N-4 in-plane ligand 4,5-dichloro-1,2-bis(pyridine-2-carboxamido)benzene (H(2)bpc) has been prepared by the reaction of [Fe(bpc)Cl(H2O)] with a stoichiometric amount of cyanide, and characterized by X-ray structure analysis. The IR and UV/Vis spectroscopic results match well with those expected from the respective previously established spectro-structure correlation. Likewise, the temperature dependence of the magnetic susceptibility shows the existence of a strong antiferromagnetic coupling between the iron(III) centers [S = 5/2; with J = -108.10(3) cm(-1)] that is consistent with the radial and angular overlap Weihe-Gudel model in mu-oxodiiron(III) complexes. Two heterometallicFe(III)Cu(II)Fe(III) (2) and (FeNiFeIII)-Ni-III-Fe-II (3) complexes have been prepared from the reaction between [Fe-III(bpc)(N-3)(2)] and [Cu-(meso-CTH)](2+) or [Ni(meso-CTH)(2+) (CTH = 5,7,7,12,14,14hexamethyl-1,4,8,11-tetraazacyclotetradecane), respectively. The structure of 2 consists of heterometallic Fe-III,(CuFeIII)-Fe-II units formed by the simultaneous coordination of two [Fe-III-(bpc) (N-3)2] units to the central [Cu(meso-CTH)] units through a mu(1,3)-azide bridging ligand. However, the structure of 3 contains isolated [Fe-III(bpc)(N-3)(2)](-) and [Ni(meso-CTH)(2+) ions. The treatment of the magnetic data of 2 revealed the existence of a small ferromagnetic interaction between Fe-III and Cull metal ions, with J(FeCu) = 3.24(7) cm(-1). The existence of 2 opens up the possibility of obtaining, in a rational manner, azide-bridged heterometallic complexes starting from the block precursor [Fe-III(bpc)(N-3)(2)](-). ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)