Synthesis, Structure, and Properties of μ‐Oxo‐Bridged Fe III 2 and Heterometallic Azide‐Bridged Fe III 2 Cu II Complexes of a Picolinamide In‐Plane Ligand

A new μ‐oxodiiron( III ) complex [{Fe III (bpc)(H 2 O)} 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(H 2 O)] 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–Güdel model in μ‐oxodiiron( III ) complexes. Two heterometallic Fe III ‐Cu II Fe III ( 2 ) and Fe III Ni II Fe III ( 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 = 5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane), respectively. The structure of 2 consists of heterometallic Fe III Cu II Fe III units formed by the simultaneous coordination of two [Fe III (bpc)(N 3 ) 2 ] units to the central [Cu( meso ‐CTH)] units through a μ 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 Cu II 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 ] – . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)