μ-η1:-N,N′-imidazolidine-bridged dicopper(II/III) complexes of a new dinucleating μ-bis(tetradentate) Schiff base ligand:: Synthesis, structural characterization, 1H NMR spectroscopy, and magnetic coupling

The copper coordination chemistry of a new imidazolidine-based doubly bridging mu-bis(tetradentate) ligand, H(3)mhbai is studied. A new family of pentacoordinate dinuclear complexes of formula [Cu-2(II)( mu-mhbai)(mu-X)]center dot 2H(2)O (1-4) [X = OAc, NO3, Cl, S2COMe], where H(3)mhbai stands for 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-4-methyl-3-aza- but-3-enyl]-2-methyl-1,3-imidazolidine, were synthesized from the ligand, H(3)mhbai in air. The complex 1 was structurally characterized by X-ray crystallography. The mu-eta(1):eta(1)-N,N'-imidazolidine bridging mode between two copper(II) ions has been identified in this complex along with a nonhelical binding mode of the mu-bis(tetradentate) ligand. Variable temperature (2-300 K) magnetic susceptibility data of 1 show the presence of a weak antiferromagnetic exchange interaction between the two triply bridged magnetically isolated chi(m)T values start to drop at tem-copper(II) (S = 1/2) ions. The chi(m)T values start to drop at temperature below 50 K, to reach a value of 0.55 cm(3) Kmol(-1) at 2 K for a coupling constant value of J = -2.2 cm(-1). The H-1 NMR spectrum of the weakly coupled complex 1 shows a total of seventeen hyperfine shifted peaks, as expected from the idealized C-s symmetry of the compound, spread over a very large window of chemical shift, spanning about 130 ppm. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)