μ-η¹: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 μ-bis(tetradentate) ligand, H3mhbai is studied. A new family of pentacoordinate dinuclear complexes of formula [Cu2III(μ-mhbai)(μ-X)]·2H2O (1-4) [X = OAc, NO3, Cl, S2COMe], where H3mhbai 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, H3mhbai in air. The complex 1 was structurally characterized by X-ray crystallography. The μ-η1:η1-N,N'-imidazolidine bridging mode between two copper(II) ions has been identified in this complex along with a nonhelical binding mode of the μ-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 copper(II) (S = 1/2) ions. TheχT values start to drop at temperature below 50 K, to reach a value of 0.55 cm3K mol-1at 2 K for a coupling constant value of J = -2.2 cm-1. The1H NMR spectrum of the weakly coupled complex 1 shows a total of seventeen hyperfine shifted peaks, as expected from the idealized Casymmetry of the compound, spread over a very large window of chemical shift, spanning about 130 ppm. (KGaA, 69451 Weinheim, Germany, 2005).