Binuclear copper(II) complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane : synthesis, spectroscopy, and spin coupling across multiple-atom bridges of variable length (3.6―7.6 Å)

Thirteen new binuclear copper(II) complexes [LCu(µ-X)CuL]2+ with L = 1,4,7-trimethyl-1,4,7-triazacyclononane and X = 2Cl–, 2Br–, 2SCN–, C2O42–, (HN)2C2O22–, Cl2C6O42–, H2C6O42–, and 2CH3CO2– have been synthesized and characterized based on i.r., electronic, and e.s.r. spectroscopy and variable-temperature (100–300 K) magnetic susceptibility measurements. A varying range of magnetic interactions, no coupling, antiferromagnetic (2J=–460 cm–1), and ferromagnetic (J=+22 cm–1) coupling, has been observed between the copper(II) ions in these binuclear systems with variable metal–metal separation estimated to be in the range of 3.6–7.6 A. The interaction is more effective through a µ-oxamato bridge (2J=–460 cm–1) than through a µ-oxalato bridge (2J=–300 cm–1). A moderately strong antiferromagnetic interaction (2J=–60 cm–1) has been found for the Cl2C6O42-bridged compound, where the Cu ⋯ Cu separation is expected to be ≈ 7.6 A. The X-band e.s.r. spectra of the polycrystalline substances at 120 K indicate square-pyramidal geometry for the copper with a (dx2– y2)1 ground state. A mixed bridged compound (µ-1,1 -N3)(µ-OH), with a ferromagnetic interaction between the copper centres is also described. The difference in magnetic exchange interaction between the different copper(II) systems is discussed.

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