Oxalato‐Bridged Dinuclear Copper(II) Complexes of N ‐Alkylated Derivatives of 1,4,7‐Triazacyclononane: Synthesis, X‐ray Crystal Structures and Magnetic Properties

The synthesis, X‐ray crystal structure and magnetic properties of two oxalato‐bridged dinuclear Cu II complexes, [L‐Cu(μ‐ox)Cu‐L](ClO 4 ) 2 , where ox = oxalate and L = 1,4,7‐trimethyl‐1,4,7‐triazacyclononane (Me 3 tacn) or 1‐benzyl‐4,7‐dimethyl‐1,4,7‐triazacyclononane (BzMe 2 tacn) are reported, as well as the X‐ray crystal structure of the mononuclear complex, [Cu(Me 3 tacn)(OH 2 ) 2 ](ClO 4 ) 2 , which features an extended H‐bonding network between the ligand and the perchlorate counterions. The crystal structures of the dinuclear complexes both feature a centrosymmetric complex cation in which the two copper centres exist in a distorted square‐pyramidal geometry, with each end capped by a facially coordinated “tacn” unit, and are bridged by an oxalate anion. Variable‐temperature magnetic susceptibility measurements revealed strong antiferromagnetic interactions between the Cu II centres, with 2 J values of ca. –300 cm –1 , even though the Cu ··· Cu separation is very long, viz. 5.18 Å (BzMe 2 tacn) and 5.47 Å (Me 3 tacn). The separation for the Me 3 tacn complex is the longest separation reported for this type of Cu II complex. No pattern could be detected between the J values and structural features for 21 oxalato‐bridged complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)