Dinuclear and tetranuclear copper(II) complexes with bridging (N-N) diazine ligands: variable magnetic exchange topologies

Dinuclear and tetranuclear copper(II) complexes of three polydentate diazin e ligands (pahap, pmhap, bdpah), based on potentially bridging N-N single b ond fragments, are reported. The 2:2 complexes [Cu-2(pahap)(2)(NO3)(H2O)(2) ][NO3](3). H2O (1) and [Cu-2(pmhap)(2)(NO3)(2)][NO3](2). 3H(2)O (2) involve dinuclear centres bridged by two N-N single bonds, and are essentially unc oupled, as a result of strict orbital orthogonality or an acute twisting of the copper magnetic planes relative to the N-N bridge. A mixed, double bri dged (pyridazine/N-N) complex [Cu-2(pahap)(dppn)(NO3)(H2O)][NO3](3) (3) has a larger angle between the magnetic planes, resulting in weak antiferromag netic behaviour (2J=-32.5 cm(-1)). The rotationally more flexible 1:1 compl exes [Cu-2(pahap)(C2O4)(2)]. 0.5H(2)O (4) (2J=-4.4 cm(-1)) and [Cu-2(pahap) (acac)(2)(H2O)(2)][NO3](2). H2O (5) (2J=-69.7 cm(-1)) involve single N-N br idges, and the angle between the copper magnetic planes depends on steric f actors and hydrogen bonding interactions respectively. A tetranuclear compl ex [Cu-2(pahap-H)(dpa)](2)[NO3](4). 4H(2)O (6) results from the linking of two {Cu-2(N-N)} subunits with a secondary ligand strap, 1,3-diamino-2-propa nol, and leads to a trans Cu-2(N-N) bridging arrangement and strong antifer romagnetic coupling (2J=-186.4 cm(-1)). The complex [Cu-2(bdpah-H)(NO3)(2)] [NO3] (7) has a locked conformation with a large Cu-N-N-Cu torsional angle (130.3 degrees), leading to moderately strong antiferromagnetic coupling (2 J=-112.0 cm(-1)). The magnetic results are entirely consistent with previou s magnetostructural correlations relating the twist of the copper magnetic planes around the N-N bond to the exchange integral.