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

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Abstract
Dinuclear and tetranuclear copper(II) complexes of three polydentate diazine ligands (pahap, pmhap, bdpah), based on potentially bridging N–N single bond fragments, are reported. The 2∶2 complexes [Cu2(pahap)2(NO3)(H2O)2][NO3]3·H2O (1) and [Cu2(pmhap)2(NO3)2][NO3]2·3H2O (2) involve dinuclear centres bridged by two N–N single bonds, and are essentially uncoupled, 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 bridged (pyridazine/N–N) complex [Cu2(pahap)(dppn)(NO3)(H2O)][NO3]3 (3) has a larger angle between the magnetic planes, resulting in weak antiferromagnetic behaviour (2J = −32.5 cm−1). The rotationally more flexible 1∶1 complexes [Cu2(pahap)(C2O4)2]·0.5H2O (4) (2J = −4.4 cm−1) and [Cu2(pahap)(acac)2(H2O)2][NO3]2·H2O (5) (2J = −69.7 cm−1) involve single N–N bridges, and the angle between the copper magnetic planes depends on steric factors and hydrogen bonding interactions respectively. A tetranuclear complex [Cu2(pahap − H)(dpa)]2[NO3]4·4H2O (6) results from the linking of two {Cu2(N–N)} subunits with a secondary ligand strap, 1,3-diamino-2-propanol, and leads to a trans Cu2(N–N) bridging arrangement and strong antiferromagnetic coupling (2J = −186.4 cm−1). The complex [Cu2(bdpah − H)(NO3)2][NO3] (7) has a locked conformation with a large Cu–N–N–Cu torsional angle (130.3°), leading to moderately strong antiferromagnetic coupling (2J = −112.0 cm−1). The magnetic results are entirely consistent with previous magnetostructural correlations relating the twist of the copper magnetic planes around the N–N bond to the exchange integral.
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