Hexanuclear Cu3O–3Cu triazole-based units as novel core motifs for high nuclearity copper(II) frameworks

The asymmetric 3,5-disubstituted 1,2,4-triazole ligand H2V (5-amino-3-picolinamido-1,2,4-triazole) by reaction with an excess of Cu(ii) perchlorate (Cu : H2V being 12 : 1) has produced a novel hexanuclear {Cu-6(mu(3)-O/H)(HV/V)(3)} fragment, with one triangular Cu-3(mu(3)-O/H) group connected to three peripheral single Cu(ii) ions through a cis-cis-trans bridging mode of the ligand, which is the building block of the three structures described here: one hexanuclear, [Cu-6(mu(3)-O)(HV)(3)(ClO4)(7)(H2O)(9)]center dot 8H(2)O (1), one dodecanuclear, [Cu-12(mu(3)-O)(2)(V)(6)(ClO4)(5)(H2O)(18)](ClO4)(3)center dot 6H(2)O (2), and one tetradecanuclear 1D-polymer, {[Cu-14(mu(3)-OH)(2)(V)(6)(HV)(ClO4)(11)(H2O)(20)](ClO4)(2)center dot 14H(2)O}(n) (3), the last two containing hexanuclear subunits linked by perchlorato bridges. The Cu-Cu av. intra-triangle distance is 3.352(2) angstrom and the Cu(central)-Cu(bridged external) av. distance is 5.338(3) angstrom. The magnetic properties of the hexanuclear "Cu3O-3Cu" cluster have been studied, resulting as best fit parameters: g = 2.18(1), J(intra-triangle) = -247.0(1) cm(-1) and j(central Cu-II - external Cu-II) = -5.15(2) cm(-1).