Coordinative versatility of guanazole [3,5-diamino-1,2,4-triazole]:: Synthesis, crystal structure, EPR, and magnetic properties of a dinuclear and a linear trinuclear copper(II) complex containing small bridges and triazole ligands

New complexes with guanazole (3,5-diamino-1,2,4-triazole = Hdatrz), [Cu-2(Hdatrz)(2)(mu-OH2)(H2O)4(SO4)](SO4)center dot 3.5H(2)O (1) and [Cu-3(Hdatrz)(4)(mu-Cl)(2)(H2O)(4)(SO4)(2)]center dot 11.4H(2)O (2), have been prepared and structurally characterized. Complex I is a noncentrosymmetric dinuclear compound in which the copper(11) ions are bridged by two triazole ligands and one mu-OH2 molecule, with a Cu(4)center dot center dot center dot Cu(2) distance of 3.4945(8) angstrom. The chromophores are Cu(1)N2O2O' (square pyramidal), and Cu(2)N2O2O'O (octahedral). Complex 2 has a linear trinuclear copper(II) structure, with two crystallographically independent copper(II) atoms. Neighboring copper(II) ions are linked by two triazole ligands and one slightly asymmetric chlorido bridge. The intratrimeric Cu(1)center dot center dot center dot Cu(2) distance is 3.5602 (4) angstrom. Cu(2), the central copper, is coordinated to N4Cl2 (octahedral) while Cu(l), the terminal copper, is coordinated to N2O2ClO' (also octahedral). Magnetic susceptibility measurements (2-300 K) are in accordance with the dinuclear (1) and trinuclear (2) nature of these compounds. The best-fit parameters, obtained with the Hamiltonian H = -J Sigma i < jSiSj, are as follows: g = 2.10 (1) and J = -94.3(2) cm(-1) for 1; and g(central) = 2.12(1), g(peripheral) = 2.07(1), and J = -89.9(3)cm(-1) for 2. Compound 1, which has an unprecedented folded bridging {Cu(N-N)(2)CU} system, exhibits a magnetic exchange comparable to that of related planar compounds. Comparison of the magneto-structural properties of 2 with those of analogous linear trinuclear compounds has made a first approach to the relative magnitude of the J value possible. The Q-band powder spectra, which were recorded in a range from 4 K to room temperature, are in agreement with the magnetic susceptibility measurements. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)