Trinuclear N,N-Bridged Copper(II) Complexes Involving a Cu3OH Core:  [Cu33-OH)L3A(H2O)2]A·(H2O)x {L = 3-Acetylamino-1,2,4-triazolate; A = CF3SO3, NO3, ClO4; x = 0, 2} Synthesis, X-ray Structures, Spectroscopy, and Magnetic Properties

The reaction of Haat [Haat = (3-acetylamino-1,2,4-triazole)] with aquated Cu(CF3SO3)2, Cu(NO3)2, and Cu(ClO4)2, respectively, in water results in the trinuclear complexes [Cu3(OH)(aat)3(CF3SO3)(H2O)2](CF3SO3) (1), [Cu3(OH)(aat)3(NO3)(H2O)2](NO3)·(H2O)2 (2), and [Cu3(OH)(aat)3(ClO4)(H2O)2](ClO4) (3). The synthesis, X-ray structure, and magnetic and spectroscopic properties of the three title complexes are described. The cation of the three complexes is trinuclear with a Cu3OH skeleton which has the N−N diazine grouping of a triazole ring as bridge between each pair of copper atoms. The Cu3OH units have an average Cu−O distance of 1.991(6) (1), 2.000(6) (2), and 2.007(6) (3) Å, an average Cu−Cu‘ distance of 3.355(2) (1), 3.341(1) (2), and 3.371(3) (3) Å, and an average Cu−O−Cu‘ angle of 114.6(3)° (1), 112.4(2)° (2), and 115.4(3)° (3). The existence of the Cu3OH fragment is confirmed by a pseudotetrahedral oxygen environment, by detection of the OH hydrogen atom, and by stoichiometry. In the trinuclear unit the metal ions show, in the first approximation, a pseudo-square-planar pyramidal environment forming a CuN2O3 chromophore; three of the basal positions are occupied by N,N,O aat ligand atoms, the fourth one is occupied by the oxygen of the central OH group, and the apical site is occupied by an oxygen atom from a water molecule in the case of two of the copper(II) atoms and by an oxygen atom from the coordinating anion in the case of the third metal ion. The three compounds exhibit strong antiferromagnetic interaction, with similar J constants [J = −197.7 (1), J = −190.9 (2), J = −198.2 (3) cm-1], reaching complete spin coupling at ca. 75 K (1)/55 K (2)/95 K (3). At very low temperature the magnetic moment (magnetic susceptibility) falls below that expected for one unpaired electron. Magnetic parameters are discussed on the basis of the structural results and compared with those reported in the literature for related trimeric Cu(II) compounds with N−O or N−N peripheral bridges. Solid state EPR spectra of the three complexes recorded at liquid N temperature show axial signals. Crystal data:  C14H20Cu3F6N12O12S2 (1) (Mw = 917.16) crystallizes in the monoclinic space group, P21/c, Z = 4, with cell dimensions a = 13.080(2) Å, b = 17.202(2) Å, c = 13.840(2) Å, β = 92.40(1)°, and V = 3111.3(7) Å3, Dcalcd = 1.958 Mg m-3; the final agreement values were R1 = 0.0582 and wR2 = 0.1462 for 7107 unique reflections. C12H24Cu3N14O14 (2) (Mw = 779.07) crystallizes in the triclinic space group, P1̄, Z = 2, with cell dimensions a = 9.647(2) Å, b = 9.985(2) Å, c = 15.314(2) Å, α = 84.080(10), β = 87.694(10), γ = 65.030(10)°, and V = 1330.1(4) Å3, Dcalcd = 1.945 Mg m-3; the final agreement values were R1 = 0.0397 and wR2 = 0.0950 for 7728 unique reflections. C12H20Cl2Cu3N12O14 (3) (Mw = 817.92) crystallizes in the monoclinic space group, P21/a, Z = 4, with cell dimensions a = 14.238(5) Å, b = 16.387(6) Å, c = 11.678(4) Å, γ = 90.45(2)°, and V = 2724.6(18) Å3, Dcalcd = 1.994 Mg m-3; the final agreement values were R1 = 0.0616 and wR2 = 0.1279 for 4038 unique reflections.