Cyclic trinuclear and chain of cyclic trinuclear copper(II) complexes containing a pyramidal Cu(3)O(H) core. Crystal structures and magnetic properties of [Cu(3)(mu(3)-OH)(aaat)(3)(H(2)O)(3)](NO(3))(2).H(2)O [aaat = 3-acetylamino-5-amino-1,2,4-triazolate] and ([Cu(3)(mu(3)-OH)(aat)(3)(mu(3)-SO(4))].6H(2)O)(n) [aat = 3-acetylamino-1,2,4-triazolate]: new cases of spin-frustrated systems.

New copper(II) complexes of the cyclic trinuclear type with 1,2,4-triazole ligands, [Cu(3)(mu(3)-OH)(aaat)(3)(H(2)O)(3)](NO(3))(2).H(2)O [Haaat = 3-acetylamino-5-amino-1,2,4-triazole] (1) and ([Cu(3)(mu(3)-OH)(aat)(3)(mu(3)-SO(4))].6H(2)O)(n) [Haat = 3-acetylamino-1,2,4-triazole] (2), have been prepared and characterized by X-ray crystallography and magnetic measurements. Compound 1, the first reported with the ligand (H)aaat, consists of discrete trinuclear cations, associated NO(3)(-) anions and lattice water molecules. Compound 2 consists of unusual chains of trinuclear units with a tridentate sulfato group linking the trimeric units and water molecules stabilizing the crystal lattice. In both complexes, 1 and 2, the trinuclear [Cu(3)(OH)L(3)] unit contains a pyramidal Cu(3)-mu(3)OH core, and an almost flat Cu(3)N(6) ring formed by the N,N-bridging triazolato groups. The Cu...Cu' intratrimeric distances are 3.35-3.37-3.39 A in 1 and 3.34-3.34-3.36 A in 2. The copper atoms are five-coordinated with a distorted square-pyramidal geometry. Magnetic measurements have been performed in the 1.9-300 K temperature range. In the high-temperature region (T > 90 K), experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -J(S(1)S(2) + S(2)S(3) + S(1)S(3)), with J = -194.6 cm(-1) and g = 2.08 for 1, and J = -185.1 cm(-1) and g = 2.10 for 2. The magnitude of the antiferromagnetic exchange in both complexes is discussed on the basis of their structural features by comparison with reported N,N-pheripherically bridged trinuclear systems. In order to fit the experimental magnetic data at low temperature, an antisymmetric exchange term, H(AS) = G(S(1)xS(2) + S(2)xS(3) + S(1)xS(3)), had to be introduced, with G = 27.8 (1) and 31.0 (2) cm(-1). Crystal data: C(12)H(27)Cu(3)N(17)O(14) (1) (MW = 824.13) crystallizes in the triclinic space group, P(-)1, Z = 2, with the cell dimensions a = 8.852(2) A, b = 11.491(3) A, c = 15.404(3) A, alpha = 70.43(3) degrees, beta = 75.11(2) degrees, gamma = 88.43(2) degrees, and V = 1423.8(5) A(3), D(calcd) = 1.922 g cm(-)(3); the final agreement values were R1 = 0.0822 and wR2 = 0.2300 for 4989 unique reflections. C(12)H(28)Cu(3)N(12)O(14)S (2) (MW = 787.14) crystallizes in the triclinic space group, P(-)1, Z = 2, with the cell dimensions a = 7.146(6) A, b = 14.26(1) A, c = 15.35(2) A, alpha = 109.0(9) degrees, beta = 93.6(9) degrees, gamma = 99.5(7) degrees, and V = 1448(2) A(3), D(calcd) = 1.806 g cm(-3); the final agreement values were R1 = 0.0628 and wR2 = 0.1571 for 3997 "observed" reflections.