Cyclic trinuclear and chain of cyclic trinuclear copper(II) complexes containing a pyramidal Cu3O(H) core.: Crystal structures and magnetic properties of [Cu3(μ3-OH)(aaat)3(H2O)3](NO3)2•H2O [aaat=3-acetylamino-5-amino-1,2,4-triazolate] and {[Cu3(μ3-OH)(aat)3(μ3-SO4)]•6H2O}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)(H2O)(3)](NO3)(2)(.) H2O [Haaat = 3-acetylamino-5-amino-1,2,4-triazole] (1) and {[Cu-3(mu3-OH)(aat)(3)(mu3-SO4)](.)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 NO3(-) 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 Cu3N6 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 Angstrom 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(S1S2 + S2S3 + S1S3), 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: C12H27Cu3N17O14 (1) (MW = 824.13) crystallizes in the triclinic space group, P (1) over bar, Z = 2, with the cell dimensions a = 8.852(2) Angstrom, b = 11.491(3) Angstrom, c = 15.404(3) Angstrom, alpha = 70.43(3), beta = 75.11(2)degrees, gamma = 88.43(2degrees), and V= 1423.8(5) Angstrom(3), D-calcd = 1.922 g cm(-3); the final agreement values were R1 = 0.0822 and wR2 = 0.2300 for 4989 unique reflections. C12H28Cu3N12O14S (2) (MW = 787.14) crystallizes in the triclinic space group, P (1) over bar, Z = 2, with the cell dimensions a = 7.146(6) A, b = 14.26(1) A, c = 15.35(2) Angstrom, alpha = 109.0(9degrees), beta = 93.6(9)degrees, gamma = 99.5(7degrees), and V = 1448(2) Angstrom(3), D-calcd = 1.806 g cm(-3); the final agreement values were R1 = 0.0628 and wR2 = 0.1571 for 3997 "observed" reflections.