Antisymmetric Exchange in Triangular Tricopper(II) Complexes: Correlation among Structural, Magnetic, and Electron Paramagnetic Resonance Parameters Sacramento Ferrer,* ,† Francesc Lloret,* ,‡ Emilio Pardo, ‡ Juan Modesto Clemente-Juan, ‡ Malva Liu-Gonza ́ lez, § and Santiago García-Granda ∥ † Departament de Química Inorga ̀ nica, Universitat de Valè ncia, Vicent Andre ́ s Estelle ́ s s/n, 46100 Burjassot, Valencia, Spain ‡ Institut de Cie ̀ ncia Molecular, Universitat de Vale ̀ ncia, Catedra ̀ tic Jose ́ Beltra ́ nn° 2, 46980 Paterna, Valencia, Spain § SCSIE-Rayos X, Universitat de Vale ̀ ncia, Vicent Andre ́ s Estellé s s/n, 46100 Burjassot, Valencia, Spain ∥ Departamento de Química Física y Analítica, Universidad de Oviedo, Julia ́ n Clavería 8, 33006 Oviedo, Spain * S Supporting Information ABSTRACT: Two new trinuclear copper(II) complexes, [Cu 3 (μ 3 -OH)(daat)(Hdat) 2 (ClO 4 ) 2 (H 2 O) 3 ](ClO 4 ) 2 ·2H 2 O (1) and [Cu 3 (μ 3 -OH)(aaat) 3 (H 2 O) 3 ](ClO 4 ) 2 ·3H 2 O(2) (daat = 3,5-diacetylamino-1,2,4-triazolate, Hdat = 3,5-diamino-1,2,4- triazole, and aaat = 3-acetylamino-5-amino-1,2,4-triazolate), have been prepared from 1,2,4-triazole derivatives and structurally characterized by X-ray crystallography. The structures of 1 and 2 consist of cationic trinuclear copper(II) complexes with a Cu 3 OH core held by three N,N-triazole bridges between each pair of copper(II) atoms. The copper atoms are five-coordinate with distorted square-pyramidal geometries. The magnetic properties of 1 and 2 and those of five other related 1,2,4-triazolato tricopper(II) complexes with the same triangular structure (3−7) (whose crystal structures were already reported) have been investigated in the temperature range of 1.9−300 K. The formulas of 3−7 are [Cu 3 (μ 3 - OH)(aaat) 3 (H 2 O) 3 ](NO 3 ) 2 ·H 2 O(3), {[Cu 3 (μ 3 -OH)(aat) 3 (μ 3 -SO 4 )]·6H 2 O} n (4), and [Cu 3 (μ 3 -OH)(aat) 3 A(H 2 O) 2 ]A·xH 2 O [A = NO 3 − (5), CF 3 SO 3 − (6), or ClO 4 − (7); x = 0 or 2] (aat =3-acetylamino-1,2,4-triazolate). The magnetic and electron paramagnetic resonance (EPR) data have been analyzed by using the following isotropic and antisymmetric exchange Hamiltonian: H = −J[S 1 S 2 + S 2 S 3 ] − j[S 1 S 3 ]+ G[S 1 × S 2 + S 2 × S 3 + S 1 × S 3 ]. 1−7 exhibit strong antiferromagnetic coupling (values for both −J and −j in the range of 210−142 cm −1 ) and antisymmetric exchange (G varying from to 27 to 36 cm −1 ). At low temperatures, their EPR spectra display high-field (g < 2.0) signals indicating that the triangles present symmetry lower than equilateral and that the antisymmetric exchange is operative. A magneto-structural study showing a lineal correlation between the Cu−O−Cu angle of the Cu 3 OH core and the isotropic exchange parameters (J and j) has been conducted. Moreover, a model based on Moriya’s theory that allows the prediction of the occurrence of antisymmetric exchange in the tricopper(II) triangles, via analysis of the overlap between the ground and excited states of the local Cu(II) ions, has been proposed. In addition, analytical expressions for evaluating both the isotropic and antisymmetric exchange parameters from the experimental magnetic susceptibility data of triangular complexes with local spins (S) of 1 / 2 , 3 / 2 , or 5 / 2 have been purposely derived. Finally, the magnetic and EPR results of this work are discussed and compared with those of other tricopper(II) triangles reported in the literature. ■ INTRODUCTION Trinuclear copper(II) complexes with trigonal symmetry have attracted significant interest because of their resemblance to the active sites of the multicopper oxidases that reduce O 2 to H 2 O. 1,2 Solomon and co-workers have studied the native system in addition to other triangular copper(II) complexes as models, and they clearly show the occurrence of strong antisymmetric exchange in all of them. 3 Although μ 3 -OH − and μ 3 -O 2− ions are the most common central bridging ligands in these compounds, 4 some μ 3 -Cl, 5 μ 3 -Br, 5 and μ 3 -MeO 6−8 clusters have been described as well. The peripheral ligands that hold the M 3 O core are mainly of the oxime-oximate (N,O bridge), 9,10 Schiff base-containing derivative (O bridge), 11 pyrazole (N,N bridge), 5a,12−14 or triazole (N,N bridge) 4,15,16 type; the bridge may also belong to a macrocycle. 17 Received: September 27, 2011 Published: December 23, 2011 Article pubs.acs.org/IC © 2011 American Chemical Society 985 dx.doi.org/10.1021/ic2020034 | Inorg. Chem. 2012, 51, 985−1001