We report electron-paramagnetic resonance ͑EPR͒ studies at ϳ9.5 GHz ͑X band͒ and ϳ34 GHz ͑Q band͒ of powder and single-crystal samples of the compound Cu 2 ͓TzTs͔ 4 ͓N-thiazol-2-yl-toluenesulfonamidatecopper͑II͔͒, C 40 H 36 Cu 2 N 8 O 8 S 8 , having copper͑II͒ ions in dinuclear units. Our data allow determining an antiferromagnetic interaction J 0 = ͑−113Ϯ 1͒ cm −1 ͑H ex =−J 0 S 1 • S 2 ͒ between Cu͑II͒ ions in the dinuclear unit and the anisotropic contributions to the spin-spin coupling matrix D ͑H ani = S 1 • D • S 2 ͒, a traceless symmetric matrix with principal values D / 4=͑0.198Ϯ 0.003͒ cm −1 and E / 4=͑0.001Ϯ 0.003͒ cm −1 arising from magnetic dipole-dipole and anisotropic exchange couplings within the units. In addition, the singlecrystal EPR measurements allow detecting and estimating very weak exchange couplings between neighbor dinuclear units, with an estimated magnitude ͉JЈ͉ = ͑0.060Ϯ 0.015͒ cm −1 . The interactions between a dinuclear unit and the "environment" of similar units in the structure of the compound produce a spin dynamics that averages out the intradinuclear dipolar interactions. This coupling with the environment leads to decoherence, a quantum phase transition that collapses the dipolar interaction when the isotropic exchange coupling with neighbor dinuclear units equals the magnitude of the intradinuclear dipolar coupling. Our EPR experiments provide a new procedure to follow the classical exchange-narrowing process as a shift and collapse of the line structure ͑not only as a change of the resonance width͒, which is described with general ͑but otherwise simple͒ theories of magnetic resonance. Using complementary procedures, our EPR measurements in powder and single-crystal samples allow measuring simultaneously three types of interactions differing by more than three orders of magnitude ͑between 113 cm −1 and 0.060 cm −1 ͒.

The coordination chemistry of the ligand N-thiazol-2-yl-toluenesulfonamidate towards the copper(II) ion has been investigated using an electrochemical synthesis method. The X-ray structure of this complex was elucidated and is discussed. The compound crystallised in the monoclinic crystal system, P2 1 /c space group with a = 17.3888( 9), b = 16.3003( 9), c = 18.3679(9) A ˚and b = 114.3640(10)°. Four bidentate sulfathiazolato anions bridge two metal centers in a paddle-wheel fashion, with the nitrogen atoms as donors to give a dimeric species with a CuÁÁÁCu distance of 2.7859(5) A ˚.

Reportamos neste trabalho os estudos magnéticos e de RPE do composto [Cu 2 (flu) 4 (dmf) 2 ] (flu = flufenamato e dmf = dimetilformamida), tendo os ions Cu II como unidades dinucleares em forma de tetracarboxilato "paddle wheel". Medidas de susceptibilidade magnética na faixa de temperatura 10 ≤ T ≤ 275 K permitiram a determinação da energia de interação antiferromagnética J 0 = -294 ± 5 cm -1 entre os íons Cu II (H ex = −J 0 S 1 ·S 2 ). Medidas de RPE (espectroscopia de ressonância paramagnética eletrônica) em temperatura ambiente com a amostra em pó e monocristal em bandas X e Q resultaram nos valores g // = 2.373, g^ = 2.073 e parâmetros de campo zero D = (-0.334 ± 0.001) cm . Um limite superior de |J´| < 5×10 -3 cm -1 para o acoplamento de intercâmbio entre unidades dinucleares vizinhas a distâncias de ca. 14.24 Å foi estimado com base na variação angular do espectro ao redor do ângulo mágico. Os resultados são discutidos com base na estrutura da unidade dinuclear e das ligações que conectam os íons de Cu II , comparando-os com compostos similares descritos na literatura.We report magnetic and EPR (electron paramagnetic resonance) spectroscopy studies of [Cu 2 (flu) 4 (dmf) 2 ] (flu = flufenamate and dmf = dimethylformamide), which has Cu II ions in tetracarboxylate "paddle wheel" dinuclear units. Susceptibility measurements at 10 ≤ T ≤ 275 K allowed the evaluation of an antiferromagnetic intradinuclear exchange coupling J 0 = -294 ± 5 cm -1 between Cu II ions (H ex = −J 0 S 1 ·S 2 ). EPR experiments at 300 K in powder and single-crystals at 9.5 and 34.4 GHz indicated g // = 2.373, g^ = 2.073 and zero field splitting parameters D = (-0.334 ± 0.001) cm −1 and E ca. 0. EPR signal intensity measurements at X-band in the range 4 ≤ T ≤ 295 K indicated that J 0 = −283 ± 5 cm −1 . A higher limit |J´| < 5×10 -3 cm -1 for the interdinuclear exchange coupling between neighbor units at ca.14.24 Å was estimated from the angular variation of the single crystal spectra around the magic angles. The results are discussed in terms of the structure of the dinuclear unit and the bridges connecting Cu II ions and compared with values reported for similar compounds.