New copper(II)-radical one dimensional chain: Synthesis, crystal structure, EPR, magnetic properties and DFT calculations

SOUZA, D. A.; FLORENCIO, A. S.; SORIANO, S.; CALVO, R.; SARTORIS, R. P.; CARNEIRO, J. W. M.; SANGREGORIO, C.; NOVAK, M. A.; VAZ, M. G. F.

JOURNAL OF THE CHEMICAL SOCIETY, DALTON TRANSACTIONS

The Royal Society of Chemistry

Lugar: Londres; Año: 2008

0300-9246

The novel chain compound [Cu(Phtfac)2(NITpPy)]n (where NITpPy = 4-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and Phtfac = 4,4,4-trifluoro-1-phenylbutane-1,3-dione) was synthesized and characterized structurally, magnetically and by EPR. It contains two non equivalent copper(II) ions, Cu1 and Cu2, located at inversion centers, bridged by a NITpPy ligand coordinating Cu1, through the pyridine donor atom and Cu2 through an N-O group, resulting in a head-to-head chain structure. The magnetic properties were investigated in the temperature range 2 to 300 K. The temperature dependence of the magnetic susceptibility was fitted considering finite 16-members rings and the parameters obtained were J1 = 29.4 cm-1, J2 = -4.4 cm-1 and g = 1.92 indicating that antiferromagnetic and ferromagnetic interactions alternate along the chain. Information from compounds described in the literature and DFT calculations allow assigning the larger ferromagnetic coupling to Cu-O   and the smaller antiferromagnetic coupling to Cu-N. Single crystal EPR spectra observed as a function of field orientation display only one resonance for most orientations, as a consequence of the collapse of the signals of the different spins produced by the exchange interactions. The comparison of the structure and magnetic properties of this compound with those of previously synthesized Cu-NITR chains bearing different substituents in the organic radicals, highlights that the ?-diketonate ligand can play an important role in determine the final architecture.