High-Frequency EPR Studies of New 2p-3d Complexes Based on a Triazolyl-Substituted Nitronyl Nitroxide Radical: The Role of Exchange Anisotropy in a Cu-Radical System.

Using the 1-(-tolyl)-1-1,2,3-triazole-4-(4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) (TlTrzNIT) radical and metal β-diketonate complexes [M(hfac)(HO)], where hfac is hexafluoroacetylacetonato, three new 2p-3d heterospin complexes were synthesized. Their structures were solved using single crystal X-ray diffraction data, and magnetic investigation was performed by DC and AC measurements and multifrequency EPR spectroscopy. Compounds and are isostructural complexes with molecular formula [M(TlTrzNIT)(hfac)] (M = Mn or Cu) while compound is the mononuclear [Co(TlTrzNIT)(hfac)] complex. In all complexes, the radical acts as a bidentate ligand through the oxygen atom of the nitroxide moiety and the nitrogen atom from the triazole group. Furthermore, in compounds and , the TlTrzNIT is bridge-coordinated between two metal centers, leading to the formation of trinuclear complexes. The fitting of the static magnetic behavior reveals antiferromagnetic and ferromagnetic intramolecular interactions for complexes and , respectively. The EPR spectra of are well described by an isolated ferrimagnetic = / (= / - / + / - / + /) ground state with a biaxial zero-field splitting (ZFS) interaction characterized, respectively, by 2nd order axial and rhombic parameters, and , such that / is close to the maximum of 0.33. Meanwhile, EPR spectra for are explained in terms of a ferromagnetic model with weakly anisotropic Cu-radical exchange interactions, giving rise to an isolated = / (= 5 × /) ground state with both an anisotropic tensor and a weak ZFS interaction. Complex represents one of only a few examples of Cu-radical moieties with measurable exchange anisotropy.