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

Author(s)

de Souza, Mateus S. ; Reis, Samira G. ; Stinghen, Danilo ; Escobar, Livia B. L. ; Cassaro, Rafael A. . Allao ; Poneti, Giordano ; Bortolot, Carolina S. ; Marbey, Jonathan ; Hill, Stephen ; Vaz, Maria G. F.

• Document type: Journal article
• Source: Inorganic Chemistry; v. 61, n. 31, p. 11-pg., 2022-07-25.

Abstract

Using the 1- (m-tolyl)-1H-1,2,3-triazole-4-(4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) (TlTrzNIT) radical and metal beta-diketonate complexes [M-(hfac)(2)(H2O)(2)], 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 1 and 2 are isostructural complexes with molecular formula [M-3(TlTrzNIT)(2)(hfac)(6)] (M-II = Mn or Cu) while compound 3 is the mononuclear [Co (TlTrzNIT)(hfac)(2)] 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 1 and 2, 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 1 and 2, respectively. The EPR spectra of 1 are well described by an isolated ferrimagnetic S = 13/2 (= 5/2 - 1/2 + 5/2 - 1/2 + 5/2) ground state with a biaxial zero-field splitting (ZFS) interaction characterized, respectively, by 2nd order axial and rhombic parameters, D and E, such that E/D is close to the maximum of 0.33. Meanwhile, EPR spectra for 2 are explained in terms of a ferromagnetic model with weakly anisotropic Cu-radical exchange interactions, giving rise to an isolated S = 5/2 (= 5 x 1/2 ) ground state with both an anisotropic g tensor and a weak ZFS interaction. Complex 2 represents one of only a few examples of Cu-radical moieties with measurable exchange anisotropy. (AU)

• FAPESP's process: 09/54082-2 - Acquisition of a vibranting sample magnetometer coupled with a superconducting quantum interference device assensor (Squid-VSM) with cryogenic closed cycle
• Grantee: Ernesto Chaves Pereira de Souza
• Support Opportunities: Multi-user Equipment Program