A New Nitronyl-nitroxide Ligand for Designing Binuclear LnIII Complexes: Syntheses, Crystal Structures, Magnetic and EPR Studies

A new nitronyl-nitroxide ligand (H2L) featuring alcoholic and phenolic groups has been synthesised starting from 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde (A). Using this ligand, three 2p-4 f binuclear complexes have been obtained and crystallographically characterized: [Ln(2)(HL)(2)(hfac)(4)], (Ln=Gd 1, Tb 2, Dy 3). Apart from the desired compounds, two by-products have been isolated as a molecular alloy containing an intermediate bearing hydroxylamino and N-oxide groups, i. e. (1-hydroxy-2-(2-hydroxy-3-(hydroxymethyl)-5-methylphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide, B, and the imino-nitroxide derivative, C. This system was characterized by single crystal X-ray diffraction, UV-VIS and EPR spectroscopy. During the synthesis of compounds 1-3, two other complexes have been obtained and characterized: [Ln(C)(hfac)(3)] (4, Ln=Tb) and [Ln(2)(A-H)(2)(hfac)(4)] (5, Ln=Tb), where (A-H) results from the deprotonation of the phenolic group in A. The synthetic procedure was optimized in order to obtain pure 1-3 complexes. The cryomagnetic properties of compounds 1-3 have been investigated. Continuous-wave (CW) electron paramagnetic resonance (EPR) measurements were carried out at X- and Q-band for compound 1. Time-dependent experiments were performed at three magnetic fields. Phase memory times, T-m, were found to be about 1000 ns at 6 K.

Automated summary

A new nitronyl-nitroxide ligand (H2L) with alcoholic and phenolic groups was synthesized. Its application in forming binuclear complexes of 2p-4 f transition metals (Gd, Tb, Dy) was investigated. The synthesis process also resulted in the formation of two by-products, which were identified and characterized using various techniques. The cryomagnetic properties of the complexes were studied, and EPR measurements were performed on one of the compounds.