Synthesis, structure, and magnetic properties of the tetranuclear complex [Cu(tmhd)₂Pb(hfa)₂]₂. Influence of temperature-dependent rotation of CF₃ groups upon EPR spectra

Abstract

A tetranuclear copper–lead complex based on 2,2,6,6-tetramethylheptane-3,5-dionate and 1,1,1,5,5,5-hexafluoropentane-2,4-dionate ligands was prepared. X-ray diffraction study of the crystal structure of the complex was performed at 296, 240, 120, 100, and 85 K. It was shown that the unit cell parameters do not substantially change, but the intramolecular angles and distances significantly changed. A polycrystalline powder of the complex was characterized by continuous wave X- and Q-band electron paramagnetic resonance (EPR) spectroscopy in the 10-350 K temperature range and by magnetic susceptibility based on the Faraday balance technique in the 77-350 K temperature range. The exchange interaction between the two copper ions was not observed which allowed recording the hyperfine interaction (HFI) with one copper nucleus and super HFI with two nonequivalent outer sphere fluorine nuclei. The outer sphere interaction results in the stabilization of the CF₃ group. Lowering the temperature resulted in the rotation of the CF₃ group and that led to the observation of super HFI from only one fluorine nucleus.

Keywords:

• Synthesis
• tetranuclear complex
• copper
• lead
• hfa ligand
• crystal structure
• EPR
• magnetic susceptibility