Structure, Magnetic Properties, Polarized Neutron Diffraction, and Theoretical Study of a Copper(II) Cubane

The paper reports the synthesis. X-ray and neutron diffraction crystal structures. magnetic properties, high field-high frequency EPR (HF-EPR). spin density and theoretical description of the tetranuclcar Cu-II complex [Cu4L4] with cubane-like structure (LH2 = 1, 1, 1 -trifluoro-7-hydroxy-4-methyl-5-aza-hept-3-en-2-one). The simulation of the magnetic behavior gives a predominant ferromagnetic interaction J(1) (+30.5cm(-1)) and a weak antiferromagnetic interaction J(2) (-5.5 cm(-1)), which correspond to short and long Cu-Cu distances, respectively, as evidence from the crystal Structure (H=-Sigma(i>j) 2J (ij)(S) over cap (i)(S) over cap (j)). It is in agreement with DFT calculations and with the saturation magnetization Value Of an S=2 ground Spin state. HF-EPR measurements at low temperatures (5 to 30 K) provide evidence for a negative axial zero-field splitting parameter D (-0.25 +/- 0.0.1 cm(-1)) Plus a small rhombic term E (0.025 +/- 0.001 cm(-1), E/D = 0.1). The experimental spin distribution from polarized neutron diffraction is mainly located in the basal plane of the Cu-II ion with a distortion of yz-type for one Cu-II ion. Delocalization on the ligand (L) is observed but to a smaller extent than expected from DFT calculations.