3d4f heterobimetallic dinuclear and tetranuclear complexes involving tetrathiafulvalene as ligands: X-ray structures and magnetic and photophysical investigations

Six new 3d4f heterobimetallic dinuclear complexes, [(L ¹) MLn(hfac) ₃] [M = Cu ^II, Ni ^II; Ln = Y ^III, Er ^III, Yb ^III; L ¹ = 4,5-bis(propylthio)tetrathiafulvalene-N,N′-phenylenebis(salicylideneimine) and hfac ^- = 1,1,1,5,5,5-hexafluoroacetylacetonate], and one tetranuclear complex, [(L ²)Cu(OH)Er(hfac) ₃] ₂ (where L ² = 4,5-bis(propylthio)tetrathiafulvalene-N,N′- phenyleneaminosalicylideneimine), have been synthesized. All of the X-ray structures of the coordination complexes have been resolved from single-crystal diffraction. A quantitative magnetic approach has allowed one to determine the Cu-Ln ferromagnetic interaction for Gd ^III (1.29 cm ^-1) and Tb ^III (0.40 cm ^-1) and the antiferromagnetic interaction for Dy ^III (-0.46 cm ^-1) and Yb ^III (-2.25 cm ^-1), while in the case of Er ^III, the magnetic interactions are negligible. The UV-visible absorption properties have been studied in a chloroform solution and rationalized by DFT and TD-DFT calculations. Upon oxidation, intramolecular SOMO → LUMO (20800 cm ^-1) and SOMO-n → SOMO (11350 cm ^-1) charge transfers appear, while the HOMO → LUMO charge transfers (20750 cm ^-1) disappear. The reversibility of the oxidation has been confirmed by electrochemistry and absorption properties upon the addition of a reducing agent. Irradiation at the HOMO → LUMO charge-transfer energy of the dinuclear complex [(L ¹)NiY(hfac) ₃] induces a ligand-centered fluorescence at 14450 cm ^-1.