3d4f Heterobimetallic Dinuclear and Tetranuclear Complexes Involving Tetrathiafulvalene as Ligands: X-ray Structures and Magnetic and Photophysical Investigations Goulven Cosquer, Fabrice Pointillart,* Boris Le Guennic, Yann Le Gal, Ste ́ phane Golhen, Olivier Cador, and Lahce ̀ ne Ouahab* Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS, Universite ́ de Rennes 1, 263 Avenue du Ge ́ ne ́ ral Leclerc, 35042 Rennes Cedex, France * S Supporting Information ABSTRACT: 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 syn- thesized. 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 . ■ INTRODUCTION Because of their strongly electron-donating and attractive reversible redox properties, tetrathiafulvalene (TTF) and its derivatives are used successfully as building blocks for molecular conductors, 1 molecular switches, 2 and solar-energy systems. 3 Nowadays, the challenge of this chemistry is to succeed the combination or the synergy between several properties to reach the elaboration of multifunctional materials. 4 Thus, one strategy consists of the combination of TTF derivatives with 3d or 4f metal ions to take advantage of their magnetic and optical properties, giving rise to the original “π-3d”, 5 “π-4f”, 6 or “π-3d4f” 7 complexes. Such systems can be obtained either by a “through-space” or a “through-bond” approach. In the former, the metallic ion and the TTF core interact through van der Waals contacts, while in the latter, the metallic ion and the TTF core are covalently linked by a chemical bridge. Using the second approach, the first 3d4f TTF-based heterobimetallic complexes were elaborated 7 to combine the strong Ising-type magnetic anisotropy 8 of the Dy III and Tb III ions and the enhancement of the intramolecular magnetic-exchange interactions when such ions are combined with 3d ions. 9 Besides their magnetic properties, another advantage of lanthanides lies in their specific luminescence properties with, among others, potential applications in chelate lasers, 10 efficient organic light-emitting diodes (OLEDs), 11 and polymer light- emitting diodes (PLEDs). 12 Following this strategy, we decided to extend the series of 3d4f coordination complexes with the near-infrared (NIR)- emitters Er III and Yb III ions associated with the [M(L 1 )] metallic precursors [where M = Cu II and Ni II and L 1 = 4,5- bis(propylthio)tetrathiafulvalene- N , N ′ -phenylenebis- (salicylideneimine); Scheme 1]. The diamagnetic Y III analogue has also been studied in order to perform quantum-chemical calculations and to corroborate the absorption properties. The obtained complexes have the following molecular formula: [(L 1 )]MLn(hfac) 3 ] [M = Cu II and Ln = Y III (1), Er III (2), Yb III (3); M = Ni II and Ln = Y III (4), Er III (5), Yb III (6), where hfac - = 1,1,1,5,5,5-hexafluoroacetylacetonate anion]. The monosub- stitution of the 4,5-bis(propylthio)tetrathiafulvalene-N,N′- phenylene unit with a salicylideneimine leads to the new ligand [L 2 = 4,5-bis(propylthio)tetrathiafulvalene-N,N′-phenyl- Received: May 22, 2012 Published: July 11, 2012 Article pubs.acs.org/IC © 2012 American Chemical Society 8488 dx.doi.org/10.1021/ic3010689 | Inorg. Chem. 2012, 51, 8488-8501