High Nuclearity Complexes of Lanthanide Involving Tetrathiafulvalene Ligands: Structural, Magnetic, and PhotoPhysical Properties Fabrice Pointillart,* ,† Boris Le Guennic, † Ste ́ phane Golhen, † Olivier Cador, † Olivier Maury, ‡ and Lahce ̀ ne Ouahab † † Organome ́ talliques: Mate ́ riaux et Catalyse, UMR 6226 CNRS-UR1 Institut des Sciences Chimiques de Rennes, Universite ́ de Rennes 1, 35042, Rennes Cedex, France ‡ Laboratoire de Chimie de l’ENS-Lyon-UMR 5182 CNRS-ENS Lyon, Universite ́ de Lyon 1, 46 Allé ed’Italie, 69364 Lyon Cedex 07, France * S Supporting Information ABSTRACT: The reaction between the tetrakis(2-pyridyl- N-oxidemethylthio)- tetrathiafulvalene ligand (L) and Ln(hfac) 3 ·2H 2 O precursors (where hfac - = 1,1,1,5,5,5- hexafluoroacetylacetonate anion and Ln = Tb III (1), Dy III (2), Er III (3), and Yb III (4) and ( 4b )) leads to the formation of fi ve tetranuclear complexes of formula [Ln 4 (hfac) 12 (L) 2 ] n ·xCHCl 3 ·yC 6 H 14 (n = 1, x = 2, y = 0 for (1), (2), and (4), n = 1, x = 4 for (3), and n = 2, x = 2.5, y = 1 for (4b)). Their X-ray structures reveal that the surrounding of each Ln III center is filled by two N-oxide groups coming from two different ligands L. These tetranuclear complexes have the highest nuclearity which is reported until now for coordination compounds of lanthanide involving TTF-based ligands. Direct current (dc) measurements highlight the paramagnetic behavior of the compounds with a significant crystal field effect. The temperature dependences of static magnetic measurements for 4 have been fitted. The ground state corresponds to M J = ±5/2 while the first excited state (M J = ±3/2) was localized at +214 cm -1 which was well correlated with the luminescence transition. UV-visible absorption properties have been experimentally measured and rationalized by time-dependent density functional theory (TD-DFT) calculations. Upon irradiation at 77 K and room temperature, in the range 24390-20835 cm -1 , both compounds 3 and 4 display a metal-centered luminescence attributed to 4 I 13/2 → 4 I 15/2 (6660 cm -1 ) and 2 F 5/2 → 2 F 7/2 (signal centered around the value of 9966 cm -1 ) transitions, respectively. The observed six transitions could be attributed to the M J state splitting due to the existence of two Yb1 and Yb2 ions with slightly different polyhedra in 4. ■ INTRODUCTION Research and design of new multifunctional materials based on tetrathiafulvalene (TTF) is a recent challenge. 1 The idea is to combine the redox activity of such ligand with magnetic metal ions to elaborate magnetic conductors. 2 Recently, 4f lanthanide ions have been employed instead of 3d ions. The motivation for using 4f elements takes its origin in their large spins and pronounced spin-orbit coupling, in particular for Dy III and Tb III ions, giving a strong Ising-type magnetic anisotropy 3 suitable for building a Single Ion Magnet (SIM), Single Molecule Magnet (SMM), and Single Chain Magnet (SCM). 4 In addition, lanthanides are widely studied for their specific luminescence properties with emission lines ranging from visible to the near- infrared (NIR) spectral range and the luminescence lifetime from microsecond to millisecond range. That allows time-gated detection and large pseudo-Stokes shifts considering a ligand excitation. 5 More specifically, the NIR emitters have some potential applications in medicine because of the transparency of biological tissues to electromagnetic radiation in the range 0.8- 1.3 μm. 6 Moreover some applications in optical telecommuni- cation devices can be envisaged. 7 The “through space” approach has been used during the past decade to obtain π-f salts. 8 To combine the electronic conductivity to the specific properties coming from the 4f elements, the “through bond” approach seems a better choice. This approach has permitted the design of coordination complexes involving both 4f ions and TTF ligands, with exciting luminescence properties 9 and SIM/SMM behavior. 10 The luminescence has been observed because of the efficient antenna effect played by the TTF ligands upon irradiation in the Intra- Ligand Charge Transfer (ILCT) 9 while molecular magnets are obtained thanks to both the Ising Dy III ion and the structural role played by the TTF ligands. 10 It is worth noticing that this “through bond” approach is also suitable to combine both 3d and 4f ions with TTF ligands to reach π-3d4f systems. 11 In a synthetic point of view, ligands offering the possibility of several coordination sites are expected to be versatile building blocks in the preparation of molecular materials. They can lead to the formation of polynuclear compounds or molecular networks. Received: November 19, 2012 Published: January 16, 2013 Article pubs.acs.org/IC © 2013 American Chemical Society 1610 dx.doi.org/10.1021/ic302532f | Inorg. Chem. 2013, 52, 1610-1620