PAPER www.rsc.org/dalton | Dalton Transactions Syntheses, characterisation, magnetism and photoluminescence of a homodinuclear Ln(III)-Schiff base family† Joy Chakraborty, a Aurkie Ray, a Guillaume Pilet, b Guillaume Chastanet, b Dominique Luneau, b Raymond F. Ziessel, c Lo¨ ıc J. Charbonni` ere, c Luca Carrella, d Eva Rentschler, d M. S. El Fallah e and Samiran Mitra* a Received 5th May 2009, Accepted 14th September 2009 First published as an Advance Article on the web 16th October 2009 DOI: 10.1039/b908910a A novel family of homodinuclear complexes of the general formula [Ln 2 L 2 (X) 2 ] (where Ln = Nd 3+ , Pr 3+ , Sm 3+ and Tb 3+ for 1, 2, 3 and 4, respectively and X, the coordinated NO 3 - or Cl - anion) has been synthesised from the corresponding lanthanide(III) salts with the pentadentate dianionic Schiff base ligand, H 2 L[N 1 ,N 3 -bis(salicylideneimino)diethylenetriamine], that exhibits a N 3 O 2 donor set. Single crystal X-ray diffraction studies evidenced the isostructurality of this family of centrosymmetric neutral dinuclear entities where the Ln(III) metal centres are coupled together by two phenolato oxygen atoms belonging to two units of ligand (H 2 L). Interestingly, the two other phenolato groups of H 2 L are mono-coordinated to the metal ions. Temperature dependence (2-300K) magnetic susceptibility studies suggest the presence of an antiferromagnetic interaction operating via double phenolato bridges. Photoluminescence activities of the complexes have been studied and compared with their precursor ligand. All the complexes have been characterised with microanalytical and several spectroscopic techniques. Introduction The coordination chemistry of lanthanide ions has been widely investigated over the last two decades because of both the useful magnetic and optical behaviours of these ions and their high coordination numbers which afford high complexity and dimen- sionality of the resulting networks. According to the magnetic aspect, such ions are involved in molecular architectures that exhibit Single Molecule Magnet 1 and Single Chain Magnet 2 behaviours with fascinating potentialities in term of magnetic anisotropy, as well as in Nuclear Magnetic Resonance Imaging 3 that use such paramagnetic systems as contrast agents to enhance image quality. The optical aspect of the lanthanides lies in their luminescent properties widely used in the lighting industry, 4 electroluminescent materials and optical fibres, 5 luminescence imaging 6 or biological assay. 7 Most trivalent lanthanide ions exhibit long-lived and line like emission bands at characteristic a Department of Chemistry, Jadavpur University, Raja S. C. Mullick Road, Kolkata, 700032, India. E-mail: smitra_2002@yahoo.com; Fax: +91-33- 2414 6414; Tel: + 91-33-2414 6193 b Groupe de Cristallographie et Ing´ enierie Mol´ eculaire, Laboratoire des Multimat´ eriaux et Interfaces, UMR 5615, Universit´ e Claude Bernard Lyon 1, Bˆ at. Jules Roulin, 43 Bd du 11 Novembre, 1918-69622, Villeurbanne Cedex, France c Laboratoire de Chimie Mol´ eculaire, UMR 7509 CNRS, ECPMULP, 25, rue Becquerel, 67087, Strasbourg Cedex 02, France d Institut f¨ ur Anorganische und Analytische Chemie, Johannes Gutenberg Universit¨ at Mainz, Duesberweg 10-14, D-55128, Mainz, Germany e Departament de Qu´ ımica Inorg` anica, Facultat de Qu´ ımica, Universitat de Barcelona, Mart´ ı i Franqu` es, 1-11, E-08028, Barcelona, Spain † CCDC reference numbers 612533, 672292, 672291, 664111 for, [Nd 2 L 2 (NO 3 ) 2 ], [Pr 2 L 2 (NO 3 ) 2 ], [Sm 2 L 2 (NO 3 ) 2 ], [Tb 2 L 2 (Cl) 2 ], respectively. For crystallographic data in CIF or other electronic format see DOI: 10.1039/b908910a wavelengths ranging from green light [Tb(III)] to near-infrared (NIR) light [Nd(III) and Er(III)]. 8 The Tb(III) and Eu(III) ions have been extensively involved in luminescent probes due to their emission in the visible region whereas, the Nd(III), Pr(III), Er(III) or Ho(III) ions emit in the Near Infrared Region (NIR). 9 The study of NIR luminescence is of specific interest because the emission around 900–1600 nm, which is highly transparent to biological systems and fibre media, is valuable for fluoro-immunoassay, 10 lasers and optical telecommunication. 11 However, for lanthanide ions, because the f –f transitions are parity forbidden, the absorption coefficients are usually very low with slow emissive rates. In order to overcome this, well- designed organic chromophores are used to excite lanthanide ions as sensitisers (antenna effect). 12 In this regard Schiff base metal complexes have played a key role to the gradual development of the Ln(III) coordination chemistry, ranging from pure synthetic work to modern physicochemical and biochemically relevant studies of metal complexes. 13 There are several reports which describe the use of modified “salen” type Schiff base ligands for the stabilisation of heteronuclear 3d –4f complexes. 14 Many of these studies have focused on magnetic behaviour while relatively few have described the photophysical properties of the compounds. 15 In addition the lanthanide cations can promote Schiff base condensation and can give access to complexes of otherwise inaccessible ligands through the template effect. This ability, combined with the applications of lanthanide macrocyclic complexes emerging from biology and medicine has boosted research in these areas. 16 Therefore, a large number of lanthanide complexes with the multidentate Schiff base derived from the condensation of different aldehyde/ketone and primary amine pairs has been published. 17 However, only recently, research work dealing with the various aspects involving different physicochemical properties and complexation behaviour This journal is © The Royal Society of Chemistry 2009 Dalton Trans., 2009, 10263–10272 | 10263