A family of dinuclear lanthanide(iii) complexes from the use of a tridentate Schiff base

Abstract

The use of N-salicylidene-o-aminophenol (H2saph) in 4f-metal chemistry has led to the isolation of seven new isostructural lanthanide(iii) [Ln(III)] complexes. More specifically the Ln(NO3)3·xH2O/H2saph/Et3N (1 : 1 : 1) reaction mixtures in DMF/MeCN gave complexes [Ln2(NO3)2(saph)2(DMF)4] (Ln = Sm (); Eu (); Gd (); Tb (); Dy (); Ho (); Er ()) in good yields (∼65%). The structures of the isomorphous complexes and were solved by single-crystal X-ray crystallography; the other complexes are proposed to be isostructural with and based on elemental analyses, IR spectra and powder XRD patterns. The two Ln(III) atoms in the centrosymmetric molecules of and are doubly bridged by the deprotonated iminophenolato oxygen atoms of two nearly planar η(1):η(1):η(2):μ saph(2-) ligands. The imino nitrogen and five terminal oxygen atoms (the salicylaldiminate, two from one bidentate chelating nitrato group and two from two DMF ligands) complete square antiprismatic coordination at each metal centre. The IR spectra of the complexes are discussed in terms of the coordination modes of the ligands present in the complexes. Solid-state emission studies for all display identical ligand-based photoluminescence. Dc magnetic susceptibility studies in the 2-300 K range reveal the presence of a weak, intramolecular antiferromagnetic exchange interaction (J = -0.19(1) cm(-1) based on the spin Hamiltonian H = -J(ŜGd·ŜGd')) for and probably ferromagnetic exchange interaction within the molecules of and . Ac magnetic susceptibility measurements in zero dc field show temperature- and frequency-dependent out-of-phase signals with two well defined, thermally-activated processes for , suggesting potential single-molecule magnetism character. The Ueff value is 17.4 cm(-1) for the higher temperature process and 16.2 cm(-1) for the lower temperature one. The combination of photoluminescence and single-molecule behaviour in the Dy complex is critically discussed.

Using the Singly Deprotonated Triethanolamine to Prepare Dinuclear Lanthanide(III) Complexes: Synthesis, Structural Characterization and Magnetic Studies

“…In accordance with this conclusion, the band at 1384 cm −1 is absent from the mull spectra of these complexes. The mull IR bands at~1480 and~1290 cm −1 in 1-5 are assigned [25] …”

“…As expected for pure Ln III systems, the exchange interaction is rather weak as a consequence of the shielded 4f orbitals that have small overlap with bridging ligand orbitals. This J value is typical for dinuclear complexes containing the {Gd III 2(μ2-OR)2} 4+ core [17,18,20,25,50]. Rov and Hughbanks performed a spin density functional (SDFT) study of dinuclear Gd III complexes containing the {Gd2(μ2-OR)2} 4+ core [20].…”

“…Intercationic interactions through the C3-HB ( The Ln-O/N bond lengths and the Ln···Ln distances in the isomorphous complexes 1·2MeOH, 2·2MeOH and 4·2MeOH follow the order Dy < Gd < Pr (for example the Dy···Dy, Gd···Gd and Pr···Pr distances are 3.669(1), 3.719(1) and 3.810(1) Å, respectively), a typical consequence of the lanthanide(III) contraction [25]. The coordination polyhedra of the Gd III (2·2MeOH) and Pr III (1·2MeOH) are closest to Johnson tricapped trigonal prism and to spherical-relaxed capped cube, respectively (Figures S7 and S8, respectively; Tables S2 and S3, respectively).…”

“…Thus, the choice of the primary organic ligands is crucial for the synthesis of Ln III 2 complexes. With all the above in mind and given the recently initiated interest of our groups in Ln III 2 complexes with interesting magnetic and/or luminescence properties [23,[25][26][27], we report here the synthesis, structures and magnetic properties of new such complexes bearing the monoanion of tris(2-hydroxyethyl)amine (the empirical name is triethanolamine, abbreviated hereafter as teaH3, Scheme 1). This ligand is very popular in 3d-and mixed 3d/4f-metal cluster chemistry (representative 3d/4f-metal compounds based on anionic forms of teaH3 are described in refs [28][29][30][31]), but with limited used in homometallic Ln III [37][38][39].…”

“…neutral capping organic ligands, which terminate oligomerization or polymerization by blocking two or three coordination sites per Ln III center [23]. Another method is the simultaneous employment of capping bidentate nitrato groups (nitrato ligands have little tendency for bridging in Ln III chemistry) and neutral or anionic organic ligands that can, in principle, bridge only two metal centers; in addition to the bridging functionality, the ligands should preferably possess "chelating" parts to satisfy the demand for high coordination numbers at the Ln III centers [24][25][26]. Thus, the choice of the primary organic ligands is crucial for the synthesis of Ln III 2 complexes.…”