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

Abstract

Abstract:The 1:1 reactions between hydrated lanthanide(III) nitrates and triethanolamine (teaH 3 ) in MeOH, in the absence of external bases, have provided access to the dinuclear complexes [Ln 2 (NO 3 ) 4 (teaH 2 ) 2 ] (Ln = Pr, 1; Ln = Gd, 2; Ln = Tb, 3; Ln = Dy, 4; Ln = Ho, 5) containing the singly deprotonated form of the ligand. Use of excess of the ligand in the same solvent gives mononuclear complexes containing the neutral ligand and the representative compound [Pr(NO 3 )(teaH 3 ) 2 ](NO 3 ) 2 (6) was characterized. The structures of the isomorphous complexes 1·2MeOH, 2·2MeOH and 4·2MeOH were solved by single-crystal X-ray crystallography; the other two dinuclear complexes are proposed to be isostructural with 1, 2 and 4 based on elemental analyses, IR spectra and powder XRD patterns. The IR spectra of 1-6 are discussed in terms of structural features of the complexes. The two Ln III atoms in centrosymmetric 1·2MeOH, 2·2MeOH and 4·2MeOH are doubly bridged by the deprotonated oxygen atoms of the two η 1 :η 1 :η 1 :η 2 :µ 2 teaH 2 − ligands. The teaH 2 − nitrogen atom and six terminal oxygen atoms (two from the neutral hydroxyl groups of teaH 2 − and four from two slightly anisobidentate chelating nitrato groups) complete 9-coordination at each 4f-metal center. The coordination geometries of the metal ions are spherical-relaxed capped cubic (1·2MeOH), Johnson tricapped trigonal prismatic (2·2MeOH) and spherical capped square antiprismatic (4·2MeOH). O-H···O H bonds create chains parallel to the a axis. The cation of 6 has crystallographic two fold symmetry and the rotation axis passes through the Pr III atom, the nitrogen atom of the coordinated nitrato group and the non-coordinated oxygen atom of the nitrato ligand. The metal ion is bound to the two η 1 :η 1 :η 1 :η 1 teaH 3 ligands and to one bidentate chelating nitrato group. The 10-coordinate Pr III atom has a sphenocoronal coordination geometry. Several H bonds are responsible for the formation of a 3D architecture in the crystal structure of 6. Complexes 1-6 are new members of a small family of homometallic Ln III complexes containing various forms of triethanolamine as ligands. Dc magnetic susceptibility studies in the 2-300 K range reveal the presence of a weak to moderate intramolecular antiferromagnetic exchange interaction (J = −0.30(2) cm −1 based on the spin HamiltonianĤ = −J(Ŝ Gd1 ·Ŝ Gd1 )) for 2 and probably weak antiferromagnetic exchange interactions within the molecules of 3-5. The antiferromagnetic Gd III ···Gd III interaction in 2 is discussed in terms of known magnetostructural correlations for complexes possessing the {Gd 2 (µ 2 -OR) 2 } 4+ core. Ac magnetic susceptibility measurements in zero dc field for 3-5 do not show frequency dependent out-of-phase signals; this experimental fact is discussed and rationalized for complex 4 in terms of the magnetic anisotropy axis for each Dy III center and the oblate electron density of the metal ion.

Diversity of Coordination Modes in a Flexible Ditopic Ligand Containing 2-Pyridyl, Carbonyl and Hydrazone Functionalities: Mononuclear and Dinuclear Cobalt(III) Complexes, and Tetranuclear Copper(II) and Nickel(II) Clusters

“…The absence of bands that would be indicative of the monodentate and bidentate coordinated nitrato groups (present in the structure of the cluster) is rather surprising. This suggests [29,30] that the nitrato ligands are replaced by bromides that are in excess in the KBr matrix, thus producing ionic nitrates (KNO 3 ); this replacement is facilitated by the pressure that is applied for the preparation of the KBr matrix. As expected, extra nitrato bands appear in the mull (nujol, hexachlorobutadiene) spectra of 2.…”

Molecular Magnetism of Lanthanides Complexes and Networks

“…Such multi-functionality is found in the collection of papers of this Special Issue with contributions that highlight the unprecedented magnetic properties of lanthanide-based molecules together with chirality [1], luminescence [2,3] or electrical conductivity properties [4]. Innovative synthetic routes such as the use of helical [1,5] or protonated ligands [6] together with cutting edge characterization techniques of 4f-SMM are presented [7].…”

Molecular Magnetism of Lanthanides Complexes and Networks

“…Such multi-functionality is found in the collection of papers of this Special Issue with contributions that highlight the unprecedented magnetic properties of lanthanide-based molecules together with chirality [1], luminescence [2,3] or electrical conductivity properties [4]. Innovative synthetic routes such as the use of helical [1,5] or protonated ligands [6] together with cutting edge characterization techniques of 4f-SMM are presented [7].First of all, this Issue features a remarkable review article from Oliver Waldman and co-workers [7] that highlights the power of neutron scattering studies for the understanding of the magnetic behavior of 4f-SMMs. This extended and remarkably accurate work provides a deep and comprehensive perspective on this technique by analyzing, among others, one of the most famous molecules in our field, the Tb 2 (µ-N 2 3− ) dimer.…”

“…Such multi-functionality is found in the collection of papers of this Special Issue with contributions that highlight the unprecedented magnetic properties of lanthanide-based molecules together with chirality [1], luminescence [2,3] or electrical conductivity properties [4]. Innovative synthetic routes such as the use of helical [1,5] or protonated ligands [6] together with cutting edge characterization techniques of 4f-SMM are presented [7].…”

“…Albert Escuer, Spyros Perlepes and co-workers [6] report a new approach to the widely used triethanolamine ligand that gives rise to a family of Ln III complexes in which the Dy III derivative behave as a SMM.…”