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

Author： Mylonas-Margaritis Ioannis Mayans Julia Sakellakou Stavroula-Melina P. Raptopoulou Catherine Psycharis Vassilis Escuer Albert P. Perlepes Spyros

Publisher： MDPI

E-ISSN： 2312-7481|3|1|5-5

ISSN： 2312-7481

Source： Magnetochemistry, Vol.3, Iss.1, 2017-01, pp. : 5-5

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Abstract

The 1:1 reactions between hydrated lanthanide(III) nitrates and triethanolamine (teaH₃) in MeOH, in the absence of external bases, have provided access to the dinuclear complexes [Ln₂(NO₃)₄(teaH₂)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(NO₃)(teaH₃)₂](NO₃)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 η¹:η¹:η¹:η²:μ₂ teaH₂⁻ ligands. The teaH₂⁻ nitrogen atom and six terminal oxygen atoms (two from the neutral hydroxyl groups of teaH₂⁻ 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 η¹:η¹:η¹:η¹ teaH₃ 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 Hamiltonian H ^ = - J ( S ^ Gd 1 ⋅ S ^ Gd 1 ′ ) ) 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 {Gd₂(μ₂-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.