Structural, Luminescent and Thermal Properties of Heteronuclear PdII⁻LnIII⁻PdII Complexes of Hexadentate N₂O₄ Schiff Base Ligand

Abstract

New Pd^II⁻Ln^III⁻Pd^II complexes of hexadentate N₂O₄ Schiff base ligand (H₄L: N,N'-bis(2,3-dihydroxybenzylidene)-1,3-diamino-2,2-dimethylpropane) with Eu (1), Tb (2), Er (3) and Yb (4) ([Pd₂Eu(H₂L)₂NO₃](NO₃)₂∙2H₂O∙2CH₃OH 1, [Pd₂Ln(H₂L)₂H₂O](NO₃)₃∙3H₂O, where Ln = Tb 2, Er 3, [Pd₂Yb(H₂L)₂H₂O](NO₃)₃∙5.5H₂O 4) were synthesized and characterized structurally and physicochemically by thermogravimetry (TG), differential thermogravimetry (DTG), differential scanning calorimetry (DSC) and luminescence measurements. The compounds 1⁻4 are built of cationic heterometallic Pd^II⁻Ln^III⁻Pd^II trinuclear units. The palladium(II) centers adopt a planar square geometry occupying the smaller N₂O₂ cavity of the Schiff base ligand. The lanthanide(III) is surrounded by two Schiff base ligands (eight oxygen atoms) and its coordination sphere is supplemented by a chelating bidentate nitrate ion in 1 or by a water molecule in 2⁻4. The complexes have a bent conformation along the Pd^II⁻Ln^III⁻Pd^II line with valence angles in the ranges of 162⁻171°. The decomposition process of the complexes results in mixtures of: PdO, Pd and respective lanthanide oxides Eu₂O₃, Tb₂O₃, Tb₄O₇, Er₂O₃, Yb₂O₃. The luminescent measurements show low efficiency intramolecular energy transfer only in the complex of terbium(III) (2).

Keywords: 4d-4f complexes; Schiff base heteronuclear complexes; luminescence; palladium complexes.