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

摘要

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).