Structural, Luminescent and Thermal Properties of Heteronuclear Pd II ⁻Ln III ⁻Pd II Complexes of Hexadentate N₂O₄ Schiff Base Ligand.

New PdII ⁻LnIII ⁻PdII 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 PdII ⁻LnIII ⁻PdII 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 PdII ⁻LnIII ⁻PdII 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 ).