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

Abstract

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).

Luminescence and Palladium: The Odd Couple

“…Tetradentate ligands are typically built from Schiff bases, and some representative examples of N 2 O 2 and N 4 -donor cores are shown in Figure 28 . Complexes of Pd bonded to Schiff bases have been mostly studied in polynuclear combinations with other elements such as silicon [ 99 ] ( 98 , Figure 28 a) or lanthanides [ 100 ] ( 99 , Figure 28 b), although homometallic Pd-species are also known [ 92 , 101 ] ( 100 , 101 in Figure 28 c,d, respectively). The bipyridyne-carbazole complex 101 represents the first example of a coordination complex behaving as a red electroluminescent emitter.…”

“… Pd(II) coordination complexes containing tetradentate Schff bases as ligands in polynuclear ( a , b ) and mononuclear ( c , d ) environments. Adapted from [ 92 , 99 , 100 , 101 ]. …”

Homo- and Hetero-Oligonuclear Complexes of Platinum Group Metals (PGM) Coordinated by Imine Schiff Base Ligands

“…The modular "chemistry on complex" approach can be applied with the use of metal cross-coupling reactions [43]. However, frequently the obtaining of ligands and complexes may be conducted in situ by one-pot reaction with simultaneous addition of SB substrates and metal salts resulting in simple self-assembling of N 2 O 2 compartmental SB coordination units [44] up to macrocyclic calixsalens [45]. The metallic species may play a catalytic and template role in such syntheses.…”