Syntheses, crystal structures, thermal and magnetic properties of new heterotrinuclear CuII–LnIII–CuII complexes incorporating N2O4-donor Schiff base ligands

New Heterotrinuclear CuIILnIIICuII (Ln = Ho, Er) Compounds with the Schiff Base: Syntheses, Structural Characterization, Thermal and Magnetic Properties

New heterotrinuclear complexes with the general formula [Cu₂Ln(H₂L)(HL)(NO₃)₂]·MeOH (Ln = Ho (1), Er (2), H₄L = N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane) were synthesized using compartmental Schiff base ligand in conjugation with auxiliary ligands. The compounds were characterized by elemental analysis, ATR-FTIR spectroscopy, X-ray diffraction, TG, DSC, TG-FTIR and XRD analysis. The N₂O₄ salen-type ligand coordinates 3d and 4f metal centers via azomethine nitrogen and phenoxo oxygen atoms, respectively, to form heteropolynuclear complexes having CuO₂Ln cores. In the crystals 1 and 2, two terminal Cu(II) ions are penta-coordinated with a distorted square-pyramidal geometry and a Ln^III ion with trigonal dodecahedral geometry is coordinated by eight oxygen atoms from [Cu^II(H₂L)(NO₃)]⁻ and [Cu^II(HL)(NO₃)]²⁻ units. Compounds 1 and 2 are stable at room temperature. During heating, they decompose in a similar way. In the first decomposition step, they lose solvent molecules. The exothermic decomposition of ligands is connected with emission large amounts of gaseous products e.g., water, nitric oxides, carbon dioxide, carbon monoxide. The final solid products of decomposition 1 and 2 in air are mixtures of CuO and Ho₂O₃/Er₂O₃. The measurements of magnetic susceptibilities and field dependent magnetization indicate the ferromagnetic interaction between Cu^II and Ho^III ions 1.

Symmetry in Recognition of Supramolecular Synthons–Competition between Hydrogen Bonding and Coordination Bond in Multinuclear CuII–4f Complexes with Bicompartmental Schiff Base Ligand

Classic Cu–O coordination bonds in 1 or elongated semi-coordination ones in 2 and 3 were applied to construct CuII–4f complexes composed of trinuclear subunits linked through μ-NO3− ions with formulae given as [Cu2Tm(H2tehy)2]2(NO3)6·H2O, (1), {[Cu2Ho(H2tehy)2(NO3)2][Cu2Ho(H2tehy)2(H2O)2]}(NO3)4·2H2O, (2), and {[Cu2Er(H2tehy)2(H2O)]2([Cu2Er(H2tehy)2(NO3)]2}(NO3)10·2H2O·4CH3OH, (3), where H2tehy = C19H20N2O4 is a tetrahydroxy Schiff base ligand. Topological analysis showed that the same characteristic motif of coordination accompanied by hydrogen bonds involving the uncoordinated nitrate oxygen atom and ligand’s phenoxy O atoms is responsible for linking trinuclear subunits into a hexanuclear one as well as for bridging the hexanuclear coordination units in 3 into a 1D supramolecular polymer, with the Cu–O distance being 3.19(1) Å, much longer than the limit of a semi-coordination bond (3.07 Å). The Cambridge Structural Database was used to discuss issues of crystallographic criteria (distance and angular preferences) for the assessment of the stabilizing or destabilizing effect of hydrogen bonding on coordination. The presented results show that the symmetrically repeated arrangement of molecules may provide a useful tool for identifying higher order non-covalently bonded supramolecular aggregates. The complexes 1–3 have been characterized by X-ray diffraction, FTIR, and thermal analysis. The magnetic studies indicated the ferromagnetic interaction between CuII and HoIII ions.

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

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).