Heterometallic ZnII–LnIII–ZnII Schiff Base Complexes with Linear or Bent Conformation—Synthesis, Crystal Structures, Luminescent and Magnetic Characterization

Abstract

A series of racemic, heteronuclear complexes [Zn2Nd(ac)2(HL)2]NO3·3H2O (1), [Zn2Sm(ac)2(HL)2]NO3·3CH3OH·0.3H2O (2), [Zn2Ln(ac)2(HL)2]NO3·5.33H2O (3–5) (where HL is the dideprotonated form of N,N′-bis(5-bromo-3-methoxysalicylidene)-1,3-diamino-2-propanol, ac = acetate ion, and Ln = Eu (3), Tb (4), Dy (5), respectively) with an achiral multisite coordination Schiff base ligand (H3L) were synthesized and characterized. The X-ray crystallography revealed that the chirality in complexes is centered at lanthanide(III) ions due to two vicinally located μ-acetato-bridging ligands. The presented crystals have isoskeletal coordination units but they crystallize in monoclinic (1, 2) or trigonal crystal systems (3–5) with slightly different conformation. In 1 and 2 the ZnII–LnIII–ZnII coordination core is linear, whereas in isostructural crystals 3–5 the chiral coordination cores are bent and lie on a two-fold axis. The complexes 1, 3–5 show a blue emission attributed to the emission of the ligand. For ZnII2SmIII complex (2) the characteristic emission bands of f-f* transitions were observed. The magnetic properties for compounds 1, 4 and 5 are characteristic for the paramagnetism of the corresponding lanthanide(III) ions.

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

“…The dihedral angle between the PdO (phenoxo)2 and LnO (phenoxo)2 planes is also small (in the range of 0–10°, σ , Table 1), similar to complexes of H 4 L with Cu II and Ln III metal ions [15] and unlike other 3d-4f complexes. For example, in complexes of Zn II –Ln III –Zn II with a ligand based on a 2-hydroxypropanyl bridge, the σ value was approximately 35° [16]. The dihedral angle between two N 2 O 2 mean planes in the coordination core in 1 – 4 is in the range of 65–70° ( ε , Table 1) and the valence angle along the Pd II –Ln III –Pd II line is in the range of 162–171° ( φ , Table 1).…”

“…The H 4 L ligand shows the two most intense absorption bands, with maxima centered at 218 nm and 264.5 nm. All transitions correspond to the π-π* and n-π* transitions in the ligand [16,21]. The absorption spectra of the synthesized Pd II –Ln III –Pd II complexes with H 4 L are characterized by two absorption maxima in the ultraviolet region between 210–290 nm and an additional small band centered at approximately 375 nm, as shown in Figure S9.…”

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

“…These structures proved the flexibility of selected bi-compartmental N2O2-O2O'2 Schiff base skeletons to accommodate simultaneously the Pd(II) or Pt(II) ions (which demand a special planar tetragonal coordination environment) in the inner N2O2 pocket and lanthanide ions in the outer O2O'2 binding site. In case of heterotrinuclear Pd(II)-4f metal complexes the appropriate geometry for the auxiliary lanthanide ion was achieved by a propeller like arrangement of two Schiff base ligands resulting in linear trinuclear complexes that was previously observed for classic nonPGM homonuclear 3d or heteronuclear 3d-4f species enabling via bridges intermetallic interactions [162][163][164][165][166].…”

“…Classic bi-or Trinuclear Systems, which are N 2 O 2 -compartmental Schiff Bases The N 2 O 2 -compartmental Schiff base (Scheme 2e,f) are intensively used for studying of various transition metal complexes, however, there are only two structural reports on a series of crystal structures of classic heterobi-and heterotrinuclear systems in which the platinum group metals (Pt or Pd) were coordinated inside the N 2 O 2 -compartmental Schiff bases coordination site (Figure 10a,b; DEMPUJ and DIPDAK) [44,157]. These structures proved the flexibility of selected bi-compartmental N 2 O 2 -O 2 O' 2 Schiff base skeletons to accommodate simultaneously the Pd(II) or Pt(II) ions (which demand a special planar tetragonal coordination environment) in the inner N 2 O 2 pocket and lanthanide ions in the outer O 2 O' 2 binding site.In case of heterotrinuclear Pd(II)-4f metal complexes the appropriate geometry for the auxiliary lanthanide ion was achieved by a propeller like arrangement of two Schiff base ligands resulting in linear trinuclear complexes that was previously observed for classic nonPGM homonuclear 3d or heteronuclear 3d-4f species enabling via bridges intermetallic interactions[162][163][164][165][166].…”

Structural Characterization of Heterodinuclear ZnII-LnIII Complexes (Ln = Pr, Nd) with a Ring-Contracted H2valdien-Derived Schiff Base Ligand

“…Polydentate Schiff base chelate ligands derived from condensation of 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) or derivatives as aldehyde component with polyamines have been exploited for the synthesis of homoand heterodinuclear complexes. These have attracted research attention because of interesting properties such as magnetism and luminescence [6][7][8][9][10][11][12][13][14][15][16][17][18]. N 1 ,N 3 -bis(3-methoxysalicylidene)diethylenetriamine (H 2 valdien), which is obtained via Schiff base condensation of two equivalents of o-vanillin with diethylenetriamine, belongs to this class of ligands.…”