Self-assembly of a tridentate Schiff-base ligand with Zn(II) in the presence of lanthanides: Novel crystal structures and spectroscopic properties

Condensation of picolinaldehyde with methyl 4-amino-3-hydroxy-benzoate resulted in the acquisition of a tridentate Schiff-base ligand (HL) which contains a structural moiety typical of octahedrally cored grid-type analogs. Reactions of HL with Zn(NO₃)₂ in the presence of Ln(NO₃)₃ Ln = Sm(III), Tb(III) and Yb(III)] result in two types of complexes, viz. Zn(HL)(L)]₂Ln(NO₃)₅] Sm(III), 1a and Tb(III), 1b] and Zn(HL)L]₂Yb(NO₃)₅]·C₃H₆O (1c). Despite applying two different synthetic protocols, the transition metal ion displayed a greater propensity towards the meridional tridentate pocket, which is reflected by XRD analysis, the ESI-MS technique and further supported by elemental analysis and IR characterization of each compound. In addition, we have compared the luminescence properties of 1a, 1b and 1c with the previously synthesized Zn(HL)(L)]₂Zn(NO₃)₄] (1d) to investigate whether a different metal in the outer coordination sphere could somehow tune the compounds’ spectral behavior.