Systematic investigation on the coordination chemistry of a sulfonated monoazo dye: Ligand-dominated d- and f-block derivatives

Abstract

Ten coordination compounds based on a sulfonated monoazo dye, formulated as M(H₂O)₂(4,4′-abs)₂ (M = Mn 3a, Co 3b, Cu 3c, Zn 3d, Cd 3e and Pb 3f; 4,4′-abs = 4-aminoazobenzene-4′-sulfonic anion), Ag(4,4′-abs) (4), [Ln(H₂O)(phen)₂(4,4′-abs)₃]·3H₂O (Ln = Gd 5a, Tb 5b, and Ho 5c; phen = 1,10-phenanthroline), as well as the parent ligand L (1) [(4,4′-Habs)₂·4H₂O] and precursor NaL·HL (2) [Na(4,4′-abs)(4,4′-Habs)] were successfully isolated. Structural analyses revealed that the structures of compounds 3a–3f, 4, and 5a–5c vary according to the coordination geometries of the metal ions, and vary from double-strand chain structures (3a–3f) to a 3-D pillared-layer framework (4) to mononuclear complexes (5a–5c). The double-strand chain structures of 3a–3f are isostructural, and are built on octahedral metal centers and double bridging 4,4′-abs ligands coordinating via terminal N- and O-donors. The silver-containing compound 4 displays a pillared-layer structure constructed from 4.8²silver sulfonate nets pillared by the linear backbones of 4,4′-abs ligands. Compounds 5a–5c, which are also isostructural, possess mononuclear structures consisting of a metal cation, three 4,4′-abs anions, two auxiliary phen ligands, one aqua ligand and three non-coordinated water molecules. Evidence on two series of isostructural compounds indicates that structures of d- and f-block metal derivatives are dominated by the coordination mode of the ligands. The surface chemistry of compound 5c has been investigated based on the LBL (layer-by-layer) technique. The as-synthesized multilayer films with different composite components exhibit different surface behaviours.