Solvothermal synthesis, structure, and fluorescence properties of three d10 polymers assembled from semi-rigid V-shaped aza-bridged multicarboxylate

Abstract

Hydro(solvo)thermal reactions between a new flexible multicarboxylate ligand, 2,2′-azanediyldibenzoic acid (H₂L), and M(OH)₂ (M = Cd, Zn) in the presence of different N-donor ancillary ligands, 4,4′-bipyridine (bpy) and pyridine (py), afford three novel coordination polymers: [Cd₂(L)₂(bpy)_1.5(H₂O)]_n (1), [Cd₂(L)(Py)₂]_n (2), and [Zn₂(L)₂]_n (3). These polymers show great differences in regard to their structures and properties due to the variation in the ancillary ligands and in the coordination geometry of the metal ions. Compound 1 exhibits a 3D supramolecular network assembled from 2D layered architecture composed of dinucelar cadmium subunits via intermolecular π⋯π and C–H⋯π interactions. The supramolecular structure of compound 2 is built from the packing of two homochiral helical chain. Compound 3 possesses two crystallographically nonequivalent metal atoms with Zn1 in a four-coordinated tetrahedron geometry and Zn2 in a five-coordinated trigonal bipyramid geometry. Five different coordination modes, ranging from μ₂, μ₃ and μ₄, have been observed in the H₂L ligands. The solid-state fluorescence spectra show that complexes 1 and 2 exhibit small shifts to the blue, while 3 is red shifted with respect to the free ligand.