Syntheses, structures, photoluminescence, and theoretical studies of d10 metal complexes of 2,2'-dihydroxy-[1,1']binaphthalenyl-3,3'-dicarboxylate

Abstract

The free solvated ligand, H2bna·CH3OH·H2O (1), and its dimeric complex, [Cd2(bna)2(H2O)6] (2) (bna = 2,2‘-dihydroxy-[1,1‘]-binaphthalene-3,3‘-dicarboxylate), were obtained by evaporation of the solutions, while two new d10 metal−hydroxy cluster-based coordination polymers, namely [Cd8(OH)4(H2O)10(bna)6]·17H2O (3) and [Hpy]2[Zn4(OH)2(H2O)2(bna)4]·2H2O·2CH3CN (4), were obtained by a hydrothermal route. All the compounds have been characterized by X-ray crystallography and photoluminescence measurements. Compound 1 consists of a three-dimensional, hydrogen-bonded supramolecular array, 2 exhibits a dimeric molecule featuring a square motif organized by two Cd(II) atoms and two bna ligands each at the corner, and 3 contains unprecedented [Cd8(μ3-OH)2(μ-OH)2(μ-H2O)2]12+ octanuclear metallacrown cores which are interlinked through bna to afford a two-dimensional structure, while 4 features layers with butterfly-shaped [Zn4(μ3-OH)2]6+ clusters. All the complexes display photoluminescent properties in the blue/green range. The manifestation of photoluminescence, as probed by molecular orbital calculations performed on the complexes and also on hypothetical multinuclear complexes, is attributed to a ligand-to-metal charge-transfer mechanism. In addition to presenting a new approach for the study of the photoluminescent properties of metal-cluster-based coordination polymers by using simple model compounds, the study also reveals the dominant role of the structure of the ligand over that of the d10 metal−hydroxy (or oxy) cluster and the presence of the cluster significantly increasing the emission lifetime.