Syntheses, Structures, Photoluminescence, and Theoretical Studies of d ¹⁰ Metal Complexes of 2,2′-Dihydroxy-[1,1′ ]binaphthalenyl-3,3′-dicarboxylate

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]·17H 2O (3) and [Hpy]2-[Zn4(OH)2(H 2O)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.