Syntheses, Structures, Photoluminescence, and Theoretical Studies of d¹⁰ Metal Complexes of 2,2‘-Dihydroxy-[1,1‘]binaphthalenyl-3,3‘-dicarboxylate

TLDR

The authors synthesized the free ligand and its dimeric Cd(II) complex by evaporation, and two d10 metal–hydroxy cluster coordination polymers by hydrothermal reaction, then characterized all structures by X‑ray crystallography and photoluminescence, attributing the observed emission to ligand‑to‑metal charge transfer as supported by molecular‑orbital calculations. The complexes exhibit distinct architectures—a 3D hydrogen‑bonded supramolecular array, a dimeric square motif, an octanuclear Cd metallacrown core, and butterfly‑shaped Zn clusters—yet all display blue/green photoluminescence, with the ligand structure dominating the emission and the metal cluster extending the lifetime.

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.