Coordination Assemblies Based on a Methylthio Carboxylic Ligand: Syntheses, Structures and Luminescent Properties

Abstract

Amphiphilic 4-(methylthio) benzoic acid (HMBA) combining soft methylthio and hard carboxylic groups was used to construct two isostructural coordination polymers of [Cu(MBA)]n (CP-1) and [Ag(MBA)]n (CP-2), and one complex of Cu2(MBA)4(CH3CN)2• CH3CN (3). This ditopic HMBA ligand realizes stable coordination of its carboxylic group with low-valent soft Cu + ion (in-situ reduction from Cu 2+ ) under the assistance of methylthio groups, forming CPs of CP-1 and CP-2. Meanwhile, based on the theory of hard and soft acid and base (HSAB), harder Cu 2+ ions (in-situ oxidation from Cu + ) only coordinate to carboxylic groups, affording a paddle-wheel dinuclear complex 3. These two CPs were also taken for luminescent researches in solid state. CP-1 exhibits single-peak emission at 540 nm while CP-2 emits both at 499 and 528 nm with green luminescence. The emissions of CP-1 and CP-2 are both attributed to 3 MLCT (triplet metal-to-ligand charge transfer) excitation state.