Copper(i) 5-phenylpyrimidine-2-thiolate complexes showing unique optical properties and high visible light-directed catalytic performance

Abstract

Solvothermal reactions of 5-phenylpyrimidine-2-thiol (5-phpymtH) with equimolar CuBr afforded one hexanuclear cluster [Cu₆(μ₃-5-phpymt)₆] (1) along with a tetranuclear by-product [{(Cu₂Br)(μ-5-phpymtH)}(μ₃-5-phpymt)]₂ (2). A two dimensional (2D) polymer [Cu₄(μ₅-5-phpymt)₂(μ-Br)₂]_n (3) was isolated from the reaction of 5-phpymtH with two equiv. of CuBr. Analogous reactions of 5-phpymtH with one or four equiv. of CuI produced one tetranuclear cluster [{Cu₂(μ-5-phpymtH)(μ-5-phpymt)}(μ₃-I)]₂ (4) and one 2D polymer [Cu₆I₂(μ₄-I)₂(μ₄-5-phpymt)₂]_n (5). Compound 1 possesses a water-wheel-shaped hexameric structure. Compound 2 has an H-shaped tetrameric structure. Compound 3 possesses a 2D network in which unique 1D [Cu₈(μ-Br)₂(μ₅-5-phpymt)₄]_n chains are connected by μ-Br⁻ ions. Compound 4 has another tetrameric structure in which two {Cu₂(μ-5-phpymtH)₂(μ-5-phpymt)} fragments are linked by a pair of μ₃-I⁻ ions. Compound 5 contains another 2D network in which hexanuclear {Cu₆I₂(μ₄-I)₂} units are linked by μ₄-5-phpymt bridges. The 5-phpymt ligand shows four coordination modes: μ–κ¹(S)–κ¹(N) (4), μ₃–κ²(S)–κ¹(N) (1 and 2), μ₄–κ¹(N)–κ²(S)–κ¹(N′) (5) and μ₅–κ¹(N)–κ³(S)–κ¹(N′) (3). Complex 1 shows strong solvatochromic behaviour and displays reversible luminescence switching upon alternate addition of CF₃COOH and Et₃N into its CHCl₃ solution. Complexes 1–5 exhibit a high photocatalytic activity towards the aerobic oxidative hydroxylation of arylboronic acids to phenols under visible light irradiation. Catalyst 5 can be reused in several cycles without any obvious decay of the catalytic efficiency. These results offer an interesting insight into how the CuX/5-phpymtH molar ratios and X⁻ ions exert great impacts on the coordination modes of the 5-phpymt⁻ ligand, the structures of the final complexes, and the luminescence and catalytic properties.