Coordination-induced emission enhancement in copper(i) iodide coordination polymers supported by 2-(alkylsulfanyl)pyrimidines

Abstract

First examples of copper(I) complexes with 2-(alkylsulfanyl)pyrimidine ligands have been synthesized. Reactions of copper(I) iodide with 2-(methylsulfanyl)pyrimidine (L¹) in various metal-to-ligand molar ratios in MeCN afford a ladder-type coordination polymer [Cu₂L¹I₂]_n with polymeric chains built from double-stranded (Cu₂I₂)_n ribbons supported on both sides by μ₂-N,S-L¹ molecules. Although the second ligand, 2-(ethylsulfanyl)pyrimidine (L²), differs from L¹ only by a methylene group, its reactions with copper(I) iodide in MeCN yield not only a congenerous coordination polymer, [Cu₂L²I₂]_n, but also [CuL²I]_n, in which a similar (Cu₂I₂)_n ribbon is decorated by N-monodentate L² molecules. Absorption spectra of all compounds represent an interplay of metal + iodine-to-ligand charge transfer (XMLCT) and ligand-centered (LC) and cluster-centered (CC) transitions, while the emission occurs from the excited states of XMLCT nature. The luminescence of [Cu₂L¹I₂]_n and [Cu₂L²I₂]_n is blue-shifted and greatly enhanced in comparison with that of [CuL²I]_n (quantum yields: 89% and 68% for [Cu₂L¹I₂]_n and [Cu₂L²I₂]_nvs. 23% for [CuL²I]_n at 77 K), which can be associated with a more rigid μ₂-N,S coordination of 2-(alkylsulfanyl)pyrimidine ligands in [Cu₂L¹I₂]_n and [Cu₂L²I₂]_n leading to a less distorted T₁ state.