Rigidity effect of the dithioether spacer on the size of the luminescent cluster (Cu2I2)n (n = 2, 3) in their coordination polymers

Abstract

Treatment of CuI with the flexible PhS(CH₂)₄SPh dithioether ligand in MeCN solution affords the strongly luminescent metal–organic 2D coordination polymer [Cu₄I₄{μ-PhS(CH₂)₄SPh}₂]_n (1). The interpenetrated 2D network of 1 is built upon by Cu₄(μ₃-I)₄ cubane-like clusters as secondary building units (SBUs), which are interconnected via bridging 1,4-bis(phenylthio)butane ligands. In contrast, the auto-assembly reaction of the unsaturated semi-flexible PhSCH₂CCCH₂SPh ligand with CuI results in formation of the 3D metallopolymer [(Cu₆I₆){μ-PhSCH₂CCCH₂SPh}₃]_n (2). The SBUs of luminescent 2 consist of discrete Cu₆(μ₃-I)₆ hexagon prisms, which are coordinated with bridging 1,4-bis(phenythio)butyne ligands via Cu–S bonds. Contrary to the other rare literature-known examples of metallopolymers incorporating Cu₆X₆ SBUs as connecting nodes, the Cu⋯Cu interactions of 2 [2.8484(6) Å] are markedly shorter, being close to the sum of the Van der Waals radii of two Cu atoms (∼2.8 Å). The photophysics of these compounds, which exhibit reversible luminescence thermochromism, has been investigated in detail. The solid-state luminescence spectra of 1 and 2 feature at room temperature intense emissions around 560 and 555 nm, respectively. The luminescence properties of the unusual Cu₆(μ₃-I)₆ hexagon prism motif are rationalized by means of DFT and TDDFT computations.