Reactivity of CuI and CuBr toward Et<sub>2</sub>S: a Reinvestigation on the Self-Assembly of Luminescent Copper(I) Coordination Polymers

CuI reacts with SEt<sub>2</sub> in hexane to afford the known strongly luminescent 1D coordination polymer [(Et<sub>2</sub>S)<sub>3</sub>{Cu<sub>4</sub>(μ<sub>3</sub>-I)<sub>4</sub>}]<sub><i>n</i></sub> (<b>1</b>). Its X-ray structure has been redetermined at 115, 235, and 275 K in order to address the behavior of the cluster-centered emission and is built upon Cu<sub>4</sub>(μ<sub>3</sub>-I)<sub>4</sub> cubane-like clusters as secondary building units (SBUs), which are interconnected via bridging SEt<sub>2</sub> ligands. However, we could not reproduce the preparation of a coordination polymer with composition [(Et<sub>2</sub>S)<sub>3</sub>{Cu<sub>4</sub>(μ<sub>3</sub>-Br)<sub>4</sub>}]<sub><i>n</i></sub> as reported in <i>Inorg. Chem.</i> <b>1975</b>, <i>14</i>, 1667. In contrast, the autoassembly reaction of SEt<sub>2</sub> with CuBr results in the formation of a novel 1D coordination polymer of composition [(Cu<sub>3</sub>Br<sub>3</sub>)(SEt<sub>2</sub>)<sub>3</sub>]<sub><i>n</i></sub> (<b>2</b>). The crystal structure of <b>2</b> has been solved at 115, 173, 195, and 235 K. The framework of the luminescent compound <b>2</b> consists of a corrugated array with alternating Cu(μ<sub>2</sub>-Br)<sub>2</sub>Cu rhomboids, which are connected through two bridging SEt<sub>2</sub> ligands to a tetranuclear open-cubane Cu<sub>4</sub>Br<sub>4</sub> SBU, ligated on two external Cu atoms with one terminal SEt<sub>2</sub>. The solid-state luminescence spectra of <b>1</b> and <b>2</b> exhibit intense halide-to-metal charge-transfer emissions centered at 565 and 550 nm, respectively, at 298 K. A correlation was also noted between the change in the full width at half-maximum of the emission band between 298 and 77 K and the relative flexibility of the bridging ligand. The emission properties of these materials are also rationalized by means of density functional theory (DFT) and time-dependent DFT calculations performed on <b>1</b>.