Cu₄I₄ Clusters Supported by P^∧N-type Ligands: New Structures with Tunable Emission Colors

Abstract

A series of Cu₄I₄ clusters (<b>1</b>–<b>5</b>) supported by two P^∧N-type ligands 2-[(di<b>R</b>phosphino)­methyl]­pyridine (<b>1</b>, R = phenyl; <b>2</b>, R = cyclohexyl; <b>3</b>, R = <i>tert</i>-butyl; <b>4</b>, R = <i>iso</i>-propyl; <b>5</b>, R = ethyl) have been synthesized. Single crystal X-ray analyses show that all five clusters adopt a rare “octahedral” geometry. The central core of the cluster consists of the copper atoms arranged in a parallelogram with μ⁴-iodides above and below the copper plane. The copper atoms on the two short edges of the parallelogram (Cu–Cu = 2.525(2)–2.630(1) Å) are bridged with μ²-iodides, whereas the long edges (Cu–Cu = 2.839(3)–3.035(2) Å) are bridged in an antiparallel fashion by the P^∧N ligands. This Cu₄I₄ geometry differs significantly from the “cubane” and “stairstep” geometries reported for other Cu₄I₄L₄ clusters. Luminescence spectra of clusters <b>3</b> and <b>4</b> display a single emission around 460 nm at room temperature that is assigned to emission from a triplet halide-to-ligand charge-transfer (³XLCT) excited state, whereas clusters <b>1</b>, <b>2</b>, and <b>5</b> also have a second band around 570 nm that is assigned to a Cu₄I₄ cluster-centered (³CC) excited state. The structural and photophysical properties of a dinuclear Cu₂I₂(P^∧N)₂ complex obtained during the sublimation of cluster <b>3</b> is also provided