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

A series of Cu4I4 clusters (1-5) supported by two (PN)-N-boolean AND-type ligands 2-[(diRphosphino)methyl]pyridine (1, R = phenyl; 2, R = cyclohexyl; 3, R = tert-butyl; 4, R = iso-propyl; 5, 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 mu(4)-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) angstrom) are bridged with mu(2)-iodides, whereas the long edges (Cu-Cu = 2.839(3)-3.035(2) angstrom) are bridged in an antiparallel fashion by the (PN)-N-boolean AND ligands. This Cu4I4 geometry differs significantly from the cubane and stairstep geometries reported for other Cu4I4L4 clusters. Luminescence spectra of clusters 3 and 4 display a single emission around 460 nm at room temperature that is assigned to emission from a triplet halide-to-ligand charge-transfer ((XLCT)-X-3) excited state, whereas clusters 1, 2, and 5 also have a second band around 570 nm that is assigned to a Cu4I4 cluster-centered ((CC)-C-3) excited state. The structural and photophysical properties of a dinuclear Cu2I2((PN)-N-boolean AND)(2) complex obtained during the sublimation of cluster 3 is also provided.