Elongation of a Trigonal-Prismatic Copper Cluster by Diphosphine Ligands with Longer Spacers.

ABSTRACT

A pair of alkynyl-diphosphine-coprotected copper(I) clusters, namely, [Cu6(4-MeO-PhC≡C)5(dppe)3](ClO4) [Cu6; dppe = 1,2-bis(diphenylphosphino)ethane] and [Cu11(H)(4-MeO-PhC≡C)8(dpppe)3](ClO4)2 [Cu11; dpppe = 1,5-bis(diphenylphosphino)pentane], featuring trigonal-prismatic frameworks have been synthesized by a reduction method. Their molecular structures are determined by X-ray crystallography and characterized by multiple techniques. The length of the spacer of the diphosphine ligand can directly affect the aspect ratio of the clusters. Cu6 with dppe as ligands has a trigonal-prismatic core. The longer alkyl spacer of dpppe helps to elongate the trigonal-prismatic framework to form Cu11, with its trigonal-prismatic framework encapsulating a Cu5H unit. Electrospray ionization mass spectrometry, 2H NMR, and liberations of hydrogen further verify the presence of a hydride in the cluster. Density functional theory calculations help to locate the position of the hydride and understand the electronic structures of the clusters. Cu11 is the first alkynyl-phosphine-coprotected copper hydride cluster. These two clusters show distinct luminescence properties. The compact Cu6 is phosphorescent upon radiation, while the longer Cu11 with more flexibility is nonluminous. This work enriches the family of copper hydrides and demonstrates the ligand effects in the extension of the length and structural complexity of clusters.