Synthesis, Structural Characterization, and H2 Evolution Study of a Spheroid-Shape Hydride-Rich Copper Nanocluster

Abstract

This study reports on new bis-2-butyl dithiophosphate-stabilized polyhydrido copper nanoclusters, [Cu32(H)20{S2P(O2Bu)2}12], 1H, and [Cu20H11{S2P(O2Bu)2}9], 2H. The clusters 1H and 2H have been characterized by a variety of techniques including multinuclear NMR (1H, 2H, 31P), electrospray ionization mass spectrometry (ESI-MS), and low temperature X-ray crystallography. The presence of hydride ligands was supported by the 2H NMR spectrum of the deuteride analogs [Cu32(D)20{S2P(O2Bu)2)12], 1D and [Cu20D11{S2P(O2Bu)2}9], 2D. The metal skeleton of 1H revealed that a hexacapped rhombohedron of fourteen copper atoms was sandwiched between two sets of eighteen (9x2) copper atoms in a cup shape and the entire cluster is an elongated triangular gyrobicupola. The metal core is stabilized by 20 hydride ligands via various (?3, ?4, ?5)-H coordination modes and 12 dithiophosphate ligands coordinated either in tetrametallic tetraconnective (?4: ?2, ?2) or trimetallic tetraconnective (?3: ?2, ?2) patterns. The structural motif of 2H showed fascinating correlations with 1H having an elongated triangular orthobicupola framework of eighteen (9x2) copper atoms with an encapsulated linear Cu2 unit along the C3 axis and protected by 11 (?3, ?4)-H and 9 dithiophosphate ligands in a tetrametallic tetraconnective (?4: ?2, ?2) mode. The isopropyl derivatives, [Cu32(H)20{S2P(OiPr)2}12], 3H and [Cu20(H)11{S2P(OiPr)2}9], 4H, were used to study H2 evolution under different physico-chemical conditions and proved to be excellent models for hydrogen storage materials. Additionally, following H2 evolution under sunlight irradiation, mild thermolysis (?60 oC) and acidification, cluster 3H converted into [Cu8(H){S2P(OiPr)2}6]+, 5H. Intriguingly 5H can react with Cu+ salt in the presence of [BH4]? and re-form 3H. Cluster 4H also reproducibly re-formed via the reaction between 5H and [BH4]? from which a continuous cycle of cluster conversion and H2 evolution is proposed. Rhombus-shaped copper nanoparticles fabricated from further reductions of 3H and 4H showed the intermediary role of metal hydrides in the formation of metal nanoparticles under wet chemical methods. ? 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim