A Copper(I) Homocubane Collapses to a Tetracapped Tetrahedron Upon Hydride Insertion

The hydrido copper(I) and silver(I) clusters incorporating 1,1-dicyanoethylene-2,2-dithiolate (i-MNT) ligands are presented in this paper. Reactions of M(I) (M = Cu, Ag) salts, [Bu4N]2[S2CC(CN)2], with the anion sources ([Bu4N][BH4] for H–, [Bu4N][BD4] for D–) in an 8:6:1 molar ratio in THF produce octanuclear penta-anionic Cu(I)/Ag(I) clusters, [Bu4N]5[M8(X){S2CC(CN)2}6] (M = Cu, X = H, 1H; X = D, 1D; M = Ag, X = H, 2H; X = D, 2D). They can also be produced from the stoichiometric reaction of M8(i-MNT)64– with the ammonium borohydride. All four compounds have been fully characterized spectroscopically (1H and 13C NMR, IR, UV–vis) and by elemental analyses. The deuteride-encapsulated Cu8/Ag8 clusters of 1D and 2D are also characterized by 2H NMR. X-ray crystal structures of 1H and 2H reveal a hydride-centered tetracapped tetrahedral Cu8/Ag8 core, which is inscribed within an S12 icosahedron formed by six i-MNT ligands, each in a tetrametallic–tetraconnective (μ2, μ2) bonding mode. The encapsulated hydride in 2H is unequivocally characterized by both 1H and 109Ag NMR spectroscopies, and the results strongly suggest that the hydride is coupled to eight magnetically equivalent silver nuclei on the NMR time scale. Therefore, a fast interchange between the vertex and capping silver atoms in solution gives a plausible explanation for the perceived structural differences between the Ag8 geometry deduced from the X-ray structure and the NMR spectra.