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Reactions of Cu (I) salts with Na (S (2) CR) (R = N (n) Pr (2), NEt (2), aza-15-crown-5), and (Bu (4) N) (BH (4) ) in an 8: 6: 1 ratio in CH (3) CN solution at room temperature yield the monocationic hydride-centered octanuclear Cu (I) clusters, Cu (8) (H) S (2) CR (6) (PF (6) ) (R = N (n) Pr (2), 1 (H) ; NEt (2), 2 (H) ; aza-15-crown-5, 3 (H) ). Further reactions of Cu (8) (H) S (2) CR (6) (PF (6) ) with 1 equiv of (Bu (4) N) (BH (4) ) produced neutral heptanuclear copper clusters, Cu (7) (H) S (2) CR (6) (R = N (n) Pr (2), 4 (H) ; NEt (2), 5 (H) ; aza-15-crown-5, 6 (H) ) and clusters 4-6 can also be generated from the reaction of Cu (BF (4) ) (2), Na (S (2) CR), and (Bu (4) N) (BH (4) ) in a 7: 6: 8 molar ratio in CH (3) CN. Reformation of cationic Cu (I) (8) clusters by adding 1 equiv of Cu (I) salt to the neutral Cu (7) clusters in solution is observed. Intriguingly, the central hydride in Cu (8) (H) S (2) CN (n) Pr (2) (6) (PF (6) ) can be oxidatively removed as H (2) by Ce (NO (3) ) (6) (2-) to yield Cu (II) (S (2) CN (n) Pr (2) ) (2) exploiting the redox-tolerant nature of dithiocarbamates. Regeneration of hydride-centered octanuclear copper clusters from the Cu (II) (S (2) CN (n) Pr (2) ) (2) can be achieved by reaction with Cu (I) ions and borohydride. The hydride release and regeneration of Cu (I) (8) was monitored by UV-visible titration experiments. To our knowledge, this is the first time that hydride encapsulated within a copper cluster can be released as H (2) via chemical means. All complexes have been fully characterized by (1) H NMR, FT-IR, UV-vis, and elemental analysis, and molecular structures of 1 (H), 2 (H), and 6 (H) were clearly established by single-crystal X-ray diffraction. Both 1 (H) and 2 (H) exhibit a tetracapped tetrahedral Cu (8) skeleton, which is inscribed within a S (12) icosahedron constituted by six dialkyl dithiocarbamate ligands in a tetrametallic-tetraconnective (μ (2), μ (2) ) bonding mode. The copper framework of 6 (H) is a tricapped distorted tetrahedron in which the four-coordinate hydride is demonstrated to occupy the central site by single crystal neutron diffraction. Compounds 1-3 exhibit a yellow emission in both the solid state and in solution under UV irradiation at 77 K, and the structureless emission is assigned as a (3) metal to ligand charge transfer (MLCT) excited state. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations on model compounds match the experimental structures and provide rationalization of their bonding and optical properties.
Liao et al. (Mon,) studied this question.