Bimetallic Nickel–Cobalt Hexacarbido Carbonyl Clusters [H_6–nNi₂₂Co₆C₆(CO)₃₆]ⁿ⁻(n= 3–6) Possessing Polyhydride Nature and Their Base-Induced Degradation to the Monoacetylide [Ni₉CoC₂(CO)_16–x]^3–(x= 0, 1)

Abstract

The reaction of [Ni 10 C 2 (CO) 16 ] 2− with Co 3 (μ 3 -CCl)(CO) 9 results in the new bimetallic Ni−Co hexacarbido carbonyl clusters [H 6−n Ni 22 Co 6 C 6 (CO) 36 ] n− (n = 3−6), which possess polyhydride nature and can be interconverted by means of acid−base reactions. The tetra-anion [H 2 Ni 22 Co 6 C 6 (CO) 36 ] 4− and the hexa-anion [Ni 22 Co 6 C 6 (CO) 36 ] 6− have been isolated in a crystalline state and structurally characterized via X-ray crystallography. The six carbide atoms are lodged into Ni 7 CoC square antiprismatic cages. Addition of strong bases to [Ni 22 Co 6 C 6 (CO) 36 ] 6− affords mixtures of the monoacetylides [Ni 9 CoC 2 (CO) 16 ] 3− and [Ni 9 CoC 2 (CO) 15 ] 3− , which have been cocrystallized as [NEt 4 ] 3 [Ni 9 CoC 2 (CO) 16−x ] (x = 0.58−0.84) salts, displaying tightly bonded interstitial C 2 units.

Molecular Nickel Phosphide Carbonyl Nanoclusters: Synthesis, Structure, and Electrochemistry of [Ni11P(CO)18]3–and [H6–nNi31P4(CO)39]n−(n= 4 and 5)

“…The data herein reported confirm the ability of interstitial heteroatoms to increase the stability of metal carbonyl clusters, favoring the formation of higher nuclearity species. ,,− As a further consequence of this enhanced stability, large molecular metal carbonyl clusters containing interstitial heteroatoms are often multivalent and may display several reversible redox processes. This point is demonstrated by comparing the rich redox behavior of [H 6– n Ni 31 P 4 (CO) 39 ] n − ( n = 4,5) with the fact that in the case of [Ni 11 P­(CO) 18 ] 3– spectroelectrochemical studies demonstrate only the reversible formation of the tetra-anion [Ni 11 P­(CO) 18 ] 4– .…”

“…[Ni 31 Sb 4 (CO) 40 ] 6– is even more electron-rich, possessing 416 CVE (6n+22 CMO). Such rich electron counts are usual for large nickel carbonyl clusters containing several interstitial heteroatoms, as found in polycarbide nickel carbonyls. − …”

“…Thus, if two isostructural clusters differing only by the charge display different electrochemical properties, then they ought to be hydrides. Conversely, if they show identical electrochemical properties, then they are the same chemical species but more or less oxidized. ,,,, …”

“…Formulation of the [H 6– n Ni 31 P 4 (CO) 39 ] n − species as polyhydrides was indirectly inferred from electrochemical and spectroelectrochemical studies (see section ), as well as their acid–base and redox chemical reactions summarized in Scheme . Indeed, as previously discussed for other large molecular metal carbonyl clusters, ,,,, all attempts to directly confirm their polyhydrido nature by 1 H NMR spectroscopy failed under any adopted experimental condition (solution and solid state experiments; VT experiments; different spectrometer frequencies; 1 H/ 2 D replacement and 2 D NMR spectroscopy in solution). Up to now, the largest molecular metal carbonyl clusters for which there is direct evidence (by 1 H NMR spectroscopy) of the presence of hydride ligands, as well as of the occurrence of protonation–deprotonation reactions, are [H 4– n Ni 22 (C 2 ) 4 (CO) 28 (CdBr) 2 ] n − ( n = 2–4) and [H 8– n Rh 22 (CO) 35 ] n − ( n = 3–7). ,,,, It must be remarked that the former Ni-clusters display very broad and temperature-dependent 1 H NMR spectra, whereas these phenomena are more limited in the case of the Rh 22 -clusters.…”

“…It has been pointed out that molecular metal nanoclusters might be interesting models for the investigation of metal aggregates at the nanolevel, as well as promising precursors for the preparation of metal nanoparticles and catalytic materials. − Thus, it is quite remarkable that molecular nickel phosphide nanoclusters have not been reported up to now. This should be contrasted with the tendency of Ni to form several molecular carbonyl clusters containing other fully interstitial p-block elements, such as C, Ga, Ge, Sn, and Sb. , Ni-carbide carbonyl clusters display a very rich chemistry and may contain 1–10 interstitial C atoms. − Conversely, heavier heteroatoms show a poorer chemistry. Ga, Ge, and Sn are limited to icosahedral Ni-carbonyl clusters containing a single fully interstitial heteroatom, , whereas [Ni 11 Bi 2 (CO) 18 ] 3– contains two semi-interstitial Bi-atoms .…”