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A new approach to the synthesis in good yields of known cobalt and iron carbidecarbonyl clusters by CO cleavage in mild conditions is reported. Cleavage of CO results from attaching an acetyl or benzoyl carbocation to the oxygen atom, and by transfer of electrons from an external source. This synthetic approach to carbide molecular clusters may be of some significance with respect to the formation of carbide atoms on to metal crystallites. Attempts to synthesize nickel carbide clusters with the same approach have only been partly successful. The new [Ni9C(CO)17]2~ and [Ni8C(CO)13]2~ have been obtained more conveniently from the reaction of [Ni6(CO)12]2- with CC14. The related reaction of [Ni6(CO)12]2- with Co3(CO)9CCl results in the formation of the mixed-metal carbide cluster [Co3Ni9C(CO)20]3_. This compound is degraded under a carbon monoxide and hydrogen mixture (25 °C, 1 atm) to Ni(CO)4, [Co(CO)4]~ and ethane. Intermediate formation of [Co3Ni7(C-C) (CO)15]3-, in which the two carbide atoms show an interatomic separation of 1.43 A, or of a related species, would provide a possible pathway for C-C bond formation.

The salts [NMe 4 ] 2 [Ni 5 (CO) 12 ], [NMe 4 ] 2 [Ni 6 (CO) 12 ], [NMe 4 ] 2 [Ni 12 (CO) 21 H 2 ] and [NEt 4 ] 3 [Ni 12 (CO) 21 H] in acetone are efficient catalysts for the polymerisation of acetylene.

The reaction of the [Pt-3n(CO)(6n)](2-) (n = 2-6) Chini's clusters with increasing amounts of PPh3 has been investigated in detail by combined FT-IR, P-31{H-1} NMR, and electrospray ionization-mass spectrometry (ESI-MS) studies, showing that up to three CO ligands are gradually substituted by PPh3, resulting in isonuclear phosphine-substituted anionic clusters of general formula [Pt-3n(CO)(6n-x)(PPh3)](2-) (n = 2-6; x = 1-3). Further addition of PPh3 results in the elimination of the neutral Pt-3(CO)(3)(PPh3)(3) species and formation of lower nuclearity anionic clusters. [Pt-12(CO)(22)(PPh3)(2)](2-) and [Pt-9(CO)(16)(PPh3)(2)](2-) have been structurally characterized, and they maintain the trigonal prismatic structures of the parent homoleptic clusters, with the two PPh3 ligands bonded to different external Pt-3-triangles in relative cis-position. Conversely, the crystal structure of [Pt-6(CO)(10)(PPh3)(2)](2-) shows that its metal cage is transformed from trigonal prismatic to trigonal antiprismatic after CO/PPh3 exchange.

The reactions of [NEt(4)](2)[Ni(6)(CO)(12)] with miscellaneous carbon halides (e.g. CCl(4), C(4)Cl(6)) in CH(2)Cl(2) have been extensively investigated particularly focusing on the stoichiometric ratio of the reagents and reaction temperature. This allowed the preparation of the previously known acetylide clusters [Ni(16)(C(2))(2)(CO)(23)](4-), [HNi(25)(C(2))(4)(CO)(32)](3-) and [Ni(22)(C(2))(4)(CO)(28)Cl](3-), as well as isolation and full characterisation of the closely related [Ni(17)(C(2))(2)(CO)(24)](4-) and [Ni(25)(C(2))(4)(CO)(32)](4-) tetraanions. From a structural point of view, all these clusters are based on a Ni(16) square orthobicupola which contain interstitial C(2), Ni(η(2)-C(2))(4) or Ni(2)(μ-η(2)-C(2))(4) moieties, displaying rather short C-C bonds. Electrochemical studies reveal that all these species undergo different redox processes, even if their stability is rather limited. This is corroborated by an extensive analysis of the interaction between interstitial C(2) acetylide units and the metal cluster cage by Extended Huckel Molecular Orbital (EHMO) calculations, which indicates that tightly bonded C-C units are less effective than isolated C-atoms in stabilising the cluster cage.

The new tetra-acetylide carbonyl clusters [H(4-n)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](n-) (n = 2-4) have been prepared by reacting [Ni(10)C(2)(CO)(15)](2-) with a large excess of CdBr(2).xH(2)O and the molecular structure of the di-anion [H(2)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](2-) has been fully elucidated by means of X-ray crystallography. The corresponding [HNi(22)(C(2))(4)(CO)(28)(CdBr)(2)](3-) and [Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](4-) conjugated bases are quantitatively obtained upon dissolution of [H(2)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](2-) salts in more basic solvents such as acetonitrile and DMSO, respectively. The hydride nature of both [H(2)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](2-) and [HNi(22)(C(2))(4)(CO)(28)(CdBr)(2)](3-) has been directly proved by (1)H NMR spectroscopy. Their resonances are very broad under all experimental conditions and their chemical shift greatly depends on solvent as well as temperature. Observation of the hydride resonances in [H(4-n)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](n-) (n = 2, 3) makes these clusters a case study of the phenomena behind the loss of any NMR signal in higher-nuclearity metal carbonyl cluster anions (MCCA). In the attempt to obtain a better insight on this experimental spectroscopic behaviour, solutions of [NMe(4)](3)[HNi(22)(C(2))(4)(CO)(28)(CdBr)(2)] have been investigated by dynamic light scattering (DLS) at various concentrations. The DLS experiments point out the presence in solution of a distribution of particles with nominal hydrodynamic diameters enormously greater than those of the free cluster ions resulting, probably, from aggregation in solution. This could formally justify the observed NMR behaviour, even if the present observations are preliminary and their quantitative assessment requires further systematic studies on MCCA aggregation in solution.

The synthesis, structure, spectroscopic characterization and electrical resistivity of the [EtV](2)[Fe(4)Pt(CO)(16)], [EtV][Fe(3)Pt(3)(CO)(15)].THF, [EtV][Fe(4)Au(CO)(16)](2)2.THF (EtV=1,1'-diethyl-4,4'-bipyridilium cation) and [NEt(4)](2)[Fe(4)Au(CO)(16)] is reported. The crystal structure of [EtV](2)[Fe(4)Pt(CO)(16)] is based on infinite stacks of [(EtV)(*+)](2) pi-dimers rotated by 90 degrees and isolated [Fe(4)Pt(CO)(16)](2-) ions. Within each pi-dimer, the [EtV](*+) radical ions are perfectly eclipsed and the distance between their mean planes is 3.275 A. The EPR spectrum of the solid material at room temperature clearly indicates the presence of a significantly populated triplet state of the pi-dimer, by showing signals both at Deltam=1 and Deltam=2. The solid-state structure of [EtV][Fe(3)Pt(3)(CO)(15)].THF is based on the ionic packing of [EtV](2+) and [Fe(3)Pt(3)(CO)(15)](2-) ions, inferred from a comparison of their molecular parameters with literature data. Significant electron transfer could have been expected to give [EtV](*+)[Fe(3)Pt(3)(CO)(15)](*-) on the basis of their formal redox potentials. In spite of their different stoichiometries, the structures of [EtV][Fe(4)Au(CO)(16)](2).2 THF and [NEt(4)](2)[Fe(4)Au(CO)(16)] both contain an isomer of the monoanion [Fe(4)Au(CO)(16)](-) in solution (previously characterized in the solid state as a [NMe(3)CH(2)Ph](2)[Fe(4)Au(CO)(16)]Cl mixed salt). Resistivity measurements on pellets of powdered samples of the above compounds indicate that their tetrasubstituted ammonium salts, and complex [EtV][Fe(4)Au(CO)(16)](2)2.THF, largely behave as insulators. However, the [EtV](2)[Fe(4)Pt(CO)(16)] and [EtV][Fe(3)Pt(3)(CO)(15)].THF samples respectively display resistivities 3 and 4 orders of magnitude less than those of their corresponding ammonium salts and could be classified as semiconductor materials.

Condensation between preformed Ni-Pt and Pt carbonyl clusters leads to the new [H(6-n)Ni(24)Pt(17)(CO)(46)](n-)(n= 5, 6) and the substitutionally Ni/Pt disordered [Ni(24)(Ni(12-x)Pt(x))Pt(20)(CO)(56)](6-) (x = 4) carbonyl clusters, the latter of which represents the highest nuclearity homoleptic carbonyl cluster anion so far reported.

The inter-conversions of platinum carbonyl dianionic clusters, ([Pt(3)(CO)(6)](n)(2-), n = 2-5), have been studied in THF and acetonitrile using in situ FTIR spectroscopy. These inter-conversions were facilitated by the addition (or removal) of molecular hydrogen. The individual reactions, namely reductions and oxidations of [Pt(3)(CO)(6)](n)(2-) were fast and reversible. BTEM analysis of the data provided the pure component spectra of the individual species without the need for physical separation. It is shown, for the first time, that the species [Pt(3)(CO)(6)](n)(2-) (n = 2) can be formed from the reduction of [Pt(3)(CO)(6)](n)(2-) (n = 3-5) by hydrogen alone in acetonitrile. Also, detection of dissolved CO(2) in solution suggests that a room-temperature water gas shift reaction occurs. This has been shown to arise from nucleophilic attack of water on a coordinated CO of [Pt(3)(CO)(6)](n)(2-) which leads to the formation of [HPt(15)(CO)(19)](3-) and [H(2)Pt(15)(CO)(19)](2-). The parent tetraanion, [Pt(15)(CO)(19)](4-), has been isolated in high yields by reaction of [Pt(3)(CO)(6)](n)(2-) (n = 2, 3) with NaOH at 60 °C and has been structurally characterized by X-ray analysis.