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The reaction of [Fe4C(CO)12(CuCl)2]2- with NaBH4 yields sequentially [Fe4C(CO)12(CuCl)]2- (1) and [Fe4C(CO)12Cu(η2-BH4)]2- (2), depending on the Fe4Cu2:NaBH4 ratio. The reaction of [Fe4C(CO)12(CuNCMe)2] with NaBH4 yields [{Fe4C(CO)12Cu2( μ-H)}2]2- (3), which, upon precipitation with 2-propanol, forms [{Fe4C(CO)12Cu2( μ-OiPr)}2]2- (4). 1 and 2 are isostructural,with a CuX linearly bonded to the exposed carbide ligand of a butterfly [Fe4C(CO)12]2- unit. 3 and 4 are also very similar, with the four copper atoms of two Fe4Cu2 octahedra connected by bridging hydrides (in 3) and bridging alkoxides (in 4). However, 3 and 4 are not isoelectronic, and in agreement with the unsaturation of 3, its Cu-Cu distance is much shorter

The reactions between [Fe 6 C(CO) 16 ] 2− and CuCl, in refluxing THF, yield [Fe 5 C(CO) 14 (CuCl)] 2− ( 1 ), [Fe 4 C(CO) 12 (CuCl) 2 ] 2− ( 2 ), or [{Fe 4 Cu 2 C(CO) 12 (μ-Cl)} 2 ] 2− ( 3 ), depending on the Fe 6 /CuCl ratio. The chloro ligands of these clusters can be displaced either spontaneously, or by metal-assisted substitution, to give the bromo derivative [Fe 5 C(CO) 14 (CuBr)] 2− ( 4 ) or the solvento complexes [Fe 5 C(CO) 14 (CuTHF)] − ( 5 ) and [Fe 4 C(CO) 12 (CuNCMe) 2 ] ( 6 ). The latter can be also obtained directly, by metal substitution from [Fe 6 C(CO) 16 ] 2− and [Cu(NCMe) 4 ]BF 4 , or by polyhedral expansion from [Fe 4 C(CO) 12 ] 2− . All the clusters are octahedral, with the copper atoms in a pseudo-linear geometry, where one of the coordination positions is occupied by the interstitial carbide. The two copper atoms in the Fe 4 Cu 2 clusters are always in cis geometry and, in the dimer [{Fe 4 Cu 2 C(CO) 12 (μ-Cl)} 2 ] 2− , they are joined through chlorides. The role of the different metal centres in determining the redox activity of the heteronuclear Fe–Cu clusters 1 , 2 , 3 , has been studied by electrochemical methods. In the bridged dimer 3 , the two Fe 4 Cu 2 C cluster units resulted electronically not communicating.

The two clusters [HFe5NiN(CO)14]2- (1) and [HFe4Ni2N(CO)13]2- (2) were obtained by reaction of [Fe4N(CO)12]- and [Ni6(CO)12]2- in refluxing MeCN and EtCN, respectively, along with other Fe-Ni mixed metal clusters. Their solid state structures were determined on the [PPh4]+ salts, and both have an octahedral metal cage, containing an interstitial nitrogen atom. The two Ni atoms in 2 are cis, with a Ni-Ni separation of 2.724(1) Å. The two anions have different stereochemistry of the carbonyl ligands: in 1, five CO's are semi-bridging, and the remaining nine are terminal; in 2 there are three asymmetric bridging and ten terminal ligands (two for each iron and one for each nickel). The hydride ligands were located in the final difference maps, both bridging a Ni-Fe edge of the clusters but, thanks to the better quality of the diffraction data, the metal-hydrogen distances were refined only in 2. In this cluster, the Fe-H and Ni-H bond lengths are 1.77(2) and 1.79(2) Å, respectively. © 2006 Elsevier B.V. All rights reserved.

The reaction between [Fe2Ir2(CO)12]2− and diphenylacetylene in refluxing CH3CN yields the substituted cluster [Fe2Ir2(CO)10(PhC2Ph)]2− (1). In the crystals, the four metal atoms define a butterfly arrangement whose Ir–Ir hinge is parallel to the acetylenic C2 unit. The neutral triangular cluster [FeIr2(CO)9(PhC2Ph)] (2) is obtained by the treatment of 1 with acids at room temperature; in this 48 valence electrons species, the C–C and the Ir–Ir bonds are also parallel, in the μ 3 – η ∥ 2 coordination mode. The cluster [Fe2Rh(CO)10]− reacts with diphenylacetylene in refluxing THF yielding [Fe2Rh(CO)8(PhC2Ph)]− (3). In this 46 C.V.E.’s cluster, the C2 unit is perpendicular to the Fe–Fe edge, exemplifying the μ 3 – η ⊥ 2 bonding mode. According to 13C NMR spectra, the structure of the three clusters is maintained in solution. Electrochemical investigations show that the one-electron oxidation of [Fe2Ir2(CO)10(L)]2− (L = 2CO, PhC2Ph) as well as the one-electron reduction of [Fe2Rh(CO)8(PhC2Ph)]− only generates the respective short lived products.

The anion [Ir 6 (CO) 15 Cl] − has been formed by treating [Ir 6 (CO) 15 ] 2− with FeCl 3 ; [Ir 6 (CO) 15 Cl] − ( 1 ) is the first species formed, but if kept standing 1 slowly loses a CO ligand to give [Ir 6 (CO) 14 Cl] − ( 2 ). Compound 1 can also be obtained by treating Ir 6 (CO) 16 with LiCl in anhydrous tetrahydrofuran, but, because of the long reaction time needed, a substantial amount of compound 2 is also formed. The crystal structures of [PPh 4 ][Ir 6 (CO) 15 Cl] · C 4 H 8 O ( 1 ) and [PPh 4 ][Ir 6 (CO) 14 Cl] ( 2 ) have been determined. Anion 1 contains an octahedron of iridium atoms surrounded by eleven terminal, one edge, and three face-bridging carbonyl groups, and by one terminal chlorine atom. The disposition of the bridging carbonyl groups can be related to that of Ir 6 (CO) 16 (red isomer) in which one face-bridging carbonyl group has become edge bridging. Selected bond distances are: IrIr(average) 2.774, IrC(terminal, average) 1.85, IrC(edge bridging, average) 2.13, IrC(face bridging, average) 2.22, IrCl 2.395(5) A. Anion 2 contains a slightly distorted octahedron of iridium atoms bearing twelve terminal and two edge-bridging carbon monoxide groups; the chlorine atom bridges an IrIr edge. The stereochemistry of anion 2 is related to that of [Ir 6 (CO) 15 ] 2− by replacing an edge-bridging carbonyl group by the μ-halogen atom [Cl bridges Ir(4)Ir(3), C(13) bridges Ir(1)Ir(6), C(14) bridges Ir(2)Ir(3)]; i.e. each of the six iridium atoms is involved in only one bridge. Average selected bond distances are: IrIr 2.767, IrC(terminal) 1.85, IrC(edge bridging) 2.05, IrCl 2.484 A.

The neutral cluster [Au8Mo4(CO)(20)(PPh3)(4)] was synthesized in low yield from [AuCl(PPh3)] and [Mo-2(CO)(10)](2-) in acetonitrile at room temperature. The cluster was characterized by X-ray analysis, IR, and P-31 NMR spectroscopy. Its solid-state structure consists of four Au3Mo tetrahedral units, fused by four Au atoms in a ring. The average bond lengths are Au-Au 2.77 angstrom and Mo-Au 2.93 angstrom. The internal angles of the planar square ring are very close to 90 degrees

The reaction between norbornene (C7H10) and Ir-6(CO)(16) in refluxing toluene yields the substituted cluster [Ir-6(CO)(14)(C7H8)]. In the solid state, the six iridium atoms define an octahedral metal cage, and one face is capped by the C7H8 ligand, coordinated through a 1,2-vinylidene unit. The loss of two hydrogen atoms from the olefin is, presumably, the result of a double oxidative addition of its C-H bonds, followed by elimination of a hydrogen molecule from the cluster. The bonding parameters of the organic fragment, as well as the architecture of the carbonyl ligands, closely match those found in the alkyne-substituted [Ir-6(CO)(14)(PhCCPh)] complex. The cluster [Ir-6(CO)(14)(C7H8)] was characterized through H-1-, C-13- and bidimensional COSY NMR.

The three clusters [Fe6Ni6N2 (CO)24]n- (n = 2-4) have been isolated, and their solid-state structures determined. The clusters are composed by three face-sharing octahedra, with the external ones filled by two interstitial nitride. The addition of electrons brings about swelling of the central, empty octahedron. Cyclic voltammetry shows that redox conversions of the three clusters are totally reversible. Extended Hückel and density functional calculations have been performed, to explain this behavior. © 2005 Académie des sciences. Published by Elsevier SAS. All rights reserved.

The cluster [FeNi5(CO)(13)] (2-) (1) was obtained by reaction of Fe(CO)(5) and [Ni-6(CO)(12)](2-) (2), in acetonitrile at room temperature. Its solid state structure was determined on the [NEt4]() salt, and consists of a trigonally distorted octahedron, with six edge-bridging ligands. This assembly strictly recalls the architecture of the prototypical [Ni-6(CO)(12)](2-) anion, by formal replacement of one Ni(CO) unit with the Fe(CO)(2) fragment. However, the requirements of the additional ligand have sterical consequences on the other carbonyl groups, which can not be coplanar as in the all-nickel cluster. [FeNi5(CO)(13)](2-) reacts readily with acids, to yield the already known [HFe3Ni(CO)(12)](-) (3), and with CO, being stepwise fragmented to species of lower nuclearity, ending with [Fe3Ni(CO)(12)](2-) (4) or [Fe-2(CO)(8)](2-). The solid state structure of the tetranuclear [Fe3Ni(CO)(12)](2-) was also determined, and is reported here. (C) 2002 Elsevier Science B.V. All rights reserved.

The neutral cluster [Ir6(CO)15(AuPPh3)21 has been obtained by reaction of [IrdC0)15I2- with [AuPPh3]+. The iridium atoms of the cluster define an octahedral frame capped by one gold-phosphine group. The second AuPPh3 unit spans one Ir-Au edge. The metal skeleton of C1 symmetry is coordinated by twelve terminal and three edge-bridging carbonyl groups. The dianionic [IrdcO)14(Hgc1)21~- has been prepared from [Irs(C0)15l2- and Hg2C12, HgC12 + Hg, or HgClz in the presence of Na2C03. The metallic framework forms an octahedron of iridium atoms bearing, on four non-adjacent faces, two ,u3-HgC1 fragments and two ,u3-C0 groups. The chemical shift of the lg9Hg NMR was found at +1508 ppm.

Reaction of [Co3(CO)9CCl] with [Ni6(CO)12]2- results in a complicated mixture of mixed Co-Ni carbide carbonyl clusters, among which the [Co3Ni9C(CO)21]3- trianion has been isolated in a pure crystalline state and fully characterized by X-ray crystallography. The metal framework of this compound is unprecedented in cluster geometries and may be described as a square antiprism of metal atoms tetra-capped on two alternate pairs of adjacent triangular faces. Despite the presence of a caged carbon atom in the square-antiprismatic cavity, the compound is readily degraded by carbon monoxide (25 "C, 1 atm) mainly to a mixture of [Co(CO)4]- and [Ni(CO)4]. Corresponding degradation of the cluster under a mixture of carbon monoxide and hydrogen yields, in addition, trace amounts of organics, mainly C1 and C2 hydrocarbons, probably derived from the carbide atom.

The synthesis, chemical behavior and single crystal X ray structure of two new CoNi bimetallic carbide clusters, namely [Co 2 Ni 10 (CO) 20 C] 2− and [Co 3 Ni 9 (CO) 20 C] 2− , are reported. The first complex was isolated in ca. 30% yield among the products of the reaction of Co 3 (CO) 9 CCl with [Ni 6 (CO) 12 ] 2− , while the second was obtained quantitatively by reaction with protonic acids of the previously reported [Co 3 Ni 9 (CO) 20 C] 3− . The two compounds are isostructural and show a metal frame which can be regarded as derived by distortion of a tetra-capped triangulated dodecahedron of D 2 d symmetry; the statistical (Co and Ni atoms being undistinguishable) idealized symmetry of the metal frame is only D 2 owing to progressive deformations toward a tetra-capped tetragonal antiprismatic geometry, which are probably related to the steric requirements of the interstitial carbide atom.

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 synthesis and properties of the new dicarbidocarbonyl bimetallic clusters [Co3Ni7(CO)16C2]2− (I), [Co3Ni7(CO)16C2]3− (II), and [Co3Ni7(CO)15C2]3− (III), are described. Compound I, which is paramagnetic, has been synthesized in high yields by redox-condensation of Co3(CO)9CCl with [Ni9(CO)17C]2−, whereas the diamagnetic trianions II and III have been respectively obtained by reduction of I, with sodium metal in THF and sodium hydroxide in methanol. The anion I has been isolated in a crystalline state in association with several tetrasubstituted ammonium or phosphonium cations, which are characterized by elemental analysis and by a single-crystal X-ray diffraction study, of the tetraphenylphosphonium salt. The anion I has a metal frame based on a 3,4,3-C2h stack of metal atoms, which may be regarded as derived by condensation of two either octahedral or trigonal-prismatic moieties. The resulting deca-vertices metal polyhedron encapsulates a C2 fragment showing a short CC interatomic separation of 1.48 A. The three cobalt atoms cannot be distinguished from the remaining seven nickel atoms and are probably randomly distributed over the ten vertices. The M-M distances are scattered over the range 2.34–2.80 A, and each carbide carbon is encapsulated in a seven-vertices cage which may be described as a distorted capped trigonal prism. The carbonyl stereochemistry comprises six carbonyl groups terminally bonded to the atoms of the top and bottom triangular layers, and ten edge-bridging CO which span the ten inter-layer edges. The structure of this decanuclear dicarbide cluster is compared with those reported for related species and a rationalization is offered for the variations of the metal geometry and the CC interatomic separation.

The synthesis and the structure of the novel tri-anion, [Fe 3 Rh 3 (CO) 17 ] 3− , is reported: the metal framework of this 88 valence electron bimetallic cluster is unusual, and consists of an Fe 2 Rh 3 trigonal bipyramid with iron and rhodium atoms in apical sites and a dangling Fe atom attached to the apical Rh.

The cluster [Ir 4 (CO) 11 (CPhCHPh)] − was obtained by reaction of [HIr 4 (CO) 11 ] − and diphenylacetylene by refluxing in tetrahydrofuran (THF), with yields approaching 80%. The solid state structure was determined on the [NEt 4 ] + salt; the cluster possesses a tetrahedral metallic framework, with three edge bridging carbonyls. The vinyl fragment, having two phenyl rings in cis , is bound in axial position and donates only one electron to the cluster, since the CC double bond (1.34 A) does not interact with any iridium atom. The 13 C-NMR of the cluster, recorded at −90°C, allows full assignment of the signals. The cluster [Ir 6 (CO) 14 (COOMe) 2 ] 2− was obtained by nucleophilic attack of MeONa on [Ir 6 (CO) 16 ], in anhydrous methanol at room temperature. The solid state structure was determined on its [N(PPh 3 ) 2 ] + salt. Two methoxycarbonyl fragments are on adjacent metal vertices of the octahedral framework.