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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

Two prototypical carbido anionic clusters, the prismatic [Rh6C(CO)15]2– and the octahedral [Ru6C(CO)16]2–, can add two electrophilic Ag–NCMe+ fragments, which were exploited to condense the clusters with bifunctional heterocyclic ligands, such as pyrazine (pyz) or 4,4 -bipyridine (bipy), forming 1D chains of formula [{Ag(OC4H8){Rh6C(CO)15}Ag(OC4H8)}pyz] and [bipy{Ag2Ru6C(CO)16}(bipy)2{Ag2Ru6- C(CO)16}·2C4H8O], both characterized by single-crystal X ray diffraction. In the former, the two Ag+ ions are on opposite sides, and the chains are tightly packed. In the latter, the two silver ions are directly bound, and the metal clusters are connected alternatively by one and two linkers, giving rise to large channels.

The cluster [Rh11(CO)14(C7H7)3] (1) was obtained from the reaction of [Rh6(CO)16] and an excess of cycloheptatriene in refluxing toluene. Initially, the substituted cluster [Rh6(CO)13(C7H8)] (2) could be identified spectroscopically, which is transformed into 1 after prolonged refluxing. In the solid state, the eleven rhodium atoms define a trioctahedral metal cage, condensed through a common edge. The three planar, equivalent C7 rings sit on the top of triangular faces. The spectroscopic characterisation of the product is hampered by its low solubility.

The carbonyl hydride cluster Ir4H8(CO)(4)(PPh3)(4) (1) has been formed in hig(31)P NMR spectra, two isomeric forms (1A and 1B) of the cluster are present in CD2Cl2 solution at room temperature, and they do not interconvert in the explored temperature range. However, if a solid sample of the cluster is dissolved at 188 K, only 1A is detected by NMR spectroscopy. The structure of 1B could be proposed on the basis of the T-1 relaxation times of the various hydrides: it results by localised exchange of H and CO around two vertices of the tetrahedral frame.h yield and purity by heating a mixture of Ir-4(CO)(12) and PPh3 in toluene at 90 degreesC under hydrogen at atmospheric pressure. The product has been characterised by microanalysis, spectroscopy (IR, H-1 and P-31 NMR) and X-ray diffraction. In the solid state one hydrogen, one CO and one triphenylphosphane ligand are terminally bonded to each iridium atom, whereas four hydride ligands are bridging. All the hydrogen atoms were directly located by X-ray analysis at an average H-Ir distance of 1.55 Angstrom. (for the terminal H) and 1.75 Angstrom (for the p-H). As shown by H-1 and P-31 NMR spectra, two isomeric forms (1A and 1B) of the cluster are present in CD2Cl2 solution at room temperature, and they do not interconvert in the explored temperature range. However, if a solid sample of the cluster is dissolved at 188 K, only 1A is detected by NMR spectroscopy. The structure of 1B could be proposed on the basis of the T-1 relaxation times of the various hydrides: it results by localised exchange of H and CO around two vertices of the tetrahedral frame

The carbonyl cluster [Ir4(CO)11(SnX3)] [X = Cl, (1a) or Br (1b)] can be formed in good yield by insertion of SnX2 in the Ir–Br bond of [Ir4(CO)11Br] or, much less efficiently, by substitution of bromine with [SnCl3] , in THF at room temperature. The disubstituted cluster [Ir4(CO)10(SnCl3)2]2 (2) was obtained in 50% yields by double substitution on [Ir4(CO)11Br] , in THF at 60 C, whereas [Ir6(CO)15(SnCl3)] (3) can be prepared by carbonyl substitution of the homoleptic complex [Ir6(CO)16] with an excess of [SnCl3] in refluxing THF. In the three compounds, the SnCl3 units act as a one electron donor, displaying terminal (in 2), edge-bridging (in 1 and 2) and face-bridging (in 3) coordination. In keeping with a reduced bond order, the Ir–Sn bond distances increase in the series, being 2.584(1) Å for a terminal group; 2.72 Å for edge-bringing units and 2.78 Å for the face-bridging SnCl3. Regardless of the coordination mode, the geometry of the three chlorine atoms is always pyramidal, with Cl–Sn–Cl angles close to 90 and Sn–Cl bond distances close to 2.42 Å. Tin is always symmetrically bridging, with Ir–Sn–Ir close to 60 .

The cluster [HIr5(CO)(12)](2-) (1) was prepared by condensation of [HIr4(CO)(11)](-) and [Ir(CO)(4)](-) (molar ratio 1:1) in refluxing THF, with almost quantitative yields. Its solid state structure was determined by X-ray diffraction at low temperature on the salt [PPh3CH2Ph](2)[HIr5(CO)(12)]. The metal atoms define a trigonal bipyramidal arrangement. The hydride ligand was located indirectly as a bridge between apical and equatorial metal atoms. The phosphine-substituted cluster [HIr4(CO)(10)PPh3](-) (2) was synthetized by CO displacement on [HIr4(CO)(11)], in THF at room temperature. This reaction is selective, with no traces of polysubstitution products. In the solid state, the hydride and the triphenylphosphine are axially bound on basal iridium atoms; the terminal hydrogen atom was directly located by X-ray analysis at a Ir-H distance of 1.57(9) Angstrom. On the contrary, two isomers are present in THF solution, and they interconvert tepidly at room temperature, as shown by H-1 and P-31 NMR spectra

The anionic clusters [Fe5MN(CO)14Cp]2- [M = Mo (1) or W (2)] were synthesized from [Fe4N(CO)12]- and [MCp(CO)3]- in refluxing acetonitrile. The clusters [Fe3M3N(CO)18]3- [M = Mo (3) orW(4)] were prepared by reaction of [Fe4N(CO)12]- with [M2(CO)10]2- under the same conditions. The molybdenum- containing anions 1 and 3 are obtained in higher yields than 2 and 4. The reaction of the tetranuclear iron cluster with [Mo(ç6-Me3C6H3)(CO)3] affords a mixture of [Fe3Mo3N(CO)18]3- and [HFe5MoN(CO)16]2- (5). The solid state structures of the clusters 1, 2 and 3 have been determined; they consist of six metal atoms, arranged in octahedral metal cages encapsulating a ì6-N ligand. The cyclo- Introduction The interest in heterometallic clusters is still growing, and several examples of their application in catalysis can be found in the literature.[1] In homogeneous catalysis, mixed metal species are preferred, due to the presence of polar metal2metal bonds which can tune electron density at the metal centres, thus modifying the reactivity of the coordinated ligands.[2] In the field of heterogeneous catalysis, mixed-metal species can be exploited for the formation of bimetallic particles which are extraordinarily uniform in their morphology and composition.[3] In this context, the stability of the cage due to the interstitial atoms can avoid [a] Dipartimento di Scienze dell’ Ambiente e del Territorio, Universita` di Milano-Bicocca Piazza della Scienza 1, 20126 Milano, Italy rpergola@mailserver.unimi.it Fax: (internat.) 1 39-02/236-2748 [b] Dipartimento di Chimica Inorganica, Metallorganica ed Analitica and Centro del CNR Universita` di Milano, via G. Venezian 21, 20133 Milano, Italy [c] Dipartimento di Biologia Strutturale e Funzionale, Universita` degli studi dell’Insubria, via J. H. Dunant 3, 21100 Varese, Italy [d] Dipartimento di Chimica Strutturale e Stereochimica Inorganica and Centro del CNR 2 Universita` di Milano via G. Venezian 21, 20133 Milano, Italy E-mail: m.manassero@csmtbo.mi.cnr.it Eur. J. Inorg. Chem. 2000, 175921765 ÓWILEY-VCH Verlag GmbH, D-69451Weinheim, 2000 143421948/00/080821759 $ 17.501.50/0 1759 pentadienyl ligand is bound to Mo in 1 and to W in 2; these anions have three edge-bridging carbonyl groups and eleven terminal carbonyl groups. The cluster 3 possesses three molybdenum atoms in a fac arrangement, and the carbonyl ligands are all terminal, or asymmetrically bridging. Inspection of the interatomic distances suggests that molybdenum interacts preferentially with the carbonyl and the nitrido ligands, whereas the iron atoms bind strongly with the other metal centres. The solid state structure of 5 could not be fully resolved owing to crystal disorder. Analytical and spectroscopic data (infrared and 1H NMR) are all consistent with the proposed formula.

The anion [HFe3Rh(CO)12]2− was obtained by reaction of [HFe(CO)4]− with Rh2(CO)4Cl2 in refluxing THF. Its solid state structure consists of a tetrahedron of metal atoms with three edge-bridging and nine terminal carbonyl groups. The hydridic ligand bridges a face containing the rhodium atom.

The anionic species [Ir12(m-CO)8(CO)18]2-, obtained by reaction of [Ir6(CO)15]2- with [Cu(CH3CN)4][BF4], contains a Ir12 metallic array formed by superimposition of three face-sharing octahedral units. The compound adopts a metal framework similar to that of [H2Rh12(C0)25] but possesses a different number of valence electrons.

The dark brown [Ir3Ni6(m-CO)6(m3-CO)2(CO)9]3- trianion has been obtained by redox condensation between [Ni(CO)4] and [Ir(CO)4]-. This new mixed-metal cluster is rapidly degraded, at room temperature and atmospheric pressure, by carbon monoxide to form the [Ni(CO)4] and [Ir(CO)4]- parent mononuclear compounds. The metal framework consists of a face-sharing bioctahedron, with the three iridium atoms located in the inner triangle.

The compound [Felr3(CO)12]- can be obtained by degradation of [Felr4(C0)l5]2- under a carbon monoxide atmosphere as well as by reduction of an equimolar mixture of [Fe(CO)5] and [Ir4(CO)12] in alcoholic NaOH under 1 atm of carbon monoxide. The molecular structure of the anion consists of a tetrahedron of metal atoms surrounded by twelve carbonyl groups: nine are terminally bound whereas three are bridging the edges of the Felr2 basal face. The dianion [Fe2lr2(C0)l2]2- was obtained by several different ways, the most selective being the condensation of [Fe2(CO)9] with [Ir(CO)4]-. The molecular structure of the dianion is based on a tetrahedral cluster of metal atoms and consists of an apical Ir(CO)3 group co-ordinated by three metal-metal bonds to a basal Fe2lr(CO)9 fragment containing two Fe(CO)2 units and one Ir(CO)2 group linked to each other by a metal-metal bond and bridging carbonyl groups.The salt [PPh4]2[Fe2lr2(CO)12] reacts with [Au(PPh3)CI] to give [PPh4][Fe2lr2(CO)12{m3-Au(PPh3)}]. The metal framework of the anion is a trigonal bipyramid with the Au(PPh3) moiety in one of the apical positions, the other being occupied by a Fe(CO)3 group. Each edge of the equatorial triangle, formed by one iron and two iridium atoms, is spanned by a bridging carbonyl ligand, and two terminal CO groups are attached to each metal of this triangle.

The salts of the monosubstituted hexanuclear anions [Ir6(CO)14X]- [X = Cl (1,)Br (2), I (3), or SCN (4)] have been prepared by treating [Ir6(CO)16] with halides or pseudohalides at room temperature in tetrahydrofuran solution. The three anions consist of slightly distorted octahedra of iridium atoms bearing twelve terminal and two edge bridging carbon monoxide groups. In all cases the halogen atoms or the pseudohalogen group adopt a bridging co-ordination on an Ir-lr edge.

The syntheses and interconversions of mixed iron-rhodium carbonyl clusters are described; a combination of X-ray analysis and multinuclear n.m.r. measurements allowed the structural characterisation of [FeRh4(CO)15]2-, [FeRh5(CO)16]-, and [Fe2Rh4(C0)16]2- which can all be obtained from the unstable cluster, [Fe2Rh(CO)x]

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 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 dianionic cluster [Co5MoN(CO)(14)](2-) (1) was synthesized from [Co6N(CO)(15)](-) and [Mo-2(CO)(10)](2-) in refluxing acetonitrile. The solid-state structure of the [Ph4P](+) salt was determined. It consists of an octahedral metal cage, enclosing a six-coordinate nitrido ligand. Typical bond lengths are: Co-N 1.88 Angstrom, Mo-N 2.03 Angstrom, Co-Co 2.61 Angstrom and Co-Mo 2.84 Angstrom showing that there is very little, if any, preferential interaction of the interstitial atom with that of molybdenum. The cluster reacts with Au(PPh3)Cl in THF at room temperature forming the derivative [Co5MoN(CO)(14){AuPPh3}](-) (2). The gold atom caps an MoCO2 face of the octahedron, with short Au-Co (2.68 Angstrom) and long Au-Mo (3.16 Angstrom) bonds, showing that both metal atoms are necessary for coordination, but Au-I binds better with the cobalt atoms. Electrochemical studies have pointed out that cluster 1 has good redox capabilities in that it is able to support reversibly the progressive addition of three electrons. EPR measurements on the corresponding trianion confirm. the lack of preferential interaction between the Mo site and the interstitial nitride atom. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

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.

The dianion [FeIr4(CO)15]2– can be obtained by reduction of an equimolar mixture of [Fe(CO)5] and [Ir4(CO)12] in alcoholic NaOH and under 1 atm of carbon monoxide. The salt [N(PPh3)2]2[FeIr4(CO)15](1) crystallizes in the triclinic space group P with unit-cell dimensions a= 11.399(3), b= 14.032(3), c= 29.163(4)A, α= 86.18(2), β= 84.52(2), γ= 80.14(2)°, and Z= 2. Its metal framework consists of a trigonal bipyramid with the equatorial triangle formed by iridium atoms. The mean values of the Fe–Ir, Ireq–Ireq′ and Irap–Ireq distances are 2.943, 2.708, 2.991 A, respectively. The monoanion [Fe2Ir3(CO)14]– was obtained from [Fe(CO)4]2– and [Ir(CO)2Cl2]–. The salt [PPh4][Fe2Ir3(CO)14](2) crystallizes in the orthorthombic space group P212121 with unit-cell dimensions a= 12.461(5), b= 14.306(5), c= 23.504(6)A, and Z= 4. Its metallic framework is comprised of an iridium triangle capped on opposite side by two iron atoms. The mean values of the Fe–Ir and Ir–Ir distances are 2.648 and 2.708 A, respectively. In the derivative (1) the trigonal bipyramid is considerably elongated in the direction of the apical atoms, When compared with that in (2). This elongation is consistent with the increased number of cluster valence electrons: 76 in (1) and 72 in (2).

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.

In the title compound two C‐atoms are located in the cavity of a cluster. The CċC distance in very short—only 1.49 Å (for comparison: CC single bond 1.54 Å)—but, as deduced from a consideration of the number of cluster valence electrons, a delocalized CC interaction is more probable than a localized one. (Figure Presented.) Copyright © 1984 by Verlag Chemie, GmbH, Germany

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 [Fe5MnN(CO)16]2 (1) was synthesized from [Fe6N(CO)15]3- and Mn2(CO)10, in refluxing EtCN, or [Fe4N(CO)12]- and [FeMn(CO)9] -. Its solid state structure was determined on the [Me3NCH2Ph] + salt, and consists of an octahedral metal cage, enclosing a six-coordinated nitrido ligand. The position of the manganese atom in the solid state could be established, despite some crystallographic disorder, by considering the local stereochemistry of the ligands. The cluster [Fe6N(CO)14NO]2- (2) was obtained in moderate yields by the reaction of [Fe4N(CO12] with Mo(CO)3(EtCN)3. The nitrosyl is formed by oxidation of the starting nitride, and the source of the oxygen is presumably a carbonyl, whose splitting is mediated by the molybdenum complex. This process is the first example of an oxidation of a nitride in a carbonyl cluster. The solid state structure of the iron cluster is also octahedral, and the linear nitrosyl ligand was unambiguously located from the short Fe–N bond distance, and from dishomogeneous distribution of ligands. Cyclic voltammetric studies have shown that electron transfer processes are followed by chemical reactions thus testifying that no stable redox congeners exist for these two nitride clusters.

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.