Closo Research Articles

Oxidation - Reduction and Photochemical Reactions of Metalladecaborane Clusters: The Interconversion ofhypercloso-[(η6-C6Me6)RuB9H9] andcloso-[(η6-C6Me6)RuB9H9]2−

Reversible hypercloso – closo interconversion by means of simple redox chemistry: Two-electron reduction of hypercloso-[1-(η6-C6Me6)-1-RuB9H9] (1) gives the closo dianion 22−, which displays the bicapped square-antiprismatic structure expected for a closo cluster with 2n+2 skeletal electrons. The dianion 22− is quantitatively oxidized back to 1 by simple air oxidation.

A Metalloid Al(14) Cluster with the Structure of a "Nano-Wheel"

An intermediate on the pathway from AlI species to aluminum metal: This is one way to view the [Al14{N(SiMe3)2}6I6]2− cluster (structure shown) formed from the reaction of an aluminum(I) iodide solution with LiN(SiMe3)2. With the help of density functional calculations it was confirmed that the observed metalloid structure is more favorable for the Al14 cluster than a polyhedral structure that follows Wade's rules.

Polyanionic Clusters and Networks of the Early p-Element Metals in the Solid State: Beyond the Zintl Boundary.

Reduction of p-element (post-transition) metals and metalloids by alkali metals leads to many salts containing polyatomic clusters or network anions of these elements. The earliest solvated examples were referred to as Zintl ions. Synthetic explorations have now established that many of the clusters can in fact be obtained from neat (solvent free) high-temperature reactions of binary to quaternary systems, particularly for the heavier tetrel (group 14) and triel (group 13) elements. Some synthetic tricks have also proven useful. Electronic guidelines such as Wade's rules, known to account well for other types of electron-deficient cluster bonding, are widely applicable to these compounds, but numerous hypoelectronic (electron-poor) trielide salts have also been discovered. These developments also extend to related infinite network structures and Zintl (valence) compounds. The Zintl boundary designation traditionally delineated the tetrel elements that form salts with the active metals from those of the triel and earlier elements that were once thought to generate only intermetallic phases. The distinction no longer seems appropriate, at least with regard to some alkali-metal compounds of the triel elements.

Aluminium Atoms at High Connectivity Sites in Polyhedral Polyborane Analogous Clusters: From Aluminaboranes to Carbaalanes

Cluster chemistry in the third main group has long been restricted to compounds of the lightest element boron. However, about 30 years ago the first compounds were synthesized and characterized in which single aluminium atoms adopted positions of high connectivity in polyhedral borane or carbaborane clusters. The next successful step in these efforts to establish a chemistry analogous to that of the polyboranes with the heavier elements of the third main-group was the synthesis of closo-dodecaaluminate [Al12iBu12]2– at the beginning of the nineties, which was the first homonuclear aluminium analogue of a polyborate anion and had a core exclusively formed by aluminium atoms. Another class of interesting new aluminium compounds was formed by the carbaalanes, which were synthesized and characterized for the first time only recently. They have clusters of aluminium and carbon atoms, and are similar to the carbaborane analogues in that their structures seem to be determined by the number of electron pairs in their molecular centers in accordance with the Wade rules.

NaK29Hg48: A Contradiction to or an Extension of Theoretical Concepts to Rationalize the Structures of Complex Intermetallics?

NaK29Hg48 is a new silver metallic, air-sensitive ternary alkali metal amalgam with metallic properties. It crystallizes in space group Pm3n (No. 223, Z=2, a=1685.3(2) pm) and shows a superconducting phase transition at 2.5 K. Its crystal structure is characterized by novel icosahedral Hg12 clusters centered by Na atoms and hexagonal antiprismatic Hg12 clusters (“drums”) centered by K atoms. Both cluster types are embedded in a matrix of K atoms. With respect to the topology of the cluster centers the three-dimensional arrangement corresponds to the A15 structure type (Nb3Sn). The crystal structure of NaK29Hg48 is closely related to that of the complex intermetallic phases A3Na29In48 (A=K, Rb, Cs) and others. It is an unexpected electron deficient borderline case with respect to electron counting rules (Wade's rules and Zintl–Klemm concept), which were successfully applied to explain the occurence of icosahedral and hexagonal antiprismatic In12/Tl12 clusters in the latter two compounds.

A Camouflagednido-Carborane Anion: Facile Synthesis of Octa-B-methyl-1,2-dicarba-closo-dodecaborane(12) and Its Deboration Reaction

Facile, efficient, and economical is the exhaustive methylation of ortho-carborane, its isomers and its derivatives under Friedel–Crafts conditions utilizing MeI and AlCl3. Regioselectively, ortho-carborane yields the 4,5,7,8,9,10,11,12-octamethyl derivative 1 which has been degraded by using KOEt under autogenous conditions. The resulting camouflaged nido anion can be protonated (2⋅H) and finally converted to the per-B-methylated C2B9 closo cluster 3.

B-frame-supported bimetallics. Isoelectronic arachno-structured [(PMe 2Ph) 4Pd 2B 8H 10] and closo-structured [(PMe 3) 4(CO) 2Ir 2B 8H 8

Reaction of [IrCl(CO)(PMe 3) 2] with [NEt 4][ nido-B 9H 12] gives the ten-vertex eight-boron cluster species [(PMe 3) 4(CO) 2Ir 2B 8H 8]. This formally has a closo cluster electron count compatible with its closo structure. By contrast, ten-vertex eight-boron [(PMe 2Ph) 4Pd 2B 8H 10], isolated from [4-(NH 2Ph)- arachno-B 9H 13] and [PdCl 2(PMe 2Ph) 2], has a closo electron count but an arachno structure. The origins of this apparent anomaly are briefly addressed and enunciated.

Formation,Photodissociation and Structures of Si,Sn,Pb/P Binary Atomic Cluster lons

the formation and photodissociation of group hv (si, ge, sn, pb)/p binary cluster ions, produced by laser ablation, were studied with a tandem tof mass spectrometer, the stability of these cluster ions is influenced by their electronic and geometric structures, and the geometric stability becomes more important for heavier group iv /p cluster ions. two types of binary clusters marked with the magic numbers were observed: one type of magic clusters may be explained by the wade's rule, in which p atom either attaches as electron-donating ligand to the close-skeleton of group iv atoms, or joins the close-skeleton directly; another type of magic clusters are isoelectronic with magic species of neutral group iv clusters or p clusters. the possible structures of magic cluster ions were studied by ab initio calculation and the wade's rule.

The Tris(trimethylsilyl)silylgallium Group as a Building Block in Gallium-Iron Clusters

Trigonal bipyramidal clusters based on iron carbonyl and gallandiyl derivatives are described. Two types of cluster cores are shown right. a) The Ga3−xCOxFe2 core (Ga3Fe2 shown) is derived from Fe2(CO)9 by the replacement of all, two, or one of the bridging CO ligands with (Me3Si)3SiGa. b) The Ga2Fe3 core is understood as a closo-type cluster following Wade's rules, whereas for a) a classical description is valid. All clusters may be obtained from the reaction of [{Ga(Cl)Si(SiMe3)3}4] with the iron carbonylates Na2Fe(CO)4, Na2Fe2(CO)8 and Na2Fe3(CO)11.

Aspects of anionic framework formation: Clustering of p-block elements

High electron delocalization and coordination numbers are typical of metals. For alloys in which the electronegativities of the components are sufficiently different, electron transfer brings the electronegative elements into new electronic configurations. This transforms metallic architectures either into classical anionic frameworks (Zintl phases) obeying the octet and 8− N valence rules, or into various complex networks in which classical valence rules no longer hold. Intermediate phases with partially delocalized bonding may form with clusters which mostly satisfy Wade's electron-counting rules. Generally, these phases have closed-shell electronic structures and the expected semiconducting properties. However, some of them display poor metallic behaviour owing to a few additional and somewhat delocalized electrons. The intermetallic chemistry of group 13 elements with alkali metals provides an interesting overview of various structural and electronic situations. Bonding within naked clusters and anionic cages of p-block elements clearly illustrates the transition between the metallic and molecular states.

Transformation of 3,4-Bis(isopropylidene)-2,5-dichloro-1,2,5-thiadiborolane intonido-2,4,5-Thiadicarbahexaborane(5) Derivatives – Formation and Computational Elucidation of a Thiadicarbanonaborane(8) with ani-9<IV+IV> Configuration

The 3,4-bis(isopropylidene)-2,5-dichloro-1,2,5-thiadiborolane (5b), obtained from 3,4-bis(dichloroboryl)-2,5-dimethyl-2,4-hexadiene (4) and (Me3Si)2S, reacts with Li[RBH3] (R = H, C6H5, C6Me4H) to yield the corresponding derivatives of the nido-4,5-diisopropyl-2,4,5-thiadicarbahexaboranes 2. Replacements of the chlorine atoms in 5b with two hydrido, or with one hydrido and one aryl (phenyl or duryl) group, followed by the hydroboration of the isopropylidene substituents with RBH2 (R = H, C6H5, C6Me4H) lead to four nido-2,4,5-thiadicarbahexaboranes (2a–d) in low yields. Their composition follows from MS and NMR data; not refined X-ray structural data of 2d support the proposed skeletal structure. In addition to 2a, larger thiacarboranes were detected by GC/MS and 11B NMR. The structure of the nine-vertex cluster 6a could be identified by applying the ab initio/IGLO/NMR method. Geometry optimizations at the MP2(fc)/6–31G* level rule out the Csnido-SC2B6H8 isomer 7. The C2v structure of 6 consists of a nine-vertex cluster with two elongated B–B distances. As this 22e cluster 6 represents an exception to the Wade rules, the nature of the bonding of nine-vertex clusters with different electron counts is discussed.

High nuclearity ruthenium carbonyl cluster chemistry VII . Synthesis, NMR studies, electrochemistry and X-ray crystal structure of [PPN] [Ru 8( μ8-P)(CO) 22

The reaction between [Ru 3( μ-H)( μ-NC 5H 4)(CO) 10] and chlorodiphenylphosphine in refluxing chlorobenzene, followed by metathesis with bis(triphenylphosphoranylidene)ammonium chloride ([PPN]Cl), affords [PPN][Ru 8( μ 8-P)(CO) 22] ( 1) in around 30% yield. 31P-NMR solution spectra are consistent with the presence of at least two isomers of the cluster anion, presumably due to differing carbonyl distributions; the chemical shifts for these configurations (600–800 ppm downfield of H 3PO 4) are consistent with a highly deshielded interstitial phosphorus atom. An X-ray structural study of one isomer of 1 reveals that the phosphorus atom occupies an interstitial square antiprismatic site defined by the eight ruthenium atoms, with two bridging carbonyl ligands on opposite faces spanning interplanar Ru–Ru bonds, and twenty terminal carbonyl ligands completing the ligand set. The solid state 31P-NMR spectrum of the crystallographically-identified isomer reveals a signal at 596.1 ppm assigned to the square antiprismatic interstitial phosphorus atom. Formal electron counting suggests that 1 has four electrons less than expected using Wade's rules. The reductive electrochemistry of 1 has been examined by cyclic voltammetry, and reveals the presence of two one-electron and one two-electron reduction waves, an uptake of four electrons in total, consistent with the cluster's theoretical electron deficiency in the resting state.

(Cp*Fe)3{(η3-As3)Fe}As6] und [(Cp*Fe)3As6][FeCl3(THF)], zwei neue Eisen–Arsen-Cluster mit As6 und As3-Fragmenten

[(Cp*Fe)3{(η3-As3)Fe}As6] and [(Cp*Fe)3As6][FeCl3(THF)], Two New Ironarsenide Cluster Containing As6 and As3 Fragments The compounds [(Cp*Fe)3{(η3-As3)Fe}As6] (1) and [(Cp*Fe)3As6][FeCl3(THF)], (2) can be obtained in good yields through the reaction of As7(SiMe3)3 with FeCl2 and LiCp*. Both compounds have been characterized by mass spectroscopy and crystal structure analysis. The As7 nortricyclane frame of As7(SiMe3)3 is still recognizable in 1. According to the Wade rules the cation of 2 has 20 valence electrons inside the clustercore. This leads to a structure very similar to closo-B9H92–.

Rhodathiaboranes with `anomalous' electron counts: synthesis, structure and reactivity

Analysis of the structures of 8,8-(PPh 3) 2-8,7- nido-RhSB 9H 10 and 9,9-(PPh 3) 2-9,7,8- nido-RhC 2B 8H 11 by RMS misfit calculations has confirmed that these rhodaheteroboranes possess nido 11-vertex cluster geometries in apparent contravention of Wade's rules. However, examination of the molecular structures of both species shows that the {RhP 2} planes are inclined by ca. 66° with respect to the metal-bonded SB 3 or CB 3 faces, and that two weak ortho-CH⋯Rh agostic interactions occupy the vacant co-ordination position thereby created. As a consequence of these agostic bonds the Rh atom, and hence the overall cluster, is provided with an additional electron pair, meaning that their nido structures are now fully consistent with Wade's rules. The chelated diphosphine compound 8,8-(dppe)-8,7- nido-RhSB 9H 10 is similar to the PPh 3 compound in showing the same agostic bonding. Attempts to prepare a bis-P(OMe) 3 analogue result in ligand scavenging and the formation of 8,8,8-{P(OMe) 3} 3-8,7- nido-RhSB 9H 10. Similarly, reaction between Cs[6- arachno-SB 9H 12] and RhCl(dmpe)CO does not result in CO loss but in formation of 8,8-(dmpe)-8-(CO)-8,7- nido-RhSB 9H 10, shown to exist as a mixture of two of three possible rotamers. Deprotonation of 8,8-(PPh 3) 2-8,7- nido-RhSB 9H 10 and 8,8-(dppe)-8,7- nido-RhSB 9H 10 with MeLi yields the anions [1,1-(PPh 3) 2-1,2- closo-RhSB 9H 9] − and [1,1-dppe-1,2- closo-RhSB 9H 9] −, respectively, with octadecahedral cage structures. It is argued that anion formation causes the agostic bonding to be `switched-off' and results in the cluster adopting the closo architecture predicted by Wade's rules. This structural change is fully reversible on reprotonation, and if reprotonation of [1,1-(dppe)-1,2- closo-RhSB 9H 9] − is carried out in MeCN, the product 8,8-(dppe)-8-(MeCN)-8,7- nido-RhSB 9H 10 forms. Interestingly, 8,8-(dppe)-8-(MeCN)-8,7- nido-RhSB 9H 10 reconverts to 8,8-(dppe)-8,7- nido-RhSB 9H 10 on standing in CDCl 3, suggesting that the agostic bonding is sufficiently strong to displace co-ordinated MeCN. All new compounds are fully characterised by multinuclear NMR spectroscopy and, in many cases, by single crystal X-ray diffraction.

A molecular orbital analysis of four chromaboranes: On the curious behavior of ( η5-C 5R 5)Cr fragments in a borane cluster environment

Fenske–Hall molecular orbital calculations have been carried out on Cp 2Cr 2B 4H 8 ( 1′), Cp 2Cr 2(CO) 2B 4H 6 ( 2′), Cp 2Cr 2B 4H 8Fe(CO) 3 ( 3′), and Cp 2Cr 2B 4H 6(S 2CH 2) ( 4′) (Cp= η 5-C 5H 5) with structures based on the known compounds with η 5-C 5Me 5 ligands. It is demonstrated that the dinuclear Cp 2Cr 2 fragment is capable of providing an additional low energy (filled) or high energy (unfilled) orbital to the cluster bonding network with only small distortions of the Cr 2B 4 cluster core geometry. By this mechanism, the cluster core geometry changes required by Wade's rules are decoupled from cluster electron count. Thus, both electron poor and electron rich clusters, as defined by the Wade prescription, are stable and exhibit the same qualitative cluster geometry. The electronic origin of this behavior resides in the close energy match of the metal fragment `t 2g' orbitals with those of the borane fragment combined with the perturbation of differing ligands associated with the cluster.

B-frame supported bimetallics. [(PMe 2ph) 2PtB 9H 11Ru( η6- isoPrC 6H 4Me)] and [(PMe 2ph) 2PtB 9H 9Ru( η6- isoPrC 6H 4Me)]; an interesting pair of electron-deficient nido and closo geometries

[7,7-(PMe 2Ph) 2-9-( η 6- iso PrC 6H 4Me)-7,9-PtRuB 9H 11] has a formal closo Wadian cluster-electron count, but a nido geometry, whereas [1-( η 6- iso PrC 6H 4Me)-4,4-(PMe 2Ph) 2-1-4-RuPtB 9H 9], which does have a closo geometry, has a formal sub- closo cluster electron count; both compounds are formed in the reaction between [6-( η 6- iso PrC 6H 4Me)- nido-6 RuB 9H 13], KH and [PtCl 2(PMe 2Ph) 2].

The synthesis and characterisation of some closed polyhedral metallocarbon clusters

Ligands containing unsaturated C 2 and C 4 units have been reacted with triruthenium dodecacarbonyl to produce new organometallic clusters with simple closo-Ru x C y polyhedral frameworks which may be regarded as quasi-carboranes. The thermolysis of [Ru 3(CO) 12] with 1,4-diphenybutadiene yields the new clusters [Ru 3(CO) 8( μ 3-CPh(CH) 2CPh)] 2 and [Ru 4(CO) 9( μ 4-CPhCCH 2CH 2Ph)] 3, while treatmentof a solution of [Ru 3(CO) 12] and diphenylacetylene with trimethylamine N–oxide (Me 3NO) yields [Ru 2(CO) 6( μ-{C 2Ph 2} 2CO)] 4 as the major product and the new cluster [Ru 4(CO) 11( μ 4-C 2Ph 2) 2] 5. The solid-state structures of 2, 3 and 5 have been established by single crystal X-ray diffraction analyses and are shown to possess closo-Ru 3C 4 pentagonal bipyramidal, closo-Ru 4C 2 octahedral and closo-Ru 4C 4 dodecahedral skeletons, respectively. The structure and bonding in all three clusters may be rationalised using the Wade–Mingos polyhedral skeletal electron pair approach.

Reactions of size-selected positively charged nickel clusters with carbon monoxide in molecular beams

Reactions of small thermalized positively charged nickel clusters with carbon monoxide were studied in a molecular beam experiment. The nickel clusters were produced in a high intensity cluster ion source and thermalized in a large helium-filled quadrupole ion guide. The clusters were size selected by a quadrupole mass spectrometer. The mass- and charge-selected nickel clusters then passed through a linear quadrupole drift tube filled with a mixture of helium buffer gas and carbon monoxide. The reaction products were then analyzed by a quadrupole mass-spectrometer. Using this technique, saturation limits for Nin+ clusters with n=4–31 were measured and the competitive reaction channels were identified. Under certain experimental conditions carbide formation was observed in the case of the nickel tetramer, pentamer, and hexamer. The structure of the nickel carbonyl clusters is discussed within the framework of the polyhedral skeletal electron pair theory. The cluster growth may be explained by a pentagonal sequence of structures for n=4–7, capping of the pentagonal bipyramid to buildup an icosahedron at Ni13+, and further capping of this icosahedron to form a double icosahedron at Ni19+.

The closo-Ge52- Anion: Synthesis, Crystal Structure, and Raman Spectrum of (2,2,2-crypt-K+)2Ge52-·THF

The isolation and structural characterization of the closo-Ge52- cluster anion by X-ray crystallography and Raman spectroscopy is reported, completing the series of five-atom homopolyatomic anions of the group 14 elements, M52- (M = Ge, Sn, Pb). The closo-Ge52- anion was obtained as the (2,2,2-crypt-K+)2Ge52-·THF salt which crystallizes in the triclinic system, space group P1, in a unit cell of dimensions a = 10.9657(4) Å, b = 12.1750(5) Å, c = 12.9142(5) Å, α = 62.163(1)°, β = 67.776(1)°, and γ = 84.187(1)°. The trigonal bipyramidal geometry observed for the Ge52- anion (∼D3h point symmetry) is in accord with that predicted by Wade's rules for a 2n + 2 skeletal electron system and has been observed for the Sn52- and Pb52- homologues and for the isovalent Tl57- and Bi53+ ions. The Raman spectrum of the Ge52- anion is compared and assigned by analogy with that of the Bi53+ cation.

Scattering and deposition of mass-selected antimony clusters

Positively charged antimony cluster ions (Sb n +: 2 < n < 13) have been scattered from the surface of highly oriented pyrolythic graphite (HOPG) at energies up to 350 eV. Main fragmentation channels for the positively charged clusters are the formation of neutral Sb 2- and Sb 4- and charged Sb 3 +-, Sb 5 +- and Sb 7 +- species. The stability of these products can be understood in the framework of the polyhedral skeletal electron pair theory. STM-images taken after the scattering of a mass selected cluster at a predefined energy from HOPG show the formation of islands with a diameter of about 30 to 40 Å. The islands are assumed to be formed by statistical diffusion of the collision products on the substrate surface. The number density of islands correlates well with the measured scattering efficiencies and the cluster intensity in the beam.