Main Group Clusters Research Articles

Ligand-free supermolecules: [Pd2@Ge18]4- and [Pd2@Sn18]4- as multiple-bonded Zintl-ion clusters based on Pd@Ge9 and Pd@Sn9 assembled units.

Understanding intercluster bonding interactions is important in the rational synthesis of building blocks for molecular materials. Such characteristics have been developed for coinage metal clusters resembling single-, double-, and triple-bonded species, coined as supermolecules. Herein, we extend such an approach for understanding main-group clusters, thus evaluating [Pd2@E18]4- clusters (E = Ge, Sn) involving the fusion of parent spherical aromatic [Pd@E12]2- building units. Our results indicate intercluster bonding provided by contribution from 2P and 1G shells centered at each building motif, leading to an overall bond order of 2.70 and 2.31 for [Pd2@Ge18]4- and [Pd2@Sn18]4-, respectively. In addition, 119Sn-NMR patterns were evaluated to complement the experimental characterization of a single peak owing to the insolution fluxional behavior of [Pd2@Sn18]4- as three peaks owing to the three sets of unique Sn atoms within the structure. Magnetic response properties revealed that spherical aromatic characteristics from parent [Pd@E12]2- building units are retained in the overall [Pd2@E18]4- oblate cluster as two spherical aromatic units. Hence, the notion of superatomic molecules is extended to Zintl-ion clusters, favoring further rationalization for the fabrication of cluster-assembled solids.

Oxidation of [Ge9{Si(SiMe3)3}3]- with LnI3 (Ln = Eu, Sm, Yb): Isomerism of Metalloid Germanium Clusters.

The oxidation of K[Ge9(Hyp)3] (Hyp = Si(SiMe3)3) with lanthanide triiodides LnI3 (Ln = Eu, Sm, Yb) leads to the formation of novel clusters with a Ge18-core isolated as a co-crystallizate of Ge*18(Hyp)6 (1a) and Ge18(Hyp)5(Si(SiMe3)2)(SiMe3) (1b). Clusters 1a and 1b differ distinctly from the known cluster Ge18(Hyp)6 (A), which has been found earlier in the reaction of K[Ge9(Hyp)3] with FeCl2 and now identified as an intermediate product in the production of compounds 1a and 1b. These three compounds A, 1a, and 1b are thus structural isomers being the first example of genuine isomerism in metalloid main-group cluster compounds.

Studying the impact of diagonal-doping on thermal stability of main-group metal clusters via Born Oppenheimer molecular dynamics

Doping with a heteroatom is considered to be an effective tool in tuning the physico-chemical properties of metal clusters. Over a period of time, several experimental and theoretical investigations have been carried out to understand the effect of doping on structure, electronic properties and reactivity of main group clusters. However, issues pertaining to thermal stabilities of metal clusters, particularly in the context of heteroatom doping remain unexplored. Filling this lacuna, this report focuses on evaluating the finite temperature behaviour of the main group metal clusters which are doped with diagonally adjacent dopant atoms. Born-Oppenheimer Molecular Dynamical (BOMD) simulations are performed on diagonally doped LiMg, BeAl and BSi () clusters (doped diagonal pairs). The thermal response of these doped diagonal pairs is also compared with the corresponding pristine clusters such as Li, Mg, Be, Al, B and Si () clusters. The simulation trajectories and ionic motions are analysed and root mean square bond length fluctuations are calculated as a function of temperature. The results indicate that the diagonally doped BSi () clusters are thermally more stable (1200 K) as compared to the other two doped clusters (LiMg, BeAl). The enhanced thermal stability is attributed to the higher binding energies noted for BSi () clusters. Moreover, it is found that for the B-Si cluster systems, diagonal doping always enhances the thermal stability, whereas both diagonal doping and the size of the cluster affect the thermal stabilities of the LiMg, and BeAl cluster systems. An in-depth analysis of thermal-structural-electronic (frontier molecular orbitals) properties revealed that the strength of dopant-to-parent cluster interactions are playing a significant role in influencing the thermal stabilities of diagonally doped clusters. Overall this study also highlights how the heuristic chemical principle of ‘diagonal relationship’ widely used in main-group chemistry may be extended to cluster science to draw new insights regarding thermal stabilities of metal clusters.

Remote Bonding in Clusters [Pd3Ge18R6]2-: Modular Bonding Model for Large Clusters via Principal Interacting Orbital Analysis.

Main group cluster compounds have attracted increasing attention in the past decades. Despite recent developments in their synthesis, the description of their electronic structures is usually limited to simply applying Wade's rule originally developed for borane compounds. This traditional approach is once again challenged by two recently reported group 14 metalloid clusters in the form of [Pd3Ge18R6]2-. In this work, we put forward a modular bonding model for these two clusters, via principal interacting orbital (PIO) analysis. The site preference for six substituents has also been analyzed.

Conversion Reactions of Atomically Precise Semiconductor Clusters.

Clusters are unique molecular species that can be viewed as a bridge between phases of matter and thus between disciplines of chemistry. The structural and compositional complexity observed in cluster chemistry serves as an inspiration to the material science community and motivates our search for new phases of matter. Moreover, the formation of kinetically persistent cluster molecules as intermediates in the nucleation of crystals makes these materials of great interest for determining and controlling mechanisms of crystal growth. Our lab developed a keen interest in clusters insofar as they relate to the nucleation of nanoscale semiconductors and the modeling of postsynthetic reaction chemistry of colloidal materials. In particular, our discovery of a structurally unique In37P20X51 (X = carboxylate) cluster en route to InP quantum dots has catalyzed our interest in all aspects of cluster conversion, including the use of clusters as precursors to larger nanoscale colloids and as platforms for examining postsynthetic reaction chemistry. This Account is presented in four parts. First, we introduce cluster chemistry in a historical context with a focus on main group, metallic, and semiconductor clusters. We put forward the concept of rational, mechanism-driven design of colloidal semiconductor nanocrystals as the primary motivation for the studies we have undertaken. Second, we describe the role of clusters as intermediates both in the synthesis of well-known material phases and in the discovery of unprecedented nanomaterial structures. The primary distinction between these two approaches is one of kinetics; in the case of well-known phases, we are often operating under high-temperature thermolysis conditions, whereas for materials discovery, we are discovering strategies to template the growth of kinetic phases as dictated by the starting cluster structure. Third, we describe reactions of clusters as model systems for their larger nanomaterial progeny with a primary focus on cation exchange. In the case of InP, cation exchange in larger nanostructures has been challenging due to the covalent nature of the crystal lattice. However, in the higher energy, strained cluster intermediates, cation exchange can be accomplished even at room temperature. This opens opportunities for accessing doped and alloyed nanomaterials using postsynthetically modified clusters as single-source precursors. Finally, we present surface chemistry of clusters as the gateway to subsequent chemistry and reactivity, and as an integral component of cluster structure and stability. Taken as a whole, we hope to make a compelling case for using clusters as a platform for mechanistic investigation and materials discovery.

Relativity and the Jahn–Teller, Berry pseudorotations of TBP clusters: group theory, spin–orbit and combinatorial nuclear spin statistics of TBP Desargues–Levi isomerization graph

Jahn–Teller and Berry pseudorotations in transition metal and main group clusters such as Hf5, Ta5, W5 and Bi5 are interesting because of the competition between relativistic effects and pseudorotations. Topological representations of various isomerization pathways arising from the Berry pseudorotation of pentamers constitute the edges of the Desargues–Levi graph. We have computed the combinatorics for multinomial colorings of the vertices, edges and 10-faces of the Desargues–Levi isomerization graph for all irreducible representations and the nuclear spin statistics of spin-7/2 181Ta5 as well as the TBP composite cluster particles. Topological insights into Jahn–Teller and Berry pseudorotations and relativistic effects are provided.

TGMin: A global-minimum structure search program based on a constrained basin-hopping algorithm

In this article, we introduce Tsinghua Global Minimum (TGMin) as a new program for the global minimum searching of geometric structures of gas-phase or surface-supported atomic clusters, and the constrained basin-hopping (BH) algorithm implemented in this program. To improve the efficiency of the BH algorithm, several types of constraints are introduced to reduce the vast search space, including constraints on the random displacement step size, displacement of low-coordination atoms, and geometrical structure adjustment after displacement. The ultrafast shape-recognition (USR) algorithm and its variants are implemented to identify duplicate structures during the global minimum search. In addition to the Metropolis acceptance criterion, we also implemented a morphology-based constraint that confines the global minimum search to a specific type of morphology, such as planar or non-planar structures, which offers a strict divide-and-conquer strategy for the BH algorithm. These improvements are implemented in the TGMin program, which was developed over the past decade and has been used in a number of publications. We tested our TGMin program on global minimum structural searches for a number of metal and main-group clusters including C60, Au20 and B20 clusters. Over the past five years, the TGMin program has been used to determine the global minimum structures of a series of boron atomic clusters (such as [B26]–, [B28]–, [B30]–, [B35]–, [B36]–, [B39]–, [B40]–, [MnB16]–, [CoB18]–, [RhB18]–, and [TaB20]–), metal-containing clusters Li n (n = 3–20), Au9(CO)8 + and [Cr6O19]2–, and the oxide-supported metal catalyst Au7/γ-Al2O3, as well as other isolated and surface-supported atomic clusters. In this article we present the major features of TGMin program and show that it is highly efficient at searching for global-minimum structures of atomic clusters in the gas phase and on various surface supports.

The Main Group Elements, Fragments, Compounds and Clusters Obey the 4n Rule and Form 4n Series: They are Close relatives to Transition Metal Counterparts via the 14n Linkage

<p>The paper presents numbers which were derived from 4n-based series in a matrix table. The numbers agree precisely with the total number of valence electrons surrounding the respective skeletal elements. The series approach focuses mainly on the number of skeletal elements and their respective number of valence electron content regardless of the origin of the electrons and the type of skeletal elements. For instance, any 6 skeletal elements of transition metal carbonyls surrounded by 86 valence electrons coded as (6,86), series S = 14n+2 normally adopt an octahedral geometry whereas (6,26) series S = 4n+2 for main group elements also tend to adopt an octahedral shape. The transition metal carbonyl cluster series were extensively covered in our previous articles. This paper demonstrates that the main group fragments, clusters and molecules which we normally explain by terms such as valency, valence electrons and octet rule also obey the 4n-based series. The fragments, molecules and clusters of the main group elements correspond well to those of respective transition metal clusters especially the carbonyls if the masking electrons are removed from them. Hence, the series approach is a qualitative method that acts as a unifier of some transition metal clusters with some main group elements clusters.</p>

Addition of ethylene or hydrogen to a main-group metal cluster under mild conditions.

Reaction of the tin cluster Sn8(Ar(Me6))4(Ar(Me6)=C6H2-2,6-(C6H3-2,4,6-Me3)2) with excess ethylene or dihydrogen at 25 °C/1 atmosphere yielded two new clusters that incorporated ethylene or hydrogen. The reaction with ethylene yielded Sn4(Ar(Me6))4(C2H2)5 that contained five ethylene moieties bridging four aryl substituted tin atoms and one tin-tin bond. Reaction with H2 produced a cyclic tin species of formula (Sn(H)Ar(Me6))4, which could also be synthesized by the reaction of {(Ar(Me6))Sn(μ-Cl)}2 with DIBAL-H. These reactions represent the first instances of direct reactions of isolable main-group clusters with ethylene or hydrogen under mild conditions. The products were characterized in the solid state by X-ray diffraction and IR spectroscopy and in solution by multinuclear NMR and UV/Vis spectroscopies. Density functional theory calculations were performed to explain the reactivity of the cluster.

ChemInform Abstract: Theoretical Aspects of Metal Cluster Chemistry

During the last twenty years the Polyhedral Skeletal Electron Pair Theory and the isolobal analogy have provided a theoretical basis for the rapid experimental developments, which have occurred in metal cluster chemistry. These theoretical principles have been underpinned by m.o. calculations on specific molecules and more generally by the Tensor Surface Harmonic Theory. This paper will review the important theoretical developments and relate them to the experimental and structural data which have been obtained for cluster compounds in our own and other laboratories. In particular the application of theoretical principles for rationalising and predicting the structures of cluster compounds of the platinum metals and gold are discussed. The bonding requirements of interstitial atoms and fragments are discussed, particularly in the context of interstitial C, B, N and transition metal atoms and diatomic fragments, e.g. C2 and C-H. POLYHEDRAL SKELETAL ELECTRON PAIR THEORY The historical development of the theoretical ideas which have contributed to the Polyhedral Skeletal Electron Pair Theory can be traced back to the pioneering work of Longuet-Higgins forty years ago. In the 1950's the contributions of Longuet-Higgins proved decisive since he not only provided a molecular orbital description of the bonding in diborane (ref. l), but also pioneered the application of molecular orbital theory ideas to deltahedral borides and boranes (ref. 2). The three-centre two-electron description of B-H-B and B-B-B bonds was elegantly generalised into the styx formalism and applied to all known boron hydrides by Lipscomb (ref. 3). The molecular orbital analysis of polyhedral boranes resulted in the successful prediction of the octahedral and icosahedral borane anions some years before they were structurally characterised (ref. 4). Hoffmann and Lipscomb (ref. 5) also developed the molecular orbital methodology of L nguet-Higgins in a general molecular orbital analysis of polyhedral borane anions, BnH;-, in 1962. In the 1960's Cotton and Haas (ref. 6) pioneered the development of molecular orbital ideas to metal cluster compounds of the early transition metals stabilised by halide ligands. Their analysis emphasised the important interactions which can result in such clusters from the overlap of the transition metal d orbitals. An alternative localised description of the bonding in such clusters, which resembled the styx methodology, was proposed by Kettle (ref. 7). These theoretical models tended to emphasise the inherent differences between metal and main group clusters and in common with ligand field theory tended to stress the role of the metal d orbitals. By the mid-nineteen sixties the major classes of transition metal IT -donor and acceptor clusters, and main group polyhedral borane and Zintl 'naked' clusters had been established but were viewed as distinct areas of inorganic chemistry. Experimental studies had, however, begun to indicate the artificiality of these subdivisions. The synthesis of polyhedral organometallic compounds from the reactions of acetylenes with metal carbonyls by HUbel and Braye and transition metallocarboranes by Hawthorne's group (ref. 8) clearly demonstrated that it was possible to synthesise polyhedral molecules with transition metal and main group atoms at the vertices. In addition the structural characterisation of Rh6(C0Il6 by Dahl (ref. 9) provided a real difficulty for the theoretical models which were most widely used. The bonding in Rh6(C0)16 could not be explained by the effective atomic number rule and was not amenable to a molecular orb'tal

ChemInform Abstract: High Nuclearity Clusters and Beyond

Abstract Separate series of neutral and anionic osmium carbonyl clusters based on 3–20 osmium atoms have been prepared and characterised in the solid by single crystal X-ray analysis and in solution largely by 13 C NMR spectroscopy and vibrational analysis (IR). They appear to fall into two distinct series, viz ., those which follow a polytetrahedral, non-metallic growth sequence, e.g. [Os 3 (CO) 12 ] and [Os 3 (CO) 11 ] 2− , [Os 4 (CO) 14 ] and [Os 4 (CO) 13 ] 2− , [Os 5 (CO) 16 ] and [Os 5 (CO) 15 ] 2− , and [Os 6 (CO) 18 ] and [Os 6 (CO) 17 ] 2− , and those which apparently follow the route to bcc packing, e.g. [Os 6 (CO) 18 ] 2− , [Os 7 (CO) 21 ] and [Os 7 (CO) 20 ] 2− , [Os 8 (CO) 23 ] and [Os 8 (CO) 22 ] 2− , [Os 9 (CO) 24 ] 2− , [Os 10 (CO) 26 ] 2− and [Os 10 C(CO) 24 ] 2− , and [Os 20 (CO) 40 ] 2− . Alternatively, the species [Os 4 (CO) 14 ] and [Os 4 (CO) 13 ] 2− , [Os 10 (CO) 26 ] 2− and [Os 10 C(CO) 24 ] 2− and [Os 20 (CO) 40 ] 2− may be viewed as forming a ‘magic number’ sequence of clusters corresponding to the tetrahedral growth pattern, viz . 4, 10, and 20. Also described are the syntheses of mixed Os-C and Os-Hg clusters. The former bear a close resemblance to the carboranes in their structural features, whereas the Os-Hg clusters represent examples of linked cluster systems containing both transition metal and main group cluster domains. The geometric relevance that all these structures bear to the ‘metallic state’ is discussed.

An overview of the electronic structure in trigonal bipyramidal clusters of main elements or mixed with transition metals

Equatorial/apical bond repartitioning in TBP clusters, formed by main group elements only (e.g., B5H5 2−, B3H3N2, etc.) or mixed with metal atoms (e.g., [(L2M)3S2] n , [(L3M)3S2] n , [(CpM)3S2] n ), is critically analyzed from the horizontal comparison of the experimental structures and in terms of basic MO concepts. The ideas are double-checked through specific DFT calculations or existing ab initio results. Based on the Wade’s rules for closo-clusters, the five vertices systems are normally characterized by six skeletal electron pairs. In the main group clusters, the electron delocalization at the equatorial edges depends on the electronegativity of the apical groups and for the Beq–Beq bonds an inverse relationship between bond strength and bond length is remarked. In [(L2M)3S2] n compounds with a total electron count (TEC) of 48, the six bonding electron pairs localize at the apical M–S bonds. In [(L3M)3S2] n or [(CpM)3S2] n , also with TEC = 48, the effective atomic number rule predicts three single M–M single bonds besides the six M–S apical ones. In actuality, only partial M–M bonding can be considered due to the intermediation of the capping sulphur atoms, that help shifting the antibonding character of populated radial levels with that of the vacant tangential ones (bonding). The qualitative MO arguments are supported by the topological nature of the calculated DFT wave functions. Moreover, the MO nature of three lowest LUMOs for 48e− species help to rationalize experimental structural trends observed for the addition of up to five electrons.

Chemical Tuning of the Electronic Properties of Nanostructured Semiconductor Films Formed through Surfactant Templating of Zintl Cluster

Inorganic/organic coassembly provides a powerful route to the formation of periodic, nanostructured materials. In this work, the surfactant cetyltriethylammonium bromide is used as an organic structure directing agent, and the inorganic phase is formed from the condensation of metal cations with reduced main group clusters know as Zintl clusters. These anionic clusters are formed by alloying alkali metals with various main group elements. The chalcogenide-based Zintl clusters used here have an affinity for gold and other transition metals and will thus nucleate the formation of films on metal surfaces. Interface nucleated inorganic/organic co-organization results in thin films with the periodicity of a liquid crystal phase, but with a cross-linking inorganic network surrounding the surfactant domains. In this work, we investigate the extent to which the band structure of these films can be tuned by altering the elemental composition of the inorganic framework of these periodic nanocomposites. For the semi...

Sn17{GaCl(ddp)}4]: A High‐Nuclearity Metalloid Tin Cluster Trapped by Electrophilic Gallium Ligands

The reduction of SnCl2 by the low-valent gallium(I) β-diketiminate GaI(ddp) gives the title complex, which is best described as a Zintl-type anionic [Sn17]4− cluster stabilized by an electrophilic shell of gallium ligands. This reaction could represent a new concept for the synthesis of metalloid main-group clusters. ddp=HC(CMeNC6H3-2,6-iPr2)2.

Observation of d‐Orbital Aromaticity.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Observation of d‐Orbital Aromaticity

While main group clusters can give rise to s- and p-aromaticity, transition-metal-containing clusters can exhibitd-orbitalaromaticityor,moreinterestingly,d-aromaticitydueto d bonding interactions. However, d-orbital aromaticityrequiressignificantd–dbondinginteractions.Unlikevalentsor p orbitals, d orbitals are spatially more contracted, andtheir tendency to participate in chemical bonding dependsstrongly on the position of the transition metals in theperiodic table and their coordination environments. ThepredictedaromaticityinthecyclicCu-containingspecies,

Photodissociation spectroscopy of Zn+(H2O) and Zn+(D2O)

We report on a study of the photodissociation spectroscopy of weakly bound Zn+(H2O) and Zn+(D2O) complexes. The work is supported by ab initio electronic structure calculations of the ground and low-lying excited energy surfaces. We assign two molecular absorption bands in the near UV correlating to Zn+ (4s-4p)-based transitions, and identify vibrational progressions associated with both intermolecular and intramolecular vibrational modes of the cluster. Partially resolved rotational structure is consistent with a C(2V) equilibrium complex geometry. Experimental spectroscopic constants are in very good agreement with ab initio theoretical predictions. Results are compared with previous work on main group and transition metal ion-H2O clusters.

Tetratellurium bis[heptachlorodigallate(III)], Te4[Ga2Cl7]2

Compounds containing main-group clusters, with focus on bismuth polycations, have been synthesized and characterized using X-ray diffraction and spectroscopic methods. Six new compounds have been isolated from synthesis in GaX3-arene media; Bi8[GaCl4]2, Bi8 [GaBr4]2, Sb8[GaCl4]2, Sb8[GaBr4]2, Te4[Ga2Cl7]2 and Te4[Ga2Br7]2. Sb2+ 8 is the first homopolyatomic antimony cation to be isolated. The cation forms a square antiprism, in correlation with Wade’s rules, and displays a significant difference in length between the inter-square and intra-square Sb–Sb distances. The geometries of the Sb2+ 8 cations in Sb8[GaCl4]2 and Sb8[GaBr4]2 are in excellent agreement; the average intra-square and intersquare Sb–Sb distances are 2.87 A and 2.97 A, respectively. A very strong Raman band attributed to Sb2+8 is found at 180 cm-1. The Bi2+8 (square antiprismatic) and Te2+4 (squareplanar) polycations are known from earlier compounds. The Bi–Bi distances in Bi8[GaCl4]2 (3.07–3.12 A) are in general agreement with previous structures, while the Bi–Bi distances of Bi8[GaBr4]2 (2.92–3.18 A) display a wider distrubution than previously observed. The Te–Te distances of the cations of Te4[Ga2Cl7]2 and Te4[Ga2Br7]2 are 2.66 and 2.67 A, respectively. Quantum chemical calculations on bismuth polycations show that all species predicted byWade’s rules are local minima on a potential energy surface. The cation–anion interactions have been considered for salts containing bismuth polycations and it has been confirmed that such interactions have a major influence on the polycation stability. The new compound Bi16I4 has been isolated from molten Bil3. The structure consists of polymerized Bi16I4 molecules forming infinite ribbons and is very similar to the structure of the known metal-rich bismuth iodides, Bi14I4 and Bi18I4. DFT calculations predict all three compounds to be metallic conductors, while Bi4I4 is a semiconductor.

Synthesis and Characterization of Ge2{Sn(X)Ar#}3 and Ga2{Ge(X)Ar#}3 (Ar# = C6H3-2,6-Mes2), X = (Cl/I): Rare Examples of Mixed Heavier Group 14/14, 13/14 Element Clusters

Treatment of Ar#ECl (Ar# = C6H3-2,6-Mes2; E = Ge or Sn) with 1 equiv of the reducing agent KC8 or ‘GaI' led to the isolation and characterization of the two new main group clusters Ge2{Sn(X)Ar#}3, 1, and Ga2{Ge(X)Ar#}3, 2 (X = Cl or Cl/I), which have trigonal bypyramidal Ge2Sn3 or Ga2Ge3 frameworks. Cluster 1 is a singlet biradicaloid, whereas 2 is a very rare heavier group 13/14 element cluster, and the first with a Ga/Ge framework.

A Unified Approach to Electron Counting in Main-Group Clusters

A unified approach to electron counting in main-group cluster chemistry is presented, wherein the different classes, electron-rich, electron-precise, and electron-deficient, are viewed simply as different regions of a continuum defined by two variables, vertex count and valence electron count. The diverse structural chemistry of all main-group clusters can then be reconciled by recognizing that, within the confines of a fixed vertex count, each reduction of two in the total electron count must be associated with a distortion that destabilizes a single molecular orbital. This simple tenet affords a consistent framework for correlating structure with electron count across the entire spectrum of clusters, including the recently discovered hypoelectronic class. The different ways in which structure responds to changes in electron count within the different domains emerges as a logical consequence of the nature (bonding or nonbonding) of the particular orbital that is destabilized.