Claudio Schrenk

The Largest Metalloid Group 14 Cluster, Ge18[Si(SiMe3)3]6 : An Intermediate on the Way to Elemental Germanium.

The oxidation of [Ge9(Hyp)3](-) (Hyp=Si(SiMe3 )3) with an Fe(II) salt leads to Ge18 (Hyp)6 (1), the largest Group 14 metalloid cluster that has been structurally characterized to date. The arrangement of the 18 germanium atoms in 1 shows similarities to that found in the solid-state structure Ge(cF136). Furthermore, 1 can be described as a macropolyhedral cluster of two Ge9 units. Quantum-chemical calculations further hint at a strained arrangement so that 1 can be considered as a first trapped intermediate on the way from Ge9 units to elemental germanium with the clathrate-II structure (Ge(cF136)).

Sn[Si(SiMe3)3]3 − and Sn3[Si(SiMe3)3]4: first insight into the mechanism of the disproportionation of a tin monohalide gives access to the shortest double bond of tin

In the course of the disproportionation reaction of a monohalide beside metalloid clusters like Sn(10)[Si(SiMe(3))(3)](6) also molecular compounds with an average oxidation state of the tin atoms larger than one must be present. First results of such oxidized species are presented where the bonding is strongly influenced by the steric bulk of the ligands leading to the shortest tin-tin double bond.

{Sn9[Si(SiMe3)3]2}2-: a metalloid tin cluster compound with a Sn9 core of oxidation state zero.

The disproportionation reaction of the subvalent metastable halide SnCl proved to be a powerful synthetic method for the synthesis of metalloid cluster compounds of tin. Now we present the synthesis and structural characterization of the anionic metalloid cluster compound [Sn(9)[Si(SiMe(3))(3)](2)](2-)3 where the oxidation state of the tin atoms is zero. Quantum chemical calculations as well as Mössbauer spectroscopic investigations show that three different kinds of tin atoms are present within the cluster core. Compound 3 is highly reactive as shown by NMR investigations, thus being a good starting material for further ongoing research on the reactivity of such partly shielded metalloid cluster compounds.

{Sn9[Si(SiMe3)3]3}− and {Sn8Si[Si(SiMe3)3]3}−: variations of the E9 cage of metalloid group 14 clusters.

The disproportionation reaction of the subvalent metastable halide SnBr proved to be a powerful synthetic method for the synthesis of metalloid cluster compounds of tin. Hence, the neutral metalloid cluster compound Sn(10)[Si(SiMe(3))(3)](6) (3) was synthesized from the reaction of SnBr with LiSi(SiMe(3))(3). In the course of the reaction anionic clusters might also be present, and we now present the first anionic cluster compound {Sn(8)E[Si(SiMe(3))(3)](3)}(-) (E = Si, Sn), where one position in the cluster core is occupied by a silicon or a tin atom, giving further insight into structural variations of E(9) cages in metalloid group 14 cluster compounds.

{Sn10 [Si(SiMe3 )3 ]4 }(2-) : A highly reactive metalloid tin cluster with an open ligand shell.

The reaction of a Sn(I) Cl solution with LiSi(SiMe3 )3 gave the anionic metalloid tin cluster {Sn10 [Si(SiMe3 )3 ]4 }(2-) (7) in good yield. The arrangement of the ten tin atoms in the cluster core can be described as a distorted centaur polyhedron. Quantum chemical calculations suggest that there are 26 bonding electrons in the cluster core, which may be described as an arachno cluster in agreement with Wades rules. NMR and mass spectrometric investigations showed that 7 is highly reactive, which may be due to the open ligand shell. The easily available tin atoms in 7 thereby open the door to further subsequent reactions, in which 7 may act as a building block to larger cluster aggregates.

Metalloid Sn clusters: properties and the novel synthesis via a disproportionation reaction of a monohalide

Abstract Metalloid cluster compounds of tin of the general formulae SnnRm with n>m (R=organic ligand), where beside ligand-bound tin atoms also “naked” tin atoms, that only bind to other tin atoms, are present, represent a novel class of cluster compounds in tin chemistry. As the “naked” tin atoms inside these clusters exhibit an oxidation state of 0, the average oxidation state of the tin atoms within such metalloid tin clusters is in between 0 and 1. Thus, these cluster compounds may be seen as intermediates on the way to the elemental state. Therefore, interesting properties are expected for these compounds, which might complement results from nanotechnology. During the last years, different syntheses of such novel cluster compounds have been introduced, leading to several metalloid tin cluster compounds, which exhibit new and partly unusual structure and bonding properties. In this review, recent results in this novel field of group 14 chemistry are discussed, whereby special attention is focused on the novel synthetic route applying a disproportionation reaction of metastable Sn(I) halides.

Reactions with a Metalloid Tin Cluster {Sn10[Si(SiMe3)3]4}2−: Ligand Elimination versus Coordination Chemistry

Chemistry that uses metalloid tin clusters as a starting material is of fundamental interest towards understanding the reactivity of such compounds. Since we identified {Sn10[Si(SiMe3)3]4}(2-) 7 as an ideal candidate for such reactions, we present a further step in the understanding of metalloid tin cluster chemistry. In contrast to germanium chemistry, ligand elimination seems to be a major reaction channel, which leads to the more open metalloid cluster {Sn10[Si(SiMe3)3]3}(-) 9, in which the Sn core is only shielded by three Si(SiMe3)3 ligands. Compound 9 is obtained through different routes and is crystallised together with two different countercations. Besides the structural characterisation of this novel metalloid tin cluster, the electronic structure is analysed by (119)Sn Mössbauer spectroscopy. Additionally, possible reaction pathways are discussed. The presented first step into the chemistry of metalloid tin clusters thus indicates that, with respect to metalloid germanium clusters, more reaction channels are accessible, thereby leading to a more complex reaction system.

{[Si(SiMe3)3]2Ge9-SiMe2-(C6H4)-SiMe2-Ge9[Si(SiMe3)3]2K}−: The Connection of Metalloid Clusters via an Organic Linker

The reaction of [(Hyp)2Ge9]2- (Hyp = Si(SiMe3)3) with ClSiMe2-C6H4-SiMe2Cl gives [K(THF)][(Hyp)2Ge9-SiMe2-C6H4-SiMe2-Ge9(Hyp)2K] K1 in 45% yield in the form of orange-red crystals. 1 is thereby the first compound where two Ge9(Hyp)2 clusters are bound together via a bridging ligand. 1 is stable in solution but cannot be transferred intact into the gas phase via electrospray ionization indicating a higher reactivity with respect to other metalloid Ge9R3 clusters. The arrangement of the nine germanium atoms within the two Ge9 units in 1 is unique for metalloid Ge9R3 clusters. Quantum chemical calculations further reveal an electronic interaction of the two Ge9 units in 1 via the bridging phenylene group.

[Sn4Si{Si(SiMe3)3}4{SiMe3}2]: A Model Compound for the Unexpected First-Order Transition from a Singlet Biradicaloid to a Classical Bonded Molecule†

Metalloid cluster compounds of the general formula MnRm (n>m ; M=metal or semi-metal, R= ligand) are ideal model compounds for the system size range encompassed by molecules and the solid state, paving the way for further understanding of element formation from oxidized species on an atomic scale. In the case of tin, metalloid cluster compounds were first synthesized by reductive coupling of Sn compounds, such as SnCl2. [2] Recently it was shown that metalloid cluster compounds of tin can also be synthesized by the disproportionation reaction of tin monohalides. The monohalides are thereby obtained by employing a preparative co-condensation technique. Hence, the reaction of SnBr with LiSi(SiMe3)3 leads to the metalloid cluster compound [Sn10{Si(SiMe3)3}6] (1) in moderate yield of approximately 17%. Because only six of the ten tin atoms in 1 bear a Si(SiMe3)3 ligand, the average oxidation state of the tin atoms is 0.6. Thus, the metalloid cluster 1 is a reduction product of the disproportionation reaction on the way to elemental tin. Because the reaction starts with the monohalide SnBr, oxidized species with an average tin atom oxidation state of greater than 1 must also be present in the reaction solution. Early examples of such compounds were anionic stannylene [Sn{Si(SiMe3)3}3] and cyclotristannene [Sn3{Si(SiMe3)3}4] (2), in which the average oxidation states of the tin atoms is + 2 and + 1.3, respectively. The shortest tin–tin double bond of 258 pm was observed in 2, caused by the steric bulk of the ligands forcing the double bond into a planar arrangement. As 2 is only obtained together with the metalloid cluster compound [Sn10{Si(SiMe3)3}6] (1), subsequent investigations on 2 are always hindered by the presence of 1. Crystallization of 2 from the reaction mixture was attempted to circumvent this problem. During these attempts, another type of black diamond shaped crystals were obtained, and single crystal X-ray diffraction analysis of these crystals revealed a yet unknown crystal system. However, solution of the crystal structure showed that the metalloid cluster compound 1 is present in the crystal lattice, this time crystallizing together with the novel polyhedral cluster compound [Sn4Si{Si(SiMe3)3}4(SiMe3)2] (3). The molecular structure of 3 is best described as a butterfly arrangement of four tin atoms bridged by a Si(SiMe3)2 group (Figure 1). Every tin atom is additionally bound to a Si(SiMe3)3 ligand, with slightly different Sn–Si distances of 261 pm (Sn11–Si7A, Sn13–Si7) and 265 pm (Sn14–Si8, Sn12–Si8A). The capping Si(SiMe3)2 group most likely comes from the degradation of the Si(SiMe3)3 ligand, and a plausible mechanism is given in the supporting information. The tin–tin distances (284 pm) inside the Sn4 butterfly unit in 3 are within the range of a normal single bond (283– 285 pm). The capping silicon atom is bound to two tin atoms, with a Si–Sn distance of 263 pm also within the range of a single bond, leading to a nearly tetrahedral arrangement for these two tin atoms (Sn11, Sn13). In spite of this arrangement,

Reactivity of [Ge9{Si(SiMe3)3}3]- Towards Transition-Metal M2+ Cations: Coordination and Redox Chemistry

Recently the metalloid cluster compound [Ge9 Hyp3 ]- (1; Hyp=Si(SiMe3 )3 ) was oxidatively coupled by an iron(II) salt to give the largest metalloid Group 14 cluster [Ge18 Hyp6 ]. Such redox chemistry is also possible with different transition metal (TM) salts TM2+ (TM=Fe, Co, Ni) to give the TM+ complexes [Fe(dppe)2 ][Ge9 Hyp3 ] (3; dppe=1,2-bis(diphenylphosphino)ethane), [Co(dppe)2 ][Ge9 Hyp3 ] (4), [Ni(dppe)(Ge9 Hyp3 )] (5) and [Ni(dppe)2 (Ge9 Hyp3 )]+ (6). Such a redox reaction does not proceed for Mn, for which a salt metathesis gives the first open shell [Hyp3 Ge9 -M-Ge9 Hyp3 ] cluster (2; M=Mn). The bonding of the transition metal atom to 1 is also possible for Ni (e.g., compound 6), in which one or even two nickel atoms can bind to 1. In contrast to this in case of the Fe and Co compounds 3 and 4, respectively, the transition-metal atom is not bound to the Ge9 core of 1. The synthesis and the experimentally determined structures of 2-6 are presented. Additionally the bonding within 2-6 is analyzed and discussed with the aid of EPR measurements and quantum chemical calculations.