Disproportionation of Sn(II){CH(SiMe3)2}2 to ˙Sn(III){CH(SiMe3)2}3 and ˙Sn(I){CH(SiMe3)2}: characterization of the Sn(I) product

Half a century after the photolytic disproportionation of Lappert's dialkyl stannylene SnR₂, R = CH(SiMe₃)₂ (1) gave the persistent trivalent radical [˙SnR₃], the characterization of the corresponding Sn(I) product, ˙SnR is now described. It was isolated as the hexastannaprismane Sn₆R₆ (2), from the reduction of 1 by the Mg(I)-reagent, Mg(BDI^Dip)₂ (BDI = (DipNCMe)₂CH, Dip = 2,6-diisopropylphenyl).

Optical absorption and shape transition in neutral SnN clusters with N ≤ 40: a photodissociation spectroscopy and electric beam deflection study

Neutral SnN clusters with N = 6-20, 25, 30, 40 are investigated in a joint experimental and quantum chemical study with the aim to reveal their optical absorption in conjunction with their structural evolution. Electric beam deflection and photodissociation spectroscopy are applied as molecular beam techniques at nozzle temperatures of 16 K, 32 K and 300 K. The dielectric response is probed following the approach in S. Schäfer et al., J. Phys. Chem A, 2008, 112, 12312-12319. It is improved on those findings and the cluster size range is extended in order to cover the prolate growth regime. The impact of the electric dipole moment, rotational temperature and vibrational excitation on the deflection profiles is discussed thoroughly. Photodissociation spectra of tin clusters are recorded for the first time, show similarities to spectra of silicon clusters and are demonstrated to be significantly complicated by the presence of multiphoton absorption in the low-energy region and large excess energies upon dissociation which is modelled by the RRKM theory. In both experiments two isomers for the clusters with N = 8, 11, 12, 19 need to be considered to explain the experimental results. Triple-capped trigonal prisms and double-capped square antiprisms are confirmed to be the driving building units for almost the entire size range. Three dominating fragmentation channels are observed, i.e. the loss of a tin atom for N < 12, a Sn7 fragment for N < 19 and a Sn10 fragment for N ≥ 19 with Sn15 subunits constituting recurring geometric motifs for N > 20. The prolate-to-quasispherical structural transition is found to occur at 30 < N ≤ 40 and is analyzed with respect to the observed optical behavior taking quantum chemical calculations and the Mie-Gans theory into account. Limitations of the experimental approach to study the geometric and electronic structure of the clusters at elevated temperatures due to vibrational excitation is also thoroughly discussed.

Higher stability of metalloid tin clusters obtained via the cation-anion interaction

The reaction of a metastable SnCl solution with KR (R = Si(SiMe₃)₂(SitBuMe₂) = Hyp^tBuMe₂ or Si(SiMe₃)₂(SiEt₃) = Hyp^Et₃) gives the metalloid tin cluster [Sn₁₀R₄]^2- in partly good yields. The tin clusters are in the solid state as well in solution coordinated by a potassium cation, leading first of all to a more static compound and novel coordination polymers in the solid state. Additionally, the coordination of the potassium cation strongly increases the stability of the cluster in solution. This higher stability is thereby an important prerequisite for future investigation of this open shell metalloid tin cluster.

Structure and Bonding in a Diamond-Shaped Tin Cluster Possessing a cyclo-Sn4 Core

A tetrameric cluster composed entirely of (aryl)Sn units, [DMPSn]₄ (DMP=2,6-dimesitylphenyl), has been prepared by reduction of [DMPSnCl]₂ with a variety of reductants. This cluster was characterized in solution by multinuclear NMR spectroscopies, as well as in the solid-state by single crystal X-ray diffraction analysis. This species is stereochemically nonrigid in solution and possesses a cyclo-Sn₄ core whose DMP substituents are equivalent at higher temperatures. The solid-state molecular structure is remarkably unsymmetrical and possesses a nearly planar cyclo-Sn₄ core. The DMP substituents are arranged such that three are approximately coplanar, while one is nearly perpendicular to the cyclo-Sn₄ core. Density functional theory calculations for a [PhSn]₄ model system show that this distorted geometry about the cyclo-Sn₄ core maximizes σ-bonding between the Sn centers in a manner reminiscent of trans-bent bonding in the heavy group 14 analogues of alkenes and alkynes.

Reductive dehydrocoupling of diphenyltin dihydride with LiAlH4: selective synthesis and structures of the first bicyclo[2.2.1]heptastannane-1,4-diide and bicyclo[2.2.2]octastannane-1,4-diide

The reaction of diphenyltin dihydride with LiAlH4 gives access to a set of charged tin cages as their lithium salts. Variation in the ratio of reactants provides a perstannabicyclooctane dianion and a perstannanorbornane as the di- and monoanions. These compounds can be synthesised selectively by careful stoichiometric control and have been characterised by single crystal X-ray diffractometry, NMR and UV-vis spectroscopy. Computational exploration of the electronic structures of these compounds was undertaken and, in agreement with structural and spectroscopic features, indicated significant σ-delocalisation in the tin skeletons.

A Re-examination of the Synthesis of Monolayer-Protected Co x(SCH2CH2Ph) m Nanoclusters: Unexpected Formation of a Thiolate-Protected Co(II) T3 Supertetrahedron

Herein, we report a re-examination of the synthesis and characterization of monolayer-protected Co _x(SCH₂CH₂Ph) _m nanoclusters. These clusters were reportedly formed by the reaction of CoCl₂ with NaBH₄ in the presence of HSCH₂CH₂Ph and were suggested to contain between 25 and 30 Co atoms. In our hands, however, we found no experimental evidence to support the existence of these large clusters in the reaction mixture. Instead, this reaction results in the relatively clean formation of the cobalt(II) coordination complex [Co₁₀(SCH₂CH₂Ph)₁₆Cl₄] (1). Complex 1 has been fully characterized using a wide variety of techniques, including single-crystal X-ray crystallography, NMR spectroscopy, mass spectrometry, and magnetometry. This complex represents the first example of a thiolate-protected Co(II) T3 supertetrahedral cluster.

Synthesis and Structure of Sn14Cl6(CH2SiMe3)12: Toward Nanoclusters of 4-Coordinate α-Sn

Orange crystals of a Sn₁₄ cluster have been isolated in up to 22% yield from a reaction between Me₃SiCH₂SnCl₃, SnCl₄, and LiAlH₄. The structure determined by single crystal X-ray diffraction shows three unique Sn atoms in a 6:6:2 ratio, with all Sn atoms 4-coordinate, similar to the tetrahedral bonding in elemental gray Sn. The solid state ¹¹⁷Sn MAS NMR spectrum shows the three types of distinct Sn atoms in the expected 3:3:1 intensity ratio with respective chemical shifts of 87.9, -66.6, and -607.1 ppm relative to Me₄Sn. The chemical shift of the two Sn atoms without ligands (bonded only to Sn), at -607.1 ppm, is the most upfield, and is the closest to the chemical shift, reported here, of bulk gray tin (-910 ppm). First-principles density functional theory calculations of the chemical shielding tensors corroborate this assignment. While the core coordination is distorted from the ideal tetrahedral arrangement in the diamond structure of gray tin, this Sn₁₄ cluster, as the largest reported cluster with all 4-coordinate Sn, represents a major incremental step toward being able to prepare atomically precise nanoparticles of gray tin.

LiGe(SiMe₃)₃: A New Substituent for the Synthesis of Metalloid Tin Clusters from Metastable Sn(I) Halide Solutions

The most fruitful synthetic route to metalloid tin clusters applies the disproportionation reaction of metastable Sn(I) halide solutions, whereby Si(SiMe₃)₃ is mostly used as the stabilizing substituent. Here, we describe the synthesis and application of the slightly modified substituent Ge(SiMe₃)₃, which can be used for the synthesis of metalloid tin clusters to give the neutral cluster Sn10[Ge(SiMe₃)₃]₆ as well as the charged clusters {Sn10[Ge(SiMe₃)₃]₅}− and {Sn10[Ge(SiMe₃)₃]₄}2−. The obtained metalloid clusters are structurally similar to their Si(SiMe₃)₃ derivatives. However, differences with respect to the stability in solution are observed. Additionally, a different electronic situation for the tin atoms is realized as shown by 119mSn Mössbauer spectroscopy, giving further insight into the different kinds of tin atoms within the metalloid cluster {Sn10[Ge(SiMe₃)₃]₄}2−. The synthesis of diverse derivatives gives the opportunity to check the influence of the substituent for further investigations of metalloid tin cluster compounds.

Ge14 Br8 (PEt3 )4 : A Subhalide Cluster of Germanium

Heating a metastable solution of Ge^I Br to room temperature led to the first structurally characterized metalloid subhalide cluster Ge₁₄ Br₈ (PEt₃ )₄ (1). Furthermore 1 can be seen as the first isolated binary halide cluster on the way from Ge^I Br to elemental germanium, giving insight into the complex reaction mechanism of its disproportionation reaction. Quantum chemical calculations further indicate that a classical bonding situation is realized within 1 and that the last step of the formation of 1 might include the trapping of GeBr₂ units.

Synthesis, solid-state structures and reduction reactions of heteroleptic Ge(II) and Sn(II) β-ketoiminate complexes

A series of new heteroleptic divalent germaniun and tin complexes of the general type L1,4GeN(SiMe3)2 (1, 2) and L1−4SnN(SiMe3)2 (3–6) were synthesized by reaction of β-ketimines L1−4H with Ge[N(SiMe3)2]2 and Sn[N(SiMe3)2]2, respectively. The reaction of 3 with the strong Mg(I) reductant L5Mg yielded the heteroleptic complex L1MgL5 7 after ligand transfer from tin to magnesium, whereas analogous reactions of L4GeN(SiMe3)2 2 and L4SnN(SiMe3)2 6 with L5Mg occurred with formation of insoluble precipitates, transfer of the amido substituent from the group 14 metal to magnesium and subsequent formation of the heteroleptic magnesium complex L5MgN(SiMe3)2 (8). 1–8 were characterized by heteronuclear NMR (1H, 13C, 119Sn) and IR spectroscopy, elemental analysis and single-crystal X-ray diffraction (L4SnN(SiMe3)2 6, L1MgL5 7).