Substituent Effects in Linear Organogermanium Catenates

Synthesis, Properties, and Derivatization of Poly(dihydrogermane): A Germanium-Based Polyethylene Analogue

Polygermanes are germanium-based analogues of polyolefins and possess polymer backbones made up catenated Ge atoms. In the present contribution we report the preparation of a germanium polyethylene analogue, polydihydrogermane (GeH₂)_n, via two straightforward approaches that involve topotactic deintercalation of Ca ions from the CaGe Zintl phase. The resulting (GeH₂)_n possesses morphologically dependent chemical and electronic properties and thermally decomposes to yield amorphous hydrogenated Ge. We also show that the resulting (GeH₂)_n provides a platform from which functionalized polygermanes can be prepared via thermally induced hydrogermylation-mediated pendant group substitution.

Oligothienyl catenated germanes and silanes: synthesis, structure, and properties

The synthesis of two new groups of oligothienyl catenated silanes and germanes, Me5M2Thn (1a-b), Me5M2ThnM2Me5 (2a-c) (terminal), and ThnM2Me4Thn (3a-d) (internal) (M = Si, Ge; n = 2, 3; Th = 2- or 2,5-thienyl), is reported. The study of their structural parameters as well as of their spectral (NMR), electrochemical (CV) and optical (UV/vis absorbance, luminescence) properties has been performed in detail; in addition, the unexpected compound [Th2Si2Me4Th]2 (3a') is also studied. Theoretical investigations have been performed for model compounds in order to establish structure-property relationships. The molecular structures of 2a (Me5Si2Th2Si2Me5), 2b (Me5Ge2Th2Ge2Me5), 3a (Th2Si2Me4Th2) and 3b (Th2Ge2Me4Th2) have been investigated by X-ray diffraction analysis. An effective conjugation with flattening of both Th planes in terminal 2a and 2b was observed. The main trends in the dependence of the optical and electrochemical properties on the structural parameters have been established. All of the compounds studied exhibit a strong emission within the 378-563 nm range, and the maximal quantum yield (up to 77%) is observed for the Si derivative 3a'. For the majority of the compounds, the quantum yields (20-30%) are significantly larger than for 2,2'-bi- and 2,2':5',5''-terthiophenes. Due to their good emission properties, these compounds could be used to develop new materials with specific spectral properties.

Incorporating Methyl and Phenyl Substituted Stannylene Units into Oligosilanes. The Influence on Optical Absorption Properties

Molecules containing catenated heavy group 14 atoms are known to exhibit the interesting property of σ-bond electron delocalization. While this is well studied for oligo- and polysilanes the current paper addresses the UV-absorption properties of small tin containing oligosilanes in order to evaluate the effects of Sn–Si and Sn–Sn bonds as well as the results of substituent exchange from methyl to phenyl groups. The new stannasilanes were compared to previously investigated oligosilanes of equal chain lengths and substituent pattern. Replacing the central SiMe₂ group in a pentasilane by a SnMe₂ unit caused a bathochromic shift of the low-energy band (λ_max = 260 nm) of 14 nm in the UV spectrum. If, instead of a SnMe_2, a SnPh₂ unit is incorporated, the bathochromic shift of 33 nm is substantially larger. Keeping the SnMe₂ unit and replacing the two central silicon with tin atoms causes shift of the respective band (λ = 286 nm) some 26 nm to the red. A similar approach for hexasilanes where the model oligosilane [(Me₃Si)₃Si]₂(SiMe₂)₂ (λ_max = 253 nm) was modified in a way that the central tetramethyldisilanylene unit was exchanged for a tetraphenyldistannanylene caused a 50 nm bathochromic shift to a low-energy band with λ_max = 303 nm.

Molecular Oligogermanes and Related Compounds: Structure, Optical and Semiconductor Properties

The optical (UV/Vis absorbance, fluorescence in the solid state and in solution) and semiconducting properties of a number of di- and trigermanes as well as related silicon- and tin-containing germanes, 1-6 ((p-Tol)₃ GeGeMe₃ (1), Ph₃ SnGe(SiMe₃ )₃ (2), (C₆ F₅ )₃ GeGePh₃ (3), (p-Tol)₃ GeSiMe₂ SiMe₃ (4), (p-Tol)₃ GeGeMe₂ Ge(p-Tol)₃ (5), (p-Tol)₃ GeSiMe₂ SiMe₂ Ge(p-Tol)₃ (6)) were investigated. Molecular structures of 5 and 6 were studied by X-ray diffraction analysis. All compounds displayed luminescence properties. In addition, a band gap (of about 3.3 eV) was measured for compounds 1-6 showing that those molecules display semiconductor properties.

σ-Bond electron delocalization of branched oligogermanes and germanium containing oligosilanes

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Oligogermanes and germaoligosilanes isostructural to oligosilanes were synthesized.

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UV absorption data and X-ray diffraction revealed only marginal differences.

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Conformational flexibility is directly reflected in the UV absorption spectrum.

In order to evaluate the influence of germanium atoms in oligo- and polysilanes, a number of oligosilane compounds were prepared where two or more silicon atoms were replaced by germanium. While it can be expected that the structural features of thus altered molecules do not change much, the more interesting question is, whether this modification would have a profound influence on the electronic structure, in particular on the property of σ-bond electron delocalization.

The UV-spectroscopic comparison of the oligosilanes with germanium enriched oligosilanes and also with oligogermanes showed a remarkable uniform picture. The expected bathochromic shift for oligogermanes and Ge-enriched oligosilanes was observed but its extent was very small. For the low energy absorption band the bathochromic shift from a hexasilane chain (256 nm) to a hexagermane chain with identical substituent patterns (259 nm) amounts to a mere 3 nm.

Synthesis, structure, and properties of the hexagermane Pri3Ge(GePh2)4GePri3

The synthesis of the hexagermane Pri3Ge(GePh2)4GePri3 was achieved starting from the cyclotetragermane (Ph2Ge)4. Ring-opening of (Ph2Ge)4 with Br2 yielded Br(GePh2)4Br that was converted to H(GePh2)4H, and this material was treated with two equiv. of Pri3GeNMe2 to furnish Pri3Ge(GePh2)4GePri3 via the hydrogermolysis reaction. The X-ray crystal structures of (Ph2Ge)4, Br(GePh2)4Br and Pri3Ge(GePh2)4GePri3 were determined. The hexagermane Pri3Ge(GePh2)4GePri3 represents the longest structurally characterized linear oligogermane reported to date and exhibits physical properties that resemble those of the larger polygermane systems. The hexagermane is luminescent and interacts with polarized light, appearing pale yellow under one orientation of polarized light and deep blue under the opposite orientation. The electrochemistry of Pri3Ge(GePh2)4GePri3 was also explored, and this species exhibits the expected five irreversible oxidation waves.

Syntheses, structures and properties of linear and branched oligogermanes

This Perspective surveys recent developments in the synthesis and characterization of discrete oligogermanes. The use of the hydrogermolysis reaction, combined with a protection/deprotection strategy for a Ge-H moiety, has resulted in the synthesis of a variety of oligogermanes where the number of catenated atoms and the identity of the organic substituents can be readily controlled. Relationships between the composition of these oligomers and their optical and electronic properties have also been established.