Electron Attachment to the Lowest Unoccupied Orbitals in Linear and Branched Permethylated Polysilanes and Hexamethyldigermane and -distannane

Access to metastable [GeH2]n materials via a molecular "bottom-up" approach

We describe the application of a mild, molecular-based, hydride metathesis protocol for the preparation of metastable germanium(II) dihydrides with compositions approaching [GeH₂]_n. The common starting material for this work [Ge(O^tBu)₂] was prepared in a high yield and shown to undergo O^tBu/H exchange at Ge with the hydride sources pinacolborane (HBpin), catecholborane (HBcat), and diisobutylaluminum hydride (DIBAL-H) to give the [GeH₂]_n materials as yellow to orange solids. Heating one of these [GeH₂]_n materials to 200 °C affords a narrowing of the optical band gap (from 2.5 eV) and the generation of amorphous Ge. Reaction of [Ge(O^tBu)₂] with excess H₃B·SMe₂ in toluene at 70 °C provides a convenient route to thin films of amorphous Ge, including its deposition onto soft substrates, such as polyethyleneterephthalate (PET). Accompanying computations give insight into the energetics of O^tBu/H exchange at Ge, and reveal a general thermodynamic preference for branched structures of [GeH₂]_n oligomers over linear forms as the Ge chain becomes longer. We also show that [Ge(O^tBu)₂] is a suitable pre-catalyst for the borylation of aldehydes.

Electron collisions with X(CH3)4 molecules (X = C, Si, Ge)

Absolute grand-total cross sections (TCSs) for electron scattering from tetramethylmethane [C(CH₃)₄], tetramethylsilane [Si(CH₃)₄], and tetramethylgermane [Ge(CH₃)₄] molecules have been measured at electron-impact energies extending from around 0.5 to 300 eV in the linear electron-transmission experiment. The measured TCS energy dependences show very pronounced broad enhancement, peaking near 5.5 eV for Si(CH₃)₄ and Ge(CH₃)₄ molecules and around 6.5 eV for C(CH₃)₄. Additional weak structures are also located at higher electron energies. We attributed the TCS features to the resonant processes involved in the electron-molecule scattering. To examine the role of permethylation in the scattering, the measured TCS energy functions for X(CH₃)₄ compounds (X = C, Si, Ge) have been compared to the TCS curves for XH₄ molecules. Additionally, the integral elastic cross section (ECS) and ionization cross section (ICS) have been calculated from intermediate to high electron-impact energies using model methods. At energies above 50 eV, the sum of ECS and ICS for the investigated targets is in satisfactory agreement with the respective measured TCS. The computed ECS+ICS values can be used as rough estimation of TCS at energies above 300 eV.