Kim M. Baines

The molecular structure of organogermanium compounds

The molecular structures, as determined by X-ray crystallography, of organogermanium compounds of the main group elements, excluding carboranes, are reviewed.

A Cryptand-Encapsulated Germanium(II) Dication

Unlike cations of metals such as sodium or calcium, oxidized silicon and germanium centers generally require strongly bound covalent ligands. We report the synthesis and characterization of a germanium(II) dication in the form of the salt (Ge·cryptand[2.2.2])(O3SCF3)2. The salt is isolated in 88% yield from the reaction of cryptand [2.2.2] and an N-heterocyclic carbene complex of GeCl(O3SCF3) as an air-sensitive, white solid. The crystal structure of the salt shows minimal interaction between the cryptand-encapsulated germanium(II) ion and the two –O3SCF3 counterions. These results suggest a widely expanded role of cryptands and related molecules in stabilizing nonmetallic cations.

Cationic Crown Ether Complexes of Germanium(II)

Fit for a king: Cationic complexes of Ge(II) can be prepared by using crown ethers to stabilize and protect the germanium center. Three different crown ethers were employed: [12]crown-4 (see structure, Ge teal, O red, C gray), [15]crown-5, and [18]crown-6. The structures of the cationic complexes depend on the cavity size of the crown ether and on the substituent on germanium.

Cationic cryptand complexes of tin(II).

A series of cationic cryptand complexes of tin(II), [Cryptand[2.2.2]SnX][SnX(3)] (10, X = Cl; 11, X = Br; 12, X = I) and [Cryptand[2.2.2]Sn][OTf](2) (13), were synthesized by the addition of cryptand[2.2.2] to a solution of either tin(II) chloride, iodide, or trifluoromethanesulfonate. The complexes could also be synthesized by the addition of the appropriate trimethylsilyl halide (or pseudohalide) reagent to a solution of tin(II) chloride and cryptand[2.2.2]. The complexes were characterized using a variety of techniques including NMR, Raman, and temperature-dependent Mössbauer spectroscopy, mass spectrometry, and X-ray diffraction.

A facile digermene-to-germylgermylene rearrangement; Bulky germylene insertion into the Si-H bond

The thermolysis of hexamesitylcyclotrigermane 1 in the presence of triethylsilane at 105 °C yields dimesityl(triethylsilyl)germane 2 and 1,1,1,2-tetramesityl(2-triethylsilyl)digermane 3; the molecular structure of 3 has been determined by X-ray crystallography.

Si K-edge and Ge K-edge X-ray absorption spectroscopy of the SiGe interface in [(Si)m(Ge)n]p atomic layer superlattices

The sensitivity of X-ray absorption near edge (XANES) spectra to the structure around the core excited atom has been explored by comparisons of the Si K-edge and Ge K-edge spectra of SiMe4, Ge(SiMe3)4, Si(GeMe3)4, Si(SiMe3)4, Ge(Me)4 an Ge2(Me)6 molecular compounds (Me = methyl); single crystal and amorphous Si; single crystal Ge; single crystal Si1−xGex alloy and [(Si)m(Ge)n]p atomic layer superlattices grown by molecular beam epitaxy. Systematic changes with changing environment are detected. The spectral trends as well as comparison with spherical wave multiple scattering calculations of variable size Si(Si)n and Si(Ge)n clusters (4 < n < 190), indicate that many aspects of the near edge (0–50 eV) spectral features in the semiconductors determined by structure far beyond the first coordination shell and that there are strong multiple scattering contributions. Two maxima separated by 0.80(3) eV are found as the lowest energy features in the Si K-edge spectrum of crystalline Si. These are attributed to 1s → 3p conduction band (CB) excitations. Even larger splittings are observed in the corresponding 1s → CB structure in Ge-richSi1−xGex alloys and the atomic layer superlattice samples. The CB splitting varies systematically with the superlattice structure. The utility of the various components of the XANES signal for characterizing the SiGe interface in [(Si)m(Ge)n]p superlattice samples is discussed.

Exploring the limits of 73Ge solid-state NMR spectroscopy at ultrahigh magnetic field

The ultrahigh field natural abundance (73)Ge solid-state wide-line NMR study of germanium dichloride complexed with 1,4-dioxane and tetraphenylgermane yields the largest (73)Ge quadrupolar coupling constant determined by NMR spectroscopy to date and the first direct observation of (73)Ge chemical shift anisotropy.

Ionic nature of Ge(II)-centered dications: a germanium K-edge X-ray absorption near edge structures study

Measurement of the ionic nature of [Ge(cryptand[2.2.2])](2+) by XANES has provided direct experimental evidence that the germanium center is best described as a nearly-naked dication encased within an electron rich cryptand cage.

Determination of the rate constant for ring opening of an α-cyclopropylvinyl radical

The rate constant for ring opening of the 1-(trans-2-phenylcyclopropyl)ethen-1-yl radical, 4, generated by photolysis of the corresponding vinyl iodide 2, is reported. The value of the rate constant was determined by the tin hydride method and was found to be (1.6 ± 0.2) × 1010 s−1, one order of magnitude smaller than the rate constant for rearrangement of the trans-2-phenylcyclopropylcarbinyl radical.

Addition polymerization of 1,1-dimesitylneopentylgermene: synthesis of a polygermene.

A new polymer with an alternating germanium-carbon backbone has been synthesized from 1,1-dimesitylneopentylgermene via addition polymerization using an anionic initiator.