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 M?ssbauer spectroscopy, mass spectrometry, and X-ray diffraction.     

Experimental and computational insights into the stabilization of low-valent main group elements using crown ethers and related ligands

A series of tin(II) triflate and chloride salts in which the cations are complexed by either cyclic or acyclic polyether ligands and which have well-characterized single-crystal X-ray structures are investigated using a variety of experimental and computational techniques. M?ssbauer spectroscopy illustrates that the triflate salts tend to have valence electrons with higher s-character, and solid-state NMR spectroscopy reveals marked differences between superficially similar triflate and chloride salts. Cyclic voltammetry investigations of the triflate salts corroborate the results of the M?ssbauer and NMR spectroscopy and reveal substantial steric and electronic effects for the different polyether ligands. MP2 and DFT calculations provide insight into the effects of ligands and substituents on the stability and reactivity of the low-valent metal atom. Overall, the investigations reveal the existence of more substantial binding between tin and chlorine in comparison to the triflate substituent and provide a rationale for the considerably increased reactivity of the chloride salts.     

Bend-induced melting of the smectic-A phase: analogy to a type-I superconductor

Using an atomic force microscope to nanopattern a substrate for liquid crystal alignment, a bend distortion is imposed on a liquid crystal. In regions of large bend the smectic-A phase melts into the nematic phase, and the width of the melted region is measured as a function of temperature. The results are consistent with type-I superconducting (nematic-smectic-A) behavior, wherein a large magnetic field (bend or twist distortion) induces an order to disorder transition. A model that accounts for non-mean-field behavior is presented.     

Photoinduced cytotoxicity and thioadduct formation by a prodigiosin analogue

[reaction: see text] The prodigiosin alkaloid 1 and the synthetic analogue 2 show photoinduced cytotoxicity against HL-60 cancer cells. Photoirradiation of 1 and 2 causes photofading, photooxidation, and thioadduct formation. These results provide a model for the redox properties of prodigiosins that play a role in their biological activity and provide a new way to functionalize their pyrromethene entity with water-soluble thiol groups.     

Solid-state 119Sn NMR and Mössbauer spectroscopy of "distannynes": evidence for large structural differences in the crystalline phase

The "distannynes" Ar'SnSnAr' (Ar' = C6H3-2,6(C6H3-2,6-Pr(i)2)2) and ArSnSnAr (Ar = C6H3-2,6(C6H2-2,4,6-Pr(i)3)2) were examined by solid-state (119)Sn NMR and M?ssbauer spectroscopy. The two compounds display substantially different spectroscopic parameters, while differing only in the absence (Ar'SnSnAr') or presence (ArSnSnAr) of a para-Pr(i) group in the flanking aryl rings of their terphenyl substituents. The spectroscopic differences can be interpreted in terms of a more trans-bent geometry and a longer Sn-Sn bond for ArSnSnAr in comparison to the wider Sn-Sn-C angle (125.24(7) degrees ) and shorter Sn-Sn bond length (2.6675(4)A) determined from the crystal structure of Ar'SnSnAr'. The differences are consistent with previously published calculations by Nagase and Takagi for ArSnSnAr.     

Near-edge Optical Properties of CuInSe2 Studied by Photoacoustic Spectroscopy

Optical absorption spectra of n-type CuInSe₂ single crystals were evaluated by means of photoacoustic spectroscopy in the photon energy range from 0.94 to 1.02 eV. At photon energies below 0.99 eV the spectra exhibit exponential tails that are ascribed to the presence of shallow impurity states. At higher photon energies the absorption coefficients follow the relation for direct allowed optical transitions between parabolic bands. The parameters of this relation are determined and compared with previous measurements.     

Optical Investigation of Defects in p-type CuInSe2 Single Crystals

Optical absorption spectra in the photon energy range from 0.03 to 1.1 eV and photoreflectance spectra in the range of the fundamental edge are measured on p-type CuInSe₂ single crystals. Besides a dominant contribution to the absorption coefficient due to intervalence band transitions below about 0.75 eV the spectra revealed five additional structures that can be ascribed to defect induced optical transitions with characteristic energies between 0.48 and 0.72 eV. Based on a comparison of the near-edge optical absorption and photoreflectance spectra a shallow defect (donor or acceptor) with an ionisation energy of about 46 meV was identified.