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Persistent URL http://purl.org/net/epubs/work/53911
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Record Id 53911
Title Ternary transition metal acetylides A(2)(I)M(0)C(2) (A(I) = K, Rb; M-0 = Pd, Pt) : neutron diffraction studies and electronic properties
Abstract The crystal structures of K2PdC2, K2PtC2, and Rb2PdC2 (P (3) over bar m1, Z = 1) were refined from time-of-flight powder neutron diffraction data (Polaris, ISIS/PAL) at room temperature and 4.5 K. The resulting C-C distances within the C-2(2-) anion are in the range 124.4-124.7 pm (295 K). This is distinctly longer than the expected distance for a C-C triple bond (120 pm). At low temperatures slightly longer C-C distances are found (125.0-126.7 pm), which is due to an increasing wobbling of the C-2 dumbbells around their center of gravity with increasing temperature. This is also reflected in the temperature dependence of the lattice parameters a and c. Lattice parameter c, which is parallel to the C-2 dumbbells, decreases with increasing temperature, whereas a shows a typical positive thermal expansion. Differing to previous work ternary palladium acetylides A(2)PdC(2) were obtained as red (A = Na) and yellow powders (A = K, Rb) by using a slightly improved synthesis. By means of diffuse reflectivity direct bandgaps were determined to 2.09 eV (A = Na), 2.55 eV (A = K), and 2.77 eV (A = Rb). This is in good agreement with direct bandgaps obtained from band structure calculations. These band structure calculations indicate very small indirect bandgaps of only a few tenth of an eV.
Keywords Chemistry , neutron diffraction , platinum , acetylides , alkali metals , band structure , palladium
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Language English (EN)
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Journal Article ZAAC 636, no. 9-10 (2010): 1834-1838. doi:10.1002/zaac.201000108 2010