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Ternary Transition Metal Acetylides A I 2 M 0 C 2 ( A I = K, Rb; M 0 = Pd, Pt): Neutron Diffraction Studies and Electronic Properties
Author(s) -
Billetter Heinrich,
Wallraff Tim,
Schwarz Ulrich,
Smith Ronald I.,
Ruschewitz Uwe
Publication year - 2010
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201000108
Subject(s) - ternary operation , atmospheric temperature range , crystallography , crystal structure , neutron diffraction , analytical chemistry (journal) , ion , chemistry , physics , thermodynamics , organic chemistry , chromatography , computer science , programming language
Abstract The crystal structures of K 2 PdC 2 , K 2 PtC 2 , and Rb 2 PdC 2 ( P $\bar3$ m 1, Z = 1) were refined from time‐of‐flight powder neutron diffraction data (Polaris, ISIS/RAL) 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.