Publication Date:
2011-05-06
Description:
The Raman spectroscopic studies on samples with the starting compositions Cs 4 [Si 2 Ge 2 ] and M 4 [Ge 2 Sn 2 ] ( M = K, Cs) verify unambiguously the presence of phases composed of the mixed cluster moieties [Si x Ge 4– x ] 4– and [Ge x Sn 4– x ] 4– ( x = 1–3) including the pure anions [ E 4 ] 4– ( E = Si, Ge, Sn). The assignment of the vibrational frequencies is supported by normal coordinate analysis (NCA). The results for the mixed cluster anions are discussed in context with their isoelectronic analogs P x As 4– x ( x = 1–3) and SbP 3 . Using the characteristic breathing frequencies, one obtains for the ratio factor of the mixed moieties κ = ν([Si x Ge 4– x ] 4– ) / ν(P x As 4– x ) = 0.79, which is in good agreement with the reported value of 0.77 for the pure cluster series [ E 4 ] 4– ( E = Si, Ge, Sn) and X 4 ( X = P, As, Sb). The experimental average force constants f (Si-Ge) = 1.01 Ncm –1 and f (Ge-Sn) = 0.77 Ncm –1 correspond to arithmetic mean of those obtained for the pure anions in the binaries M 4 E 4 ( M = K, Rb, Cs; E = Si, Ge, Sn). The phonon frequencies of binary M 4 E 4 ( M = K, Cs; E = Si, Ge, Sn) and ternary K 4 E x E ′ 4– x ( E , E ′ = Si, Ge or Ge, Sn, E ≠ E ′, x = 1, 2, 3) were calculated by using pseudopotential electronic structure method SIESTA. Excellent agreement between the calculated and experimental frequencies was obtained for the pure binaries. The theoretical results compare also well with experimental values for the mixed series [Si x Ge 4– x ] 4– , whereas for the corresponding mixed Ge-Sn species the differences between measured and calculated frequencies are greater than 10 %.
Print ISSN:
0044-2313
Electronic ISSN:
1521-3749
Topics:
Chemistry and Pharmacology
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