[Al₂P₄]^6-, [Al₂As₄]^6-, [Ga₂P₄]^6- und [Ga₂As₄]^6-, Zintl-Anionen mit 1,3-Dimethylencyclobutan-Struktur / [Al₂P₄]^6-, [Al₂As₄]^6-, [Ga₂P₄]^6- and [Ga₂As₄]^6-, Zintl Anions with 1.3-Dimethylene-cyclobutane Structure

Abstract

The compounds Cs 6 M 2 X 4 (M = Al, Ga; X = P, As) were synthesized from stoichiometric mixtures of Cs, M and Cs 4 X 6 in sealed Nb ampoules at 950 K. They are isotypic and crystallize in the monoclinic space group P2 1 /c (No. 14) with Z = 4 formula units per unit cell. The anion partial structure is characterized by isolated [M 2 X 4 ] 6- units with relatively short distances for the terminal d(M–X) bonds corresponding to a Pauling Bond Order PBO = 1.5. The distances d(M–X) of the four-membered M 2 X 2 rings correspond to single bonds. The FIR spectra have been interpreted on the basis of the [M 2 X 4 ] 6- units with 2/m 2/m 2/m-D 2h , symmetry by considering a factor group splitting. The assignment of the observed frequencies is supported by a normal coordinate analysis.