Mixed Pentele-Chalcogen Cationic Chains from Aluminum and Gallium Halide Melts

The reactions of tellurium or selenium with bismuth or antimony in chloridogallate and iodidoaluminate melts in the presence of group 15 trihalides as weak oxidants yielded the compounds (Sb₂Te₂)­[GaCl₄] (1), (Sb₂Te₂)­I­[AlI₄] (2), (Bi₂Te₂)­Cl­[GaCl₄] (3a), (Bi₂Se₂)­Cl­[GaCl₄] (3b), (Sb₃Te₄)­[GaCl₄] (4), and (SbTe₄)­[Ga₂Cl₇] (5). In the crystal structures one-dimensional polymeric cations (Sb₂Te₂⁺)_n (1), (Sb₂Te₂²⁺)_n (2), (Bi₂Te₂²⁺)_n (3a), (Bi₂Se₂²⁺)_n (3b), (Sb₃Te₄⁺)_n (4), and (SbTe₄⁺)_n (5) are present. The polymeric cationic strands in 2, 3a, 3b, and 4 consist of pentele/chalcogen dumbbells, which are connected to ladder-shaped bands. The strands in 1 and 5 consist of condensed rings that involve four-membered Sb₂Te₂ rings for 1, and five-membered SbTe₄ rings for 5. The counteranions are the weakly coordinating [GaCl₄]⁻, [AlI₄]⁻, and [Ga₂Cl₇]⁻ in addition to Cl^– and I^– anions, which are coordinated to the atoms of the cations. The crystal structures of 1–4 are characterized by a statistical disorder in the anions with alternatively occupied positions for the Al and Ga atoms. For 4 superstructure reflections appear in the diffractions patterns, indicating a partial order. A correct assignment of the Sb and Te positions in the cation of 5 was achieved by periodic quantum-chemical calculations, which were performed via a Hartree–Fock density functional theory hybrid method. A clear preference of the 4-fold coordinated site was obtained for Sb.