Non-centrosymmetric coordination polymers based on thallium and acetylenedicarboxylate

Single crystals of anhydrous thallium acetylenedicarboxylate (Tl₂(C₄O₄), 1) and thallium acetylenedicarboxylate oxalate (Tl₄(C₄O₄)(C₂O₄), 2) precipitated from aqueous solutions containing thallium(I)-acetate and the respective organic acids. Both compounds crystallize in non-centrosymmetric space groups (1: P2₁2₁2₁; 2: C2) and contain stereochemically active lone pairs at Tl(I). The crystal structures of 1 and 2 show some similarities. Tl atoms are organized in corrugated layers, which are connected by the respective carboxylate anions. Upon heating 1 decomposes at 195 °C to form elemental pyrophorous thallium powder. 2 starts decomposing at approx. 150 °C forming elemental thallium next to another compound, which could not be identified up to now. TlHADC was also synthesized, but its crystal structure could not be solved either from powder or single crystal diffraction data. Upon heating it decomposes to form 1.