Thermal decomposition of sulphonamide derivative complexes: II. Thermal behaviour of complexes of acetazolamide with Ni(II), Co(II), Zn(II), Cd(II), Hg(II) and Ag(I)

Abstract

The thermal behaviour of complexes of acetazolamide (Acm) with Ni(II), Co(II), Zn(II), Cd(II) Hg(II) and Ag(I) has been studied using TG and DTA techniques in flowing air and nitrogen atmospheres, and IR spectroscopy. The complexes decompose in two steps: (A) deammination or dehydration, and (B) pyrolytic decomposition. In the second step, different behaviours are observed. Degradation of the ligand of the Ni(Acm) 2(NH 3) 4, Zn(Acm) 2 (NH 3) 2, Co(Acm) 2(NH 3) 2 and Cd(Acm)·1.5 H 2O complexes leads to the metal oxide (in air) or sulphide (in nitrogen). During the formation of these compounds in air, the DTA curves show important exothermic peaks attributable to oxidation processes such as the formation of sulphates. In this sense, CoSO 4 and CdSO 4 can be isolated at intermediate stages of the degradation. The sulphates presumably originate not from the Acm sulphonamido moiety but from oxidation of a thiadiazole (tdz) derivative. This behaviour is similar to that which has been previously observed for Cu(II)-Acm complexes. Thermal degradation of K 2Ni 2(Acm) 2 3·5H 2O gives a mixture of potassium sulphate and nickel(II) oxide (in air) or nickel(II) sulphide (in nitrogen). In the case of the Ag(I) and Hg(II) complexes, the formation of sulphides in both air and nitrogen atmospheres is tentatively proposed as an intermediate stage of the pyrolysis. Finally, the HgS sublimates and the Ag 2S decomposes to give Ag.