The feasibility of the Hofmann clathrates Ni(CN)2(NH3)·G(G=guest molecule) and the octahedral Werner-type complexes Ni(X)2(L)4 (X=NCS, NCO, CH3CO2, C6H5CO2; L=Py, 4-Mepy) as a scavenger for organic substrates in a polluted aqueous or organic medium is dependent on the complex lability, thermal stability and reversibility in solvent trapping which can be conveniently studied by thermogravimetric means. Besides the parent monomeric octahedral complexes, all the thermal decompositional intermediates, namely, monomeric tetrahedral, dimeric octahedral and polymeric octahedral, are also potential scavengers for selected organic substances though they operate via a cycle of bond-making and bond-breaking processes.