Adducts of Niobium(V) and Tantalum(V) Halogenides. IX. Relative stability of the adducts of the chlorides and bromides with some dialkylchalcogenides

The relative stability of adducts formed by Nb(V) and Ta(V) pentachlorides and bromides with some dimethylchalcogenides and nitriles has been determined by ¹H-NMR. in dichloromethane at ? 60°. The stabilities are explained in terms of the HSAB principle and Jørgensen's symbiotic effect. A good correlation exists between the ionisation potential of the valence p orbital of the chalcogen atom in the ligand and the logarithm of the relative stability of the adduct formed with a given acid.