Aluminium shows a uniform oxidation state of+3 in its compounds. Like aluminium, thallium also shows +3 oxidation state in some of its compounds like TlCl3 , Tl2O3 , etc. Al is known to form octahedral complexes like [AlF6]3- . Similarly, Tl also forms octahedral complexes as [TlF6]3- .
Thallium also resembles group 1 metals. Like group 1 metals which show a stable oxidation state of +1 in their compounds Tl, due to inert pair effect, also shows +1 oxidation state in some of its compounds such as Tl2O, TlCl, TlClO4 , etc. Similarly, like group 1 oxides, Tl2O is strongly basic.
