I thought the answer for the question attached was:
[Al(H2O)6]3+ + 3H2NCH2CH2NH2 --> [Al(H2NCH2CH2NH2)3]3+ + 6H2O
Is there a reason why you're not meant to use ligand substitution here? The question even mentions that H2NCH2CH2NH2 can act both as a base and ligand. Perhaps I am missing something important in the question?
Any help is much appreciated