I'm pretty sure that they are rotational isomers 

Maybe I am wrong, but I've seen the different shape of pore in these two types structure. Did you see? And the alpha Keggin's structure consists of the 4 building blocks connected to each other by the common corner only, but as a result consecutive rotation of these building blocks the 5-isomer contains the building blocks connected throgh the common edge only.

Thanks for your feedback. It helped me to understand the difference between alpha and epsilon structures.

Mr/Miss/Mrs Samarakoon,

Please pay attention to paper:

On the Origin of the Inverted Stability Order of the Reverse-Keggin [(MnO4)(CH3)12Sb12O24]6−: A DFT Study of α, β, γ, δ, and ε Isomers

F. Zhang, W. Guan, Y. Zhang, M. Xu, J. Li, Z. Su, Inorg. Chem., 2010, 49 (12), pp 5472–5481, DOI: 10.1021/ic100343t

Thanks Dr. Ivanova. By the way I am Mr....