1. Hill, C.L., Chem. Rev., 1998, vol. 98, no. 1, p. 1.
2. Nikitina, E.N., Geteropolisoedineniya (Heteropoly Compounds), Moscow: Goskhimizdat, 1962.
3. Maksimov, G.V., Usp. Khim., 1995, vol. 64, no. 5, p. 480.
4. Pop, M.T., Geteropoli- i izopolioksometallaty (Heteropoly- and Isopolyoxometallates), Novosibirsk: Nauka, 1990.
5. Kazanskii, L.P., Torchenkova, E.A., and Spitsyn, V.I., Usp. Khim., 1974, vol. 43, no. 7, p. 1137.