Blue [{Cu(2,2′-bipy)
2}
2{α-SiW
12O
40}] (bipy = bipyridyl) (
1) and pale yellow [Mn(2,2′-bipy)
3]
2[α-SiW
12O
40] (
2) have been synthesized hydrothermally and characterized by IR spectroscopy and single crystal X-ray structure analysis. In
1, the [α-SiW
12O
40]
4− ion acts as a bridge between the two [{Cu(2,2′-bipy)
2]
2+ moieties via coordination through the terminal oxygen atoms, while in
2, the [Mn(2,2′-bipy)
3]
2+ ion balances the charge on the polyoxo anion without forming any covalent bond. To the best of our knowledge, this is the
first example of transition metal-mediated transformation of [α-SiW
9O
34]
10− to [α-SiW
12O
40]
4−.