Penta-kis(l-prolinium) dodeca-tungsto-borate trihydrate.

The title polyoxometalate-based organic-inorganic hybrid compound, (C(5)H(10)NO(2))(5)[BW(12)O(40)]·3H(2)O, consists of one α-Keggin-type [BW(12)O(40)](5-) polyoxoanion, five crystallographically independent l-prolinium cations and three uncoordin-ated water mol-ecules. The polyoxoanion shows characteristic features with respect to bond lengths and angles. Several N-H⋯O and O-H⋯O hydrogen bonds between the organic cations, inorganic anions and crystal water mol-ecules lead to a three-dimensional supra-molecular structure.