Email (record): catena-Poly[[[tetra­kis­(cyanido-κC)tungstate(IV)]-di-μ-cyanido-κ(4) C:N-bis­[diaqua­(2,2′-bipyridyl-κ(2) N,N′)manganese(II)]-di-μ-cyanido-κ(4) N:C] hexa­hydrate]