Chemical rearrangement under hydrothermal conditions : Formation of polymeric chains (CuX)(2)(dpiz) and (CuX)(3)(dpiz) (X = Cl, Br; dpiz = dipyrido[1,2-a : 2 ',3 '-d]imidazole) and crystal structures of (1)(infinity)[(CuCl)(2)(C10H7N3)] and (1)(infinity)[(CuBr)(3)(C10H7N3)]