Catalyzes the specific cleavage of pyrophosphate. diphosphate + H2O = H(+) + 2 phosphate Magnesium. Can also use iron, nickel, cobalt and manganese, but not zinc ions. Optimum pH is 8-8.5. Tetramer. Strongly induced upon phosphate (Pi) starvation. Belongs to the HAD-like hydrolase superfamily.