The crystal structures of two new diphosphates, sodium silver tricobalt bis(diphosphate), (Na(1.42)Ag(0.58))Co(3)(P(2)O(7))(2), and sodium silver copper(II) diphosphate, (Na(1.12)Ag(0.88))CuP(2)O(7), provide examples of the effect of mixing Na and Ag in the same site of known host phosphate compounds. The small differences in ionic radii of the two monocations do not lead to significant differences in the structural details. In the latter compound, the Cu atom lies on an inversion center.