and Pb 8 O 5 (PO 4 ) 2 , which provides an alternative interpretation of the data. There are four predicted compounds in the A-lab dataset based on the Ni 2 (PO 3 ) 4 struc-ture, a kind of tetrametaphosphate with two inequivalent metal sites, both octahedrally coordinated but with slightly differently sized coordination environments. This M 2 (PO 3 ) 4 structure type is known to form with a variety of M(II) cations, namely M = Mg, Mn, Fe, Co, Ni, Cu, Zn. These previously reported compounds are listed in the ICSD. The fact that there are two distinct metal sites offers a possibility that two metals could order over these sites. A few of these bimetallic tetrametaphosphates ((M,M') 2 (PO 3 ) 4 have been synthesised