A series of Mixed‐Valent Molybdenum Monophosphates, isotypic with leucophosphite represented by CsMo 2 P 2 O 10 and K 1.5 Mo 2 P 2 O 10 · H 2 O

The structure of two mixed valent molybdenum phosphates, CsMo 2 P 2 O 10 and K 1.5 Mo 2 P 2 O 10 · H 2 O has been solved from single crystals by X‐ray diffraction in the space group P2 1 /c with a = 9.428(1), b = 9.943(2), c = 12.348(2) Å and β = 127.38(1)° for CsMo 2 P 2 O 10 and a = 9.721(2), b = 9.805(3), c = 12.329(3) Å and β = 128.73(2)° for K 1.5 Mo 2 P 2 O 10 · H 2 O. These compounds isotypic with NH 4 Mo 2 P 2 O 10 · H 2 O and RbMo 2 P 2 O 10 · (1 − x)H 2 O exhibit the leucophosphite structure. The possibility of cationic non stoichiometry in this structure is also shown by the synthesis of two isotypic compounds A 1.5 Mo 2 P 2 O 10 · xH 2 O (A = Rb, Tl). In these monophosphates, one site Mo(1) is fully occupied by Mo V , whereas the other octahedral site Mo(2) exhibits a variable valency Mo III Mo IV to Mo V . The main difference between these different phosphates deals with the distribution of the A cations inside the tunnels, depending upon their size and their content.