SIGNIFICANT STRUCTURAL DISORGANIZATION IN ALKALINE MOLYBDENUM(V) ALUMINOPHOSPHATES

Three new molybdenum(V) aluminophosphates, K2CS7Mo9Al3P11O59, K4Cs5Mo9 Al3P11O59, and Rb9Mo9Al3P11O59, isotypic With the tunnel structure Cs9 Mo9Al3P11O59, have been synthesized. Their single-crystal X-ray diffra ction study evidences high thermal factors for most of the atoms and s plittings of several sites which are interpreted as a significant diso rganization of the framework [Mo9Al3P11O59]infinity, resulting from va rious tiltings of the chains of polyhedra rather than from a distortio n of the latter. The second important feature deals with the distribut ion of the interpolated A cations in the tunnels: exclusive occupancy of the large tunnels by cesium ions, whereas the potassium ions are lo cated in the smaller ones, and existence of additional sites for Rb+ i n Rb9Mo9Al3P11O59. The abnormally large A-O distances are also discuss ed in connection with the high thermal factors observed for the A(+) c ations.