A6Mo2P4O19 (A = Rb, Cs) and Rb2MoP2O9: new molybdophosphates with distinct polyanionic configurations

The exploration of A-Mo-P-O (A = Rb, Cs) systems has allowed several new Mo(V) phosphates, Rb2MoP2O9, Rb6Mo2P4O19 and Cs6Mo2P4O19, to be synthesized through the spontaneous nucleation method. Single-crystal X-ray diffraction analysis reveals that the identical stoichiometry compounds Rb2MoP2O9 and Cs2MoP2O9 belong to different space groups C2/c and Pbca, respectively. Both compounds consist of dissimilar 1D [Mo-O-P]∞ chains with different repeated building units, while monovalent cations fill in spaces to form 3D structures. However, Rb6Mo2P4O19 and Cs6Mo2P4O19 are isostructural and crystallize in the same space group of P21/c. They exhibit a 3D framework structure with 0D Mo2O5O6P4O8 groups, which are separated by Rb/Cs atoms. Interestingly, structural relationships between the different monophosphates of the A-Mo-P-O (A = Rb, Cs) systems are presented in which distinct polyanionic configurations appear owing to the A/P ratios, as well as the size of the univalent cations. Further, detailed structural comparisons, optical properties and theoretical calculations are also discussed.