A 6 Mo 2 P 4 O 19 (A = Rb, Cs) and Rb 2 MoP 2 O 9 : new molybdophosphates with distinct polyanionic configurations.

The exploration of A-Mo-P-O (A = Rb, Cs) systems has allowed several new Mo(V) phosphates, Rb 2 MoP 2 O 9 , Rb 6 Mo 2 P 4 O 19 and Cs 6 Mo 2 P 4 O 19 , to be synthesized through the spontaneous nucleation method. Single-crystal X-ray diffraction analysis reveals that the identical stoichiometry compounds Rb 2 MoP 2 O 9 and Cs 2 MoP 2 O 9 belong to different space groups C 2/ 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, Rb 6 Mo 2 P 4 O 19 and Cs 6 Mo 2 P 4 O 19 are isostructural and crystallize in the same space group of P 2 1 / c . They exhibit a 3D framework structure with 0D Mo 2 O 5 O 6 P 4 O 8 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.