Binary molybdates K4M2+(MoO4)3 (M2+=Mg, Mn, Co) and crystal structure of K4Mn(MoO4)3

Binary molybdates K₄M²⁺ (MoO₄)₃ (M²⁺=Mg, Mn, Co) isostructural to triclinic ga-K₄Zn(WO₄)₃ were synthesized, and optimal conditions for their spontaneous crystallization were found. It was established by XRPA and DTA that at 530°C the structure of the compound with cobalt undergoes a transition to the orthorhombic structure of K₄Zn(MoO₄)₃. The structure of K₄Mn(MoO₄)₃ was determined from single crystal diffraction data (a=7.613, b=9.955, c=10.156 Å,α=92.28,β=106.66,γ=105.58°, Z=2, space group $Pbar 1$ , R=0.030). In this compound, Mn has a higher coordination number (CN=5+1) than that of Zn inα-K₄Zn(WO₄)₃ (CN=4+1). The main structural feature is pairs of MnO₆ octahedra linked by the bridging MoO₄ tetrahedra into ribbons stretching along the a axis. The structure is compared with related structures of binary molybdates and other members of the alluaudite family.