Synthesis and characterization of new fluoride-containing manganese vanadates A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F

• Single crystals of A2Mn2V2O7F2, (A=Rb, Cs) and Mn2VO4F were grown hydrothermally.
• The use of fluoride mineralizers in the synthesis led to the formation of new compounds without OH− groups.
• The structure of A2Mn2V2O7F2 features zigzag chains of MnO4F2 units.
• Cs2Mn2V2O7F2 exhibits antiferromagnetic ordering with a Neel temperature of ~3 K.
• Mn2VO4F possesses a condensed framework structure with disordered fluorine atoms.

Large single crystals of A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F were grown using a high-temperature (~600 °C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO4F2 building blocks. The A2Mn2V2O7F2 series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb2Mn2V2O7F2: a=7.4389(17) Å, b=11.574(3) Å, c=10.914(2) Å; Cs2Mn2V2O7F2: a=7.5615(15) Å, b=11.745(2) Å, c=11.127(2) Å). The structure is composed of zigzag chains of edge-sharing MnO4F2 units running along the a-axis, and interconnected through V2O7 pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn2+ indicated that Cs2Mn2V2O7F2 is antiferromagnetic with a Neél temperature, TN=~3 K and a Weiss constant, θ, of −11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs2Mn2V2O7F2. Mn2(VO4)F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) Å, b=6.8036(7) Å, c=10.1408(13) Å and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn2+. These interpenetrating chains are additionally connected through isolated VO4 tetrahedra to form the condensed structure.

New vanadate fluorides A2Mn2V2O7F2 (A=Rb, Cs) and Mn2(VO4)F have been synthesized hydrothermally. Upon cooling, the one-dimensional Mn(II) substructure results in antiferromagnetic ordering.Figure optionsDownload as PowerPoint slide