Dipotassium sodium niobium dioxide tetrafluoride, K2NaNbO2F4, crystal structure and characterization Original Research Article

The paper presents a new data on the crystal structure of K2NaNbO2F4. Single crystals of K2NaNbO2F4, were obtained from the system of KF–NaF–Nb2O5. The compound is cubic, space group Fm3̄m (No. 225), and the unit cell parameters are a=8.4726(4) Å, Z=4, Volume=608.21(5) Å3. The structure was solved by the direct methods and refined to the reliability factors R1=0.0116 (wR2=0.0302). Its structure can be described as three-dimensional frameworks formed of (0 1 0) [Na2Nb2O4F8]∞ layers stacked along b axis. In the framework, niobium, oxygen, fluorine atoms form a rare [NbO2F4]3− anion group in an anhydrous solid state environment. The IR spectrum further confirmed the presence of NbO2 and NbF4 groups in the structure. The thermal analysis suggests that K2NaNbO2F4 is an incongruently melting compound.