Crystal structures of new pyrovanadates A2MnV2O 7 (A = Rb, K)

The new compounds A2MnV2O7 (A - K, Rb) with structures related to the melilite-type have been synthesized by a solid state reaction route. The crystal structures of K2MnV 2O7, Rb2MnV2O7 and KRbMnV2O7 have been determined using X-ray single crystal diffraction data. The compound K2MnV2O7 crystallizes with a melilite-type structure with tetragonal unit cell parameters a = 8.609(3), c = 5.538(4) Åand space group P4̄21m. The structures of Rb2MnV2O7 and KRbMnV 2O7 are derived from the mehlite-type structure with space group P42mnm and unit cell parameters a = 8.577(6), c=11.809(6) Å, and a = 8.530(6), c = 11.466(5) Å, respectively. The three structures consist of [MnV2O7]2- layers perpendicular to the c axis separated by A+ layers. The [MnV 2O7]2- layers feature corner-sharing MnO 4 tetrahedra and V2O7 pyrovanadate units, the linkage leading to rings of five tetrahedra. The doubling of the c parameter for Rb2MnV2O7 or Rb2MnV 2O7 is explained by the existence of a mirror plane perpendicular to the [001] direction between two [MnV2O 7]2- layers. The A+ alkali cations occupy distorted square antiprisms of oxygen atoms in K2MnV 2O7 and distorted square prisms of oxygen atoms in Rb 2MnV2O7 and Rb2MnV2O 7. © 2007 Verlag der Zeitschrift für Naturforschung,.