A. Guesdon

Review on vanadium phosphates with mono and divalent metallic cations: syntheses, structural relationships and classification, properties

Abstract The vanadium phosphates with mono or divalent metallic cations (with A=Li, Na, K, Rb, Cs, Ag, Tl, Ca, Sr, Ba, Cd, Co, Cu, Hg, Mn, Ni, Pb, Zn) form a huge family of compounds with complicated structures. In this review 126 phosphates are included with their synthetic and structural characteristics. More particularly the environment of the vanadium atom, the connections of the vanadium polyhedra and the connections with the phosphates groups into V x O y and V x P y O z units and chains are discussed. A classification based on the connection of the vanadium polyhedra is proposed. One can observe that the vanadium atom adopts octahedral, square pyramidal, trigonal bipyramidal and tetrahedral coordinations. The trivalent, tetravalent and pentavalent vanadium are generally characterized by zero, one and two short V–O distances, respectively, in these compounds. The vanadium polyhedra are either isolated or connected into V x O y units (with 2≤ x ≤9) or connected into infinite chains. The arrangements of the vanadium, phosphorus and A cations are noted according to the A, V and P ratios. The magnetic and catalytic properties of 45 and 15 compounds, respectively, are reviewed and their structures–properties relationships are discussed.

Two molybdenum (VI) monophosphates with a tunnel structure: AMoO2PO4 (A=Cs, Tl) and structural relationships in the series

Abstract Two new molybdenum (VI) monophosphates CsMoO2PO4 and TlMoO2PO4 have been synthesized by solid state chemistry. Their structure were determined from single crystal X-ray diffraction studies. The frameworks MoO2PO4 delimit tunnels in which are located the univalent cations. Structural relationships between the different monophosphates of the AMoO2PO4 series with A = Ag, Na, K, Tl, Cs, are presented in which two kinds of frameworks appear owing to the size of the univalent cations.

The vanadium monophosphates AVOPO4 : Synthesis of a second form β-KVOPO4 and structural relationships in the series

Abstract A new form of potassium vanadophosphate β -KVOPO 4 has been synthesized using hydrothermal technique which showed the role of the extra adduct, here W or WO 3 . The structure of this phase, isotypic to Rb and Cs monophosphates, has been determined from a single crystal X-ray study. Structural relationships between the different monophosphates of the AVOPO 4 series with A = Li, Na, K, Rb, Cs, NH 4 are presented in which K + appears as a boundary cation: with cations smaller than K + the vanadium(IV) is octahedral and pyramidal with larger ones, both coordinations existing with K + .

On the intersecting tunnel structure of the monophosphates A3(V, W)4O9(PO4)2 with A = Rb, Tl, Cs

Abstract The structure determination of a single crystal with composition Rb3V1.63W2.37O9(PO4)2 shows that this phase belongs to the ‘KNbW’ type (K3Nb3WO9(PO4)2). This intersecting tunnel structure which consists of octahedral [MO3]∞ chains interconnected with ‘MPO9’ units is closely related to the ‘KVW’-type (K3V2W2O9(PO4)2), and differs only from the latter by the relative orientation of the [MO3]∞ chains. In the same way, the X-ray powder diffraction study of the phosphates A3V2W2O9(PO4)2 with A = Rb, Tl, Cs and Rb3VxW4 − x O9(PO4)2 (1.5 ≤ x ≤ 3), shows that they all belong to the same structural ‘KNbW’-type and not to the ‘KVW’-type. These results demonstrate the great flexibility of the ‘KNbW’ structure with regard to the ‘KVW’-structure only observed for one compound.