A. Leclaire

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.

K4MoV8P12O52, a tunnel structure characterized by an unusual valence of molybdenum

Abstract A new phosphate of molybdenum (V) K 4 Mo v 8 P 12 O 52 has been isolated and its structure solved from a single crystal X-ray diffraction study. It crystallizes in a monoclinic cell, space group C2–c , with the parameters a = 10.7433(16)A, b = 14.0839(9)A, c = 8.8519(7)A, and β = 126.42(1)°. After refinement of the different parameters, the reliability factors were lowered to R = 0.026 and w = 0.029. The framework “Mo 8 P 12 O 52 ” can be described as corner-sharing PO 4 tetrahedra, P 2 O 7 groups, and MoO 6 octahedra. Although the “O 6 ” octahedron surrounding the molybdenum ion is almost regular, the metal ion is strongly off center so that its coordination is better described as a MoO 5 pyramid. This particular coordination, which characterizes Mo(V), is discussed.

Redetermination of the β-Ca2P2O7 structure

β Dicalcium diphosphate is composed of eclipsed P 2 O 7 groups linked through Ca 2+ cations. The P-Ob bonds involving the bridging O atoms arelonger [average 1.620 (5) A] than the others [average 1.517 (5) A]. As the «O 4 » tetrahedra are almost regular the displacement of the P atoms involves two sets of O-P-O angles: O-P-O≃112.7 (2) and O-P-O b ≃106.0 (2) o

K2−xTi2(PO4)3 with 0 ≤ x ≤ 0.5: A mixed-valence nonstoichiometric titanophosphate with the langbeinite structure

A new nonstoichiometric titanophosphate, K2−xTi2(PO4)3, has been isolated for 0 ≤ x ≤ 0.5. This compound which belongs to the Langbeinite structure is characterized by a mixed valence of titanium TiIIITiIV. The structures of two compositions x = 0 and x = 0.25 have been determined from a single-crystal X-ray diffraction study. This cubic phase (a = 9.8559 A for x = 0.25, a = 9.8688 A for x = 0; space group P213) is compared to Nasicon NaxTi2(PO4)3. The evolution of the TiO distances and calculations of the mean oxidation state of titanium allow a distribution of the TiIII and TiIV ions on the two types of site to be proposed. The possibility of extending this structure to other univalent cations has been demonstrated with the synthesis of the isotypic compounds Rb2Ti2(PO4)3 and Tl2Ti2(PO4)3.

Two forms of sodium titanium(III) diphosphate: α-NaTiP2O7 closely related to β-cristobalite and β-NaTiP2O7 isotypic with NaFeP2O7

Abstract The structures of two new forms of a titanium(III) phosphate NaTiP2O7 have been determined. One of them, β-NaTiP2O7 [a = 7.394(1)A, b = 7.936(3)A, c = 9.726(3)A β = 11.85(2)° P2 1 c ], is isotypic with NaFeP2O7 which has been previously described. The other form, α-NaTiP2O7 [a = 8.697(1)A, b = 5.239(7)A, c = 13.293(3)A, β = 116.54(1)°, P2 1 c ], is found to be closely related to the structure of β-cristobalite and of carnegieite and is described as a “pseudo-hexagonal” framework characterized by intersecting tunnels.

TIMoIV2P3O12: A molybdenophosphate with a tunnel structure

A molybdenophosphate, TIMoIV2P3O12, with an original tunnel structure, has been isolated. Its structure has been determined by X-ray diffraction on a single crystal. It crystallizes in the orthorhombic system with a = 8.836(1), b = 9.225(1), c = 12.288(1), A, possible space groups Pbcm and Pbc21 with Z =4. The structure was solved and refined in the centrosymmetric space group Pbcm. The host lattice “Mo3P3O12” is built up from corner-sharing octahedra and tetrahedra and forms tunnels running along the b axis and cages where the Tl+ ions are located. The relationships of this framework with that of the phosphate tungsten bronze CsP8W8O40 and that of the hexagonal tungsten bronze are discussed.

Concerning the intersecting tunnel structure of a novel vanadyldiphosphate K2(VO)3(P2O7)2 and its structural relationships with other V(V) and V(IV) phosphates and relatives

K2V3P4O17, Mr = 626.91, orthorhombic, Pna21, a = 17.407(1), b = 11.3438(7), c = 7.2964(15), A, V = 1440.8(5), A3, Z = 4, Dx = 2.89 Mg m−3, λ(MoKα) = 0.71073, A, μ(MoKα) = 2.96 mm−1, F(000) = 1212, T = 293 K, R = 0.049, and Rw = 0.055 for 574 independent observed reflections with I ≥ 3σ(I). The host lattice [V3P4O17] is built up from corner-sharing VO6 octahedra, VO5 square pyramids, and PO4 tetrahedra. The structure can be described in terms of mixed chains [V2P8O30]∝ linked through [V2O10] units. The [V2P8O30]∞ chains are formed of ReO3-type chains connected to diphosphate groups whereas the [V2O10] units are formed from one corner-shared VO6 octahedron and one VO5 pyramid. The framework delimits intersecting tunnels running along c and b which suggest possible ion exchange properties. The ability of V(IV) to form a short vanadyl bond VO2+ is observed in all the vanadium polyhedra leading to the formula K2(VO)3(P2O7)2. A comparison of the structure with that of different V(IV) and V(V) phosphates and related compounds is carried out.

A new three-dimensional sodium molybdenum(V) hydroxymonophosphate: Na8(Mo2O4OH)3(PO4)3(PO3OH)·12.25H2O

A new sodium molybdenum(v) hydroxymonophosphate, Na8(Mo2O4OH)3(PO4)3(PO3OH)·12.25 H2O has been synthesized. It crystallizes in the monoclinic space group P21 /c with a=13.024(4), b=25.936(4), c=13.276(3) A, β=111.72(2)°. Its structure involves Na[Mo6P4O27(OH)4 ]2clusters similar to those encountered in several other molybdenum(v) hydroxyphosphates. Such clusters built up of two rings of six edge-sharing Mo octahedra interconnected through one NaO6 octahedron differ from those previously described by the fact that hydrogen is mainly connected to the Mo–O bond forming twelve Mo(O5OH) octahedra, whereas among the eight tetrahedra one observes two P(O3OH) tetrahedra and six PO4 tetrahedra. The originality of this structure deals with the fact that such clusters form with several sodium octahedra, Na(H2O)4O2 and Na(H2O)2O4 , a three-dimensional framework that delimits intersecting tunnels running along a, b and c. The coordination of other sodium cations and H2O molecules that can be considered as intercalated species is also discussed.

Two molybdenum diphosphates with a tunnel structure involving Mo(III): KMoP2O7 and K0.17MoP2O7

The structure of two novel molybdenum diphosphates KMoP2O7 and K0.17MoP2O7 has been determined. The trivalent molybdenum diphosphate KMoP2O7 is monoclinic with a = 7.375(1) A, b = 10.348(1) A, c = 8.351(2) A, β = 106.88(1)°, space group P21c, whereas the mixed valence Mo(III)Mo(IV) diphosphate K0.17MoP2O7 crystallizes in the tetragonal system with a = b = 21.278(2) A, c = 4.921(6) A, space group I41a. Both oxides have their mixed framework built up from [MoP2O11] units in which a P2O7 group shares two of its corners with the same octahedron. KMoP2O7 is isostructural with KFeP2O7 and CsMoP2O7 whereas K0.17MoP2O7 exhibits an original structure. Both oxides have a tunnel structure: heptagonal tunnels and smaller hexagonal running along [001] and [110], respectively, are observed in KMoP2O7, whereas very large tunnels formed of rings of eight polyhedra and running along [001] are present in K0.17MoP2O7.

A Mo(III) phosphate with a cage structure: NaMoP2O7

Abstract A new Mo(III) phosphate, NaMoP2O7, was synthesized and its structure determined from single-crystal X-ray data. This phosphate is isotypic with NaFeP2O7 and has the following parameters: a = 7.4195(3) A, b = 8.1084(4) A, c = 9.7598(4) A, β = 111.868(3)°, space group P2 1 c . The behavior of Mo(III) in this oxide is compared to that of Fe(III) in NaFeP2O7. The structure, described in terms of corner-sharing PO4 tetrahedra and MoO6 octahedra, is compared to other molybdenum phosphates which exhibit a mixed framework: MoP3SiO11, Mo4P6Si2O25, and AMo3P6Si2O25.