J. Chardon

BaV2P2O10, a new tetravalent vanadium phosphate with a tunnel structure

Abstract A new vanadium (IV) phosphate, BaV2P2O10, with a tunnel structure has been isolated. Its structure was solved by single crystal X-ray diffraction. It crystallizes in the monoclinic system with the space group P21c. The cell parameters are a = 5.2204(3), b = 9.1702(7), c = 16.3247(9)A; β = 92.757(5)°; V = 780.6(3)A3; Z = 4; Dm= 3.93(6); Dx = 3.92; R = 0.031 and Rw = 0.035 for 4039 unique reflections with I > 3σ(I). The three-dimensional framework [V2P2O10∞ can be described as the assemblage of [P2VO9 rows formed of VO5 pyramids and PO4 tetrahedra, linked to each other through VO6 octahedra. The existence of [V2O10 units involving one VO5 pyramid and one VO6 octahedron, already observed in other V(IV) phosphates is also considered, as well as the existence of [V2P2O14 units corresponding to the association of one [V2O10 unit with two PO4 tetrahedra and which allow the whole structure to be described. This host lattice delimits large elliptic tunnels running along a where double rows of barium cations are located. The particular coordination of vanadium (IV), which corresponds to the existence of vanadyl ion as well in VO5 pyramids, as in VO6 octahedra (coordination “5 + 1”) is emphasized.

A mixed valent Keggin polyoxometallate involving molybdenum and tungsten

Abstract A new mixed valent “Mo-W” polyoxometallate K 6 Mo 3 W 9 PO 40 . 13H 2 O has been synthesized in the form of single crystals. The structure determination of this cubic phase (a=21.381 A) shows that it is isotypic to K 5.5 Na 1.5 PW 10 Cu 2 (H 2 O) 2 O 38 . 13H 2 O The two structures differ by the nature of the ligands that form the Keggin units “PMo 3 W 9 O 40 ” and “PW 10 Cu 2 (H 2 O) 2 O 38 ” respectively and by the stoichiometry and distribution of the alcaline cations located outside the Keggin units.

(Tl, Bi) Sr2CaCu2O7 “1212” superconducting single crystal A structural and magnetic study

Single crystals of Tl23Bi13Sr2CaCu2O7 with Tc = 86 K have been grown and their structure has been refined from a single crystal X-ray diffraction study in the space group P4/mmm with a = 3.7922 (6) A and c = 12.0661 (25) A. The structure of this oxide is very similar to those of (Tl, Pb)Sr2CaCu2O7 and TlSr2CaCu2O7. Nevertheless, the oxygen O(3) at the level of the thallium layer is found to be in a xx0 site which is unusual for such compounds. The superconducting properties have been studied by performing magnetic measurements in the H‖c geometry. The critical current densities have been extracted and the JcH = 0(t) have been found to be similar to those of Tl0.5Pb0.5Sr2CaCu2O7. The comparison of the irreversibility line location for the (Tl, Bi)-1212 with those of other 1212 thallium crystals supports the model which predicts that, in this series, the H∗(t) location depends essentially on the thickness of the rock salt type layer and is not greatly affected by the presence of Bi or Pb in the TlO layer.

Self-Association Of Benzene-1,3,5-Tris-(Methylenephosphonic Acid): Evidence of Charge-Assisted Hydrogen Bonds

The synthesis and the solid-state structure of benzene-tris-(methylene-phosphonic acid) is reported in the following article. Surprisingly the three methylenephosphonic acid groups are located on the same side of the benzene ring leading to the formation of an octopus shaped molecule. Furthermore the number of proton per phosphonic acid function is different from the expected value of two per phosphophonic acid function. The single crystal X-ray diffraction reveals that this interesting behaviour arises from the formation of a dimer in the solid-state. Interestingly both charge-assisted hydrogen bonds and hydrogen bonds are observed in this dimer.

A cadmium vanadophosphate built up from rutile and HTB-TYPE ribbons: CdVO2(H2O)PO4

Abstract A new cadmium vanadophosphate, CdVO2(H2O)PO4 involving V(V), has been synthesized using hydrothermal technique. Its structure has been solved from a twinned crystal. It crystallizes in the space group P21 with a=5.3086(8), b=7.1465(9), c=7.6871(9) A, β=115.48(2)°. The framework is simple and original: it consists of rutile ribbons [CdO4]∞ and hexagonal tungsten bronze (HTB) ribbons [VO5]∞ running along b → , and forming six-sided tunnels. The rutile and HTB ribbons share the apices of their CdO5(H2O) and VO5(H2O) octahedra forming [CdVO6(H2O)]∞ layers parallel to b, c and interconnected through PO4 tetrahedra. The presence of H2O in this framework, in the form of rather strong Vue5f8H2Oue5f8Cd bonds, explains the great stability of this phosphate, which decomposes only above 300°C.

The niobium phosphate bronze β-K2Na2−xNb8P5O34, second form of the first member of the series (K3Nb6P4O26)n KNb2PO8

Abstract A new niobium phosphate bronze β-K2Na2−xNb8P5O34 has been isolated. Its structure was solved by single crystal X-ray diffraction for x = 0.27. It crystallizes in the space group P 4 m 2 with a = 10.612 (1) and c = 6.384 (1) A. This phase is the second form of the first member of the series (K3Nb6P4O26)n KNb2PO8. The structural relationships with the other members of this series and especially with K7Nb14P9O60 (n = 2) are discussed.

Nonstoichiometry in the LiMo2O3(PO4)2 structure: The molybdenotungsten monophosphate Li0.5MoWO3(PO4)2

A new molybdenotungsten monophosphate, Li0.5MoWO3(PO4)2 has been synthesized that crystallizes in the space group P21/m with a = 7.735(1) A, b = 12.655(1) A, c = 8.324(1) A, b = 105.97(1) °. The [MoWP2O11]∞ framework is isotypic with that previously observed for LiMo2O3(PO4)2, lithium being located in six-sided tunnels running along a with an octahedral coordination. This phase differs from LiMo2O3(PO4)2, by the absence of lithium in the tetrahedral sites, showing that a significant lithium nonstoichiometry is possible. The stability is discussed with respect to other lithium monophosphates LiMoWO2(PO4)2 and Li0.2Mo2O3(PO4)2 that have different original structures.

New molybdeno-and tungstodiphosphates with the (NH4)2MoO2P2O7 chain-like structure

Abstract Three diphosphates of Mo(VI), A 2 MoO 2 P 2 O 7 with A = K, Rb and W(VI), K 2 WO 2 P 2 O 7 have been synthesized. These phosphates crystallize in the space group C2/c and are isotypic with the chain-like structure (NH 4 ) 2 MoO 2 P 2 O 7 . The single crystal X-ray structure determination performed on the tungsten diphosphate K 2 WO 2 P 2 O 7 shows that the geometry of its [WP 2 O 9 ] ∞ chains is practically identical to that observed for (NH 4 ) 2 MoO 2 P 2 O 7 : the nature of the M elements (M = Mo, W) and of the A site cation (K, Rb or NH 4 ) does not influence the interatomic distances.