Doppeloktaeder‐Cluster [V₂O₉] in der Kristallstruktur von Vanadium(III)‐diphosphat, V₄(P₂O₇)₃

Abstract

Als erstes Beispiel für MIII‐Diphosphate wurde an Einkristallen rötgeno‐graphisch die Kristallstruktur von V4(P2O7)3 („I”︁) bestimmt (Diskrepanz‐Index R = 0,094). I – nach [7] herstellbar durch thermische Umsetzung von V2O5, H3PO3 und H3PO4 – kristallisiert orthorhombisch mit a = 7,443(1), b = 9,560(2), c = 21,347(4) Å; V = 1518,9 Å3, Raumgruppe Pmcn (D 2h16; No. 62); Z = 4; Dx = 3,17 g cm−1. Im Gitter sind zwei Arten von isolierten Doppel‐oktaedern (Clustern) [V2O9] der Symmetrie Cs vorhanden. Infolge einer Flächen‐Verknüpfung der Oktaeder resultieren innerhalb der Cluster relativ kurze V–V‐Abstände von 2,774(8) und 3,026(7) Å. Die Diphosphat‐Anionen O3POPO34− (drei Arten; Symmetrie jeweils Cs; Konformation jeweils gestaffelt), haben für Nicht‐Zentrosymmetrie bemerkenswert große POP‐Brückenbindungswinkel von 170°. Wegen der [M2IIIO9]‐Cluster in I ‐ und auch in den isostrukturellen Diphosphaten Cr4(P2O7)3 und Fe4(P2O7)3 – erscheinen magnetische Untersuchungen angebracht.

Crystal Structures and Low-Dimensional Ferromagnetism of Sodium Nickel Phosphates Na5Ni2(PO4)3·H2O and Na6Ni2(PO4)3OH

“…The formation of face-sharing bioctahedral M 2 O 9 units has been previously observed for nickel orthophosphates and pyrophosphates K 2 NiP 2 O 7 and Na 4 Ni 5 (PO 4 ) 2 (P 2 O 7 ) 2 , though this feature is more common for vanadium polyanion compounds, such as K 11 V 15 P 18 O 73 , V 3 P 4 SiO 19 , V 4 (P 2 O 7 ) 3 , and complex ruthenium and iridium oxides, such as Ba 5 M 3– x Al x O 11 . , Fragments consisting of a NiO 6 octahedron sharing edge with PO 4 tetrahedron can be found in many nickel phosphates, for example, Na 4 Ni 7 (PO 4 ) 6 , Ni 3 (PO 4 ) 2 , and NH 4 NiPO 4 ·H 2 O…”

Crystal Structure, Magnetic Properties, and Ionic Conductivity of a New Mixed-Anion Phosphate Na4Ni5(PO4)2(P2O7)2

“…a U(eq) is defined as one-third of the trace of the orthogonal Uij tensor. It is remarkable that the M 2 O 9 units of face-sharing octahedra are also present in K 11 V 15 P 18 O 73 , 26 V 3 P 4 -SiO 19 , 27 V 4 P 6 O 21 , 28 and SrFe 3 (PO 4 ) 3 (HPO 4 ), 29 and NiPO 8 units of an octahedron edge-sharing with a tetrahedron have been previously observed in other nickel phosphates as Na 4 Ni 7 (PO 4 ) 6 , 18 Ni 3 (PO 4 ) 2 ‚H 2 O, 30 and NH 4 -NiPO 4 H 2 O. 31 It is worth noting that this structure is quite similar to that of Na 4 Co 3 (PO 4 ) 2 (P 2 O 7 ).…”

Hydrated Iron Phosphates FePO[sub 4]⋅nH[sub 2]O and Fe[sub 4](P[sub 2]O[sub 7])[sub 3]⋅nH[sub 2]O as 3 V Positive Electrodes in Rechargeable Lithium Batteries

“…20 For the present study, we used as the pristine material an amorphous powder of Fe 4 (P 2 O 7 ) 3 •4H 2 O ͑Aldrich͒ whose total surface calculated by BET was of 5 m 2 g Ϫ1 and which, on annealing up to 900°C, led to pure and well-crystallized Fe 4 (P 2 O 7 ) 3 particles, isostructural with V 4 (P 2 O 7 ) 3 . 15 The general trends described in the previous sections for the electrochemical behavior of FePO 4 •nH 2 O apply for Fe 4 (P 2 O 7 ) 3 •nH 2 O as well: ͑i͒ the electrochemical reactivity with Li is much improved through ballmilling of the active material with conductive carbon, as seen in Fig. 14 3 •4H 2 O powder, departure of water, and then particle growth and crystallization occur that lead to a solid with much less electrochemical activity than for the pristine powder ͑compare Fig.…”