ISSN:
0044-2313
Keywords:
Chromium(II, III)pyrophosphate
;
preparation
;
crystal structure
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Description / Table of Contents:
Contributions on the Thermal Behaviour of Anhydrous Phosphates. IX. Synthesis and Crystal Structure of Cr6(P2O7)4. A Pyrophosphate Containing Di- and Trivalent ChromiumCr6(P2O7)4 (Cr22+Cr43+(P2O7)4) can be obtained reducing CrPO4 by phosphorus (950°C, 48 h, 100 mg iodine as mineralizer). By means of chemical transport reactions (transport agent iodine; 1050 → 950°C) the compound has been separated from its neighbour phases (Cr2P2O7, CrP3O9) and crystallized (greenish, transparent crystals; edge length up to 0.3 mm). The crystal structure of Cr6(P2O7)4 (Spcgrp.: P-1; z = 1; a = 4.7128(8) Å, b = 12.667(3) Å, c = 7.843(2) Å, α = 89.65(2)°, β = 92.02(2)°, γ = 90.37(2) has been solved and refined from single crystal data (2713 unique reflections, 194 parameter, R = 0.035). Cr2+ is surrounded by six oxygen atoms which occupy the corners of an elongated octahedron (4 × dCr—O ≍ 2.04 Å; 2 × dCr—O ≍ 2.62 Å). The Cr3+ ions are also coordinated octahedraly (1.930 Å ≤ dCr—O ≤ 2.061 Å). The crystallographically independent pyrophosphate groups show nearly eclipsed conformation. The bridging angles (P—O—P) are 136.5° and 138.9° respectively.
Notes:
Cr6(P2O7)4 (Cr22+Cr43+(P2O7)4) entsteht bei der Reduktion von CrPO4 mit Phosphor (950°C, 48 h, 100 mg Iod als Mineralisator). Mittels chemischer Transportreaktionen (Transportmittel Iod; 1050→ 950°C) kann die Verbindung von Nachbarphasen (Cr2P2O7, CrP3O9) getrennt und kristallisiert werden (grünliche, transparente Kristalle; Kantenlänge bis 0,3 mm). Die Kristallstruktur von Cr6(P2O7), (RG.: P-1; z = 1; a = 4,7128(8) Å, b = 12,667(3) Å, c = 7,843(2) Å, α = 89,65(2)°), β = 92,02(2)°, γ = 90,37(2)°) wurde anhand von Einkristalldaten (2713 symmetrieunabhängige Reflexe, 194 freie Parameter, R-Wert: 3,5%) bestimmt und verfeinert. Cr2+ ist gestreckt oktaedrisch von Sauerstoff koordiniert (4×dCr-O ≍ 2,04 Å; 2×dCr-O ≍ 2,62 Å). Die Koordination der Cr3+-Ionen ist ebenfalls oktaedrisch (1,930 Å ≤ dCr-O, ≤ 2,061 Å). Die beiden symmetrieunabhängigen Pyrophosphatgruppen haben nahezu ekliptische Konformation, während die Winkel (P—O—P) 136,5° bzw. 138,9° betragen.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/zaac.19926161008
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