Na3Co2(As0.52P0.48)O4(As0.95P0.05)2O7

Youssef Ben Smida,Abderrahmen Guesmi,Ahmed Driss,Mohamed Faouzi Zid

doi:10.1107/s1600536813032029

Youssef Ben Smida, Abderrahmen Guesmi + Show 2 more

Open Access

https://doi.org/10.1107/s1600536813032029

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Abstract

The title compound, trisodium dicobalt(II) (arsenate/phosphate) (diarsenate/diphosphate), was prepared by a solid-state reaction. It is isostructural with Na3Co2AsO4As2O7. The framework shows the presence of CoX22O12 (X2 is statistically disordered with As0.95P0.05) units formed by sharing corners between Co1O6 octahedra and X22O7 groups. These units form layers perpendicular to [010]. Co2O6 octahedra and X1O4 (X1 = As0.54P0.46) tetrahedra form Co2X1O8 chains parallel to [001]. Cohesion between layers and chains is ensured by the X22O7 groups, giving rise to a three-dimensional framework with broad tunnels, running along the a- and c-axis directions, in which the Na+ ions reside. The two Co2+ cations, the X1 site and three of the seven O atoms lie on special positions, with site symmetries 2 and m for the Co, m for the X1, and 2 and m (× 2) for the O sites. One of two Na atoms is disordered over three special positions [occupancy ratios 0.877 (10):0.110 (13):0.066 (9)] and the other is in a general position with full occupancy. A comparison between structures such as K2CdP2O7, α-NaTiP2O7 and K2MoO2P2O7 is made. The proposed structural model is supported by charge-distribution (CHARDI) analysis and bond-valence-sum (BVS) calculations. The distortion of the coordination polyhedra is analyzed by means of the effective coordination number.

Highlights

The title compound, trisodium dicobalt(II), was prepared by a solid-state reaction
The framework shows the presence of CoX22O12 (X2 is statistically disordered with As0.95P0.05) units formed by sharing corners between Co1O6 octahedra and X22O7 groups
Cohesion between layers and chains is ensured by the X22O7 groups, giving rise to a threedimensional framework with broad tunnels, running along the a- and c-axis directions, in which the Na+ ions reside

Summary

Data collection

Laboratoire de Matériaux et Cristallochimie, Faculté des Sciences de Tunis, Université de Tunis ElManar, 2092 Manar II Tunis, Tunisia. The title compound, trisodium dicobalt(II) (arsenate/phosphate) (diarsenate/diphosphate), was prepared by a solid-state reaction. The framework shows the presence of CoX22O12 (X2 is statistically disordered with As0.95P0.05) units formed by sharing corners between Co1O6 octahedra and X22O7 groups. These units form layers perpendicular to [010]. Na atoms is disordered over three special positions [occupancy ratios 0.877 (10):0.110 (13):0.066 (9)] and the other is in a general position with full occupancy. A comparison between structures such as K2CdP2O7, -NaTiP2O7 and K2MoO2P2O7 is made. The proposed structural model is supported by charge-distribution (CHARDI) analysis and bond-valencesum (BVS) calculations. The distortion of the coordination polyhedra is analyzed by means of the effective coordination number

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