Na3Co2(As0.52P0.48)O4(As0.95P0.05)2O7.
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 octa-hedra and X22O7 groups. These units form layers perpendicular to [010]. Co2O6 octa-hedra and X1O4 (X1 = As0.54P0.46) tetra-hedra 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 Co(2+) 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.
Laboratoire de Matériaux et Cristallochimie, Faculté des Sciences de Tunis, Université de Tunis ElManar, 2092 Manar II Tunis, Tunisia.
Youssef
Y
Ben Smida
Laboratoire de Matériaux et Cristallochimie, Faculté des Sciences de Tunis, Université de Tunis ElManar, 2092 Manar II Tunis, Tunisia.
Abderrahmen
A
Guesmi
Laboratoire de Matériaux et Cristallochimie, Faculté des Sciences de Tunis, Université de Tunis ElManar, 2092 Manar II Tunis, Tunisia.
Mohamed Faouzi
MF
Zid
Laboratoire de Matériaux et Cristallochimie, Faculté des Sciences de Tunis, Université de Tunis ElManar, 2092 Manar II Tunis, Tunisia.
Ahmed
A
Driss