Na(3)Co(2)(As(0.52)P(0.48))O(4)(As(0.95)P(0.05))(2)O(7)

The title compound, trisodium dicobalt(II) (arsenate/phosphate) (diarsenate/diphosphate), was prepared by a solid-state reaction. It is isostructural with Na(3)Co(2)AsO(4)As(2)O(7). The framework shows the presence of CoX2(2)O(12) (X2 is statistically disordered with As(0.95)P(0.05)) units formed by sharing corners between Co1O(6) octa­hedra and X2(2)O(7) groups. These units form layers perpendicular to [010]. Co2O(6) octa­hedra and X1O(4) (X1 = As(0.54)P(0.46)) tetra­hedra form Co2X1O(8) chains parallel to [001]. Cohesion between layers and chains is ensured by the X2(2)O(7) 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 K(2)CdP(2)O(7), α-NaTiP(2)O(7) and K(2)MoO(2)P(2)O(7) 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.