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 Co1O6octahedra andX22O7groups. These units form layers perpendicular to [010]. Co2O6octahedra andX1O4(X1 = As0.54P0.46) tetrahedra form Co2X1O8chains parallel to [001]. Cohesion between layers and chains is ensured by theX22O7groups, giving rise to a three-dimensional framework with broad tunnels, running along thea- andc-axis directions, in which the Na+ions reside. The two Co2+cations, theX1 site and three of the seven O atoms lie on special positions, with site symmetries 2 andmfor the Co,mfor theX1, and 2 andm(× 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-NaTiP2O7and K2MoO2P2O7is 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.