Disodium molybdenum dioxide diarsenate, Na2MoO2As2O7, has been synthesized by a solid-state reaction. The structure is built up from MoAs2O12 linear units sharing corners to form a three-dimensional framework containing tunnels running along the a-axis direction in which the Na+ cations are located. In this framework, the AsV atoms are tetra­hedrally coordinated and form an As2O7 group. The MoVI atom is displaced from the center of an octa­hedron of O atoms. Two Na+ cations are disordered about inversion centres. Structural relationships between different compounds: A 2MoO2As2O7 (A = K, Rb), AMOP2O7 (A = Na, K, Rb; M = Mo, Nb) and MoP2O7 are discussed.

A 30-month-old male infant presented with sacrococcygeal and pre-sacral mass. Ultrasound (US) abdomen revealed a huge pre-sacral mass with irregular margins extending into the pelvis, pushing the rectum antero-laterally. CT scan and MRI confirmed the US findings. Serum alpha fetoprotein level was abnormally elevated. Histopathological examination of surgical-specimen suggested sacrococcygeal yolk sac tumor (YST).

The asymmetric unit of the title compound, Na2(MoO2)3(As2O7)2, is composed of two cyclic MoAs2O11 units and an MoO6 corner-sharing octa­hedron. The anionic framework can be decomposed into two types of layers, viz. MoO2As2O7 and Mo2As2O14, which use mixed Mo—O—As and As—O—Mo bridges to achieve a new three-dimensional structure with two types of large channels in which the Na+ cations are located. Two O atoms are disordered and are located in two positions close to their initial positions with occupancy ratios of 0.612 (17):0.388 (17) and 0.703 (12):0.298 (12).