The single crystal of sodium manganese arsenate (1.72/3.28/12), Na(1.72)Mn(3.28)(AsO(4))(3), used for analysis was prepared by solid-state reaction at 1073 K. The compound crystallizes in the monoclinic system in space group C2/c. The structure consists of a complex network of edge-sharing MnO(6) octahedral chains, linked together by AsO(4) tetrahedra, forming two distinct channels, one containing Na(+) cations and the other occupied statistically by Mn(+) and Na(+) cations.