The crystal structure of oxonium neodymium bis(sulfate), (H(3)O)Nd(SO(4))(2), shows a two-dimensional layered framework assembled from SO(4) tetrahedra and NdO(9) tricapped trigonal prisms. One independent sulfate group makes four S-O-Nd linkages, while the other makes five such connections to generate an unprecedented anhydrous anionic [Nd(SO(4))(2)](-) layer. To achieve charge balance, H(3)O(+) cations are inserted between adjacent layers where they participate in hydrogen-bonding interactions with the sulfate O atoms of adjacent layers.