Unprecedented 2-D hydrated proton encapsulated in supramolecular framework built of [Mo3O4(C2O4)(H2O)3]2−

The unprecedented 2-D hydrated proton consisting of the fused H+(H2O)18 ring has been found in Et4N · H+(H2O)8 · [Mo3O4(C2O4)3(H2O)3] (1). The proton has been found to be located around the disordered three-connected nodes of the water sheet as revealed by the unusually short O⋯H+⋯O bonds. The protonated water layer is supported by the H-bonds between the ring water molecules and the host framework constructed from the triangular trimolybdenum(IV) cluster dianion, [Mo3O4(C2O4)3(H2O)3]2−.