Tetra­methyl­ammonium pentaborate 0.25‐hydrate

The title compound, tetramethylammonium 4,4′,6,6′‐tetrahydroxy‐2,2′‐spirobi(cyclotriboroxane) 0.25‐hydrate, C₄H₁₂N⁺·B₅H₄O₁₀⁻·0.25H₂O, was synthesized under mild solvothermal conditions. The B₅O₆(OH)₄⁻ clusters are connected by strong hydrogen‐bonding interactions into a three‐dimensional structure containing rectangular channels along the a axis, in which the C₄H₁₂N⁺ ions and water mol­ecules are located.