The structure of the dichloride hexahydrate cube, [Cl₂(H₂O)₆]²⁻, as a salt with the tris(diisopropylamino)cyclopropenium cation, [C₃(NⁱPr₂)₃]⁺, has been determined by low-temperature X-ray and neutron-diffraction studies. H atoms not involved in O–HCl bonding are disordered over two 0.5 occupancy sites around the O₆ ring. Calculations of the dianionic cube in the gas phase show remarkably good agreement with the solid-state structures with the exception of short O–H bond distances around the O₆ ring that suggests the involvement of a dynamic process. The cluster was also characterised by single-crystal infrared spectroscopy, and vibrational wavenumbers were found to be in good agreement with hydrogen bonding distances. Dibromide and difluoride hexahydrates were also studied theoretically, and OO distances were found to decrease in the order difluoride > dichloride > dibromide > (H₂O)₆ and as OOO angles increased towards an almost planar ring in (H₂O)₆. NMR spectra of a chloroform solution of the hydrated salt at −25 °C is consistent with cluster formation.