Structural, theoretical and spectroscopic studies of the dichloride hexahydrate cube [Cl2(H2O)6]2-

The structure of the dichloride hexahydrate cube, [Cl-2(H2O)(6)](2-), as a salt with the tris(diisopropylamino)-cyclopropenium cation, [C-3((NPr2)-Pr-i)(3)](+), has been determined by low-temperature X-ray and neutron-diffraction studies. H atoms not involved in O-H center dot center dot center dot Cl bonding are disordered over two 0.5 occupancy sites around the O-6 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 O-6 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 O center dot center dot center dot O distances were found to decrease in the order difluoride > dichloride > dibromide > (H2O)(6) and as O center dot center dot center dot O center dot center dot center dot O angles increased towards an almost planar ring in (H2O)(6). NMR spectra of a chloroform solution of the hydrated salt at -25 degrees C is consistent with cluster formation.