Abstract:
The evidence for the existence of metal complexes containing H<sub>3</sub>O<sup>+</sup> as a ligand in the solid state is examined. Each of the 68 examples in the Cambridge Structural Database in which H<sub>3</sub>O<sup>+</sup> is bound to a transition metal, lanthanoid, actinoid, or main group metal ion is detailed and critically appraised. It is concluded that none of the reported examples of complexes containing coordinated H<sub>3</sub>O<sup>+</sup> have been unequivocally characterized and that they result from either curation errors or misinterpretations of the crystallographic data. These conclusions are supported by computational techniques, which show that three purported H<sub>3</sub>O<sup>+</sup> complexes based on the 1,4,7,10,13,16,21,24-octa-azabicyclo(8.8.8)hexacosane azacryptand skeleton are better described as aqua complexes, with protonation occurring at the amine ligand.