Evaluating chemical bonding in dioxides for the development of metal–oxygen batteries: vibrational spectroscopic trends of dioxygenyls, dioxygen, superoxides and peroxides

Dioxides (dioxygenyl (O2+), dioxygen (O2), superoxide (O2˙−) and peroxide (O22−)) are of immense biological, chemical and environmental importance. The ability to accurately detect and measure the changing strength of their chemical bonding and coordination in situ or operando is extremely beneficial in order to evaluate their chemical properties, this has been particularly important recently in the field of metal–oxygen batteries, where understanding the reactivity of the O2˙− intermediate is crucial in the development of more stable electrolytes. Meta-analysis of the collated vibrational Raman and IR spectral bands of numerous (>200) dioxygen species was used to interpret the effect that the immediate chemical environment has on the O–O bond. Subsequently, the dioxide vibrational spectral bands were empirically related directly with the bond electron density and other fundamental bond properties, with surprisingly high accuracy, allowing each property to be estimated, simply, from experimental spectroscopic observations. Important chemical information about the strength of secondary interactions between reduced oxygen species and its chemical environment can be also elucidated which provides a convenient method for determining the attractive strength an ion exerts over neighbouring counter ions.