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SrO2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr is bonded in a distorted q4 geometry to ten equivalent O atoms. There are eight shorter (2.64 Å) and two longer (2.66 Å) Sr–O bond lengths. O is bonded to five equivalent Sr and one O atom to form a mixture of distorted edge, corner, and face-sharing OSr5O pentagonal pyramids. The O–O bond length is 1.51 Å.
Three competing bonding mechanisms have been identified for the alkaline-earth metal superoxides: these result in a change in the optimal structure and ground state as the alkaline-earth metal becomes heavier. For example, BeO2 has a linear 3Sigma(-)g ground-state structure, whereas both CaO2 and SrO2 have C(2v)1A1 structures. For MgO2, the theoretical calculations are less definitive, as the 3A2 C(2v) structure is computed to lie only about 3 kcal/mol above the 3Sigma(-)g linear structure. The bond dissociation energies for the alkaline-earth metal superoxides have been computed using extensive Gaussian basis sets and treating electron correlation at the modified coupled-pair functional or coupled-cluster singles and doubles level with a perturbational estimate of the triple excitations.