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CaO2 is Calaverite structured and crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one CaO2 sheet oriented in the (0, 0, 1) direction. Ca is bonded to six equivalent O atoms to form distorted edge-sharing CaO6 octahedra. All Ca–O bond lengths are 2.36 Å. O is bonded in a trigonal non-coplanar geometry to three equivalent Ca atoms.
The vibrational frequencies of several states of CaO2, ScO2, and TiO2 are computed at using density functional theory (DFT), the Hatree-Fock approach, second order Moller-Plesset perturbation theory (MP2), and the complete-active-space self-consistent-field theory. Three different functionals are used in the DFT calculations, including two hybrid functionals. The coupled cluster singles and doubles approach including the effect of unlinked triples, determined using perturbation theory, is applied to selected states. The Becke-Perdew 86 functional appears to be the cost effective method of choice, although even this functional does not perform well for one state of CaO2. The MP2 approach is significantly inferior to the DFT approaches.
CaO2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ca is bonded in a distorted q4 geometry to ten equivalent O atoms. There are eight shorter (2.45 Å) and two longer (2.74 Å) Ca–O bond lengths. O is bonded in a 6-coordinate geometry to five equivalent Ca and one O atom. The O–O bond length is 1.52 Å.
CaO2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ca is bonded in a body-centered cubic geometry to eight equivalent O atoms. There are six shorter (2.42 Å) and two longer (2.45 Å) Ca–O bond lengths. O is bonded to four equivalent Ca atoms to form a mixture of edge and corner-sharing OCa4 tetrahedra.
CaO2 is Fluorite-like structured and crystallizes in the monoclinic C2 space group. The structure is three-dimensional. there are two inequivalent Ca sites. In the first Ca site, Ca is bonded in a body-centered cubic geometry to eight O atoms. There are a spread of Ca–O bond distances ranging from 2.39–2.46 Å. In the second Ca site, Ca is bonded in a body-centered cubic geometry to eight O atoms. There are a spread of Ca–O bond distances ranging from 2.38–2.46 Å. There are four inequivalent O sites. In the first O site, O is bonded to four Ca atoms to form a mixture of edge and corner-sharing OCa4 tetrahedra. In the second O site, O is bonded to four Ca atoms to form a mixture of edge and corner-sharing OCa4 tetrahedra. In the third O site, O is bonded to four Ca atoms to form a mixture of edge and corner-sharing OCa4 tetrahedra. In the fourth O site, O is bonded to four Ca atoms to form a mixture of edge and corner-sharing OCa4 tetrahedra.
CaCO3 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional and consists of four formaldehyde molecules and one CaO2 framework. In the CaO2 framework, Ca2+ is bonded in a distorted square co-planar geometry to four equivalent O2- atoms. There are two shorter (2.43 Å) and two longer (2.44 Å) Ca–O bond lengths. O2- is bonded in a 3-coordinate geometry to two equivalent Ca2+ and one O2- atom. The O–O bond length is 1.47 Å.
Efforts to prepare Ca(O2) sub 2 from reactions of calcium compounds with 100% O3 and with O(D-1) atoms generated by photolysis of O3 at 2537 A are described. Samples of Ca(OH) sub 2, CaO, CaO2, Ca metal, and mixtures containing suspected impurities to promote reaction have been treated with excess O3 under static and flow conditions in the presence and absence of UV irradiation. Studies with KO2 suggest that the superoxide anion is stable to radiation at 2537 A but reacts with oxygen atoms generated by the photolysis of O3 to form KO3. Calcium superoxide is expected to behave in an analogous.
A practical synthesis and a discussion of some chemical properties of pure strontium peroxide and calcium peroxide are presented. The general synthesis of these peroxides involves precipitation of their octahydrates by addition of H2O2 to aqueous ammoniacal Sr(NO3)2 or CaCl2. The octahydrates are converted to the anhydrous peroxides by various dehydration techniques. A new x-ray diffraction powder pattern for CaO2 x 8H2O is given from which lattice parameters a=6.212830 and c=11.0090 were calculated on the basis of the tetragonal crystal system.
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.