Electronic shell structure in monoxides and dioxides of sodium

Abstract

Metal–metal bonding interactions are important for the structure and properties of sodium-rich monoxide and dioxide clusters Na_nO, Na_nO₂n⩽10. DFT calculations show that such bonding is due to occupied molecular orbitals of mostly Na:3s character and provide evidence that these orbitals resemble the 1s, 1p electronic shells of pure metal clusters. Calculated properties of the sodium oxides (ionisation potential and sodium abstraction energy) follow those of pure sodium clusters in both magnitude and overall trend. Structural anomalies can also be explained by the electronic shell model, as illustrated with clusters possessing four ‘metallic’ electrons (1s²1p²). Singlets show Jahn–Teller distortion to prolate shapes; triplets distort to become oblate. In addition, the shell model rationalises the stereoelectronic conditions for the metal-to-peroxide electron transfer which leads to O–O cleavage.