Electronic structures of solids from a simple viewpoint: some structures derived from the cesium chloride arrangement

Abstract

Molecular-orbital techniques well established in the theoretical analyses of the electronic structures of molecules are used to study the structures of some solid-state systems. By analogy with four-coordinate molecules, the CsC1 structure, shown to be stable for eight electrons per AX unit, is found to be potentially unstable for the ten-electron case and a distortion may result (e.g. to red PbO). The tendency to distort increases with the AX electronegativity difference. In molecular-orbital language the central atom of the CsCI structure is isolobal with a regular tetrahedron of atoms and the electronic structure of an MA 4 species, where a tetrahedron is placed inside a primitive cubic cell, is examined. A stuffed tetrahedron behaves analogously and the cuprite structure results. The site preferences in this structure are found to be dependent on the total electron count. The CaB 6 structure is approached in a similar way and the possibility of defect structures investigated.

Isoelectronic and isolobal O, CH2, CH3+and BH3as electron pairs; similarities between molecular and solid-state chemistry

“…The structure of SF 4 obtained at 152.2 K by Mootz & Korte (1984) exhibits positional disorder of the F atoms, but one of the present conformations agrees with the square-pyramidal conformer suggested by Burdett & Lin (1981) and drawn in Fig. 4.…”

“…Both moieties, SF 4 and [PbO 4 ] 6À are isoelectronic, isolobal and isostructural in spite of their molecular or extended solid character, respectively (Burdett & Lin, 1981, 1982. The structures are represented in Fig.…”

“…For example, explicitly bridging the molecular and solid-state sciences are the related 'molecular unit-cell approach' (Messmer et al, 1972;Messmer & Watkins, 1973) and the 'small-periodic cluster technique' (Zunger, 1974a(Zunger, ,b, 1975. Particularly evocative studies using the 'fragment formalism' are Burdett & Lin (1981, 1982 wherein bands and bonds, VSEPR models and MO pictures, molecules, parts of molecules, and 'infinite' crystals comfortably and indeed synergistically and symbiotically coexist.…”

Isoelectronic and isolobal O, CH2, CH3+and BH3as electron pairs; similarities between molecular and solid-state chemistry

“…The structure of SF 4 obtained at 152.2 K by Mootz & Korte (1984) exhibits positional disorder of the F atoms, but one of the present conformations agrees with the square-pyramidal conformer suggested by Burdett & Lin (1981) and drawn in Fig. 4.…”

“…The molecule SF 4 (34 electrons in the valence shell) (Mootz & Korte, 1984) and the isoelectronic [PbO 4 ] 6À fragment separated from the red PbO structure (Moore & Pauling, 1941), provide a nice example of the small-periodic cluster technique (Zunger, 1974a(Zunger, ,b, 1975. Both moieties, SF 4 and [PbO 4 ] 6À are isoelectronic, isolobal and isostructural in spite of their molecular or extended solid character, respectively (Burdett & Lin, 1981, 1982. The structures are represented in Fig.…”