Application of ‘molecular’ theories to the structure of the crystalline state
Recent years have seen the development of simple molecular orbital based ideas to view the structures of molecular ring, cage and cluster compounds. The principles of these methods are used here to demonstrate in a new way how the structures of solids depend on electronic configuration.
Pyrite, marcasite, and arsenopyrite type minerals: Crystal chemical and structural principles
Quantitative molecular orbital (MO) calculations and qualitative perturbational MO arguments are used to interpret the spectra and structure of transition metal dichalcogenides and related compounds. Competition between pyrite (FeS2), marcasite (FeS2) and loellingite (FeAs2) structure types is explained in terms of the number of electrons occupying a set of MO's obtained from the mixing of dianion (A2) orbitals and metal (M) dσ orbitals. Direct metal-metal d orbital interaction is argued to be small. Attention is focused upon the M - A - M angles which differ substantially among the three structure types as a consequence of varying numbers of electrons in orbitals which closely resemble the pπ* orbitals of the dianions. Variations in M - A and A - A distances can also be understood in terms of the occupations of this set of MO's. Disulfide valence region photo-emission spectra are interpreted in terms of calculations on MS6 and S6 molecular clusters. M3d orbitals are found to progressively approach the S3p orbitals with increasing atomic number of M from Fe to Ni. For CuS2 comparison of calculation and experiment supports an approximate electron configuration of Cu+1 S2−1.
The intermediate dicarba-nido-boranes
Abstract