Computational inorganic chemistry : unriddling the periodic table

Abstract

This dissertation aims to showcase some applications of ab initio quantum chem- istry as a relatively new entrant to computational inorganic chemistry. In the first application, the equilibrium bond lengths, harmonic vibrational frequencies, and dissociation energies of the ground state homonuclear 3d transition-metal diatomics (scandium through copper) were determined using six density functional or hybrid Hartree-Fock/density functional methods and unrestricted Hartree-Fock theory. Results are compared to other theoretical studies and to experimental values when available. The accuracy of the DFT results is found to be highly dependent upon the functional employed, with the pure DFT methods, BLYP and BP86, often performing signifcantly better than the hybrid HF/DFT methods. For the van der Waals complex Mn2, all six functionals predict the ground state to be high-spin, disagreeing with experiment; the true (antiferromagnetic) ground state was not found for any functional. No functional gives results directly comparable for all nine species. Dissociation energy results are severely overestimated in many instances and negative in others. Anecdotal reports of success for density functional theory for these systems may have been overblown.|In the second application, the group 13 - group 16 chalcogen heterocubanes [RM(?3-E)]4 (R = H, CH3; M = Al, Ga, In; E = O, S, Se, Te) and group 13 - group 13 pure cubanes [RM(?3-M)]4 (R = F, Cl, CH3, NO2; M = Al, Ga, In) have been studied using density functional theory. Geometries and thermodynamic properties were computed at the B3LYP/SRLC level. All structures were found to be true minima with at most 0.08 A and 2.5? deviation from experiment. These chalcogen heterocubanes appear thermodynamically resistant to fragmentation. The M4E4 core for each structure proved to be insensitive to ligand choice for the group 13 - group 16 heterocubanes. By contrast, the electron deficient M8 cores of the pure cubanes were variously affected by the electronegativity of various R groups. The entropically disfavored nature of the synthesis may hold the key to the as-yet- unsynthesized [RAl(?3-O)]4.