Novel Approach to Environmental Domain and Effects on Electronic Structures and Spectra of Complexes Containing Heavy Elements: Theory and Applications




Trevino, Amanda

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Ab initio electronic structure theory using spin-orbit configuration interaction method is applied in the study of spectral transitions in platinum and rhenium complexes. Environmental domain effects on electronic spectra are investigated for charged gas phase complexes, a point-charge-neutralized complexes, and a pseudopotential-neutralized complexes. The whole ion effective core potentials were developed as nodeless valence spinors from first principles. It is seen that the use of whole-atom relativistic effective core potentials to approximate the environmental domain provides the most accurate picture of the electronic structure of charged complexes without increasing the complexity of the calculation and its computational demand. The incorporation of relativistic effects is requisite with heavy atom containing complexes and is accomplished using the spin-orbit configuration interaction (SOCI) method, which ensures that their electronic wave functions are eigenfunctions of the total angular momentum operator defined as one of the irreducible representations of the molecular double group. Such wave functions describe electronic-nuclear motion in an intermediate angular momentum coupling scheme that is a combination of Hund's coupling cases a, b, and c. Specific effects on electronic spectra are investigated as a function of ligand type and chemical environment. Ligands for the platinum complexes were chosen to provide a spectrochemical set to gain insight into trends seen in spin-orbit splitting patterns . In depth spin-orbit analysis of tetrachloroplatinate (II) demonstrated spin-orbit splitting of the first 2 sets of A2', B1', and B2' to be 4.683 meV and 34.450 meV for the dianionic, 20.729 meV and 16.550 meV for the proton neutralized, and 0.807 meV and 25.329 meV for the K+ RECP neutralized tetrachloroplatinate (II) complex. This was the first demonstration of a relativistic ab initio approach including a rigorous spin-orbit coupling treatment while incorporating environmental neutralization techniques for a complex of this size. Whole ion RECPs were developed as a method of environmental neutralization and exhibited utility in improving electronic structure calculations at various levels of theory. Within the PtCl4-2 complex, incorporation of the whole ion K+RECP improved transition energies at B3LYP, ROHF, CASSCF, and CISD levels of theory. Stabilizing polarization effects from the incorporated K+RECP were evidenced in Mulliken charge distributions for each tetrachloroplatinate (II) system. Utility was also well demonstrated in the tetrakis(thiocyanato-N)-platinate (II) complex with similar trends in transition energies and Mulliken charge distribution.


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computational chemistry, electronic structure, relativistic ab initio methods, relativistic effective core potentials, spin-orbit coupling