A full understanding of the nature of excited states of transition metal complexes is important for understanding their chemical reactivity and role as intermediates in photochemically induced reactions. The ground and excited states of the [Pt(2)(pop)(4)](4-) ion are investigated using density functional theory (DFT). Calculations with different functionals employing quasi-relativistic Pauli and ZORA formalisms all predict a Pt-Pt bond shortening and a slight Pt-P lengthening upon excitation to the lowest triplet state, the latter in apparent contradiction to experimental EXAFS results. The PW86LYP functional with the ZORA relativistic treatment is found to produce good agreement with time-resolved crystallographic and spectroscopic results. A topological bond path between the Pt atoms is found in both the ground and the excited states, though the electron localization function (ELF) indicates weak Pt-Pt covalent bonding for the excited state only. The spin density is mainly localized on the Pt atoms, giving insight into the ability of the triplet excited state to abstract hydrogen and halogen atoms from organic substrates.
The nature of the ground state and the lowest triplet excited state of the [Rh(2)(1,3-diisocyanopropane)(4)](2+) ion have been investigated by the density functional theory. Two locally stable geometrical conformations are found on the potential energy surfaces of both the ground and excited states, corresponding to the eclipsed and twisted conformations, the eclipsed conformation being more stable and having the shorter Rh-Rh bond length. While the Rh-Rh distances of the two conformations differ by approximately 0.4 A, they shorten to the same value upon excitation ( approximately 3.1 A). The excited state originates from the d(z)()()2 (metal antibonding) to p(z)() (ligand-metal bonding) electronic transition. The Mayer Rh-Rh bond order increases from approximately 0.2 to more than 0.8 upon excitation, while the Rh-C(N) bond order shows a slight decrease. A topological bond path between the Rh atoms is found in both the ground and excited states, while the electron localization function (ELF) indicates weak Rh-Rh covalent bonding for the excited state only.
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