Spin-Orbit TDDFT Electronic Structure of Diplatinum(II,II) Complexes

[Pt_2(μ-P_2O_5H_2)_4]^(4–) (Pt(pop)) and its perfluoroborated derivative [Pt_2(μ-P_2O_5(BF_2)_2)_4]^(4–) (Pt(pop-BF_2)) are d^8–d^8 complexes whose electronic excited states can drive reductions and oxidations of relatively inert substrates. We performed spin–orbit (SO) TDDFT calculations on these complexes that account for their absorption spectra across the entire UV–vis spectral region. The complexes exhibit both fluorescence and phosphorescence attributable, respectively, to singlet and triplet excited states of dσ*pσ origin. These features are energetically isolated from each other (∼7000 cm^(–1) for (Pt(pop-BF_2)) as well as from higher-lying states (5800 cm^(–1)). The lowest ^3dσ*pσ state is split into three SO states by interactions with higher-lying singlet states with dπpσ and, to a lesser extent, pπpσ contributions. The spectroscopically allowed dσ*pσ SO state has ∼96% singlet character with small admixtures of higher triplets of partial dπpσ and pπpσ characters that also mix with 3dσ*pσ, resulting in a second-order ^1dσ*pσ–^3dσ*pσ SO interaction that facilitates intersystem crossing (ISC). All SO interactions involving the dσ*pσ states are weak because of large energy gaps to higher interacting states. The spectroscopically allowed dσ*pσ SO state is followed by a dense manifold of ligand-to-metal–metal charge transfer states, some with pπpσ (at lower energies) or dπpσ contributions (at higher energies). Spectroscopically active higher states are strongly spin-mixed. The electronic structure, state ordering, and relative energies are minimally perturbed when the calculation is performed at the optimized geometries of the ^1dσ*pσ and ^3dσ*pσ excited states (rather than the ground state). Results obtained for Pt(pop) are very similar, showing slightly smaller energy gaps and, possibly, an additional ^1dσ*pσ – ^3dσ*pσ second order SO interaction involving higher ^1dπpσ* states that could account in part for the much faster ISC. It also appears that ^1dσ*pσ → ^3dσ*pσ ISC requires a structural distortion that has a lower barrier for Pt(pop) than for the more rigid Pt(pop-BF_2)

Photochemical Route to Actinide-Transition Metal Bonds: Synthesis, Characterization and Reactivity of a Series of Thorium and Uranium Heterobimetallic Complexes

A series of actinide-transition metal heterobimetallics has been prepared, featuring thorium, uranium and cobalt. Complexes incorporating the binucleating ligand N[-(NHCH2PiPr2)C6H4]3 and Th(IV) (4) or U(IV) (5) with a carbonyl bridged [Co(CO)4]- unit were synthesized from the corresponding actinide chlorides (Th: 2; U: 3) and Na[Co(CO)4]. Irradiation of the isocarbonyls with ultraviolet light resulted in the formation of new species containing actinide-metal bonds in good yields (Th: 6; U: 7); this photolysis method provides a new approach to a relatively rare class of complexes. Characterization by single-crystal X-ray diffraction revealed that elimination of the bridging carbonyl is accompanied by coordination of a phosphine arm from the N4P3 ligand to the cobalt center. Additionally, actinide-cobalt bonds of 3.0771(5) and 3.0319(7) for the thorium and uranium complexes, respectively, were observed. The solution state behavior of the thorium complexes was evaluated using 1H, 1H-1H COSY, 31P and variable-temperature NMR spectroscopy. IR, UV-Vis/NIR, and variable-temperature magnetic susceptibility measurements are also reported