Optical Spectroscopic Studies of Square Planar d⁸ Dimers

Citation

Rice, Steven Frederick (1982) Optical Spectroscopic Studies of Square Planar d⁸ Dimers. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z2CJ-J714. https://resolver.caltech.edu/CaltechETD:etd-03102005-155606

Abstract

The single crystal polarized absorption spectra of rhodium(I) diisocyanide dimers presented confirm the assignment of Mann and Gray for the intense visible absorption band as ¹A_1g → ¹A_2u. The structured ¹A_1g → ³A_2u absorption band in RH₂(b)₄(Bph₄)₂ shows the ³A_2u excited state to have a metal-metal vibrational frequency of 149 cm^-1. This is compared to the 85 cm^-1 ground state frequency which results in the orbital assignment of this transition as d _z^2σ* → p_zσ. The excited state has an internuclear bond distance .31 Å shorter than that of the ground state. The bonding description obtained through the analysis of the spectra depicts a ground state that is formally nonbonding stabilized through configurational interaction with a low lying, strongly bonded excited state.

The ³A_2u state in these dimers has a pronounced phosphorescence with a 77K lifetime of 20 μsec. The quantum yields and lifetimes are very temperature sensitive with several 300K lifetimes of about 10 nsec. This temperature dependence, characteristic of a strong coupling limit, is interpreted in terms of a nonradiative pathway depopulating the ³A_2u through another excited state associated with a d_z² → d_x²-y² transition.

A compound isoelectronic with these rhodium diisocyanides, Pt₂(H₂P₂O₅)^4-₄, is shown to have a similar metal-metal interaction in both the ground and lowest excited states. Recent results regarding the low temperature photophysics of this compound have been verified and extended through an analysis of the vibronically structured ³A_2u → ¹A_1g luminescence. The ³A_2u state is demonstrated to have an internuclear distance of 2.71 Å, .21 Å shorter than that of the ground state. The metal-metal vibrational frequency in the ³A_2u is 155 cm^-1, distinctly higher than the 110 cm^-1 of the ground state.

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