Intersystem Crossing in Diplatinum Complexes.
Intersystem crossing (ISC) in solid [(C4H9)4N]4[Pt2(μ-P2O5(BF2)2)4], abbreviated Pt(pop-BF2), is remarkably slow for a third-row transition metal complex, ranging from τISC≈ 0.9 ns at 310 K to τISC≈ 29 ns below 100 K. A classical model based on Boltzmann population of one temperature-independent and two thermally activated pathways was previously employed to account for the ISC rate behavior. An alternative we prefer is to treat Pt(pop-BF2) ISC quantum mechanically, using expressions for multiphonon radiationless transitions. Here we show that a two-channel model with physically plausible parameters can account for the observed ISC temperature dependence. In channel 1,1A2uintersystem crosses directly into3A2uusing a high energy B-F or P-O vibration as accepting mode, resulting in a temperature-independent ISC rate. In channel 2, ISC occurs via a deactivating state of triplet character (which then rapidly decays to3A2u), using Pt-Pt stretching (160 cm-1) as a distorting mode to provide the energy needed. Fitting indicates that the deactivating state,3X, is moderately displaced (S = 0.5-3) and blue-shifted (ΔE = 1420-2550 cm-1) from1A2u. Our model accounts for the experimental observation that ISC in both temperature independent and thermally activated channels is faster for Pt(pop) than for Pt(pop-BF2): in the temperature independent channel because O-H modes in the former more effectively accept than B-F modes in the latter, and in the thermally activated pathway because the energy gap to3X is larger in the latter complex.
Beckman Institute, California Institute of Technology , Pasadena, California 91125, United States.
Yan Choi
YC
Lam
Beckman Institute, California Institute of Technology , Pasadena, California 91125, United States.
Harry B
HB
Gray
Beckman Institute, California Institute of Technology , Pasadena, California 91125, United States.
Jay R
JR
Winkler