Characterization of Deformational Isomerization Potential and Interconversion Dynamics with Ultrafast X-ray Solution...

Area of Science:

• Inorganic Chemistry
• Physical Chemistry
• Computational Chemistry

Background:

• Dimeric complexes with d8 square planar metal centers and rigid bridging ligands serve as models for understanding dispersion forces and steric strain.
• The [Ir2(dimen)4]2+ complex (dimen = para-diisocyanomenthane) exhibits two ground state deformational isomers due to structural distortions counteracting attractive forces.

Purpose of the Study:

• To investigate the equilibrium distribution and exchange dynamics between the two ground state deformational isomers of the [Ir2(dimen)4]2+ complex.
• To provide a critical test for density functional approximations in modeling bridged d8-d8 metal complexes.

Main Methods:

• Ultrafast X-ray solution scattering (XSS) and optical transient absorption spectroscopy (OTAS) were employed to probe isomer dynamics.
• Selective photoexcitation of individual isomers using femtosecond visible light pulses.

Main Results:

• Distinct electronic excitations allowed for selective excitation and tracking of ground state population dynamics.
• Restoration of ground state equilibrium was observed within 2.3 picoseconds.
• Density functional theory calculations accurately reproduced experimental observations when dispersion interactions were included and a hybrid functional was used.

Conclusions:

• The study elucidates the interplay of dispersion forces and steric strain in dictating the structure of metal dimer complexes.
• Ultrafast spectroscopy provides powerful insights into the dynamics of isomer interconversion.
• Hybrid density functional theory with dispersion corrections is effective for modeling such d8-d8 metal complexes.