Excited State Distortions in Ligand to Ligand Charge Transfer Excited States of Metal Diimine Dithiolate Mixed Ligand Complexes

Abstract

The electronic absorption and resonance Raman spectra of the metal diimine dithiolate complexes M(mnt)-(baba) where M = Ni and Pd, mnt = l,Zmaleonitrile, and baba = biacetylbisaniline are reported. The absorption spectra obtained from a low temperature frozen glass exhibit weakly resolved vibronic structure.The spectra are interpreted by using the time-dependent theory of spectroscopy. The electronic spectra are fit by using a calculation method for electron transfer spectra that includes coupling between potential surfaces (including the coupling of electronic and nuclear motions, i.e. the breakdown of the Born-Oppenheimer approximation). The results of this detailed calculation are compared to those involving uncoupled potential surfaces. Quantitative bond length changes are calculated. The distortions on both ligands that are observed support the assignment of the lowest energy excited state as arising from a ligand to ligand electron transfer transition from the dithiolate ligand to the diimine ligand.

The Electronic Structure and Spectroscopy of Metallo‐Dithiolene Complexes

“…Interestingly, considerable metal-ligand bond distortions were found to accompany the LLCT in Ni[biacetylbis(aniline)](mnt). This distortion was attributed to a combination of metal-ligand bond covalency and electrostatic changes (297). The fact that the RR studies indicate distortions along both the NiÀ ÀN and NiÀ ÀS bonds may suggest that the diimine and dithiolene orbitals are more highly mixed in the HOMO and LUMO than predicted by extended Hückel calculations.…”

“…Resonance Raman spectroscopy has been used to quantitate these molecular distortions in Ni[biacetylbis(aniline)](mnt) by using a time-dependent formalism (297). The largest distortions on the mnt 2À ligand are those along the C À À À ÀC and CÀ ÀS bonds, while the largest distortions that occur within the biacetylbis(aniline) ligand are along the C À À À ÀN bonds.…”

Self-quenching and Cross-quenching Reactions of Excited Platinum(II) Diimine Complexes

“…Complexes such as Pt(tmphen)(tdt) (l max ¼ 535 nm, 7160 M À1 cm À1 , CH 2 Cl 2 ; 526 nm, DMSO; Figure 9c) exhibit a broad, solvent-sensitive, charge-transfer absorption band shifted to the red of the lowest 1 MLCT absorption bands. Studies by Eisenberg [36,37] and others [10,[38][39][40][41][42][43] have established that the highest occupied levels in these complexes have considerable dithiolate character, and the lowest unoccupied levels have mostly diimine character. Because of extensive mixing of the Pt and dithiolate orbitals, the low-energy band has been assigned as a mixed-metal-ligand(dithiolate)-to-ligand(diimine) charge transfer (MMLLCT) transition.…”

Resonance Raman Investigation of the MLCT Transition in [Pt(dppm)2(PhC⋮C)2] and the MMLCT Transition in [Pt2(μ-dppm)2(μ-PhC⋮C)(PhC⋮C)2]+

“…Several research groups have used resonance Raman intensity analysis in order to determine the vibrational reorganizational energies of many different photoinduced electron-transfer reactions which have diffuse charge transfer electronic transitions such as metal to ligand charge transfer (MLCT), ligand to ligand charge transfer (LLCT), intervalence transitions of inorganic compounds, organic noncovalent donor-acceptor complexes charge transfer transitions, and very recently an organic covalent donoracceptor compound. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] In this paper we present a resonance Raman intensity analysis of the MLCT absorption at ∼344 nm for [Pt(dppm) 2 -(PhCtC) 2 ] in dichloromethane solution and of the MMLCT absorption band at ∼393 nm for [Pt 2 (µ-dppm) 2 (µ-PhCtC)-(PhCtC) 2 ] + in acetonitrile solution. We have taken resonance Raman spectra including absolute Raman cross section measurements at five excitation wavelengths for [Pt(dppm) 2 -(PhCtC) 2 ] and at six excitation wavelengths for [Pt 2 (µ-dppm) 2 (µ-PhCtC)(PhCtC) 2 ] + .…”