Metal–Sulfur Valence Orbital Interaction Energies in Metal–Dithiolene Complexes: Determination of Charge and Overlap Interaction Energies by Comparison of Core and Valence Ionization Energy Shifts

Abstract

The electronic interactions between metals and dithiolenes are important in the biological processes of many metalloenzymes as well as in diverse chemical and material applications. Of special note is the ability of the dithiolene ligand to support metal centers in multiple coordination environments and oxidation states. To better understand the nature of metal-dithiolene electronic interactions, new capabilities in gas-phase core photoelectron spectroscopy for molecules with high sublimation temperatures have been developed and applied to a series of molecules of the type Cp2M(bdt) (Cp = η5-cyclopentadienyl, M = Ti, V, Mo, and bdt = benzenedithiolato). Comparison of the gas-phase core and valence ionization energy shifts provides a unique quantitative energy measure of valence orbital overlap interactions between the metal and sulfur orbitals that is separated from the effects of charge redistribution. The results explain the large amount of sulfur character in the redox-active orbitals and the ‘leveling’ of oxidation state energies in metal-dithiolene systems. The experimentally-determined orbital interaction energies reveal a previously unidentified overlap interaction of the predominantly sulfur HOMO of the bdt ligand with filled π orbitals of the Cp ligands, suggesting that direct dithiolene interactions with other ligands bound to the metal could be significant for other metal-dithiolene systems in chemistry and biology.

Pulsed Electron Paramagnetic Resonance Spectroscopy of33S-Labeled Molybdenum Cofactor in Catalytically Active Bioengineered Sulfite Oxidase

“…20,67,69,71,72 Our calculations for Moco in the Mo(V) oxidation state are consistent with the results of those reports, which establish that oxo-Mo(V) centers have a doublet ( S = 1/2) electronic ground state with the unpaired electron occupying the metal d xy orbital (Figure 11a). …”

“…The electronic structures of Moco with the metal formally in the +4, +5, or +6 oxidation state have been reported previously within the context of the spectroscopy of model complexes relevant to various Mo and W enzymes, 20,62–70 including work specifically addressing the MPT “fold angle”. 20,67,69,71,72 Our calculations for Moco in the Mo(V) oxidation state are consistent with the results of those reports, which establish that oxo-Mo(V) centers have a doublet ( S = 1/2) electronic ground state with the unpaired electron occupying the metal d xy orbital (Figure 11a).…”

Large Ligand Folding Distortion in an Oxomolybdenum Donor–Acceptor Complex

“…35,36 For these higher valent oxomolybdenum dithiolenes, dithiolene → Mo(dx 2 −y 2 ) LMCT character admixed into the ground state is responsible for dithiolene ligand folding (Figure 2). 35,38–41 …”

Scorpionate Complexes as Models for Molybdenum Enzymes

“…Post‐2000 investigations have focused on scorpionate salts, [Tp*MoOCl(OAr)] and [Tp*MoO(OR) 2 ] (OAr = para ‐phenolate derivative; R = alkyl, aryl) complexes,, [Tp*MoO(bdt)] and its derivatives 37 ,, [Tp*MoO(qdt)] (qdt = quinoxaline‐2,3‐dithiolate),, [Tp*Mo(NO)(bdt)] and its derivatives, and [Cp 2 M(bdt)] (M = Ti, V, Mo) , , . Many complexes have been crystallographically characterized, the structure of [Tp*MoO(qdt)] (Figure ) being typical of oxido‐Mo V Tp* species.…”