Infrared Multiple Photon Dissociation Spectroscopy of a Gas-Phase Oxo-Molybdenum Complex with 1,2-Dithiolene Ligands

Abstract

Electrospray ionization (ESI) in the negative ion mode was used to create anionic, gas-phase oxo-molybdenum complexes with dithiolene ligands. By varying ESI and ion transfer conditions, both doubly and singly charged forms of the complex, with identical formulas, could be observed. Collision-induced dissociation (CID) of the dianion generated exclusively the monoanion, while fragmentation of the monoanion involved decomposition of the dithiolene ligands. The intrinsic structure of the monoanion and the dianion were determined by using wavelength-selective infrared multiple-photon dissociation (IRMPD) spectroscopy and density functional theory calculations. The IRMPD spectrum for the dianion exhibits absorptions that can be assigned to (ligand) C=C, C–S, C—C≡N, and Mo=O stretches. Comparison of the IRMPD spectrum to spectra predicted for various possible conformations allows assignment of a pseudo square pyramidal structure with C2v symmetry, equatorial coordination of MoO2+ by the S atoms of the dithiolene ligands, and a singlet spin state. A single absorption was observed for the oxidized complex. When the same scaling factor employed for the dianion is used for the oxidized version, theoretical spectra suggest that the absorption is the Mo=O stretch for a distorted square pyramidal structure and doublet spin state. A predicted change in conformation upon oxidation of the dianion is consistent with a proposed bonding scheme for the bent-metallocene dithiolene compounds [J. Am. Chem. Soc.19769817291742], where a large folding of the dithiolene moiety along the S···S vector is dependent on the occupancy of the in-plane metal d-orbital.

Theoretical Study of the Interaction of 1,2-Dithiolene Ligands with the Mg2+ and Ca2+ Aquacations: Electronic, Geometric and Energetic Analysis

“…55 specie, where the cation is surrounded by neutral ligands, whereas the second substitution occurs in the neutral complex [M(H 2 O) 4 L]. In the latter, the metal center has a weaker attraction for the second dithiolene ligand due to the interaction with the first dithiolene that largely neutralized its electronic charge, decreasing its electrophilicity.…”

“…[1][2][3][4] Homoleptic dithiolene complexes are important precursors of molecular devices, 5 semiconductors for field-effect transistors, 6 near infrared (NIR) dyes for lasers, 7,8 liquid crystal and non-linear optical devices, 9,10 electronic recording disks 11 and in olefin purification systems. 12 In the heteroleptic dithiolene complexes, the metal cation interacts with the dithiolate ligand and also with several other ligands, such as cyclopentadienyl, ortho-diimines and diphosphines.…”

A mixed valence zinc dithiolene system with spectator metal and reactor ligands

“…This level of theory was chosen due to its well documented ability to model metal dithiolenes. [20, 21] The vibrational frequency calculations were performed to (a) confirm that structures were true minima and (b) to aid in the assignment of molecular vibrational modes. The calculated infrared spectrum for 4 is presented in Figure 4.…”

“…[20] To this end, we have been engaged in studying metal-ligand interactions using a dithione ligand, i.e., the fully oxidized π-accepting ligand using a redox-active metal. [20, 21] In the case presented, an electron rich π-donating dithiolate ligand is added alongside a dithione ligand, and a molecular system with built-in electron rich and electron deficient moieties can be created, a situation made possible by the redox versatility of the dithione ligand. Because of the presence of potential ligand to ligand charge transfer (LLCT) transitions, these electronic donor-acceptor systems are of great interest as materials for information storage and switching.…”

Recent developments in the study of molybdoenzyme models

“…Conjugation within the dithiolene ligand mediated through the sulfur atoms to the molybdenum creates a highly covalent system that adjusts to variable electron density at the metal. The dithiolene can further influence the Mo electronic environment by a bending movement, 31 that can change electron donation through pi interactions in response to Mo oxidation state so that larger dithiolene ‘fold angles’ are observed for the higher oxidation states of Mo. 32 Both of these modes of modulating the electronic environment have led to the dithiolene ligand’s description as an “electronic buffer”.…”