Mass Spectrometric and Vibrational Characterization of Reaction Intermediates in [Ru(bpy)(tpy)(H₂O)]²⁺ Catalyzed Water Oxidation

Abstract

Mass spectrometry coupled with an in-line electrochemical electrospray ionization source is used to capture some of the reactioni ntermediates formed in the [Ru(bpy)(tpy)(H 2 O)] 2 + (bpy = 2,2'-bipyridine, tpy = 2,2':6',2"-terpyridine) catalyzed water oxidation reaction. By controlling the appliede lectrochemicalp otential, we identified the parentc omplex, as well as the first two oxidation complexes, identifieda s[ Ru(bpy)-(tpy)(OH)] 2 + and [Ru(bpy)(tpy)(O)] 2 + .T he structures of the parenta nd first oxidationc omplexes are probedd irectly in the mass spectrometer by using infrared predissociation spectroscopy of D 2 -tagged ions. Comparisons between experimental vibrational spectra and density functional theory calculations confirmed the identity and structure of these two complexes. Moreover,t he frequencyo ft he OÀHs tretching mode in [Ru(bpy)(tpy)(OH)] 2 + shows that this complex features aR u-OH interaction that is more covalent than ionic.Studying reaction intermediates can provide fundamental insight into the mechanism of ac hemical reaction. However, such key reaction species are typically presenti no nly minor concentrations, necessitating as ensitive and selectivep robe, such as electrospray ionization mass spectrometry (ESI-MS). [1][2][3][4][5][6][7][8] MS identifies ions by their mass-to-charge (m/z)r atio, and with additional characterization tools such as collision-induced dissociation, can also provides ome structural information.C oupling spectroscopicc haracterization with MS, by schemes such as infraredm ultiple photon dissociation (IRMPD), [9] UV + IR resonant photodissociation, [10] and cryogenic ion vibrational predissociation (CIVP), [11] can further provide rich and detailed structural information as well as benchmarks fort heoretical methods used to characterizer eaction processes. ESI can be easily adapted to directly probe differenttypes of analytes. [12][13][14][15][16][17] Particularly,a ni n-line electrochemical (EC) cell can be coupled to an ESI source,s uch that intermediates and products formed under specific EC potentials can be sampled. Severale xamples of such EC-ESI experimentsh ave been previously demonstrated. [18][19][20][21] Herein, we present the application of an EC-ESI source to study the intermediates presenti nt he electrochemical water oxidation reaction catalyzed by the mononuclear ruthenium complex [22][23][24] [Ru(bpy)(tpy)(H 2 O)] 2 + (hereafter denoted as [Ru(H 2 O)] 2 + ;b py = 2,2'-bipyridine, tpy = 2,2':6',2"-terpyridine). This family of ruthenium complexess erves as ap rototypical single-metal-centerh omogeneous water oxidation catalyst, and has been the subjecto fn umerous studies. [4,5,22,[25][26][27][28][29][30] We show that we can selectively detectt he first two oxidized complexes in the proposed catalytic cycle by controlling the applied EC potential. We further probed the structures of these mass-selected species directly in the mass spectrometer by CIVP.T hisc ombination of approaches allows us to directly capture and characterize complexes form...

Vibrational Characterization of Microsolvated Electrocatalytic Water Oxidation Intermediate: [Ru(tpy)(bpy)(OH)]2+(H2O)0–4

“…The vibrational spectra of the [ Ru (OH)] 2+ (H 2 O) n clusters with n = 0–4 were acquired using a dual cryogenic ion trap infrared predissociation mass spectrometer described in detail previously . The [ Ru (OH)] 2+ intermediate species was generated using an in-line electrochemical–electrospray (EC–ESI) setup, similar to those of Johnson and van Berkel, and described previously . Briefly, a millimolar solution of [ Ru (H 2 O)]­(ClO 4 ) 2 in water was pushed through an electrochemical flow cell equipped with a glassy carbon working electrode held at 1.2 V with respect to a stainless steel counter electrode.…”

“…Specifically, we probed the effect of solvation on the OH bond lengths at the active site of the catalyst via a stepwise addition of water molecules to the isolated catalyst ion . We also showed that the product of the first oxidation step, the open-shell [ Ru (OH)] 2+ complex, can be isolated and characterized utilizing an in-line electrochemical cell with the electrospray source …”

Ruthenium Complexes with a SWCNT‐Modified Terpyridine Ligand as an Efficient Electrocatalyst for Oxygen Evolution Reaction

“…Bands at 1571, 1722, 1217, 1108 cm −1 in the infrared spectrum of SWCNT‐tpyRubpy (Figure 4a) are attributed to C═C stretching vibration, C–OH stretching vibration, C–O stretching vibration, C–O stretching vibrations of the carbon nanotube structure, [ 41 ] respectively, and the vibration bands between 700–1500 cm −1 can be assigned to ligands of terpyridine and bipyridine. [ 42 ] The presence of these bands indicate the successful incorporation of tpyRubpy in SWCNTs.…”

Spectroscopy of Reactive Complexes and Solvated Clusters: A Bottom-Up Approach Using Cryogenic Ion Traps

“…We were able to isolate some of the more stable intermediates in the catalytic cycle using an electrochemical flow cell coupled to an ESI source . However, no [ Ru (O 2 )] 2+ complex could be isolated even with such a source.…”

“…59 We were able to isolate some of the more stable intermediates in the catalytic cycle using an electrochemical flow cell coupled to an ESI source. 60 However, no [Ru(O 2 )] 2+ complex could be isolated even with such a source. We thus set out to form the [Ru(O 2 )] 2+ complex using the reaction trap via the reverse reaction, i.e., O 2 + [Ru] 2+ → [Ru(O 2 )] 2+ .…”