Co-reporter:Erin M. Duffy;Dr. Brett M. Marsh;Jonathan M. Voss ; Etienne Gar
Angewandte Chemie International Edition 2016 Volume 55( Issue 12) pp:4079-4082
Publication Date(Web):
DOI:10.1002/anie.201600350
Abstract
For homogeneous mononuclear ruthenium water oxidation catalysts, the Ru–O2 complex plays a crucial role in the rate determining step of the catalytic cycle, but the exact nature of this complex is unclear. Herein, the infrared spectra of the [Ru(tpy)(bpy)(O2)]2+ complex (tpy=2,2′:6′,2′′-terpyridine; bpy=2,2′-bipyridine) are presented. The complex [Ru(tpy)(bpy)(O2)]2+, formed by gas-phase reaction of [Ru(tpy)(bpy)]2+ with molecular O2, was isolated by using mass spectrometry and was directly probed by cryogenic ion IR predissociation spectroscopy. Well-resolved spectral features enable a clear identification of the O−O stretch using 18O2 substitution. The band frequency and intensity indicate that the O2 moiety binds to the Ru center in a side-on, bidentate manner. Comparisons with DFT calculations highlight the shortcomings of the B3LYP functional in properly depicting the Ru–O2 interaction.
Co-reporter:Erin M. Duffy;Dr. Brett M. Marsh;Jonathan M. Voss ; Etienne Gar
Angewandte Chemie 2016 Volume 128( Issue 12) pp:4147-4150
Publication Date(Web):
DOI:10.1002/ange.201600350
Abstract
For homogeneous mononuclear ruthenium water oxidation catalysts, the Ru–O2 complex plays a crucial role in the rate determining step of the catalytic cycle, but the exact nature of this complex is unclear. Herein, the infrared spectra of the [Ru(tpy)(bpy)(O2)]2+ complex (tpy=2,2′:6′,2′′-terpyridine; bpy=2,2′-bipyridine) are presented. The complex [Ru(tpy)(bpy)(O2)]2+, formed by gas-phase reaction of [Ru(tpy)(bpy)]2+ with molecular O2, was isolated by using mass spectrometry and was directly probed by cryogenic ion IR predissociation spectroscopy. Well-resolved spectral features enable a clear identification of the O−O stretch using 18O2 substitution. The band frequency and intensity indicate that the O2 moiety binds to the Ru center in a side-on, bidentate manner. Comparisons with DFT calculations highlight the shortcomings of the B3LYP functional in properly depicting the Ru–O2 interaction.
Co-reporter:Brett M. Marsh, Jonathan M. Voss, Jia Zhou and Etienne Garand
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 35) pp:23195-23206
Publication Date(Web):11 Aug 2015
DOI:10.1039/C5CP03914B
Infrared vibrational predissociation spectra of transition metal hydroxide clusters, [MOH]+(H2O)1–4·D2 with M = Mn, Fe, Co, Ni, Cu, and Zn, are presented and analyzed with the aid of density functional theory calculations. For the [MnOH]+, [FeOH]+, [CoOH]+ and [ZnOH]+ species, we find that the first coordination shell contains three water molecules and the four ligands are arranged in a distorted tetrahedral geometry. [CuOH]+ can have either two or three water molecules in the first shell arranged in a planar arrangement, while [NiOH]+ has an octahedral ligand geometry with the first shell likely closed with five water molecules. Upon closure of the first coordination shell, characteristic stretch frequencies of hydrogen-bonded OH in the 2500–3500 cm−1 region are used to pinpoint the location of the water molecule in the second shell. The relative energetics of different binding sites are found to be metal dependent, dictated by the first-shell coordination geometry and the charge transfer between the hydroxide and the metal center. Finally, the frequency of the hydroxide stretch is found to be sensitive to the vibrational Stark shift induced by the charged metal center, as observed previously for the smaller [MOH]+(H2O) species. Increasing solvation modulates this frequency by reducing the extent of the charge transfer while elongating the M–OH bond.
Co-reporter:Brett M. Marsh, Jia Zhou and Etienne Garand
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 39) pp:25786-25792
Publication Date(Web):31 Mar 2015
DOI:10.1039/C5CP01522G
Charge transfer between a metal and its ligand is fundamental for the structure and reactivity of a metal complex as it directly dictates the distribution of electron density within the complex. To better understand such charge transfer interactions, we studied the vibrational spectra of mass-selected MOH(H2O)+ (M = Mn, Fe, Co, Ni, Cu, or Zn) complexes, acquired using cryogenic ion infrared predissociation spectroscopy. We find that there is a partial charge transfer from the hydroxide anion to the metal center for these first-row transition metals, the extent of which is in the order of Mn < Fe < Co < Ni < Cu > Zn, dictated by the 2nd ionization energy of the bare metal. This gradual change across the metal series points to the complexity in the electronic structures of these transition metal complexes. Interestingly, the hydroxide ligand in these complexes can serves as a sensitive in situ probe of this charge transfer. Its vibrational frequency varies by >150 cm−1 for different metal species, and it is dependent on the electric field produced by the charged metal center. This dramatic vibrational Stark shift is further modulated by the charge present on the hydroxide itself, providing a well-defined relationship between the observed hydroxide frequency and the effective electric field.
Co-reporter:Brett M. Marsh, Jia Zhou and Etienne Garand
RSC Advances 2015 vol. 5(Issue 3) pp:1790-1795
Publication Date(Web):18 Nov 2014
DOI:10.1039/C4RA09655J
The gas-phase vibrational predissociation spectra of deprotonated copper–triglycine ([Cu + G3-3H]−) and deprotonated copper–tetraglycine ([Cu + G4-4H]2−), a known water oxidation catalyst, are presented. Unambiguous determination of the coordination structure in these complexes is made by comparison of the experimental spectra with calculations. We found both complexes to have an approximately square planar geometry in which all the amide groups are deprotonated and coordinating to the Cu center. Our experimentally determined structure for [Cu + G3-3H]−, in which the terminal carboxylate and amine groups provide the additional coordination interaction, agrees with previous studies. However, the [Cu + G4-4H]2− complex is found to have the carboxylate group coordinated to the Cu center rather than NH2, as determined in previous solution-phase studies. Our results also highlight the sensitivity of the amidate CO stretch frequencies to the charge and coordination environment in these complexes. The observed experimental frequencies alone are capable of providing qualitative information on the interactions present in these species.
Co-reporter:Erin M. Duffy, Brett M. Marsh, and Etienne Garand
The Journal of Physical Chemistry A 2015 Volume 119(Issue 24) pp:6326-6332
Publication Date(Web):May 22, 2015
DOI:10.1021/acs.jpca.5b04778
The infrared spectra of gas-phase mass-selected [Ru(bpy)(tpy)(H2O)]2+·(H2O)0–4 clusters (bpy = 2,2′-bipyridine; tpy = 2,2′:6,2″-terpyridine) in the OH stretching region are reported. These species are formed by bringing the homogeneous water oxidation catalyst [Ru(bpy)(tpy)(H2O]2+ from solution into the gas phase via electrospray ionization (ESI) and reconstructing the water network at the active site by condensing additional water onto the complex in a cryogenic ion trap. Infrared predissociation spectroscopy is used to probe the structure of these clusters via their distinctive OH stretch frequencies, which are sensitive to the shape and strength of the local hydrogen-bonding network. The analysis of the spectra, aided by electronic structure calculations, highlights the formation of strong hydrogen bonds between the aqua ligand and the solvating water molecules in the first solvation shell. These interactions are found to propagate through the subsequent solvation shells and lead to the stabilization of asymmetric solvation motifs. Electronic structure calculations show that these strong hydrogen bonds are promoted by charge transfer from the H atom of the aqua ligand to the Ru–OH2 bond.
Co-reporter:Brett M. Marsh, Erin M. Duffy, Michael T. Soukup, Jia Zhou, and Etienne Garand
The Journal of Physical Chemistry A 2014 Volume 118(Issue 22) pp:3906-3912
Publication Date(Web):May 8, 2014
DOI:10.1021/jp501936b
The infrared spectra of deprotonated glycine peptides, (Gn–H)− with n = 1–4, in the 1200–3500 cm–1 spectral region are presented. Comparisons between the experimental and calculated spectra reveal the chain length dependent hydrogen bonding motifs that define the geometries of these species. First, an interaction between the terminal carboxylate and the neighboring amide N–H is present in all the peptide structures. This interaction is strong enough to align this amide group in the same plane as the carboxylate. However, we found that the vibrational frequency shift of this hydrogen bonded N–H group is not well reproduced in the calculations. Second, in the longer (G3–H)− and (G4–H)− species, the peptide chain folds such that the terminal NH2 group also interacts with the carboxylate. Both of these folded structures display an interaction between the terminal NH2 and the neighboring N–H as well. Lastly, an amide–amide interaction is observed in the longest (G4–H)− structure. Analysis of the N–H peak positions reveals the interplay among the different hydrogen bonds, especially around the negatively charged carboxylate moiety.
Co-reporter:Brett M. Marsh, Jia Zhou, and Etienne Garand
The Journal of Physical Chemistry A 2014 Volume 118(Issue 11) pp:2063-2071
Publication Date(Web):February 25, 2014
DOI:10.1021/jp411614t
Coordinated copper hydroxide centers can play an important role in copper catalyzed water oxidation reactions. To have a better understanding of the interactions involved in these complexes, we studied the vibrational spectra of D2 tagged CuOH+(H2O)n clusters in the OH stretch region. These clusters are generated by electrospray ionization and probed via cryogenic ion vibrational spectroscopy. The results show that the copper center in the n = 3 clusters has a distorted square planar geometry. The coordination in CuOH+(H2O)n is therefore more akin to Cu2+(H2O)n with four ligands in the first solvation shell than Cu+(H2O)n with two ligands in the first solvation shell. There is also no evidence of any strong axial ligand interactions. The well-resolved experimental spectra enabled us to point out some discrepancies in the calculated spectra, which were found to be highly dependent on the level of theory used.
Co-reporter:Brett M. Marsh, Jonathan M. Voss, Jia Zhou and Etienne Garand
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 35) pp:NaN23206-23206
Publication Date(Web):2015/08/11
DOI:10.1039/C5CP03914B
Infrared vibrational predissociation spectra of transition metal hydroxide clusters, [MOH]+(H2O)1–4·D2 with M = Mn, Fe, Co, Ni, Cu, and Zn, are presented and analyzed with the aid of density functional theory calculations. For the [MnOH]+, [FeOH]+, [CoOH]+ and [ZnOH]+ species, we find that the first coordination shell contains three water molecules and the four ligands are arranged in a distorted tetrahedral geometry. [CuOH]+ can have either two or three water molecules in the first shell arranged in a planar arrangement, while [NiOH]+ has an octahedral ligand geometry with the first shell likely closed with five water molecules. Upon closure of the first coordination shell, characteristic stretch frequencies of hydrogen-bonded OH in the 2500–3500 cm−1 region are used to pinpoint the location of the water molecule in the second shell. The relative energetics of different binding sites are found to be metal dependent, dictated by the first-shell coordination geometry and the charge transfer between the hydroxide and the metal center. Finally, the frequency of the hydroxide stretch is found to be sensitive to the vibrational Stark shift induced by the charged metal center, as observed previously for the smaller [MOH]+(H2O) species. Increasing solvation modulates this frequency by reducing the extent of the charge transfer while elongating the M–OH bond.
Co-reporter:Brett M. Marsh, Jia Zhou and Etienne Garand
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 39) pp:NaN25792-25792
Publication Date(Web):2015/03/31
DOI:10.1039/C5CP01522G
Charge transfer between a metal and its ligand is fundamental for the structure and reactivity of a metal complex as it directly dictates the distribution of electron density within the complex. To better understand such charge transfer interactions, we studied the vibrational spectra of mass-selected MOH(H2O)+ (M = Mn, Fe, Co, Ni, Cu, or Zn) complexes, acquired using cryogenic ion infrared predissociation spectroscopy. We find that there is a partial charge transfer from the hydroxide anion to the metal center for these first-row transition metals, the extent of which is in the order of Mn < Fe < Co < Ni < Cu > Zn, dictated by the 2nd ionization energy of the bare metal. This gradual change across the metal series points to the complexity in the electronic structures of these transition metal complexes. Interestingly, the hydroxide ligand in these complexes can serves as a sensitive in situ probe of this charge transfer. Its vibrational frequency varies by >150 cm−1 for different metal species, and it is dependent on the electric field produced by the charged metal center. This dramatic vibrational Stark shift is further modulated by the charge present on the hydroxide itself, providing a well-defined relationship between the observed hydroxide frequency and the effective electric field.
