Ligand Influence on the Electronic Spectra of ... - ACS Publications

Subscriber access provided by UNIV LAVAL

Article

Ligand Influence on the Electronic Spectra of Dicationic Ruthenium-Bipyridine-Terpyridine Complexes Shuang Xu, James Earle Thompson Smith, and J. Mathias Weber J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.6b02926 • Publication Date (Web): 01 Apr 2016 Downloaded from http://pubs.acs.org on April 7, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry A is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Ligand Influence on the Electronic Spectra of Dicationic Ruthenium-Bipyridine-Terpyridine Complexes Shuang Xu1, James E. T. Smith2 and J. Mathias Weber2* 1

JILA and Department of Physics, University of Colorado, Boulder, CO 80309-0440, USA

2

JILA

and

Department

of

Chemistry

and

Biochemistry,

University

of

Colorado,

Boulder, CO 80309-0440, USA

ABSTRACT. We report electronic spectra of a series of ruthenium polypyridine complexes of the form [(trpy)(bipy)RuII-L]2+ (bipy = 2,2′-bipyridine and trpy = 2,2′:6′,2″-terpyridine), where L represents a small molecular ligand that occupies the last coordination site. Species with L = H2O, CO2, CH3CN and N2 were investigated in vacuo using photodissociation spectroscopy. All species exhibit bright metal-to-ligand charger transfer (MLCT) bands in the visible and near UV, but with different spectral envelopes and peak energies, encoding the influence of the ligand L on the electronic structure of the complex. Several individual electronic bands can be resolved for L = H2O and CO2, while the spectra for L = N2 and CH3CN are more congested, even at low ion temperatures. The experimental results are discussed in the framework of time-dependent density functional theory.

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 32

Introduction Ruthenium polypyridine complexes form an important group of organometallic compounds. They have found a wide range of applications, e.g. in dye-sensitized solar cells,1–3 or as photoand electrochemical catalysts for water oxidation and CO2 reduction.4–15 They absorb visible light with high extinction coefficients (about 14,000 M-1cm-1 for Ruthenium-tris-bipyridine16), and can drive charge transfer reactions that can be used in artificial photosynthesis.17 In addition, ruthenium polypyridine complexes are of interest as shape- and enantioselectively dyes binding to DNA and other biomolecules.18,19 In many applications of ruthenium polypyridine complexes the organic polypyridine framework occupies not all coordination positions of the central metal atom, leaving one or more open sites. These open coordination sites afford interaction with other ligands, which can be used as the starting point of interesting chemistry. In the case of photocatalysis, for example, it is proposed that the binding of water or CO2 to an open coordination site is the starting point of a catalytic cycle for water oxidation or CO2 reduction.8,20 The interaction with such additional ligands often strongly influences the photophysical and photochemical properties of the complex, but it is not a trivial task to predict such ligand effects in detail. For a systematic investigation of these effects, a common approach is to alter one single ligand in the complex at a time and observe the change in the properties of the complex.21–30 However, such experiments often require complicated synthesis and purification steps in solution. In addition, reactive intermediates (e.g. in catalysis) are often unstable with regard to exchanging a particular type of ligand with solvents or other reagents, and purification and isolation may not be even possible. As a result, controlling specific ligands and characterizing a single species is difficult under typical conditions in solution. An attractive alternative that circumvents many of these problems


2

Page 3 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


is to use mass selected ions in vacuo. This approach allows unprecedented and precise selection of the composition of the complex, and in some cases even control over the number and type of solvent molecules in the microenvironment of the complex. Due to the absence of reactants, many unstable species also can become accessible in such experiments.

Figure 1. Structural template of the complexes under study. The ligand L represents a small molecule (here: H2O, CO2, CH3CN, N2).

In this paper we report a spectroscopic study of a series of mass-selected octahedrally coordinated ruthenium complexes in vacuo. The complexes are built on the [(trpy)(bipy)RuIIL]2+ structural template (see Figure 1), denoted as [Ru-L]2+, where five of the coordination positions on the Ru atom are occupied by 2,2’:6’,2”-terpyridine (trpy) and 2,2’-bipyridine (bipy), and L represents a small, molecular ligand filling the last coordination site. Recent work has focused on Ru2+ and its derivatives as an important prototypical complex for the study of electrochemical and photoelectrochemical catalysis.31–33 In this work, we compare the electronic spectra of [Ru-L]2+ for L = H2O, CO2, CH3CN and N2. The first species in this series, [Ru-


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 32

OH2]2+ (L = H2O), has been invoked as the starting point of a catalytic circle using Ru2+ as a water oxidation catalyst.34 In previous work, we presented the first observation of resolved electronic states of this complex in vacuo.35 Here we include it in a larger series and focus our discussion on the comparison with other species. The complex [Ru-OCO]2+ (L = CO2) may be an intermediate in CO2 reduction catalysis where CO2 is converted to formate.4 Many of the reactions of Ru2+ and similar catalysts have been studied via cyclic voltammetry experiments in acetonitrile solution, and it is conjectured that the catalytic cycle is initialized by photon induced ligand substitution of [Ru-NCCH3]2+ (L = CH3CN).13,36 Hence we also include [Ru-NCCH3]2+ in this study. Acetonitrile is a very common solvent and frequently used as a displaceable ligand. In our experiment we found the existence of [Ru-N2]2+ (L = N2). Nitrogen is usually a very inert molecule and is relatively rarely used as a molecular ligand in transition metal chemistry. However, it can bind to suitable undercoordinated transition metal complexes and form a dinitrogen complex. The first isolation of a dinitrogen complex, Ru(NH3)5-N2, in 196737 inspired the study of nitrogen-fixing agents, but despite growing interest, there have been relatively few spectroscopic studies on dinitrogen complexes.

Methods Experimental Our experimental setup is described in detail in a previous publication, and an overview is given in Figure 2.38 Briefly, gas phase ions are produced via electrospray ionization and guided by a series of octupole ion guides through several differential pumping stages. They are accumulated in a 3D quadrupole ion trap for 45 ms, where they interact with buffer gas (He, N2, or CO2) and then injected into a Wiley-McLaren time-of-flight mass spectrometer. The ions are


4

Page 5 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


mass selected and then irradiated by tunable pulsed radiation from an optical parametric converter system in the region 354 – 670 nm. Ionic fragments resulting from photon absorption and the parent ions are separated by a reflectron, which acts as a secondary mass analyzer. Photodissociation spectra are recorded by monitoring the intensity of the fragment ion as a function of photon energy. In the current work, the only dissociation channel that we were able to observe was the loss of the ligand L, which in all cases represents the lowest energy fragment channel, as its binding energy to the central ruthenium ion is much lower than that of trpy or bipy. We therefore monitored the yield of Ru2+ in all cases. The ion trap is operated at 20 Hz repetition rate while the laser is triggered at 10 Hz, allowing background subtraction for each data point. The fragment ion yield is normalized to the photon fluence, converted from the laser pulse energy monitored by a pyroelectric joulemeter. The ion trap is mounted on a helium cryostat, allowing us to form the desired parent ions by condensation of the ligand molecules onto Ru2+, which in some cases requires low temperatures.

Figure 2. Schematic of the experimental apparatus. A: electrospray needle; B: desolvation capillary; C: skimmers; D: octupole ion guides; E: quadrupole bender; F: helium cryostat; G: quadrupole ion trap and acceleration unit (inset shows details, see text); H: ion lens and deflectors; I: mass gate; J: reflectron; K: microchannel plate detector; L: laser power meter; M: reactant gas inlet.


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 32

Each spectrum presented in this paper is composed of several overlapping sections corresponding to the tuning range of the light source for different crystal configurations. Each section represents an average of several scans taken on multiple days to reduce noise and ensure reproducibility. The part of the complex that is common to all target ions in this series, Ru2+, was synthesized according to established procedures in literature.32 In brief, 0.25 mmol of 2,2’-bipyridine, 2,2’:6’,2”-terpyridine and RuCl3 were dissolved in 15 mL ethanol and 5 mL water. The solution was added to 1.25 mmol LiCl and 0.05 mL triethylamine and then refluxed for 4 hours at 90 °C. The crude solution was filtered, diluted 1:100 with ethanol, and electrosprayed without further purification. Water, CO2 and nitrogen adducts are formed in the trap by interaction with water vapor, CO2 and N2 from the buffer gas. The lowest temperatures for ion formation in these are ca. 180 K (for water and CO2 adducts) and 70 K (for N2 adducts), respectively, since the ligand gases freeze out at lower temperatures. The acetonitrile adduct is formed by admitting acetonitrile vapor into the second differential pumping stage where the Ru2+ complex ion can pick up an acetonitrile ligand. Since it was formed outside the cryogenic trap, we used lower trap temperatures down to 30 K.

Computational The ground state geometry of each ion under study was calculated using density functional theory39 (DFT) with def2-TZVP basis sets40 for all atoms. Two functionals, PBE041 and B3LYP42,43, were employed to test the sensitivity of the results to the functional used. Singlet excitation energies were calculated by time-dependent DFT (TDDFT44–46) with the same basis


6

Page 7 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


sets and functionals. In order to improve the agreement with the experimental spectra, all predicted transition energies were shifted to lower energies by constant offsets for all species under study. These shifts were -0.15 eV for B3-LYP and -0.3 eV for PBE0, consistent with our earlier work on [Ru-OH2]2+.35 Charges were computed using natural population analysis.47 All computations were performed using the TURBOMOLE program suite.48,49

Results and Discussion Complexes with L = H2O and CO2 The aqua complex, [Ru-OH2]2+, and its derivatives have received much attention as the starting point in a catalytic cycle for water oxidation.20 The vibrational50 and electronic spectra35 of this complex in vacuo have been studied in previous work, and it will only briefly be discussed here in comparison with the CO2 complex, [Ru-OCO]2+. The structures of the aqua complex and of two isomers of the CO2 complex are shown in Figure 3. The CO2 complex has two η1 isomers, one with the CO2 ligand binding to the Ru atom through an O atom, the other binding with the C atom to the metal in a metalloformate motif. While this metalloformate motif has been invoked in other ruthenium polypyridine complexes8 and in several metal-CO2 clusters51–56 in the context of CO2 reduction catalysis, it is calculated to be 4.6 eV higher in energy than the end-on isomer of the complex under study. Therefore, we only consider the pseudo-linear structure here. Interestingly, while one may naively expect the Ru-O-C configuration to be linear, the calculated Ru-O-C angle is 156°, which could be a result of the sp2 hybridization of the oxygen atoms in the CO2 ligand. The remaining lone pair on the O atom could interact with the nearest CH group on the bipy. In the aqua complex, the angle between the Ru-O bond and the aqua plane


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 32

(123°) deviates even more strongly from 180° in a geometry that is consistent with sp3 hybridization on the O atom.

Figure 3. Calculated minimum energy structures of [Ru-L]2+ for L = H2O and CO2 (the latter with two different isomers). Carbon atoms are shown in brown, nitrogen in blue, ruthenium in gold, oxygen in red, and hydrogen in white.

The photodissociation spectra of [Ru-OH2]2 and [Ru-OCO]2+ at 180 K trap temperature are remarkably similar (see Figure 4), and the spectrum of the aqua complex at this temperature is nearly the same as at room temperature.35

Both species exhibit broad, partially resolved

electronic bands within the 1MLCT envelope. The width of the observed features is likely due to lifetime broadening, which has its origin in the ultrashort intersystem crossing lifetimes that are well known for Ru complexes.57 Transition energies predicted by TDDFT calculations recover the experimental spectroscopic pattern of both complexes with similar quality (see Table I), although at higher energies the calculations for the aqua complex are in slightly better agreement with experimental values than in the case of the CO2 complex. The lowest electronic bands (feature I) are found at 2.17 eV and are assigned to the S1 state for both complexes (see Table I).


8

Page 9 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


They are predominantly transitions from the highest occupied molecular orbital (HOMO, Ru based) to the lowest unoccupied molecular orbital (LUMO, trpy based). Feature II, assigned to the S2 state in each case, is a shoulder at slightly higher energy (see Table I). We attribute the next higher feature to the S3 state in both complexes. The two dominant features (IV and V) in both spectra are around the peak of the 1MLCT envelope, which is at ca. 2.9 eV for the aqua complex and at ca. 3.0 eV for the CO2 complex. The higher energy feature (V) in the aqua complex has been observed to diminish in relative intensity as solvent molecules are added to the complex, despite the fact that there is no change in the (relatively weak) calculated oscillator strength.35

We therefore assume that feature V is composed of the weak electronic band

calculated in this energy range and the Franck-Condon envelope of the more intense band (feature IV). The similarity in the calculated and experimental spectra of the aqua- and CO2 complexes suggests that this is the case for both of these species. The solvatochromic shift of the aqua complex in aqueous solution is ca. 0.3 eV to the red.35

Table I. Positions of spectroscopic features observed in the spectra of [Ru-L]2+ for L = H2O and CO2 at 180 K trap temperature, compared to their positions as predicted by TDDFT (B3-LYP functional, shifted by -0.15 eV). No comparison is made for feature V in each case (see text). Error bars refer to experimental peak positions. Eexp / Ecalc [eV] ± 0.03 eV Feature

I

II

III

IV

V

[Ru-OH2]2+

2.17 / 2.18

2.38 / 2.30

2.65 / 2.54

2.80 / 2.67

2.97

[Ru-OCO]2+

2.17 / 2.19

2.41 / 2.31

2.77 / 2.63

2.92 / 2.76

3.11


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 32

Figure 4. Photodissociation spectra of [Ru-L]2+. The ligands are given in each panel. Dots are raw data, full lines are 30-point sliding averages. The resolved features are labeled I through V (see also Table I). The vertical columns represent transitions predicted by TDDFT calculations. The transition energies are shifted by -0.15 eV for B3-LYP (open columns) and -0.3 eV for PBE0 (filled columns). Spectra for L = H2O and L = CO2 were acquired at 180 K trap temperature. Spectra for L = CH3CN were recorded at room temperature (red) and at 30 K trap temperature (blue), spectra for L = N2 were taken at room temperature (red) and at 70 K (blue).


10

Page 11 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table II. Ligand binding energies EL and charge distribution calculated for [Ru-L]2+ using the B3-LYP functional. Charge distribution was calculated with natural binding orbitals. species

EL [eV]

charge [e] Ru

L

bonding atom in L / bipy in free molecule

trpy

[Ru-OH2]2+

1.1

0.65

0.16

-0.86 / -0.92

0.50

0.69

[Ru-OCO]2+

0.4

0.66

0.09

-0.54 / -0.49

0.53

0.72

[Ru-NCCH3]2+

1.7

0.57

0.20

-0.34 / -0.32

0.48

0.75

[Ru-NN]2+

0.9

0.54

0.11

0.006 / 0

0.52

0.83

Ru2+

-

0.74

-

-

0.55

0.71

It is important to note that we can exclude kinetic shift effects that would serve to skew the overall shape of the spectrum, based on our earlier work on the aqua complex.35 Since the calculated binding energy of the CO2 ligand is even lower than that of the aqua ligand (see Table II), we rule out kinetic shift effects for the [Ru-OCO]2+ complex as well.

Complexes with L = CH3CN and N2 In contrast to the complexes with L = H2O and L = CO2, the acetonitrile and molecular nitrogen ligands have Ru-N-C and Ru-N-N angles of close to 180° (see Figure 5). Just as the ligand alignment in the cases of L = H2O and L = CO2 can be explained by hybridization, we can rationalize the linear arrangement of acetonitrile and nitrogen ligands. Different from water and carbon dioxide, the binding N atoms in acetonitrile and nitrogen have sp hybrid orbitals, consistent with the calculated geometries.


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 32

Figure 5. Calculated minimum energy structures of [Ru-L]2+ for L = CH3CN and N2 (the latter with two different isomers). Carbon atoms are shown in brown, nitrogen in blue, ruthenium in gold, oxygen in red, and hydrogen in white.

The spectra of [Ru-NCCH3]2+ and [Ru-N2]2+ do not exhibit clearly resolved features like those of [Ru-OH2]2+ or [Ru-OCO]2+ (see Figure 4), even at trap temperatures of 70 K and lower. The absence of resolved features at low temperatures is consistent with the explanation that the large width of the electronic bands is due to the ultrashort intersystem crossing lifetime in Ru complexes,57 which we already invoked for [Ru-OH2]2+ and [Ru-OCO]2+.

It is, however,

surprising that the lowest energy excitations are less pronounced than in the spectra of the latter, despite having similar oscillator strengths, at least for L = CH3CN (see Supporting Information). The calculated density of electronic states is somewhat greater than for [Ru-OH2]2+ and [RuOCO]2+, which also contributes to the greater spectral congestion for the complexes with Ncoordinating ligands. The spectrum of [Ru-NCCH3]2+ has a peak at 2.87 eV with a pronounced high-energy tail. The spectra taken at room temperature and at 30 K trap temperature are not very different from each other, although the low temperature spectrum is overall somewhat narrower, most likely due to the suppression of hot bands. Interestingly, the solvatochromic shift for L = CH3CN in bulk acetonitrile solution5 is ca. 130 meV to the red, much smaller than for the complex with L = H2O in bulk aqueous solution35 (ca.


12

Page 13 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


300 meV to the red). At first glance, this may seem counterintuitive, since acetonitrile has a much stronger dipole moment than water. However, this behavior is consistent with the higher calculated binding energy of CH3CN to Ru2+ and suggests that the polarity of the solvent, while important, has a smaller effect on the solvatochromic shift than the interaction strength of a solvent acting as a ligand coupled to the metal center. Moreover, complexes with water will be strongly influenced by H-bonding and water network formation in solution, as evidenced by isotope effects on electronic relaxation solutions in H2O vs. D2O.58 The spectrum of [Ru-N2]2+ has a broad absorption profile peaking around 3.24 eV (at 70 K trap temperature), and the only discernible structure is a broad shoulder at ca. 2.9 eV. The room temperature spectrum shows strong hot bands. The envelopes of the calculated excited states are consistent with the experimentally observed spectra. Interestingly, the calculated energies for the S1 states are significantly higher than for L = H2O and CO2 (2.31 eV for L = CH3CN, 2.61 eV for L = N2). The calculated oscillator strength for the transition to the S1 state for L = N2 is an order of magnitude smaller than for any of the other ligands under study. Despite the relatively high binding energy of the CH3CN ligand (calculated to be 1.7 eV), there is no indication for kinetic shift effects, judging from the difference between the spectra at room temperature and at 30 K trap temperature. The binding energy of the N2 ligand is calculated at 0.9 eV, ruling out kinetic shift effects.

Calculated Electronic Properties The charge distributions for the ground state complexes calculated from natural orbitals (see Table II) show only few general trends, and they can be grouped according to O-coordinating vs


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 32

N-coordinating ligands. The small molecular ligands carry only little positive charge in each case. This is not unexpected, since the canonical inorganic chemistry picture invokes σ donation to the metal and π back donation to the ligand,59 so the net charge on the ligand may not change much. The ligands can be polarized by the presence of the central Ru ion, and the polarization is generally stronger for the O-coordinating ligands than for the N-coordinating ligands (see Table II). The charge on the Ru atom becomes less positive upon complexation, and the O-coordinating complexes have a similar and more positive charge on the Ru atom than the N-coordinating ligands, which are again similar to each other regarding the charge on Ru. The charge on the bipy does not show a systematic variation, but the charge on trpy becomes more positive along the series H2O < CO2 < CH3CN < N2. Compared to Ru2+, i.e., the complex without the ligand L, there are only small changes introduced by the O-coordinating ligands, whereas the effect of acetonitrile is somewhat stronger, and N2 changes the charge on the trpy substantially. The changes in charge distributions cannot be related to simple properties of the ligands that would be immediately apparent as their origin, such as ionization potential, electric dipole moment or polarizability. We note, however, that the charge on the binding atom of the ligand L is roughly correlated with the charge distribution on Ru and trpy. The charge on the Ru ion becomes more positive as the charge on the binding atom in the ligand L becomes more negative (see Table II). In other words, the charge on the binding atom in the ligand stabilizes (or destabilizes) the positive charge on the Ru ion. This is not a very strong trend, and – as seen before – the ligands with O atoms and those with N atoms show close similarities in charge distribution. The character of the transitions is similar for all the complexes under study. The lowest two transitions all are HOMO→LUMO and (HOMO-1)→LUMO, with the HOMO mainly of metal d-orbital character, and the LUMO having π* character on trpy (see Supporting Information).


14

Page 15 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The transitions at higher energies often involve a mixture of several initial and final orbitals (see Table III), but all can be characterized as metal to ligand charge transfer (MLCT) transitions to a π* orbital on trpy and/or bipy. The TDDFT calculations predict for all complexes that one transition has a significantly higher oscillator strength than the other transitions in this energy range. Its dominant character is (HOMO-1) → (LUMO+1). All four species also have charge transfer states from Ru to the small molecular ligand L, but they are mostly calculated to be at higher energies and have lower oscillator strengths. For example, the lowest MLCT state in the aqua complex that involves the aqua ligand is calculated at 3.10 eV, and it does not correspond to an experimentally observed feature. The exception in this series is [Ru-OCO]2+, where the lowest energy MLCT transition involving the CO2 ligand is calculated at 2.63 eV. Overall, the similarity in the character of the excitations suggests that the changes in the spectra are caused by the differences in the charge distributions and orbital stabilization and destabilization. The role of the binding atom in the ligand L is highlighted by the similarities between spectra for complexes with the same binding atoms (H2O and CO2 vs. CH3CN and N2). Calculations on the excited states of Ru2+ allow a comparison of the properties of the undercoordinated complex with the different experimentally accessible complexes (see Table III). The lowest three transitions to LUMO have much lower energies than in the fully coordinated complexes. This can be traced to the MO energies, since the LUMO in Ru2+ is destabilized by the addition of the ligand L (see Supporting Information).


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 32

Table III. Calculated selected transition energies (B3-LYP, shifted by -0.15 eV) sorted by the dominant orbitals involved in the transition. Species

Calculated transition energy using B3-LYP [eV] HOMO-1

HOMO-1

> LUMO

HOMO-2 HOMO > LUMO > LUMO+1

> LUMO+1

> LUMO+2

2.18

2.30

2.54

2.67

2.81

2.98

2.19

2.31

2.63

2.79

2.86

2.97

[Ru-NCCH3]2+ 2.32

2.43

2.65

2.50

2.83

3.01

[Ru-NN]2+

2.61

2.80

3.10

2.95

3.17

3.34

Ru2+

1.58

1.69

1.91

2.65

2.92

2.96

HOMO

HOMO-1

> LUMO [Ru-OH2]2+ [Ru-OCO]2+

Summary We have studied the 1MLCT spectra of [Ru-L]2+ complexes with different small molecular ligands L by cryogenic photodissociation spectroscopy and density functional theory. A comparison of the spectra shows a strong influence of the ligand on the electronic structure of the complex. The aqua complex and the complex with L = CO2 have similar spectra, with several partially resolved electronic bands. In contrast, the complexes with L = CH3CN and N2 have much more congested spectra, and different electronic bands cannot be resolved at all, even at trap temperatures down to 30 K. Electronic spectra predicted by TDDFT calculations are in good qualitative agreement with the experimental data. The charge distribution in the complex is on the binding atom of the ligand L is roughly correlated with the charge distribution on Ru and trpy. Our data for the two complexes for which solvatochromic shift data are available (L = CH3CN and H2O) show that the strength of the interaction of a solvent molecule in the role of a coordinating ligand is more important than the polarity of the solvent.


16

Page 17 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Corresponding Author *Email: [email protected]; Phone: ++1-303-492-7841

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

ACKNOWLEDGMENT We thank the National Science Foundation for support under Grant CHE-1361814.

Supporting Information. Laser intensity dependence of peak absorption signals; molecular orbital level diagram for all complexes under study; calculated electronic transitions, selected orbitals and coordinates for all species under study.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 32

References (1)

Chen, C.; Wu, S.; Wu, C.; Chen, J.; Ho, K. A Ruthenium Complex with Superhigh LightHarvesting Capacity for Dye-Sensitized Solar Cells. Angew. Chem. Int. Ed. 2006, 118, 5954–5957.

(2)

Gao, F.; Wang, Y.; Zhang, J.; Shi, D.; Wang, M.; Humphry-Baker, R.; Wang, P.; Zakeeruddin, S. M.; Grätzel, M. A New Heteroleptic Ruthenium Sensitizer Enhances the Absorptivity of Mesoporous Titania Film for a High Efficiency Dye-Sensitized Solar Cell. Chem. Commun. 2008, No. 23, 2635–2637.

(3)

Wang, P.; Zakeeruddin, S. M.; Moser, J. E.; Nazeeruddin, M. K.; Sekiguchi, T.; Grätzel, M. A Stable Quasi-Solid-State Dye-Sensitized Solar Cell with an Amphiphilic Ruthenium Sensitizer and Polymer Gel Electrolyte. Nat. Mater. 2003, 2, 402–407.

(4)

Pugh, J. R.; Bruce, M. R. M.; Sullivan, B. P.; Meyer, T. J. Formation of a Metal-Hydride Bond and the Insertion. Key Steps in the Electrocatalytic Reduction of Carbon Dioxide to Formate Anion. Inorg. Chem. 1991, 30, 86–91.

(5)

Chen, Z.; Chen, C.; Weinberg, D. R.; Kang, P.; Concepcion, J. J.; Harrison, D. P.; Brookhart, M. S.; Meyer, T. J. Electrocatalytic Reduction of CO2 to CO by Polypyridyl Ruthenium Complexes. Chem. Commun. 2011, 47, 12607–12609.

(6)

Nagao, H.; Mizukawa, T.; Tanaka, K. Carbon-Carbon Bond Formation in the Electrochemical Reduction of Carbon Dioxide Catalyzed by a Ruthenium Complex. Inorg. Chem. 1994, 33, 3415–3420.

(7)

Ishida, H.; Tanaka, K.; Tanaka, T. Electrochemical CO2 Reduction Catalyzed by


18

Page 19 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[Ru(bpy)2(CO)2]2+ and [Ru(bpy)2(CO)Cl]+. The Effect of pH on the Formation of CO and HCOO-. Organometallics 1987, 6, 181–186. (8)

Tanaka, K.; Ooyama, D. Multi-Electron Reduction of CO2 via Ru-CO2, -C(O)OH, -CO, CHO, and -CH2OH Species. Coord. Chem. Rev. 2002, 226, 211–218.

(9)

Ishida, H.; Fujiki, K.; Ohba, T.; Ohkubo, K.; Tanaka, K.; Terada, T.; Tanaka, T. Ligand Effects of Ruthenium 2,2’-bipyridine and 1,10-Phenanthroline Complexes on the Electrochemical Reduction of CO2. J. Chem. Soc. Dalt. Trans. 1990, 2, 2155.

(10)

Concepcion, J. J.; Jurss, J. W.; Brennaman, M. K.; Hoertz, P. G.; Patrocinio, A. O. T.; Murakami Iha, N. Y.; Templeton, J. L.; Meyer, T. J. Making Oxygen with Ruthenium Complexes. Acc. Chem. Res. 2009, 42, 1954–1965.

(11)

Gersten, S. W.; Samuels, G. J.; Meyer, T. J. Catalytic Oxidation of Water by an OxoBridged Ruthenium Dimer. J. Am. Chem. Soc. 1982, 104, 4029–4030.

(12)

Wasylenko, D. J.; Ganesamoorthy, C.; Koivisto, B. D.; Henderson, M. a; Berlinguette, C. P. Insight into Water Oxidation by Mononuclear Polypyridyl Ru Catalysts. Inorg. Chem. 2010, 49, 2202–2209.

(13)

Zong, R.; Thummel, R. P. A New Family of Ru Complexes for Water Oxidation. J. Am. Chem. Soc. 2005, 127, 12802–12803.

(14)

Yagi, M.; Kaneko, M. Molecular Catalysts for Water Oxidation. Chem. Rev. 2001, 101, 21–35.

(15)

Blakemore, J. D.; Crabtree, R. H.; Brudvig, G. W. Molecular Catalysts for Water Oxidation. Chem. Rev. 2015, 115, 12974–13005.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(16)

Page 20 of 32

Kalyanasundaram, K. Photophysics, Photochemistry and Solar Energy Conversion with Tris(bipyridyl)ruthenium(II) and Its Analogues. Coord. Chem. Rev. 1982, 46, 159–244.

(17)

Alstrum-Acevedo, J. H.; Brennaman, M. K.; Meyer, T. J. Chemical Approaches to Artificial Photosynthesis. 2. Inorg. Chem. 2005, 44, 6802–6827.

(18)

Sun, Y.; Collins, S. N.; Joyce, L. E.; Turro, C. Unusual Photophysical Properties of a Ruthenium(II) Complex Related to [Ru(bpy)2(dppz)]2+. Inorg. Chem. 2010, 49, 4257– 4262.

(19)

Ji, L.-N.; Zou, X.-H.; Liu, J.-G. Shape- and Enantioselective Interaction of Ru(II)/Co(III) Polypyridyl Complexes with DNA. Coord. Chem. Rev. 2001, 216-217, 513–536.

(20)

Concepcion, J. J.; Tsai, M.-K.; Muckerman, J. T.; Meyer, T. J. Mechanism of Water Oxidation by Single-Site Ruthenium Complex Catalysts. J. Am. Chem. Soc. 2010, 132, 1545–1557.

(21)

Rillema, D. P.; Meyer, T. J.; Conrad, D. Redox Properties of Ruthenium(II) Tris Chelate Complexes Containing the Ligands 2,2’-Bipyrazine, 2,2'-Bipyridine, and 2,2'Bipyrimidine. Inorg. Chem. 1983, 22, 1617–1622.

(22)

Crutchley, R. J.; Lever, A. B. P. Comparative Chemistry of Bipyrazyl and Bipyridyl Metal Complexes: Spectroscopy, Electrochemistry and Photoanation. Inorg. Chem. 1982, 21, 2276–2282.

(23)

Knoll, J. D.; Albani, B. A.; Durr, C. B.; Turro, C. Unusually Efficient Pyridine Photodissociation from Ru (II) Complexes with Sterically Bulky Bidentate Ancillary Ligands. J. Phys. Chem. A 2014, 118, 10603–10610.


20

Page 21 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24)

Knoll, J. D.; Albani, B. A.; Turro, C. New Ru(II) Complexes for Dual Photoreactivity: Ligand Exchange and 1O2 Generation. Acc. Chem. Res. 2015, 48, 2280–2287.

(25)

Chen, Y. J.; Xie, P.; Heeg, M. J.; Endicott, J. F. Influence of The “innocent” ligands on the MLCT Excited-State Behavior of mono(bipyridine)ruthenium(II) Complexes: A Comparison of X-Ray Structures and 77 K Luminescence Properties. Inorg. Chem. 2006, 45, 6282–6297.

(26)

Bomben, P. G.; Koivisto, B. D.; Berlinguette, C. P. Cyclometalated Ru Complexes of Type [Ru(II)(N^N)2(C^N)]z: Physicochemical Response to Substituents Installed on the Anionic Ligand. Inorg. Chem. 2010, 49, 4960–4971.

(27)

Madeja, K.; Konig, E. Zur Frage Der Bindungsverhaltnisse in Komplexverbindungen Des eisen(II) Mit 1,10 Phenanthrolin. J. Inorg. Nucl. Chem 1963, 25, 377–385.

(28)

Spettel, K. E.; Damrauer, N. H. Synthesis, Electrochemical Characterization, and Photophysical Studies of Structurally Tuned Aryl-Substituted Terpyridyl Ruthenium(II) Complexes. J. Phys. Chem. A 2014, 118, 10649–10662.

(29)

Bargawi, K. R.; Llobet, A.; Meyer, T. J. Synthetic Design of MLCT Excited States. Ligand-Substituted, Mono-2,2’-bipyridine Complexes of ruthenium(II). J. Am. Chem. Soc. 1988, 110, 7751–7759.

(30)

Ernst, S. D.; Kaim, W. Energy Level Tailoring in ruthenium(II) Polyazine Complexes Based on Calculated and Experimental Ligand Properties. Inorg. Chem. 1989, 28, 1520– 1528.

(31)

Balzani, V.; Juris, A.; Ciamician, C. G.; Bologna, I. Photochemistry and Photophysics of


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 32

Ru ( II ) Polypyridine Complexes in the Bologna Group . From Early Studies to Recent Developments. Coord. Chem. Rev. 2001, 211, 97–115. (32)

Takeuchi, K. J.; Thompson, M. S.; Pipes, D. W.; Meyer, T. J. Redox and Spectral Properties of Monooxo Polypyridyl Complexes of Ruthenium and Osmium in Aqueous Media. Inorg. Chem. 1984, 23, 1845–1851.

(33)

Jakubikova, E.; Chen, W.; Dattelbaum, D. M.; Rein, F. N.; Rocha, R. C.; Martin, R. L.; Batista,

E.

R.

Electronic

Structure

and

Spectroscopy

of

[Ru(tpy)2]2+,

[Ru(tpy)(bpy)(H2O)]2+, and [Ru(tpy)(bpy)(Cl)]+. Inorg. Chem. 2009, 48, 10720–10725. (34)

Liu, F.; Concepcion, J. J.; Jurss, J. W.; Cardolaccia, T.; Templeton, J. L.; Meyer, T. J.; Carolina, N. Mechanisms of Water Oxidation from the Blue Dimer to Photosystem II. Inorg. Chem. 2008, 47, 1727–1752.

(35)

Xu, S.; Weber, J. M. Absorption Spectrum of a Ru(II)-Aquo Complex in Vacuo: Resolving Individual Charge-Transfer Transitions. J. Phys. Chem. A 2015, 119, 11509– 11513.

(36)

Hecker, C. R.; Fanwick, P. E.; McMillin, D. R. Evidence for Dissociative Photosubstitution Reactions of [Ru(trpy)(bpy)(NCCH3)]2+. Crystal and Molecular Structure of [Ru(trpy)(bpy)(py)](PF6)2·(CH3)2CO. Inorg. Chem. 1991, 30, 659–666.

(37)

Allen, A. D.; Bottomley, F. Inorganic Nitrogen Fixation. Nitrogen Compounds of the Transition Metals. Acc. Chem. Res. 1968, 1, 360–365.

(38)

Xu, S.; Gozem, S.; Krylov, A. I.; Christopher, C. R.; Weber, J. M. Ligand Influence on the Electronic Spectra of Monocationic Copper-Bipyridine Complexes. Phys. Chem. Chem.


22

Page 23 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Phys. 2015, 17, 31938–31946. (39)

Parr, R. G.; Yang, W. Density-Functional Theory of Atoms and Molecules; Oxford University Press: New York, 1989.

(40)

Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297–3305.

(41)

Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865–3868.

(42)

Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785–789.

(43)

Becke, A. D. Density-Functional Exchange-Energy Approximation with Correct Asymptotic Behavior. Phys. Rev. A 1988, 38, 3098–3100.

(44)

Furche, F. On the Density Matrix Based Approach to Time-Dependent Density Functional Response Theory. J. Chem. Phys. 2001, 114, 5982–5992.

(45)

Bauernschmitt, R.; Ahlrichs, R. Treatment of Electronic Excitations within the Adiabatic Approximation of Time Dependent Density Functional Theory. Chem. Phys. Lett. 1996, 256, 454–464.

(46)

Bauernschmitt, R.; Häser, M.; Treutler, O.; Ahlrichs, R. Calculation of Excitation Energies within Time-Dependent Density Functional Theory Using Auxiliary Basis Set Expansions. Chem. Phys. Lett. 1997, 264, 573–578.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(47)

Page 24 of 32

Reed, A. E.; Weinstock, R. B.; Weinhold, F. Natural Population Analysis. J. Chem. Phys. 1985, 83, 735–746.

(48)

Weigend, F.; Häser, M.; Patzelt, H.; Ahlrichs, R. RI-MP2: Optimized Auxiliary Basis Sets and Demonstration of Efficiency. Chem. Phys. Lett. 1998, 294, 143–152.

(49)

Ahlrichs, R.; Bär, M.; Häser, M.; Horn, H.; Kölmel, C. Electronic Structure Calculations on Workstation Computers: The Program System Turbomole. Chem. Phys. Lett. 1989, 162, 165–169.

(50)

Duffy, E. M.; Marsh, B. M.; Garand, E. Probing the Hydrogen-Bonded Water Network at the Active Site of a Water Oxidation Catalyst: [Ru(bpy)(tpy)(H2O)]2+·(H2O)0–4. J. Phys. Chem. A 2015, 119, 6326–6332.

(51)

Knurr, B. J.; Weber, J. M. Solvent-Driven Reductive Activation of Carbon Dioxide by Gold Anions. J. Am. Chem. Soc. 2012, 134, 18804–18808.

(52)

Knurr, B. J.; Weber, J. M. Structural Diversity of Copper − CO2 Complexes: Infrared Spectra and Structures of [Cu(CO2)n]- Clusters. J. Phys. Chem. A 2014, 118, 10246– 10251.

(53)

Knurr, B. J.; Weber, J. M. Solvent-Mediated Reduction of Carbon Dioxide in Anionic Complexes with Silver Atoms. J. Phys. Chem. A 2013, 117, 10764–10771.

(54)

Knurr, B. J.; Weber, J. M. Infrared Spectra and Structures of Anionic Complexes of Cobalt with Carbon Dioxide Ligands. J. Phys. Chem. A 2014, 118, 4056–4062.

(55)

Knurr, B. J.; Weber, J. M. Interaction of Nickel with Carbon Dioxide in [Ni(CO2)n]Clusters Studied by Infrared Spectroscopy. J. Phys. Chem. A 2014, 118, 8753–8757.


24

Page 25 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(56)

Weber, J. M. The Interaction of Negative Charge with Carbon Dioxide – Insight into Solvation, Speciation and Reductive Activation from Cluster Studies. Int. Rev. Phys. Chem. 2014, 33, 489–519.

(57)

Yoon, S.; Kukura, P.; Stuart, C. M.; Mathies, R. a. Direct Observation of the Ultrafast Intersystem Crossing in Tris(2,2′-bipyridine) Ruthenium(II) Using Femtosecond Stimulated Raman Spectroscopy. Mol. Phys. 2006, 104, 1275–1282.

(58)

Hewitt, J. T.; Concepcion, J. J.; Damrauer, N. H. Inverse Kinetic Isotope Effect in the Excited-State Relaxation of a Ru(II)-Aquo Complex: Revealing the Impact of HydrogenBond Dynamics on Nonradiative Decay. J. Am. Chem. Soc. 2013, 135, 12500–12503.

(59)

Pelikán, P.; Boča, R. Geometric and Electronic Factors of Dinitrogen Activation on Transition Metal Complexes. Coord. Chem. Rev. 1984, 55, 55–112.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 32

Table of Contents Graphic


26

Page 27 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. Structural template of the complexes under study. The ligand L represents a small molecule (here: H2O, CO2, CH3CN, N2). 84x75mm (150 x 150 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2. Schematic of the experimental apparatus. A: electrospray needle; B: desolvation capillary; C: skimmers; D: octupole ion guides; E: quadrupole bender; F: helium cryostat; G: quadrupole ion trap and acceleration unit (inset shows details, see text); H: ion lens and deflectors; I: mass gate; J: reflectron; K: microchannel plate detector; L: laser power meter; M: reactant gas inlet. 84x46mm (220 x 220 DPI)


Page 28 of 32

Page 29 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. Calculated minimum energy structures of [Ru-L]2+ for L = H2O and CO2 (the latter with two different isomers). Carbon atoms are shown in brown, nitrogen in blue, ruthenium in gold, oxygen in red, and hydrogen in white. 153x143mm (150 x 150 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. Photodissociation spectra of [Ru-L]2+. The ligands are given in each panel. Dots are raw data, full lines are 30-point sliding averages. The resolved features are labeled I through V (see also Table I). The vertical columns represent transitions predicted by TDDFT calculations. The transition energies are shifted by -0.15 eV for B3-LYP (open columns) and -0.3 eV for PBE0 (filled columns). Spectra for L = H2O and L = CO2 were acquired at 180 K trap temperature. Spectra for L = CH3CN were recorded at room temperature (red) and at 30 K trap temperature (blue), spectra for L = N2 were taken at room temperature (red) and at 70 K (blue). 84x179mm (300 x 300 DPI)


Page 30 of 32

Page 31 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. Calculated minimum energy structures of [Ru-L]2+ for L = CH3CN and N2 (the latter with two different isomers). Carbon atoms are shown in brown, nitrogen in blue, ruthenium in gold, oxygen in red, and hydrogen in white. 173x86mm (150 x 150 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TOC Figure 56x44mm (150 x 150 DPI)


Page 32 of 32

Ligand Influence on the Electronic Spectra of ... - ACS Publications

Recommend Documents