Daniel Weidinger 1, Cassidy Houchins 2 and Jeffrey C. Owrutsky 3 (1)National Research Council Postdoctoral Researcher (2)SRA International (3)Chemistry Division, Naval Research Laboratory, Washington, DC 1 of 11 OSU International Symposium on Molecular Spectroscopy June 23, 2011 Vibrational Dynamics of Tricyanomethanide

2 of 11 Tricyanomethanide Infrared Spectroscopy A. Why study tricyanomethanide (TCM)? Ionic liquids for fuel cells, solar cells Similar to anion N(CN) 2 - (DCA) low viscosity → high conductivity B.Vibrational probes and solvation probes Anion studies: NCO -, N 3 -, N(CN) 2 -, NCS - TCM hydrophilic & strong IR absorber C.Metal cyanides Contrast with metal cyanides, e.g. Au(CN) 2 - Prussian blue and CN adsorbates D.New res earch Steady state and dynamic spectra Ab initio calculations Source: Source: D. Weidinger et al., J. Chem. Phys. 134 (2011)

3 of 11 Tricyanomethanide Vibrations IR-active frequencies around 2170 cm -1 Asymmetric CN-stretch (E’) High Intensity (~50,000 M -1 cm -2 ) TCM Raman Spectrum (solid KTCM) TCM Vibrational Modes (D 3h symmetry) Raman A’ band at 2222 cm -1 ; previous spectra: Beaumont et al., Inorg. Chim. Acta 84 (1984) 141 Hipps et al., J. Phys. Chem. 89 (1985) 5459 Dixon et al., J. Am. Chem. Soc. 108 (1986) 2582

4 of 11 Tricyanomethanide IR Spectra Vibrational Band Frequencies TCM Spectra 1 Dahl et al., J. Chem. Phys. 123 (2005) Dixon et al., J. Am. Chem. Soc. 108 (1986 ) 2582 TCM Center Freq. (cm -1 ) DCA Center Freq. (cm -1 ) NCS - Center Freq. (cm -1 ) H2OH2O D2OD2O Methanol Formamide [BMIM][BF 4 ] Solid DMSO

5 of 11 IR Pump-Probe – Vibrational Relaxation ν = Transient Absorption Transient Bleach Pump-probe diagram Ultrafast Pump-Probe IR setup: 4 μJ, ~350 fs IR pulses 5 cm -1 resolution Ti:Sapphire Oscillator Regenerative Amplifier OPA DFG Crystal Sample Monochromator Delay Stage IR Detector To Lock-in, Computer

6 of 11 IR Pump-Probe – Vibrational Relaxation Strong transient absorption (as much as 40 mOD with 1 uJ pump) Concentrations of ~0.1 M Similar widths, decay times from adsorption, bleach features FWHM = 10 cm -1 Anharmonicities of ~16 cm -1 Transient Spectrum: TCM in DMSO, 1 ps Delay

7 of 11 IR Pump-Probe – Vibrational Relaxation Slower vibrational relaxation than DCA, N 3 - Relaxation in MeOH slower than H 2 O, opposite of frequency trend TCM TA Lifetime (ps) TCM TB Lifetime (ps) DCA T 1 (ps) NCS - T 1 (ps) H2OH2O D2OD2O Methanol Formamide [BMIM][BF 4 ] DMSO TCM TA Decay Decay lifetimes vary from 5 to 30 ps Solvent trend is similar to DCA & most small anions Table of VER lifetimes

8 of 11 Calculations of CN bands Calculated TCM Frequencies Model / Basis SetSymmetricAnti-Symmetric ν cn S cm -1 IR Intensity km / mole ν cn AS,1 cm -1 IR Intensity km / mole MP2/aug-cc-pVDZ B3LYP/aug-cc-pVDZ B3LYP/aug-cc-pVTZ Experimental Calculations performed using Gaussian 09 Structures optimized within the C 1 point group Frequencies calculated for all optimized structures to ensure minimum

9 of 11 Calculations of CN bands Experimental and Calculated TCM and DCA Frequencies Model DCA 1 TCM ν cn S cm -1 ν cn AS,1 cm -1 ν cn S cm -1 ν cn AS,1 cm -1 MP B3LYP Experiment MP2 calculations for DCA and TCM have same reversed energy order Order is correct in B3LYP calculations 1Georgieva et al.., J. Mol. Struct. 752 (2005) 14

10 of 11 Calculations of Thermochemistry Electron affinities: Structures optimized at MP2/aug-cc-pVDZ and B3LYP/aug-cc-pVXZ (x=2,3) Proton Affinity calculated from MP2 and B3LYP optimized structures Pertinent to transport properties & electrolytic applications 1,2 ModelVDE (eV) ADE (eV) PA (eV) MP2/aug-cc-pVDZ B3LYP/aug-cc-pVDZ B3LYP/aug-cc-pVTZ Calculated electron detachment energies and proton affinities (TCM) 1S. Y. Kim et al., Nature Communications 1 (2010) 2Q. Dai et al., Comptes Rendus Chimie 9 (2006) 601 3B. Jagoda-Cwiklik et al., J. Phys. Chem. A 111 (2007) 7719 Observed 3 DCA electron affinity (ADE) = eV Calculated DCA ADE (by MP2) is 4.1 eV

11 of 11 Conclusions IR Spectroscopy and IR Pump-Probe Studies of TCM “New” IR solvent probe High frequency Strong CN stretch Good solubility Shift-lifetime trend similar to DCA Long decay time for CN-containing anion MeOH is anomalous solvent Computations IR and Raman frequencies Electron Affinities Proton Affinities and transport properties

Acknowledgements Scientists Jeffrey C. Owrutsky (NRL) Cassidy Houchins (SRA International) Code 6111 Funding: Office of Naval Research Sponsorship: National Research Council 12 of 11

Extras TCM TA Lifetime (ps) TCM TB Lifetime (ps) DCA T 1 (ps) NCS - T 1 (ps) H2OH2O 4.8 ± ± 0.4 D2OD2O12.2 ± ± 0.4 Methanol12.0 ± ± ± ± 2.1 Formami de 18.1 ± ± 0.4 [BMIM][B F 4 ] 27.5 ± ± ± ± 3.1 DMSO28.1 ± ± ± ± 5.6 Model / Basis Set SymmetricAnti-symmetric ν cn S cm - 1 IR Inten sity km / mole ν cn A S,1 cm - 1 IR Inten sity km / mole ν cn AS,2 cm -1 IR Inten sity km / mole MP2/aug-cc- pVDZ B3LYP/aug- cc-pVDZ B3LYP/aug- cc-pVTZ