Vibrational Spectroscopy and Theory of Cu+(CH4)n and Ag+(CH4)n (n=1-6) Abdulkadir Kocak Muhammad Affawn Ashraf Ricardo Metz June 19, 2014

M+ + CH4 MCH2+ + H2 M+(CH4) Interest Some 3rd row transition metal ions can activate methane Entrance channel complexes M+ + CH4 MCH2+ + H2 Spectroscopy structure and bonding M+(CH4)

Open Questions What is the geometry of M+(CH4)? h2 h3 vs

Open Questions How does the 2nd CH4 bind? Eclipsed vs Staggered

Open Questions How does the 3rd CH4 bind? Equilateral Tee vs

Open Questions Structures of larger complexes? 2nd Solvation Shell? 1st Shell vs 2nd Shell How does the 4th CH4 bind? Tetrahedral Square Planar vs

Calculated Binding Energies CAM-B3LYP functional Cu:6-311++G(3df,3pd) Ag:aug-cc-pVTZ-PP C,H: 6-311++G(3df,3pd) Vibrational Spectroscopy! Binding energies (cm-1) for : M+(CH4)n-1-(CH4)  M+(CH4)n-1 + CH4 Metal n=1 n=2 n=3 n=4 n=5 n=6 Cu 8473 8261 1943 585 335 138 Ag 5450 5385 1903 1214 431 183

Apparatus Overview Laser Make Ions Mass Select Spectrometer Spectroscopy Laser Lasers Metal rod Accelerator Ion optics Mass gate Reflectron Detector CH4, He, Ar Ablation laser Here is the instrument. I know you are all very familiar with the instrument from the former students but let me overview again briefly. Our experimental setup includes three sections. First make ions; then mass select the narrow range of masses that you are interested in; then get the spectra… Metal ions are produced by laser ablation to a metal rod. Metal ions then reacted with either H2O or CH4 in carrying gas. Then ions are expanded into vacuum and cooled to rotational temperatures of 10-20K. photodissociated by a second laser which can be an IR OPO/OPA or visible dye laser. Finally photofragment ions are collected at detector at different time than parent ions. Scanning laser and monitoring the fragment ion signal photodissociation spectrum is produced. If laser is resonance with transition, molecule will absorb… If the absorbed energy is enough to break any bond in the molecule, it will dissociate… So two key points here: molecule must absorb, and must dissociate to see fragment… R. B. Metz, Adv. Chem. Phys. 138, 331 (2008)

Characteristic features of η2 complexes rCu-C: 2.158 Å Cu+(CH4)

Characteristic features of η3 complexes rFe-C: 2.106 Å Fe+(CH4) rMn-C: 2.636 Å Mn+(CH4)

Cu+(CH4)(Ar)2 and Ag+(CH4) Calculations: B3LYP/6-311++G(3df,3pd) scaled Cu+(CH4)(Ar)2 Red shift (~300 cm-1) Both η2 rCu-C=2.189 Å Ag+(CH4) Calculations:B3LYP/ aug-cc-pVTZ on Ag and 6-311++G(3df,3pd) on C,H scaled IRMPD Silver spectra is IRMPD, therefore broad peaks… Small shift suggest small binding energy, since Ag bigger in size… rAg-C=2.511 Å Smaller red shift (~200 cm-1) A. Kocak, M. A. Ashraf and R. B. Metz, to be submitted.

smaller red shift than Cu Cu+(CH4)2Ar and Ag+(CH4)2 Cu+(CH4)2Ar Eclipsed, C2v rCu-C=2.201 Å Staggered, Cs rCu-C=2.184, 2.186 Å Erel=0 cm-1 Erel= 72 cm-1 Ag+(CH4)2 Similar red shifts to n=1 All η2 Staggered, D2d rAg-C=2.474 Å Ag+(CH4)2 by IRMPD smaller red shift than Cu

Cu+(CH4)3 and Ag+(CH4)3 Smaller red shifts than n=1,2 Symmetrical Equilateral, D3h rCu-C=2.328 Å Ag+(CH4)3 Ag smaller red shift than Cu; n=3 clearly smaller red shift than n=1,2 Equilateral, D3h rAg-C=2.628 Å

Cu+(CH4)4 and Ag+(CH4)4 Symmetrical All η2 Cu+(CH4)4 Tetrahedral rCu-C:2.472 Å Erel=0 cm-1 Trigonal pyramidal rCu-C:3@2.326 Å 1@3.594 Å Erel=19 cm-1 Ag+(CH4)4 Symmetrical All η2 Tetrahedral rAg-C=2.746 Å

Cu+(CH4)5 and Ag+(CH4)5: 1st shell vs. 2nd shell Tetrahedral+1CH4 rCu-C:2@2.466 2.459, 2.497, 4.466 Å (η3) Erel=17 cm-1 Trigonal bipyramidal rCu-C: 3@2.328 Å 2@3.680 Å (η3) Erel=0 cm-1 Ag+(CH4)5 Increased intensity near free C-H Td + 1CH4 Mostly h2 Tetrahedral+1CH4 rAg-C=2.727, 2.732, 2.739, 2.795 4.277Å (η3) Erel=236 cm-1 Trigonal bipyramidal rAg-C: 2.804, 2@2.827 Å 2@2.928 Å Erel=0 cm-1

Cu+(CH4)6 and Ag+(CH4)6: 1st shell vs. 2nd shell Tetrahedral + 2CH4 rCu-C:2@2.454 Å, 2@2.488 Å, 2@4.458 Å (η3) Erel=147 cm-1 Trigonal bipyramidal + 1CH4 rCu-C: 3@2.326 Å, 2@3.695 Å (η3), 1@4.974 Å Erel=0 cm-1 Ag+(CH4)6 Trigonal bipyramidal+ 1 CH4 rAg-C=2@2.81 Å 2@2.94 Å 1@4.749 Å Erel=0cm-1 Tetrahedral+2CH4 rAg-C=2@2.729 Å 2@2.767 Å 2@4.497 Å (η3) Erel=82 cm-1 Octahedral rAg-C=6@2.96 Å Erel=100 cm-1

Summary Ground state geometries determined Since it is d10, molecules choose highly symmetric structures Cu+ binds 4 CH4, Ag+ binds 6 CH4 for first shell 5th and 6th CH4 are in the second shell and η3 for Cu+ All first shell CH4 are η2 for Ag+

Acknowledgements Prof. Metz Abdulkadir Kocak Chris Copeland Dave Johnston NSF Thank you all! Questions