ANION PHOTOELECTRON SPECTROSCOPIC STUDIES OF NbCr(CO) n ‾ (n = 2,3) HETEROBIMETALLIC CARBONYL COMPLEXES Melissa A. Baudhuin, Praveenkumar Boopalachandran, and Doreen G. Leopold University of Minnesota – Chemistry Department June 25 th,

2 SAFETY MOMENT Gas Cylinder Safety ALWAYS wear safety glasses: ▫ When connecting/disconnecting regulators Do NOT leave gas cylinder: ▫ Uncapped without a regulator

3 METAL CARBONYL COMPLEXES Motivation Transition metal carbonyl complex ▫ Used for CO-releasing molecules (CORMs) as a therapeutic agent Method Anion Photoelectron Spectroscopy ▫ Obtain electron affinities, vibrational frequencies, and excited state energies ▫ Provide benchmark values for computational studies Garcia-Gallego, S.; Bernardes, G. J. L. Angew. Chem. Int. Ed. 2014, 53, 9712

Flowing Afterglow Ion-Molecule Reactor Magnetic Sector Mass Analyzer Photoelectron Spectroscopy Chamber Slits Argon Ion Laser Electron Kinetic Energy Analyzer Chamber 1 Chamber 2 Chamber 3 Chamber 4 Chamber 5 hν (488 or 514 nm) 4 Electron Detector MINNESOTA ANION PHOTOELECTRON SPECTROMETER (MAPELS)

5 INTERPRETING DATA (eKE) Electron Kinetic Energy (eBE) Electron Binding Energy eBE = hν - eKE X+ e ‾ ←X‾X‾ +hνhν X*+ e ‾ ←X‾X‾ +hνhν X‾X‾ X X* 1 eV ≈ 8065 cm -1

6 MASS SPECTRUM OF FLOW TUBE REACTION PRODUCTS: Nb + Cr(CO) 6

7 PHOTOELECTRON SPECTRUM OF NbCr(CO) 2 ‾ AT 488 nm A

8 Neutral moleculeTransition A Electron affinity (eV)1.668 ± ν 1 (cm -1 )1935 ± 20 ν 2 (cm -1 )395 ± 20 AnionTransition A ν 2 (cm -1 )380 ± 20 A 395 cm cm cm -1 PHOTOELECTRON SPECTRUM OF NbCr(CO) 2 ‾ AT 488 nm

Complexes have small number of active modes ▫ Expect high symmetry structures ▫ Small geometry changes between anion and neutral states DFT – B3LYP/gen ▫ Identify the isomeric structure ▫ Determine anion and neutral electronic states ▫ Compare calculated values to our experimental measurements 9 gen: Nb & Cr → SDD C & O → G(df,pd) NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS

10 NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS Geometry & Frequency Calculations: ▫ NbCr(CO) 2 ‾  Spin Multiplicity (2S + 1): 1, 3, & 5 states ▫ NbCr(CO) 2  Spin Multiplicity: 2, 4, & 6 states Calculated Franck-Condon Progression: ▫ NbCr(CO) 2 ← NbCr(CO) 2 ‾  Spin allowed transitions  1 electron transitions Isomers Tested:

11 NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS Isomers Tested: ISOMERS ELIMINATED DUE TO: 1)Calculated Franck-Condon progression did not match experimental spectrum 2)Imaginary frequencies in the anionic state 3)Convergence failure in the geometry optimization

12 NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS

13 NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS Anion State 1 A 1 ← Neutral State 2 A 1 π back bonding σ bonding

14 NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS Anion State 1 A 1 ← Neutral State 2 A 1 Electron Detached: sσ type MO π back bonding σ bonding

15 NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS Anion State 1 A 1 ← Neutral State 2 A 1 r (Cr-Nb) = Å r (C-O) = Å r (Nb-C) = Å r (Nb-C) = Å r (Cr-Nb) = Å r (C-O) = Å 81° 83° π back bonding σ bonding v CO = 2040 cm -1 v CO = 1860 cm -1

16 NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS Neutral moleculeTransition AB3LYP/gen Electron affinity (eV)1.668 ± ν 1 (cm -1 )1935 ± ν 2 (cm -1 )395 ± AnionTransition AB3LYP/gen ν 2 (cm -1 )380 ± ν 1 : CO stretch

17 NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS Neutral moleculeTransition AB3LYP/gen Electron affinity (eV)1.668 ± ν 1 (cm -1 )1935 ± ν 2 (cm -1 )395 ± AnionTransition AB3LYP/gen ν 2 (cm -1 )380 ± ν 2 : M-M stretch + M-L bend

18 PHOTOELECTRON SPECTRUM OF NbCr(CO) 3 ‾ AT 488 nm A

19 Neutral moleculeTransition A Electron affinity (eV)1.162 ± ν 1 (cm -1 )1910 ± 20 ν 2 (cm -1 )1445 ± 20 ν 3 (cm -1 )560 ± 20 ν 4 (cm -1 )260 ± 20 AnionTransition A ν 3 (cm -1 )560 ± 20 ν 4 (cm -1 )275 ± 20 PHOTOELECTRON SPECTRUM OF NbCr(CO) 3 ‾ AT 488 nm A

20 NbCr(CO) 3 AND NbCr(CO) 3 ‾ DFT ANALYSIS Isomers Tested : Geometry & Frequency Calculations: ▫ NbCr(CO) 3 ‾  Spin Multiplicity: 1, 3, 5, & 7 states ▫ NbCr(CO) 3  Spin Multiplicity: 2, 4, & 6 states Calculated Franck-Condon Progression: ▫ NbCr(CO) 3 ← NbCr(CO) 3 ‾  Spin allowed transitions  1 electron transitions

21 NbCr(CO) 3 AND NbCr(CO) 3 ‾ DFT ANALYSIS Isomers Tested: ALL ISOMERS AND SPIN STATES TESTED THUS FAR HAVE: 1)Calculated Franck-Condon progression did not match experimental spectrum 2)Imaginary frequencies in the anionic state 3)Convergence failure in the geometry optimization

22 NbCr(CO) 3 AND NbCr(CO) 3 ‾ DFT ANALYSIS Isomers Tested: ISSUES COULD BE FROM: 1)Large deviations in the S 2 values  Calculated complexes are spin contaminated  DFT is not an appropriate treatment for these complexes 2)Multiple low-lying excited states Spin Multiplicity Calculated S 2 value True S 2 value S(S + 1) Singlet Doublet Triplet Quartet

Thank You 23 Current Group Members Doreen Leopold Melissa Baudhuin Alex Schnepper Previous Group Members Dr. Praveen Boopalachandran Dr. Steve Miller Dr. Ashfaq Bengali Srijay Rajan Funding NSF

Questions 24

25 MoleculeElectron Affinity (eV) Neutral State v CO stretch (cm -1 ) NbCr0.793 ± CO2143 Cr(CO) 3 * ± ± 10 NbCr(CO) ± ± 20 NbCr(CO) ± ± 20 SUMMARY OF EXPERIMENTAL RESULTS *Bengali, A. A.; Casey S. M.; Cheng, C.-L.; Dick, J. P.; Fenn, T.; Villalta, P. W.; Leopold, D. G. J. Am. Chem. Soc. 1992, 114,

26 NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS Anion State 1 A 1 ← Neutral State 2 A Å Å (1860 cm -1 ) Å Å Å Å (2040 cm -1 ) 81°83° Electron Detached: sσ type MO

27 r1r1 r2r2 r3r3 α1α1 NbCr(CO) 2 & NbCr(CO) 2 ‾ B3LYP/gen Geometric Parameters Anion ( 1 A 1 )Neutral ( 2 A 1 ) r 1 (Å) r 2 (Å) r 3 (Å) α 1 (°)8183 NbCr Experimental & B3LYP/SDD Geometric Parameters Anion ( 1 ∑ + )Neutral ( 2 ∆) Experiment r (Å)1.815 ± a ± b B3LYP/SDD r (Å) a Baudhuin, M. A.; Boopalachandran, P.; Rajan, S.; Leopold, D. G. (to be published) b Sickafoose, S. M.; Langenberg, J. D.; Morse, M. D. J. Phys. Chem. A. 2000, 104, r NbCr(CO) 2 AND NbCr(CO) 2 ‾ DFT ANALYSIS

28 NbCr(CO) 3 AND NbCr(CO) 3 ‾ DFT ANALYSIS Anion State 7 A Neutral State 6 A ← Å Å Å2.717 Å Å Å

29 r1r1 r2r2 r3r3 α1α1 NbCr(CO) 3 & NbCr(CO) 3 ‾ B3LYP/gen Geometric Parameters Anion ( 7 A)Neutral ( 6 A) r 1 (Å) r 2 (Å) r 3 (Å) α 1 (°) NbCr Experimental & B3LYP/SDD Geometric Parameters Anion ( 1 ∑ + )Neutral ( 2 ∆) Experiment r (Å)1.815 ± a ± b B3LYP/SDD r (Å) a Baudhuin, M. A.; Boopalachandran, P.; Rajan, S.; Leopold, D. G. (to be published) b Sickafoose, S. M.; Langenberg, J. D.; Morse, M. D. J. Phys. Chem. A. 2000, 104, r NbCr(CO) 2 AND NbCr(CO) 3 ‾ DFT ANALYSIS

30 NbCr(CO) 3 AND NbCr(CO) 3 ‾ DFT ANALYSIS

31 NbCr(CO) 3 AND NbCr(CO) 3 ‾ DFT ANALYSIS Neutral moleculeTransition AB3LYP/gen Electron affinity (eV)1.162 ± ν 1 (cm -1 )1910 ± ν 2 (cm -1 )1445 ± 20- ν 3 (cm -1 )560 ± ν 4 (cm -1 )260 ± AnionTransition AB3LYP/gen ν 3 (cm -1 )560 ± ν 4 (cm -1 )275 ± 20402

Cr(CO) 2 ‾ PHOTOELECTRON SPECTRUM 32 Bengali, A. A. Ph.D. Thesis, University of Minnesota, Minneapolis, MN, 1992

Cr(CO) 3 ‾ PHOTOELECTRON SPECTRUM 33 Bengali, A. A.; Casey S. M.; Cheng, C.-L.; Dick, J. P.; Fenn, T.; Villalta, P. W.; Leopold, D. G. J. Am. Chem. Soc. 1992, 114,

Cr(CO) 3 ‾ DFT ANALYSIS 34 Bengali, A. A.; Casey S. M.; Cheng, C.-L.; Dick, J. P.; Fenn, T.; Villalta, P. W.; Leopold, D. G. J. Am. Chem. Soc. 1992, 114,

35 Cr(CO) 3 AND Cr(CO) 3 ‾ DFT ANALYSIS Anion State 2 A 1 Neutral State 1 A 1 ← Electron Detached: sσ type MO Å Å Å Å

Cr(CO) 3 ‾ DFT ANALYSIS 36 Bengali, A. A.; Casey S. M.; Cheng, C.-L.; Dick, J. P.; Fenn, T.; Villalta, P. W.; Leopold, D. G. J. Am. Chem. Soc. 1992, 114, Neutral moleculeTransition AB3LYP/gen Electron affinity (eV)1.349 ± ν 1 (cm -1 ) 2000 ± ν 2 (cm -1 ) 680 ± ν 3 (cm -1 ) 480 ± AnionTransition AB3LYP/gen ν 2 (cm -1 )680 ± 10700