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Exploring the redox states and reactivity of a vanadium bistetrazinylpyridine complex with DFT tetrazinylpyridine complex with DFT Adam M. Terwilliger (GVSU) Kenneth G. Caulton (Indiana) Kenneth G. Caulton (Indiana) Richard L. Lord (GVSU)
Microsoft PowerPoint - 2014_MU3C_Terwilliger_Final (2).pptxExploring the redox states and p g reactivity of a vanadium bis
tetrazinylpyridine complex with DFTtetrazinylpyridine complex with DFT
Adam M. Terwilliger (GVSU)
Richard L. Lord (GVSU)
• Recognized for ability to “accept” an electron
• Idea: make the ligand more electron acceptingIdea: make the ligand more electron accepting  by introducing additional nitrogens
Luca, O.R.; Crabtree, R.H. Chem. Soc. Rev. 2013, 42, 14401459.  Caulton, K.G. Eur. J. Inorg. Chem. 2012, 13, 435443.
RedoxActive Ligands
– VIV + btzp1–
VanadiumOxo Applications
• Biological reactions and enzyme inhibitionBiological reactions and enzyme inhibition
Figure from: Crans, D.C.; Smee, J.J.; Ernestas, G.; Yang, L. Chem. Rev. 2004, 104, 849902.
VanadiumOxo Applications
Figures from: Hirao, T. Chem. Rev. 1997, 97, 27072724.
• Calculations used Gaussian09Calculations used Gaussian09 
• B3LYP/LANL2DZ/631G(d,p) level of theory
f i fi d b bl• Wavefunctions confirmed to be stable
• Minima verified through harmonic analysis
• Redox states were assigned by – visualizing spin densitiessua g sp de s es
– analyzing corresponding orbitals
• What are the oxidation states of the metal andWhat are the oxidation states of the metal and  ligands in the lowest energy spin state of  [(btzp)VCl2O]0?[(btzp)VCl2O] ?
• Which N atom does H atom prefer to bind to  in this complex?in this complex?
• How does the electron distribution change  h h H bi d b ?when the H atom binds to btzp?
doublet (S = 1/2)
quartet (S = 3/2)( / ) ( / )
C2N3 1.346 1.356
N3N4 1.321 1.320
C3N4 1.333 1.335
Unpaired electron Spin density
Conclusions for [(btzp)VCl2O]0
• The spin density and SOMO show that thep y unpaired electron density is concentrated around the metal center with no concentration on the btzp ligandbtzp ligand.
• The spin density plot shows a slight excess of spin (white) at the oxygen; however, the corresponding orbital analysis (used to generate the SOMO) did not identify an unpaired electron on Oon O.
• This finding of one unpaired electron at the metal is consistent with VIV and btzp0.
Which N Does H Bind To?
• H atom can bind to N2, N3, N4, ,
• Proton or H(dot)?
• If H+ where does that• If H+, where does that electron go to?
III / ( )• VIII / btzpH+ (seems unlikely)
• VIV / btzpH0 (where is radical?)
• VV / btzpH– (can btzp oxidize VIV?)
• [(btzp)VCl O] + (triplet) or (singlet)[(btzp)VCl2O] +  (triplet) or  (singlet)
Species Spin State H Position Relative
Species Spin State H Position Free Energy
2S Singlet N2 –1.54
2T Triplet N2 +0.38T
3S Singlet N3 0.00
3T Triplet N3 +1.36
4T Triplet N4 +7.21
2 /3 l t i 3 t h ll ith• 2S/3S lowest in energy. 3S matches well with  experimental structure. Is 2S artificially stabilized?
intramolecular Hbondintramolecular Hbond
Topdown view of the optimized structures showing Hbonding in 2S (left) vs. 3S (right).
What Are Redox/Spin States in 3S?
• Consistent with VIV and btzpH0 , AFcoupled
Conclusions for [(btzpH)VCl2O]0Conclusions for [(btzp H)VCl2O]
• Excellent structural agreement with expExcellent structural agreement with exp.
• Crystallography suggested anionic btzpH 
C l l i h b i h d• Calculations show btzpH is uncharged
• The metal SOMO does notmix significantly  with the ligand SOMO (S = 0.36); spatial  separation of opposite spins is found to give a  more stable electronic structure 
Submitted to Acta Crystallographica C
• Prof. Caulton and his group at IU for provoking o . Cau to a d s g oup at U o p o o g our interest in this chemistry (NSF/CHE0822838)
• GVSU Office of Undergraduate Research and g Scholarship for a Modified Student Summer  Scholar Award to Adam Terwilliger
• GVSU Center for Scholarly and Creative  Excellence Faculty Research GrantinAid to  Richard LordRichard Lord
• MU3C for Computational Resources (NSF/CHE 1039925)1039925)