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.
Methods
• 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
Goals
• 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
AcknowledgementsAcknowledgements
• 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)
