The Great Divide”: Carbene Silylene Germyle Advisors: Assoc. Prof. Ponnadurai Ramasami ([email protected]) University of Mauritius, Mauritius Prof. Henry F. Schaefer III Centre for Computational Quantum Chemistry (CCQC) University of Georgia, Athens, Georgia, USA Presented by: BUNDHUN Ashwini (MPhil/PhD) Department of Chemistry, University of Mauritius, Mauritius Doctoral Consortium e-poster Research Week 2009-2010 15-19 February 2010
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“The Great Divide”: Carbene Silylene Germylene” Advisors: Assoc. Prof. Ponnadurai Ramasami ([email protected]) University of Mauritius, Mauritius.
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Research Interests : Benchmarking Density Functional Theory (DFT) functionals against experimental data and high-quality
computations on GeX2 and GeXY (X, Y = H, F, Cl, Br, I, CN, CH3, SiH3, GeH3) germylene derivatives and
their tin analogues. These studies consist of the predicted trends in the geometrical parameters, the different forms of electron affinities and singlet-triplet gaps.
My current research also focuses on the “Quantum Mechanical Modeling for the GeX2/GeHX + GeH4
Reactions (X = H, F, Cl, and Br)”. I am using DFT to study in all seven reactions in the gas-phase and the stationary points on the potential energy surface are characterized. The gist is that the energetics for the GeH2 + GeH4 Ge2H6 system is consistent vis-à-vis available experimental data. Hence the trend in the
energetics and thermochemical data for the all mono- and di-substituted systems are further studied and compared to the parent reaction.
Other interests :
DFT study of the carbon chains CnX, CnX+ and CnX– (X = O and Se; n = 1–10).
DFT study of dicyanogermylenes and XGeCY3 species (X, Y = H, F, Cl, Br, I).2
Introduction – Importance of germylene species, Application processes
Supporting Information Available via the internet at J. Phys.Chem. A 2009, 113, 8080. http://pubs.acs.org.
Table 2. Experimental structural parameters, singlet-triplet gaps, electron affinities (eV) of available germylene derivatives.
EA (GeH2) = 1.0970 ± 0.0027 kcal mol-1
EA (GeF2) > 1.30 ± 0.30 kcal mol-1
EA (GeCl2) = 2.56 kcal mol-1
EA (GeBr2) >1.6 kcal mol-1
More Compounds
Table 1. Experimental Techniques
• Electron impact appearance energy
• Laser photoelectron spectroscopy
• UV photoelectron spectroscopy
• Microwave spectroscopy
• Infrared spectroscopy
• Laser-induced fluorescence spectroscopy
BH&HLYP BLYP B3LYP
GeH2 1.01 (1.03) 1.02 (1.05) 1.15 (1.18)
GeF2 0.85 (0.87) 0.81 (0.83) 0.96 (0.98)
GeCl2 1.65 (1.66) 1.49 (1.50) 1.69 (1.70)
GeBr2 1.81 (1.82) 1.60 (1.61) 1.83 (1.84)
GeI2 2.06 (2.07) 1.76 (1.77) 2.03 (2.04)
Ge(CN)2 2.73 (2.56) 2.56 (2.73) 2.78 (2.78)
Ge(CH3)2 0.44 (0.46) 0.49 (0.52) 0.60 (0.62)
Ge(SiH3)2 1.87 (1.90) 1.83 (1.86) 1.99 (2.06)
Ge(GeH3)2 1.91 (1.95) 1.89 (1.93) 2.04 (2.08)
BH&HLYP BLYP B3LYP
GeH2 1.06 (24.4) 1.23 (28.3) 1.16 (26.7)
GeF2 3.57 (82.4) 3.72 (85.9) 3.69 (85.0)
GeCl2 2.66 (61.4) 2.83 (65.2) 2.78 (64.1)
GeBr2 2.38 (54.8) 2.52 (58.1) 2.48 (57.2)
GeI2 2.08 (47.9) 2.05 (47.2) 2.07 (47.7)
Ge(CN)2 1.76 (40.6) 1.87 (43.2) 1.85 (42.7)
Ge(CH3)2 1.26 (29.1) 1.38 (31.9) 1.34 (31.0)
Ge(SiH3)2 0.48 (11.0) 0.68 (15.6) 0.60 (13.8)
Ge(GeH3)2 0.57 (13.2) 0.77 (17.8) 0.69 (16.0)
Table 4. Singlet-triplet gaps (eV) (kcal mol-1 in parentheses).
Table 3. Germylene adiabatic electron affinities EAad and zero-point corrected EAad values (in parentheses) in eV.
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“Predicted Electron Affinities and Singlet-Triplet Gaps”
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BH&HLYP BLYP B3LYP
GeH2 0.99 1.01 1.14
GeF2 0.69 0.67 0.81
GeCl2 1.38 1.25 1.44
GeBr2 1.56 1.39 1.60
GeI2 1.84 1.58 1.83
Ge(CN)2 2.78 3.06 2.71
Ge(CH3)2 0.35 0.36 0.51
Ge(SiH3)2 1.66 1.61 1.78
Ge(GeH3)2 1.72 1.70 1.84
BH&HLYP BLYP B3LYP
GeH2 1.02 1.03 1.16
GeF2 1.04 0.98 1.14
GeCl2 1.97 1.76 1.99
GeBr2 2.11 1.86 2.10
GeI2 2.32 1.97 2.26
Ge(CN)2 2.80 2.35 2.76
Ge(CH3)2 0.50 0.53 0.66
Ge(SiH3)2 2.04 1.99 2.19
Ge(GeH3)2 2.08 2.05 2.20
Table 6. Vertical detachment energy (VDE) in eV.Table 5. Vertical electron affinity (VEA) in eV.
BHLYP functional provides the best agreement of the predicted structures with
experimentally geometrical parameters
“Predicted VEA and VDE”
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H F Cl Br I CN H F Cl Br I CN
Graph of adiabatic electron affinities EAad(ZPVE) (eV) versus halogen substituents.
Graph of singlet-triplet gaps (eV) versus halogen substituents.
“Graphical :- Electron Affinities & Singlet-Triplet Gaps”
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.3
0 1 2 3 4 5 6
Eaa
d(Z
PV
E)
(eV
)
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H F CH3 SiH3 GeH3
Graph of adiabatic electron affinities EAad(ZPVE) (eV) versus H, F, CH3, SiH3 and GeH3 substituents.
“Graphical :- Electron Affinities & Singlet-Triplet Gaps”
0.5
1
1.5
2
2.5
3
3.5
4
0 1 2 3 4 5 6
Sing
let-
trip
let
gap
(eV
)
H F CH3 SiH3 GeH3
Graph of singlet-triplet (eV) versus H, F, CH3, SiH3 and GeH3 substituents..
“Factors Affecting Electron Affinities”
Electronegativities of the halo-substituents
Size of the central divalent germanium centre
Size of the halogen substituents
Electron density clouding the divalent germanium centre
Interelectron repulsion
Electronegative substituents withdraw electron density from Ge resulting in more positive charge making Ge a better -acceptor, enhancing -donation from the halo-substituents
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“Fluoro Substituents”
EAad(ZPVE) containing fluoro substituents decreases sharply due to:
Shortness of the Ge-F bond distance
Fluorine lone pair crowds into the germanium -orbital
4p contribution of the Ge atom higher in the singlet states
4s contribution of the Ge atom is less in the triplet state
Enhanced polarity of the Ge-F bond :- polarizability effect
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“Chloro/bromo/iodo Substituents”
Ge-Cl, Ge-Br and Ge-I bonds are less polarized
Poorer withdrawing abilities of the Ge-Cl, Ge-Br and Ge-I bonds
Less effective donor abilities of non-bonding electron pairs
Accounting for the sizes of the Chloro/bromo/iodo substituents
No large difference in the withdrawing abilities of the Ge-Cl/Ge-Br/Ge-I bonds
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“Standard Pauling Electronegativities”
F(3.98) > Cl (3.16) > Br (2.96) > I (2.66) > C (2.55) > H (2.20) > Ge (2.01) > Si (1.90)
Electronegative substituents withdraw charge from the divalent germanium centre leading
to an increase in the central atom’s positive charge
Despite electronegativities decrease in the order F > Cl > Br > I , EAad(ZPVE) increases in the opposite order
Hence electronegativity is not the sole factor in determining the ability of germylenes
to accept an extra electron
21Allfred A. L. J. Inorg. Nucl. Chem. 1961, 17, 215.
“Conclusions”
Dimethylgermylene also binds an electron, though weakly, ranging from 0.44 eV – 0.60 eV
Down the periodic table, there is an increasing ability to bind an electron
GeH3 and SiH3 groups behave similarly
No neutral structure of C2v symmetry was found for Ge(CH3)2 on the PES
Singlet-triplet splittings for germylene derivatives are consistently larger than those for methylene and silylene
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EAad(ZPVE) values (eV) obtained with the B3LYP functional range from 0.62 eV to [Ge(CH3)2] to
2.08 eV [Ge(GeH3)2]
Results compare satisfactorily with the few available experimental values
Largest singlet-triplet gaps is predicted for GeF2, with Ge(GeH3)2 having the smallest value of 0.57 eV
Singlet-triplet splittings for germylene derivatives are consistently larger than those for methylene and silylene
Invariably, as one progresses down the periodic table C Si Ge, the “great divide” occurs between carbon and silicon
“Conclusions”
“Acknowledgments”
Hassan H. Abdallah (Universiti Sains Malaysia)
Paul Blowers (The University of Arizona)
Centre for Computational Quantum Chemistry (CCQC)
Facilities at the University of Mauritius (UOM)
Mauritius Tertiary Education Commission (TEC)
Reviewers
The Organizing Committee of Doctoral Consortium
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“Representative Publications”
“Germylene Energetics: Electron Affinities and Singlet−Triplet Gaps of GeX2 and GeXY Species
(X, Y = H, CH3, SiH3, GeH3, F, Cl, Br, I)”
Bundhun A.; Ramasami P.; Schaefer H. F. J. Phys. Chem. A 2009, 113, pp 8080–8090. -------------------------------------------------------------------------------------------------------------------------------
“Quantum Mechanical Modeling for the GeX2/GeHX + GeH4 Reactions (X = H, F, Cl, and Br)”
Bundhun A.; Blowers P.; Ramasami P.; Schaefer H. F. J. Phys. Chem. A (Accepted Manuscript)
“DFT study of the carbon chains CnX, CnX+ and CnX– (X = O and Se; n = 1–10)”
Bundhun A.; Ramasami P. EPJ D (Accepted Manuscript) ---------------------------------------------------------------------------------------------------------------