“The Great Divide”: Carbene Silylene Germylene” Advisors: Assoc. Prof. Ponnadurai Ramasami...
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Transcript of “The Great Divide”: Carbene Silylene Germylene” Advisors: Assoc. Prof. Ponnadurai Ramasami...
“The Great Divide”: Carbene Silylene Germylene”
Advisors:
Assoc. Prof. Ponnadurai Ramasami ([email protected])
University of Mauritius, Mauritius
Prof. Henry F. Schaefer IIICentre 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 2009-201015-19 February 2010
Ashwini Bundhun
Advisors : Assoc. Prof. (Dr) Ponnadurai Ramasami & Prof. Henry. F. Schaefer III
BSc Chemistry MSc in Chemistry [email protected]
University of Mumbai University of Mauritius
India Mauritius
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
Theoretical Methods – Programs Suite, Optimization, Functionals, Basis sets
Geometrical Parameters – Symmetries, States, Multiplicities, Bond lengths, Bond angles
Predicted trends in:-
Singlet-Triplet Gaps
Electron Affinities
Graphical representation of singlet-triplet gaps and electron affinities
Conclusions
Acknowledgements
3
“Presentation Overview”
“Introduction”
• Germylenes : Divalent germanium compounds are important chemical species
Intermediates in processes employed in the semiconductor industry
Processes:
- Plasma-etching
- Chemical vapor deposition (CVD)
Areas in which electron affinities play important roles:
MicroelectronicsSiliconSchottky diodes Molecular clustersPolymer photoluminescence
4
“Theoretical Methods”
Program Suite : Gaussian 03 & GaussView
Functionals : BH&HLYP, BLYP and B3LYP
Basis sets : DZP++ for all atoms except the 6-311G(d,p) for iodine atom
Frequency Analysis : Harmonic vibrational frequencies
Predicted are the four different forms of electron affinities:
Adiabatic electron affinities (EAad)
Corrected adiabatic electron affinity (EAad(ZPVE))
Vertical electron affinity (VEA) & Vertical detachment energy of the anion (VDE)
Singlet-triplet splittings
5http://www.gaussian.com/
EAad = E(optimized neutral) − E(optimized anion) [1]
EAvert = E(optimized neutral) − E(anion at optimized neutral geometry) [2]
VDE = E(neutral at optimized anion geometry) – E(optimized anion) [3]
EAad(ZPVE) = [E(optimized neutral) + ZPVEneutral] – [E(optimized anion) + ZPVEanion] [4]
The singlet-triplet splittings are predicted as the energy difference between the neutral ground state and the lowest triplet state.
“Theoretical Computations”
6
7
r/Å
X
X–
VDE EA VEA
= 2
= 1
= 0, J = 0
= 2
= 1
= 0, J = 0
1.0 2.0
1.0
0.5
Energy (eV)
Potential energy surfaces representing diatomic and polyatomic molecules for an anionic molecule, X– and its corresponding neutral molecule X.
The transitions show the adiabatic electron affinity (EA), vertical electron affinity (VEA) and vertical detachment energy (VDE).
For the non-linear and polyatomic molecules with n number of atoms, there are (3n – 6) modes allowing a cut through the active mode(s).
“Potential Energy Surfaces”
Rienstra-Kiracofe J. C.; Tschumper G. S; Schaefer H. F.; Nandi S.; Ellison B. Chem. Rev. 2002, 102, 231.
Methylene is a ground state triplet
Silylene and germylene are ground state singlets
In all MH2 (C, Si and Ge) species with six valence electrons the singlet state has two electrons
in an orbital of -symmetry (a1). In the triplet state this electron pair is unpaired and one
electron resides in an orbital of -symmetry (b1)
8
“Multiplicities of Carbene Analogues”
Triplet 3B1 Singlet 1A1Singlet 1A1
C
a1
b1 Si
a1
Ge
a1
9
Energy(Units)
“HOMO-LUMO Gaps in SiH2 and GeH2 larger than in CH2”
1a1
2a1
3a1
1b1
1b2
2b2
Apeloig Y.; Pauncz R.; Karni M.; West R., Steiner W.; Chapman D. Organometallics 2003, 22, 3250.
10
r(Si-Br) = 2.249 Å, (Br-Si-Br) = 102.7 EA > 1.7 kcal mol-1
r(C-Br) = 1.740 Å, (Br-C-Br) = 112.0 EA = 1.928 ± 0.082 kcal mol-1
EA = 1.880 ± 0.070 kcal mol-1
MBr2
r(Si-Cl) = 2.088 Å, (Cl-Si-Cl) = 102.8 r(Si-Cl) = 2.041 Å, (Cl-Si-Cl) = 114.5 EA = 0.77 ± 0.13 kcal mol-1
r(C-Cl) = 1.716 Å, (Cl-C-Cl) = 109.2r(C-Cl) = 1.714 Å, (Cl-C-Cl) = 109.3
MCl2
r(Si-F) = 1.590 Å, (F-Si-F) = 100.8r(Si-F) = 1.586 Å, (F-Si-F) = 113.1 EA = 0.10 ± 0.10 kcal mol-1
r(C-F) = 1.304 Å, (F-C-F) = 104.8r(C-F) = 1.300 Å, (F-C-F) = 104.9ES-T = 237.14 0.02 kJ mol-1
EA = 0.180 ± 0.020 kcal mol-1 87
EA = 0.1790 ± 0.0050 kcal mol-1
EA = 0.07 ± 0.15 kcal mol-1 EA = < 1.30 ± 0.80 kcal mol-1 EA > 0.2005 kcal mol-1
EA = 2.6495 kcal mol-1
MF2
r(Si-H) = 1.514 Å, (H-Si-H) = 92.1 r(Si-H) = 2.861 Å, (H-Si-H) = 92.0 EA = 1.123 ± 0.022 kcal mol-1
r(C-H) = 1.078 Å, (H-C-H) = 136.0r(C-H) = 1.077 Å, (H-C-H) = 134.0r(C-H) = 1.107 Å, (H-C-H) = 102.4ES-T = 9.09 0.20 kcal mol-1
EA = 0.6520 ± 0.0060 kcal mol-1 EA = 0.210 ± 0.015 kcal mol-1
EA = 0.208 ± 0.031 kcal mol-1 EA > 0.90 ± 0.40 kcal mol-1
MH2
Si CM
Table 1. Experimental structural parameters, singlet-triplet gaps, electron affinities (eV) for the carbon and silicon analogues.
All references are listed in Table 6. Bundhun A.; Ramasami P.; Schaefer H. F. J. Phys. Chem. A 2009, 113, 8080.
11
“Structural Parameters of Germylene Derivatives”
B3LYP 1.601 ÅBLYP 1.618 ÅBHLYP 1.584 Å
90.790.291.5
1.629 Å1.647 Å1.612 Å
91.591.292.2
1.548 Å1.565 Å1.533 Å
119.6119.5119.6
GeH2 Triplet (3B1)GeH2 Neutral (1A1) GeH2¯ Anion (2B1)
B3LYP 1.771 ÅBLYP 1.798 ÅBHLYP 1.744 Å
97.698.496.8
1.863 Å1.893 Å1.834 Å
96.197.295.0
GeF2 Neutral (1A1) GeF2¯ Anion (2B1)
1.769 Å1.802 Å1.738 Å
GeF2 Triplet (3B1)
115.0116.0113.8
100.8102.399.5
2.394 Å2.425 Å2.368 Å
100.8101.7100.0
B3LYP 2.226 ÅBLYP 2.254 ÅBHLYP 2.200 Å
119.2119.9118.4
2.210 Å2.251 Å2.176 Å
GeCl2 Neutral (1A1) GeCl2¯ Anion (2B1) GeCl2 Triplet (3B1)
12
“Structural Parameters of Germylene Derivatives”
B3LYP 2.383 ÅBLYP 2.413 ÅBHLYP 2.358 Å
102.2103.2101.3
2.556 Å2.588 Å2.532 Å
102.3103.8101.0
2.369 Å2.411 Å2.334 Å
121.1121.6120.4
GeBr2 Neutral (1A1) GeBr2¯ Anion (2B1) GeBr2 Triplet (3B1)
104.2105.7102.8
2.786 Å2.819 Å2.764 Å
103.9105.0103.0
B3LYP 2.611 ÅBLYP 2.643 ÅBHLYP 2.587 Å
122.0121.9121.8
2.596 Å2.641 Å2.560 Å
GeI2 Neutral (1A1) GeI2¯ Anion (2B1) GeI2 Triplet (3B1)
Supporting Information Available via the internet at J. Phys.Chem. A 2009, 113, 8080. http://pubs.acs.org.
Ge(CN)2 Neutral (1A1) Ge(CN)2¯ Anion (2B1) Ge(CN)2 Triplet (3B1)
B3LYP 1.987 ÅBLYP 2.005 ÅBHLYP 1.972 Å
1.172 Å1.187 Å1.156 Å
93.093.392.9
170.5169.7171.5 93.4
94.092.8
2.022 Å2.038 Å2.012 Å
170.2169.3171.3
1.178 Å1.192 Å1.162 Å
1.893 Å1.912 Å1.881 Å
174.2174.4174.7
117.0115.9117.01.175 Å
1.191 Å1.158 Å
13
Ge(CH3)2
Ge(GeH3)2
Ge(SiH3)2
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.
14
“Predicted Electron Affinities and Singlet-Triplet Gaps”
15
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”
16
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
)
17
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
18
“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
19
“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
20
“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
22
23
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
24
“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) ---------------------------------------------------------------------------------------------------------------
25