“The Great Divide”: Carbene Silylene Germylene”

“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)


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


119.2119.9118.4

2.210 Å2.251 Å2.176 Å

GeCl2 Neutral (1A1) GeCl2¯ Anion (2B1) GeCl2 Triplet (3B1)

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“Structural Parameters of Germylene Derivatives”


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


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)


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

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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.

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“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

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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) ---------------------------------------------------------------------------------------------------------------

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“The Great Divide”: Carbene Silylene Germylene”

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