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“The Great Divide”: Carbene  Silylene  Germylene”

Doctoral Consortium e-poster Research Week 2009-2010 15-19 February 2010. “The Great Divide”: Carbene  Silylene  Germylene”. Presented by: BUNDHUN Ashwini (MPhil/PhD) Department of Chemistry, University of Mauritius, Mauritius. Advisors:

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“The Great Divide”: Carbene  Silylene  Germylene”

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  1. Doctoral Consortium e-poster Research Week 2009-201015-19 February 2010 “The Great Divide”: Carbene  Silylene  Germylene” Presented by: BUNDHUN Ashwini (MPhil/PhD) Department of Chemistry, University of Mauritius, Mauritius Advisors: Assoc. Prof. Ponnadurai Ramasami (ramchemi@intnet.mu) University of Mauritius, Mauritius Prof. Henry F. Schaefer III Centre for Computational Quantum Chemistry (CCQC) University of Georgia, Athens, Georgia, USA

  2. Ashwini Bundhun • Advisors :Assoc. Prof. (Dr) Ponnadurai Ramasami & Prof. Henry. F. Schaefer III • BSc ChemistryMSc in Chemistryashwinibilly@gmail.com • 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

  3. “Presentation Overview” • 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

  4. “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: • Microelectronics • Silicon • Schottky diodes • Molecular clusters • Polymer photoluminescence 4

  5. “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 5 http://www.gaussian.com/

  6. “Theoretical Computations” 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. 6

  7. Energy (eV) X  = 2  = 1  = 0, J = 0 1.0 X– VEA EA VDE 0.5  = 2  = 1  = 0, J = 0 r/Å 1.0 2.0 “Potential Energy Surfaces” 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). 7 Rienstra-Kiracofe J. C.; Tschumper G. S; Schaefer H. F.; Nandi S.; Ellison B. Chem. Rev.2002, 102, 231.

  8. a1 a1 a1 b1 C Si Ge “Multiplicities of Carbene Analogues” • 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) Triplet 3B1 Singlet 1A1 Singlet 1A1 8

  9. 2b2 3a1 1b1 2a1 1b2 “HOMO-LUMO Gaps in SiH2 and GeH2 larger than in CH2” Energy (Units) 1a1 9 Apeloig Y.; Pauncz R.; Karni M.; West R., Steiner W.; Chapman D. Organometallics2003, 22, 3250.

  10. M C Si MH2 r(C-H) = 1.078Å, (H-C-H) = 136.0 r(C-H) = 1.077 Å, (H-C-H) = 134.0 r(C-H) = 1.107 Å, (H-C-H) = 102.4 ES-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 r(Si-H) = 1.514Å, (H-Si-H) = 92.1 r(Si-H) = 2.861 Å, (H-Si-H) = 92.0 EA = 1.123 ± 0.022 kcal mol-1 MF2 r(C-F) = 1.304 Å, (F-C-F) = 104.8 r(C-F) = 1.300 Å, (F-C-F) = 104.9 ES-T = 237.14  0.02 kJ mol-1 EA = 0.180 ± 0.020 kcal mol-187 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 r(Si-F) = 1.590Å, (F-Si-F) = 100.8 r(Si-F) = 1.586 Å, (F-Si-F) = 113.1 EA = 0.10 ± 0.10 kcal mol-1 MCl2 r(C-Cl) = 1.716 Å, (Cl-C-Cl) = 109.2 r(C-Cl) = 1.714 Å, (Cl-C-Cl) = 109.3 r(Si-Cl) = 2.088Å, (Cl-Si-Cl) = 102.8r(Si-Cl) = 2.041 Å, (Cl-Si-Cl) = 114.5EA = 0.77 ± 0.13 kcal mol-1 MBr2 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 r(Si-Br) = 2.249Å, (Br-Si-Br) = 102.7EA > 1.7 kcal mol-1 Table 1. Experimental structural parameters, singlet-triplet gaps, electron affinities (eV) for the carbon and silicon analogues. 10 All references are listed in Table 6. Bundhun A.; Ramasami P.; Schaefer H. F. J. Phys. Chem. A2009, 113, 8080.

  11. GeH2¯Anion (2B1) GeH2 Triplet (3B1) GeH2 Neutral (1A1) B3LYP 1.601 Å BLYP 1.618 Å BHLYP 1.584 Å 1.629 Å 1.647 Å 1.612 Å 1.548 Å 1.565 Å 1.533 Å 90.7 90.2 91.5 91.5 91.2 92.2 119.6 119.5 119.6 GeF2¯Anion (2B1) GeF2 Triplet (3B1) GeF2 Neutral (1A1) B3LYP 1.771 Å BLYP 1.798 Å BHLYP 1.744 Å 1.863 Å 1.893 Å 1.834 Å 1.769 Å 1.802 Å 1.738 Å 97.6 98.4 96.8 96.1 97.2 95.0 115.0 116.0 113.8 GeCl2¯Anion (2B1) GeCl2 Neutral (1A1) GeCl2 Triplet (3B1) 2.210 Å 2.251 Å 2.176 Å 2.394 Å 2.425 Å 2.368 Å B3LYP 2.226 Å BLYP 2.254 Å BHLYP 2.200 Å 119.2 119.9 118.4 100.8 101.7 100.0 100.8 102.3 99.5 “Structural Parameters of Germylene Derivatives” 11

  12. “Structural Parameters of Germylene Derivatives” GeBr2 Neutral (1A1) GeBr2¯Anion (2B1) GeBr2 Triplet (3B1) B3LYP 2.383 Å BLYP 2.413 Å BHLYP 2.358 Å 2.556 Å 2.588 Å 2.532 Å 2.369 Å 2.411 Å 2.334 Å 102.2 103.2 101.3 102.3 103.8 101.0 121.1 121.6 120.4 GeI2 Neutral (1A1) GeI2¯Anion (2B1) GeI2 Triplet (3B1) 2.786 Å 2.819 Å 2.764 Å 2.596 Å 2.641 Å 2.560 Å B3LYP 2.611 Å BLYP 2.643 Å BHLYP 2.587 Å 103.9 105.0 103.0 122.0 121.9 121.8 104.2 105.7 102.8 Ge(CN)2 Neutral (1A1) Ge(CN)2¯Anion (2B1) Ge(CN)2 Triplet (3B1) B3LYP 1.987 Å BLYP 2.005 Å BHLYP 1.972 Å 2.022 Å 2.038 Å 2.012 Å 1.893 Å 1.912 Å 1.881 Å 170.2 169.3 171.3 170.5 169.7 171.5 174.2 174.4 174.7  93.0 93.3 92.9 117.0 115.9 117.0  93.4 94.0 92.8 1.172 Å 1.187 Å 1.156 Å 1.178 Å 1.192 Å 1.162 Å 1.175 Å 1.191 Å 1.158 Å 12 Supporting Information Available via the internet at J. Phys.Chem. A2009, 113, 8080. http://pubs.acs.org.

  13. More Compounds Ge(CH3)2 Table 1. Experimental Techniques • Electron impact appearance energy • Laser photoelectron spectroscopy • UV photoelectron spectroscopy • Microwave spectroscopy • Infrared spectroscopy • Laser-induced fluorescence spectroscopy Ge(SiH3)2 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) >1.6kcal mol-1 Ge(GeH3)2 13 Supporting Information Available via the internet at J. Phys.Chem. A2009, 113, 8080. http://pubs.acs.org.

  14. BH&HLYP BLYP B3LYP BH&HLYP BLYP B3LYP GeH2 1.01 (1.03) 1.02 (1.05) 1.15 (1.18) GeH2 1.06 (24.4) 1.23 (28.3) 1.16 (26.7) GeF2 0.85 (0.87) 0.81 (0.83) 0.96 (0.98) GeF2 3.57 (82.4) 3.72 (85.9) 3.69 (85.0) GeCl2 1.65 (1.66) 1.49 (1.50) 1.69 (1.70) 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) GeBr2 1.81 (1.82) 1.60 (1.61) 1.83 (1.84) GeI2 2.08 (47.9) 2.05 (47.2) 2.07 (47.7) GeI2 2.06 (2.07) 1.76 (1.77) 2.03 (2.04) Ge(CN)2 1.76 (40.6) 1.87 (43.2) 1.85 (42.7) Ge(CN)2 2.73 (2.56) 2.56 (2.73) 2.78 (2.78) Ge(CH3)2 1.26 (29.1) 1.38 (31.9) 1.34 (31.0) Ge(CH3)2 0.44 (0.46) 0.49 (0.52) 0.60 (0.62) Ge(SiH3)2 0.48 (11.0) 0.68 (15.6) 0.60 (13.8) 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) Ge(GeH3)2 0.57 (13.2) 0.77 (17.8) 0.69 (16.0) “Predicted Electron Affinities and Singlet-Triplet Gaps” Table 3. Germylene adiabatic electron affinities EAad and zero-point corrected EAad values (in parentheses) in eV. Table 4. Singlet-triplet gaps (eV) (kcal mol-1 in parentheses). 14

  15. BH&HLYP BLYP B3LYP BH&HLYP BLYP B3LYP GeH2 0.99 1.01 1.14 GeH2 1.02 1.03 1.16 GeF2 0.69 0.67 0.81 GeF2 1.04 0.98 1.14 GeCl2 1.38 1.25 1.44 GeCl2 1.97 1.76 1.99 GeBr2 2.11 1.86 2.10 GeBr2 1.56 1.39 1.60 GeI2 2.32 1.97 2.26 GeI2 1.84 1.58 1.83 Ge(CN)2 2.80 2.35 2.76 Ge(CN)2 2.78 3.06 2.71 Ge(CH3)2 0.50 0.53 0.66 Ge(CH3)2 0.35 0.36 0.51 Ge(SiH3)2 2.04 1.99 2.19 Ge(SiH3)2 1.66 1.61 1.78 Ge(GeH3)2 2.08 2.05 2.20 Ge(GeH3)2 1.72 1.70 1.84 “Predicted VEA and VDE” Table 5. Vertical electron affinity (VEA) in eV. Table 6. Vertical detachment energy (VDE) in eV. BHLYP functional provides the best agreement of the predicted structures with experimentally geometrical parameters 15

  16. H F Cl Br I CN H F Cl Br I CN “Graphical :- Electron Affinities & Singlet-Triplet Gaps” Graph of adiabatic electron affinities EAad(ZPVE) (eV) versus halogen substituents. Graph of singlet-triplet gaps (eV) versus halogen substituents. 16

  17. “Graphical :- Electron Affinities & Singlet-Triplet Gaps” H F CH3 SiH3 GeH3 H F CH3 SiH3 GeH3 Graph of adiabatic electron affinities EAad(ZPVE) (eV) versus H, F, CH3, SiH3 and GeH3 substituents. Graph of singlet-triplet (eV) versus H, F, CH3, SiH3 and GeH3 substituents. . 17

  18. “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

  19. “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

  20. “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

  21. “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 centreleading • 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 21 Allfred A. L. J. Inorg. Nucl. Chem. 1961, 17, 215.

  22. “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. “Conclusions” • 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 23

  24. “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

  25. “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

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