Rotational Spectra Of Cyclopropylmethyl Germane And Cyclopropylmethyl Silane: Dipole Moment And Barrier To Methyl Group Rotation Rebecca A. Peebles, Sean A. Peebles, Michael D. Foellmer, Jonathan M. Murray, Michal M. Serafin, Amanda L. Steber Department Of Chemistry, Eastern Illinois University, 600 Lincoln Avenue, Charleston, IL Gamil A. Guirgis, Richard Liberatore Department Of Chemistry And Biochemistry, The College Of Charleston, Charleston, SC James R. Durig, Charles J. Wurrey Department Of Chemistry, University Of Missouri - Kansas City, Kansas City, MO 64110

Introduction Three possible conformers Three possible conformers Possible methyl group internal rotation Possible methyl group internal rotation Multiple isotopologues Multiple isotopologues 70 Ge, 72 Ge, 73 Ge, 74 Ge, 76 Ge 70 Ge, 72 Ge, 73 Ge, 74 Ge, 76 Ge 28 Si, 29 Si, 30 Si 28 Si, 29 Si, 30 Si Only one isotope ( 73 Ge, I = 9/2) is quadrupolar Only one isotope ( 73 Ge, I = 9/2) is quadrupolar Model for fitting internal rotation Model for fitting internal rotation Ge or Si

Conformers cis gauche trans

Cyclopropylmethylgermane (CMG) Relative Energy / cm A / MHz B / MHz C / MHz  a / D  b / D  c / D  tot / D cis gauche trans MP2/6-311+G(d), no ZPE corrections

CMG Experimental Technique Samples synthesized at College of Charleston (SC) Samples synthesized at College of Charleston (SC) Fourier-transform microwave (FTMW) spectroscopy at Eastern Illinois University Fourier-transform microwave (FTMW) spectroscopy at Eastern Illinois University Liquid samples Liquid samples Vapor pressure = ~3 Torr Vapor pressure = ~3 Torr Transferred as vapor to glass bulb Transferred as vapor to glass bulb Concentration <0.5% in ~1 atm He/Ne Concentration <0.5% in ~1 atm He/Ne Optimizations at MP2/6-311+G(d) level Optimizations at MP2/6-311+G(d) level No ZPE corrections No ZPE corrections

Frequency / MHz A E 7.8% 36.5% 7.8% 27.4% 20.5% Combination of two data files 100 scans each S/N ~ 40

CMG Fit Using XIAM 1 1 XIAM: H.Hartwig and H.Dreizler, Z.Naturforsch, 51a (1996) 923. Parameter 70 Ge 72 Ge 73 Ge 74 Ge 76 Ge A / MHz (10) (10) (26) (8) (11) B / MHz (35) (4) (11) (26) (4) C / MHz (33) (4) (11) (25) (4)  J / kHz 0.618(8)0.622(8)0.48(4)0.600(6)0.597(9)  JK / kHz –4.4(9)–4.358(26)–4.7(7)–4.29(7)–4.18(10)  J / kHz 0.183(5)0.179(6)0.179(fixed)0.195(4)0.181(6) V 3 / kJ mol – (8)4.737(8)4.734(23)4.736(6)4.740(9) F 0 / GHz 159.8(3)159.1(3)159.2(7)159.18(21)159.3(3) I  / u Å (5)3.176(6)3.175(13)3.175(4)3.173(6)  / rad (4)0.8537(10)0.858(4)0.8580(7)0.8593(10) s.d. / kHz N

Ab Initio c Observed c  a / D (10)  b / D (4)  c / D (9)  tot / D (5) Ab Initio Observed A / MHz (7) B / MHz (3) C / MHz (2) I  / u Å 2 ~3.1 a 3.179(4) V 3 / kJ mol (6)  ia  (4)  ib  (4)  ic  b CMG Comparison With Ab Initio a Estimate, used as XIAM input b Angle  fixed at 3° c For 72 Ge a b c

73 Ge Quadrupole Coupling Constants Series of density functional theory predictions with varying basis sets – B3LYP worked best Series of density functional theory predictions with varying basis sets – B3LYP worked best Basis Set ClGeH 3  zz / MHz MeGeH 3  zz / MHz aug-cc-pvdz– G(2d,2p)– aug-cc-pvtz– G(3df,3pd)– aug-cc-pvqz– aug-cc-pv5z– Experiment 1 –93.032(15) 3 (max) 1 For many calculated quadrupole coupling constants and comparison with experimental data:

Frequency / MHz Ge E A E A E A Frequency / MHz

73 Ge A state E state Predicted B3LYP/ G(3df,3pd) Observed

Comparison with Calculated 73 Ge Coupling Constants ParameterExperimentalPredicted % Difference  aa / MHz 8.134(8)7.914 –2.7  bb –  cc / MHz 7.693(26)  aa / MHz 8.134(8)7.914 –2.7  bb / MHz –0.2205–0.099 –55  cc / MHz –7.9135–7.815 –1.2

Comparison of Experimental 73 Ge Coupling Constants Compound  zz (MHz) 1 ClGeH 3 –93.032(15) FGeH 3 –93.03(10) MeGeH 3 3 Cyclopropylmethylgermane ~9 – 10 HCCGeH For many calculated quadrupole coupling constants and comparison with experimental data:

Cyclopropylmethylsilane (CMS) Relative Energy / cm A / MHz B / MHz C / MHz  a / D  b / D  c / D  tot / D cis gauche trans MP2/6-311+G(d), no ZPE corrections

CMS Experimental Details Liquid samples Liquid samples Concentration ~1% in ~2.5 atm He/Ne Concentration ~1% in ~2.5 atm He/Ne Lines split into A and E states, some appear as “triplets” Lines split into A and E states, some appear as “triplets” Spectra of all three isotopologues assigned in natural abundance Spectra of all three isotopologues assigned in natural abundance 28 Si = 92.2%, 29 Si = 4.7%, 30 Si = 3.1% 28 Si = 92.2%, 29 Si = 4.7%, 30 Si = 3.1% Consistent only with gauche conformation Consistent only with gauche conformation Optimizations performed at MP2/6-311+G(d) Optimizations performed at MP2/6-311+G(d)

A E 28 Si 4 04 – scans Frequency / MHz

Parameter 28 Si 29 Si 30 Si A / MHz (9) (21) (21) B / MHz (6) (9) (9) C / MHz (6) (7) (7)  J / kHz 0.871(10) a  JK / kHz –7.40(11) –7.40 a  J / kHz 0.211(3) a V 3 / kJ mol –1 6.83(9)6.82(1)6.84(1) F 0 / GHz 164(3) 164 a I  / u Å (5) 3.09 a  / rad 0.745(4) a s.d. / kHz N CMS Fit Using XIAM a fixed at 28 Si value

CMS Spectroscopic Fitting Ab Initio Observed A / MHz (9) B / MHz (6) C / MHz (6) I  / u Å a 3.09(5) V 3 / kJ mol (9)  ia  (2)  ib  (2)  ic  (fixed) Ab Initio Observed  a / D (2)  b / D (11)  c / D (19)  tot / D (13) a Estimate, used as XIAM input

MeXH 2 (C 3 H 5 ) MeXH 3 MeXH 2 F Me 2 XH 2 Me 3 XCl Me 3 XBr Me 3 XI References: see extra slides at end of Powerpoint (too many to fit here!)

Conclusions Barriers to rotation comparable to similar species Barriers to rotation comparable to similar species Silane barriers typically higher than germane Silane barriers typically higher than germane B3LYP/ G(3df,3pd) appears to predict 73 Ge quadrupole coupling constants accurately B3LYP/ G(3df,3pd) appears to predict 73 Ge quadrupole coupling constants accurately Gauche conformer dominates for both CMG and CMS Gauche conformer dominates for both CMG and CMS Ab initio energies indicate that higher energy cis conformer could also be present Ab initio energies indicate that higher energy cis conformer could also be present

Acknowledgements ? ? ? Richard Liberatore (College of Charleston summer research funding)

Barrier to Rotation Compound V 3 / kJ mol -1 Reference 1 X = Ge X = Si MeXH 2 (C 3 H 5 ) 4.736(6)6.83(9) This work MeXH (11)6.67(20) Laurie 1959; Kivelson 1954 MeXH 2 F 3.94(8)6.52(13) Roberts 1976; Pierce 1958 Me 2 XH Thomas 1969; Niide 2004 Me 3 XCl (3)6.901(11) Schnell 2006; Merke 2002 Me 3 XBr 4.783(12)-- Schnell 2008 Me 3 XI (36) Merke See next slide for full references

References for Barrier Comparisons D. Kivelson, J. Chem. Phys. 22 (1954) V. W. Laurie, J. Chem. Phys. 30 (1959) I. Merke, W. Stahl, S. Kassi, D. Petotprez, G. Wlodarczak, J. Mol. Spect. 216 (2002) 437. I. Merke, A. Lüchow, W. Stahl, J. Mol. Struct (2006) 295. Y. Niide, M. Hayashi, J. Mol. Spect. 223 (2004) 152. L. Pierce, J. Chem. Phys. 29 (1958) 383. R. F. Roberts, R. Varma, J. F. Nelson, J. Chem. Phys. 64 (1976) M. Schnell, J.-U. Grabow, Phys. Chem. Chem. Phys. 8 (2006) M. Schnell, J.-U. Grabow, Chem. Phys. 343 (2008) 121. E. C. Thomas, V. W. Laurie, J. Chem. Phys. 50 (1969) 3512.

a) “  / E 2 (calc)” is the Stark coefficient obtained from a second-order perturbation theory calculation, using the fitted rotational constants given in Table 3.1. b) “% Difference” is obtained from “  / E 2 (calc)” – “  / E 2 (obs)” Table 3.6: Dipole moment data for the 72 Ge isotopomer. Transition  / E 2 (calc) a) (10 5 MHz cm 2 / V 2 )  / E 2 (obs) (10 5 MHz cm 2 / V 2 ) % Difference b) 1 10 ← 1 01 |M| = ← 0 00 |M| = ← 1 01 |M| = ← 1 01 |M| = ← 2 02 |M| = ← 2 02 |M| = ← 3 03 |M| = ← 3 03 |M| =  a = (10) D  b = 0.581(4) D  c = 0.305(9) D  total = 0.680(5) D

Table 3.7: Kraitchman single isotopic substitution coordinates (germane). All errors are to ±0.0001Å. 70 Ge 72 Ge 73 Ge 76 GeAb initio |a| / Å |b| / Å |c| / Å

Squared Dipole Component Dipole Component A / / B / / C / / Total / Debyes Transition |M| Observed Calculated Obs-Calc Percent 1( 1, 1) - 0( 0, 0) E E E ( 1, 2) - 1( 0, 1) E E E ( 1, 1) - 1( 0, 1) E E E ( 1, 0) - 0( 0, 0) E E E ( 1, 0) - 1( 0, 1) E E E ( 1, 1) - 1( 0, 1) E E E RMS E Silane Dipole Data