1. Susanna L. Stephens, John Mullaney, Matt Sprawling Daniel P. Zaleski, Nick R. Walker, Antony C. Legon 69 th International Symposium on Molecular Spectroscopy, Champaign-Urbana, Illinois 20 th June 2014 Broadband rotational spectroscopy reveals structural distortion in ethene and ethyne on coordination to gold iodide

2. 2008 Gold: Chemistry, Materials and Catalysis Theoretical chemistry of gold. III Pekka Pyykko, Chem. Soc. Rev., 2008, 37, 1967 M. Barysz and Y. Ishikawa (eds.), Relativistic Methods for Chemists, Challenges and Advances in Computational Chemistry and Physics 10, Springer Science+Business Media Theory and simulation in heterogeneous gold catalysis Coquet et al., Chem. Soc. Rev., 37, 2046 (2008)

3. C 2 H 4 ···AgCl JCP, 135, 024315 (2011)

4. Unbound AgI molecule Free I − ion Na +  I - χ(I) = -262.14 MHz88% Cu-I χ(I) = -938.4 MHz59% Ag-I χ(I) = -1062.52 MHz54% Au-I χ(I) = -1707.9 MHz26% H-I χ(I) = -1823.4 MHz21% The ionicity constant a measure of proton transfer -coupling of the spin of a quadrupolar nuclei with the overall rotation Ag χ aa (X) Nuclear quadrupole coupling constant in complex, eQq (n,1,0) (X) Nuclear quadrupole coupling constant that would result from a single electron in a np z orbital I (2292.71 MHz) C. H. Townes and B. P. Dailey, J. Chem. Phys., 17, 782 (1949)

5. Carbonyl metal halide series OC···MXMX χ aa (X)/MHzi C /%χ aa (X)/MHzi C /% CuCl-21.580-32.171 CuBr171.678261.266 CuI-593.574-938.459 AgCl-28.274-36.467 AgBr223.971297.061 AgI-769.866-1062.654 AuCl-36.467-62.044 AuBr285.163492.336 AuI−961.358−1707.925 CO···AgI; JCP, 136, 064306 (2012)

6. Frequency /MHz 10 0 10 8.5 7 ← 9 0 9 7.5 6 J’ kakc F F ← J’’ kakc F F 10 2 9 9.5 10 ← 9 2 8 8.5 9 10 3 8 9.5 8 ← 9 3 7 8.5 7 10 3 7 9.5 8 ← 9 3 6 8.5 7 10 2 9 9.5 9 ← 9 2 8 8.5 8 10 2 9 8.5 7 ← 9 2 8 7.5 6 Spectrum of C 2 H 4 ···AuI

7. Frequency /MHz Spectrum of C 2 H 4 ···AuI

8. Frequency /MHz C 2 H 2 ···AuI C 2 D 2 ···AuI Spectrum of C 2 H 2 ···AuI ~700 000 averages (<24 hrs) sample ~1 % CF 3 I, ~ 3 % C 2 H 4 balance 6 bar Ar

9. 12 C 2 H 4 ···AuI 12 C 2 D 4 ···AuI 12 C 2 H 2 ···AuI 12 C 2 D 2 ···AuI A 0 /MHz 23805(13)16241(33)34409(41)25180(13) B 0 /MHz 690.429514(60)656.79112(17)711.28209(13)692.747831(74) C 0 /MHz 676.981333(63)642.30720(17)696.65461(12)673.887362(77)  JK /kHz 2.4991(77)2.65(20)3.998(23)3.460(25)  J /Hz 29.08(18)23(6)31.69(23)30.25(26)  J /Hz 9.018(57)(9.018)8.5(24)(8.5) χ aa (Au) /MHz -819.352(63)-822.7(19)-808.698(57)-809.875(80) χ bb  χ cc (Au) /MHz 202.01(19)201.11(769)358.28(12)360.35(29) χ aa (I) /MHz -973.328(58)-972.1(12)-1012.990(47)-1012.445(83) χ bb  χ cc (I) /MHz -186.760(184)-187.98(83)-219.58(14)-219.81(28) N 648329513443 σ r.m.s. / kHz 7.2117.17.4 12 C 2 H 4 12 C 2 D 4 C 0 /MHz 24824.2016895(1) 12 C 2 H 2 12 C 2 D 2 B 0 /MHz 35274.9693(54)25418.6291 C 2 H 4 ···AuI and C 2 H 2 ···AuI Spectral constants 12 C 2 H 4 J. Phys. Chem. A., 110, 7461 (2006), Mol. Phys., 104, 273 (2006), 12 C 2 D 4 Mol. Phys., 43, 737 (1981), 12 C 2 H 2 12 C 2 D 2 J. Phys. Chem. Ref. Data., 32, 921 (2003), OC···CuI Chem. Phys. Lett., 422, 192 (2006), OC···AuI Mol. Phys., 105, 861 (2007), C 2 H 4 ···CuI Unpublished work a a χ aa (Au)χ aa (I)χ aa (Cu)χ aa (I) AuI78.273-1707.88CuI7.9013-938.377 OC···AuI-981.038-961.273OC···CuI64.504-593.465 C 2 H 4 ···AuI prediction from OC···MI-872.74-933.34C 2 H 4 ···CuI57.38-576.23 C 2 H 4 ···AuI prediction from MI568.46-1048.74

10. C 2 H 4 ···AuIC 2 H 2 ···AuI Experiment CCSD(T)-F12* aug-cc-pvtz (pp I and Ag) Experiment CCSD(T)-F12* aug-cc-pvtz (pp I and Ag) r 0 (Au-I) /Å2.472 2.5261 2.475(98)2.5207 r 0 (*···AuI) /Å2.1892.07702.204422(18)2.0773 r 0 (C-C) /Å(1.3796)1.3796(1.2342)1.2342 r 0 (C-H) /Å(1.0827)1.0827(1.0685)1.0685 r 0 (C-C-H) /°(7.30)7.30(13.85)13.85 Dipole μ A /Debey --7.17--7.16 C2H4C2H4 C2H2C2H2 AuI r 0 (C-C) /Å1.3386(14)1.206553(6)r e (AuI) /Å2.95171(70) r 0 (C-H) /Å1.0849(13)1.06238(2) Experimental and ab initio geometries a

11. a C 2 H 4 ···AuIC 2 H 2 ···AuI Experiment CCSD(T)-F12* aug-cc-pvtz (pp I and Ag) Experiment CCSD(T)-F12* aug-cc-pvtz (pp I and Ag) A 0 /MHz34409(41) 34459.0245 34409(41) 34459.0245 B 0 /MHz711.28209(13)702.0582711.28209(13)702.0582 C 0 /MHz696.65461(12)688.0402696.65461(12)688.0402 Experimental and ab initio rotational constants 12 C 2 H 4 ···AuI 12 C 2 D 4 ···AuI 12 C 2 H 2 ···AuI 12 C 2 D 2 ···AuI k σ /Nm -1 59.1(2) 66.8(4) 54.8(4) 56.0(6) ω /cm -1 197(4)197(1) 192(2) P b /uA 2 17.90(1)17.89(1)14.80(2)20.23(2) P c /uA 2 3.361(2)3.345(2)-0.1155(1)-0.187(2) Δ 0 /MHz0.2612(1)0.295(2)0.231(1)0.374(3) icic 57.547(5) 55.817(3)55.841(5) 12 C 2 H 4 P a /uA 2 16.8664 P b /uA 2 3.4919 D.J. Millen, Can. J. Chem., 63, 1477 (1985)

12. Acknowledgements Newcastle John Mullaney Matt Sprawling Nick Walker Daniel Zaleski Dror Bittner Tony Legon Bristol David Tew

13. r 0 (M-X)/År 0 (*···M)/Åi C /%ω /cm -1 k σ /Nm -1 AuI2.95171-26-- OC···AuI2.5336(4)2.501(1)57228(-) C 2 H 2 ···AuI2.475(40)2.20(20)56196.6(2)54.8(4) C 2 H 4 ···AuI2.4722.18958197.2(1)59.1(2) AgI2.54662697(7)-54-- OC···AgI2.5336(4)2.051(1)5717847 C 2 H 2 ···AgI2.600(94)2.11(22)65161(2)35.5(1) C 2 H 4 ···AgI2.54(13)2.23(27)67166(1)41(1) CuI2.3406-53-- OC···CuI2.3563(4)1.8154(9)74-- C 2 H 2 ···CuI(2.220)(2.182)74-- C 2 H 4 ···CuI(2.356)(1.974)75-- AgCl2.28356-67-- C 2 H 2 ···AgCl2.2716(6)2.1841(82)74197(3)51.4(26) C 2 H 4 ···AgCl2.2724(8)2.2701(2)75202(3)57.2(21) C 2 H 4 ···AgCl JCP, 135, 024315 (2011); C 2 H 2 ···AgCl JCP, 137, 174302 (2012); AuI Gerry, JMSp 205, 344 (2001) OC···AuI Walker & Legon, Mol. Phys., 5, 861 (2007) OC···CuI Legon, Chem. Phys. Lett., 422, 192 (2006)