Supplementary Material (ESI) for Dalton Transactions This journal is (c) The Royal Society of Chemistry 2006 1 Synthetic and Structural Studies on C-Ethynyl- and C-Bromo-Carboranes. Gas Phase Electron Diffraction Studies of C-Ethynyl- and C-Trimethylsilylethynyl-para- carbaboranes. Mark A. Fox, a* Audrey M. Cameron, a Paul J. Low, a Michael A.J. Paterson, a Andrei S. Batsanov, a Andrés E. Goeta, a David W.H. Rankin, b* Heather E. Robertson b and Julien T. Schirlin b Data for Electronic Supplementary Information Table S1 Least-squares correlation matrix (x100) for GED structure refinement of 1-Me 3 SiCC-1,12-C 2 B 10 H 11 . a Table S2 Least-squares correlation matrix (x100) for GED structure refinement of 1-HCC-1,12-C 2 B 10 H 11 . a Table S3 Distances, amplitudes of vibration, r h1 corrections and original amplitudes of vibration from the GED structure refinement of 1-Me 3 SiCC-1,12-C 2 B 10 H 11 . All distances are in pm. Table S4 Distances, amplitudes of vibration, r h1 corrections and original amplitudes of vibration from the GED structure refinement of 1-HCC-1,12-C 2 B 10 H 11 . All distances are in pm. Table S5 Cartesian coordinates for the GED structure of 1-Me 3 SiCC-1,12-C 2 B 10 H 11. Table S6 Cartesian coordinates for the GED structure of 1-HCC-1,12-C 2 B 10 H 11. Table S7 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1-Me 3 SiCC-1,12-C 2 B 10 H 11. Table S8 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1-HCC-1,12-C 2 B 10 H 11. Table S9 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1,12-(Me 3 SiCC) 2 -1,12-C 2 B 10 H 10. Table S10 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1,12-(HCC) 2 -1,12-C 2 B 10 H 10. Table S11 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1-F-1,12-C 2 B 10 H 11. Table S12 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1-Cl-1,12- C 2 B 10 H 11. Table S13 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1-HO 2 C-1,12- C 2 B 10 H 11. Table S14 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1-H 3 C-1,12- C 2 B 10 H 11. Table S15 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1-NC-1,12- C 2 B 10 H 11. Table S16 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1-Ph-1,12- C 2 B 10 H 11. Table S17 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1,12-Ph 2 -1,12- C 2 B 10 H 10. Table S18 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1-(1’-1’,12’- C 2 B 10 H 11 )-1,12- C 2 B 10 H 11 – C,C’-bis(para-carborane). Table S19 Cartesian coordinates for the MP2(fc)/6-31G* optimised structure of 1-HCC-1,2-C 2 B 10 H 11. Table S20 Non-bond distances (r a /Å) and amplitudes of vibration (u/Å) obtained in the GED refinement of 5. Table S21 Non-bond distances (r a /Å) and amplitudes of vibration (u/Å) obtained in the GED refinement of 6. Table S22 Calculated (r e ) and experimental (r h1 ) structure of 1,12-C 2 B 10 H 11 -C≡CH. All bond lengths in pm and all angles in °. Figure S1 Experimental and final weighted difference (experimental-theoretical) molecular scattering intensities for 1- Me 3 SiCC-1,12-C 2 B 10 H 11. Figure S2 Experimental and final weighted difference (experimental-theoretical) molecular scattering intensities for 1- HCC-1,12-C 2 B 10 H 11.