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1 Electronic Supplementary Material (ESI) for ChemComm. This journal is The Royal Society of Chemistry 201 Reactions of Laser ablated U Atoms with (CN) 2 : Infrared Spectra and Electronic Structure Calculations of UNC, U(NC) 2, and U(NC) in Solid Argon Yu Gong, a Lester Andrews,* a Benjamin K. Liebov, a Zongtang Fang, b Edward B. Garner, III, b and David A. Dixon* b a University of Virginia, Department of Chemistry, Charlottesville, VA, USA E- mail: lsa@virginia.edu b The University of Alabama, Department of Chemistry, Tuscaloosa, AL, 87-0, USA E- mail: dadixon@ua.edu Supporting Material Experimental methods The matrix isolation apparatus and procedure for studying laser ablated metal atom reactions has been described previously. The Nd:YAG laser fundamental (Continuum II, 10 nm, 10Hz repetition rate with 10 ns pulse width) was focused onto a uranium metal target (high purity, depleted of 2 U obtained from Oak Ridge National Laboratory) mounted on a rotating rod which produced a bright blue emission plume from the target surface. Laser-ablated uranium species (mostly atoms) were co-deposited with argon or neon (research grade) containing 0. to 1% cyanogen gas prepared in this laboratory. We employed thermal decomposition of AgCN at 0-80 deg C until a constant pressure was reached in a stainless steel vacuum line following earlier work. The product gas was condensed at 77 K and evacuated before use. Isotopic reagents were synthesized using K 1 CN and KC 1 N (99% enriched, Cambridge Isotopic Laboratories) and silver nitrate to prepare the silver cyanide. FTIR spectra were recorded at 0. cm 1 resolution on a Nicolet 70 FTIR instrument with a HgCdTe range B detector. Matrix samples were annealed at different temperatures and cooled back to K for spectral recording. Selected samples were subjected to broad band photolysis by a medium-pressure mercury arc street lamp (Philips, 17W) with the outer globe removed using optical glass filters. References 1. L. Andrews and A. Citra Chem. Rev. 2002, 102, L. Andrews Chem. Soc. Rev. 200,,

2 Table S1. Relative energies in kcal/mol for U(NC) n and U(CN) n compounds predicted with BLYP functional using the aug-ccpvtz basis set on C and N and the ECP0MWB effective core potential and ECP0MWB_SEG basis set on U at 0K. Molecule ΔE Molecule ΔE Molecule ΔE Molecule ΔE (0K) UNC(C v ) 0.0 U(NC) 2 (C 2v ) 0.0 U(NC) (C v ) 0.0 U(NC) (S ) 0.0 UNC(C v ) 27. U(CN) 2 (C 2v ) 11.2 U(CN) (C v ) U(NC) (C 1 ) 28. UCN(C v ) 28.7 U(CN) 2 (C 2v ) U(NC) (C v ) 18. U(CN) (C 2v )* 0. UCN(C v ).0 U(NC) 2 (C 2v ) U(CN) (C v ). 1 U(CN) (D 2d ) 8. 2 CUN(C v ). 1 U(NC) 2 (C 2v ) 9.2 U(NC) (C v ) 91.7 * Approximate T d Symmetry 1 U(CN) 2 (C 2v ). U(CN) (C v ) Table S2 Complete frequencies (cm -1 ) and intensities (km.mole -1 ) for the ground state U(NC) n and U(CN) n compounds calculated with BLYP functional. U(NC) n Freq (Inten) U(CN) n Freq (Inten) UNC (C v ) 91.9(1), 118.7(0), 89.(7), (9) UCN(C v ) 171.(0), 219.8(7), 297.(0), (12) U(NC) 2 (C 2v ) U(NC) (C v ) U(NC) (S ) * Approximate T d Symmetry 0.(11), 107.(0), 112.(0), 11.8(0), 11.9(0),.(11), 8.7(), 2072.(81), 208.0(171) 8.8(2), 2.7(), 7.(7), 1.(), 9.8(0), 127.7(1), 11.(1), 1.1(1), 21.1(1), 79.0(19), 82.7(19), 9.(2), 2072e (1), ().2(0),.(1), 7.(1), 8.8e(2), 98.0(0), 102.(0), 102.(0), 118.1e(2), 1.(0), 12.9(2), 18.8(0), 0.e(1), 0.1(17), 2.7(0), 20.(927), 20. (927), 20.e (2100), 208 (0) U(CN) 2 (C 2v ) U(CN) (C v ) U(CN) (C 2v )* 8.(12), 117.(0), 128.(0), 1.2(0), 187.2(0), 20.2 (99), 0.0(22), 221.(7), 221.8(1) 1.0(2), 7.7(9), 9.1(9), 117.(), 121.8(2), 1.(0), 18.8(0), 182.9(1), 18.(1),.e(210), 0.1(17), 2219e (19), (17) 2.1(7),.2(8),.1(1), 7.0(12), 9.() 10.(0), 1.2(0), 18.(0), 17.(1), 170.7(0), 17.(0), 191.1(0), 2.0(0), 1.(),.2 (79),. (12),.9(121), (21), (210), (217), (2)

3 Table S. NBO Population Analysis with the BLYP Functional for the lowest energy states of U(NC) n for n = 1 to Molecule Spin, electron config UNC (f ) UNC (s 1 d 1 f ) U(NC) 2 (C 2v ) (s 1 f ) U(NC) (C v ) ( f ) U(NC) (S ) 2 ( f 2 ) 7s total pop spin (α, β) 1.87 (0.9, 0.9) 0.9 (0.90, 0.0) 0.8 (0.77, 0.0) 0.1 (0.09, 0.0) 0.1 (0.07, 0.07) f total pop spin(α, β).0 (.02, 0.0).1 (.1, 0.02).07 (.02, 0.0).08 (2.98, 0.10) 2.2 (2.17, 0.2) d total pop spin (α, β) 0.2 (0.1, 0.12) 1.0 (1.01, 0.0) 0. (0.1, 0.1) 0. (0.0, 0.2) 0.9 (0.9, 0.) 7p total pop spin (α, β) (, ) (, 0 ) (,0 ) ( 0,0 ) (, ) UCN (f ) (0.87, 0.07) (2.97, 0.0) UCN (s 1 d 1 f ) (0.92, 0.07) (., 0.02) U(CN) 2 (C 2v ) (s 1 f ) (0.7, 0.11) (.02, 0.0) U(CN) (C V ) ( f ) (0.1, 0.1) (2.99, 0.07) U(CN) (C 2v )* 2 ( f 2 ) (0.17, 0.17) (2.17, 0.22) * Approximate T d Symmetry. Charges on C and N averaged (0.2, 0.90) 0.70 (0., 0.0) 0. (0.8, 0.1) 0.7 (0., 0.1) 1.22 (0., 0.9) 0.02 (, ) 0.02 ( 0.02, 0 ) (,0 ) 0 ( 0,0 ) (, ) Table S. BLYP Bond Distances (Å) in U(NC) n and U(NC) n isocyano r(nc) r(un) cyano r(nc) r(uc) UNC UCN UNC UCN U(NC) 2 (C 2v ) U(CN) 2 (C 2v ) U(NC) (C v ) U(CN) (C V ) U(NC) (S ) U(CN) (C 2v )* * Approximate T d Symmetry. Bond distances averaged.

4 Table S. NPA Charges for U(NC) n and U(NC) n isocyano U N C NC Cyano U C N CN UNC UCN UNC UCN U(NC) 2 (C 2v ) U(CN) 2 (C 2v ) U(NC) (C V ) U(CN) (C V ) U(NC) (S ) U(CN) (C 2v )* * Approximate T d Symmetry. Charges on C and N averaged.

5 Table S. Total energies at 0K with the BLYP functional (E total, a.u.) and geometries (x, y, z Cartesian coordinates in Å) for the lowest energy states of U(NC) n and U(CN) n for n = 1 to. U(NC) n UNC C infv E total = U C N UNC C infv E total = U C N U(NC) 2 C 2v E total =-2.90 U N N C C U(NC) 2 C 2v E total =-2.22 U N N C C U(NC) C v E total = U C C C N N N U(NC) C v E total =-7.89

6 U N N N C C C U(NC) S E total = U N N N N C C C C U(NC) C 1 E total = U N N N N C C C C

7 U(CN) n UCN C infv E total = C U N UCN C infv E total = C U N U(CN) 2 C 2v E total = U C C N N U(CN) 2 C 2v E total = U C C N N U(CN) C v E total = U C C C N N N U(CN) C v E total = U C C

8 C N N N U(CN) T d E total = U C C C C N N N N U(CN) C 2v E total = U C C C C N N N N