Laser-Ablated U Atom Reactions with (CN) 2 to Form UNC, U(NC) 2 , and U(NC) 4 : Matrix Infrared Spectra and Quantum Chemical Calculations.

Laser-ablated U atoms react with (CN) ₂ in excess argon and neon during codeposition at 4 K to form UNC, U(NC) ₂ , and U(NC) ₄ as the major uranium-bearing products, which are identified from their matrix infrared spectra using cyanogen substituted with ¹³ C and ¹⁵ N and from quantum chemical calculations. The ^12/13 CN and C ^14/15 N isotopic frequency ratios computed for the U(NC) _1,2,4 molecules agree better with the observed values than those calculated for the U(CN) _1,2,4 isomers. Multiplets using mixed isotopic cyanogens reveal the stoichiometries of these products, and the band positions and quantum chemical calculations confirm the isocyanide bonding arrangements, which are 14 and 51 kJ/mol more stable than the cyanide isomers for UNC and U(NC) ₂ , respectively, and 62 kJ/mol for U(NC) ₄ in the isolated gas phase at the CCSD(T)/CBS level. The studies further demonstrate that the isocyano nitrogen is a better π donor, so it interacts with U(VI) better than carbon. Although the higher isocyanides are more stable than the corresponding cyanides, U(NC) ₅ and U(NC) ₆ were not observed here most likely because unfavorable or endothermic routes are required for their production from U(NC) ₄ . The computed U-NC bond dissociation energies decrease from 581 kJ/mol for ⁴ [UNC] to 168 kJ/mol for ¹ [U(NC) ₆ ]. The ionic nature of U(NC) _n decreases as the number of isocyano groups increases.