Probing relativistic effects in the gas-phase CS2 ligation of late transition metal cations (groups 9-11) with rate measurements and quantum chemical calculations of ligation energies

Striking relativistic effects are demonstrated for the ligation of carbon disulphide to late atomic transition metal cations (Groups 9-11) with both measurements of rate coefficients for ligation in helium buffer gas at 0.35 +/- 0.01 Torr and 295 +/- 2 K and quantum chemical calculations of ligation energies. The rates of ligation with one CS2 molecule were observed to be enhanced by a factor of about 10 going from second row to third-row atomic transition metal cations (Groups 9-11). The addition of a second CS2 ligand, although intrinsically much faster due to effects of degrees of freedom on the lifetime of the intermediate, also exhibits enhancement of the ligation rate for the third-row atomic cations for Groups 10 and 11. The trends in the computed M+-CS2 bond dissociation energies down Groups 9-11 clearly follow the trends in the measured rate coefficients for the first addition of CS2 and, to a degree, the second addition. A novel isodesmic reaction method was used to estimate the percent relativistic contribution to the M+-CS2 bond energy down the periodic table which exceeds 25% for third-row atomic ions. The computations also provided optimized structures for the ligated ions M+(CS2) and M+(CS2)(2). A correlation between the measured ligation efficiency and the computed ligation energy provided a measure of the number of vibrational modes active in the stabilization of these ligated ions. (C) 2021 Elsevier B.V. All rights reserved.