Toward ICP‐SIFT mass spectrometry and atomic cation ligation as a probe of relativistic effects—A personal journey

Abstract

The ICP-SIFT mass spectrometer at York University, a derivative of flowing afterglow (FA) and selected-ion flow tube (SIFT) mass spectrometers, has provided a powerful technique to measure the chemistry and kinetics of atomic cation-molecule reactions. Here, I focus on periodic trends in the kinetics of ligation reactions of atomic ions with small molecules. I examine trends in ammonia ligation kinetics across the first two rows of the atomic transition metal cations and their correlation with ligand bond enthalpies and ligand field stabilization energies. Also explored are trends down Groups 1 and 2 in the kinetics of noncovalent electrostatic ligand bonding and the tendency for s electron solvation of the atomic alkaline-earth cations with ammonia. Finally, I briefly review trends observed with 12 different ligands in the ligation rate down the periodic table with Group 9-12 transition atomic metal cations. These trends provide a compelling probe for the presence of relativistic effects that influence the strengths of the metal-ion ligand bonds that are formed. There is a clear third-row rate enhancement with Ir + , Pt + , Au + , and Hg + , the extent of which depends on the nature of the ligand. This large set of kinetic data provides an unprecedented broad perspective of relativistic effects in ligand bonding. With CS 2 as a ligand, the third-row relativistic effect is apparent in the formation of both the first and the second ligand bond with the Groups 10 and 11 atomic cations as predicted by our quantum chemical calculations of ligation energies.

Relativistic Effects in the Ligation of Atomic Coinage Metal Cations with O2 and C6H6: Anomalous Formation of Relativistic Mono- and Bis-adducts with Au+

“…The efficiency plots also exhibit the “third row enhancement” with Au + , with the same exception. Such a mimic is expected since the rate of ligation is influenced by the lifetime of the intermediate encounter complex and so the binding energy of the ligated product, as we have shown previously for other atomic cation ligation reactions. , …”

“…The rate coefficient for ligation is proportional to the lifetime τ of the unimolecular dissociation of the intermediate encounter complex back to the ligand and atomic metal cation, eq , where D is the binding energy of the encounter complex. , Here, τ 0 is the collision lifetime, r is the number of rotational square terms contributing to the internal energy of the encounter complex when contributions of vibrational degrees of freedom are ignored, and s is the number of coupled harmonic oscillators (degrees of freedom).…”

“…Thus, in the ligation of atomic coinage metal cations Cu + , Ag + , and Au + , the subject of the study reported here, a n enhanced ligand interaction due to relativistic effects should be manifested by an enhanced ligation energy going down the periodic table. Furthermore, since the magnitude of the rate coefficient for ligation is determined by the binding energy of the intermediate encounter complex, a n enhanced ligation energy due to relativistic effects should be manifested by an enhanced rate of ligation . , This means that laboratory measurements of rates of atomic coinage metal cation ligation down Group 11 on the periodic table should serve as a probe of relativistic effects.…”

“…Large relativistic stabilization was observed for the bonding of Au + to NH 3 and C 2 H 4 ; the binding energies with Au + were seen to be almost twice as high as those with Cu + and Ag + . In our laboratory, we would later, in 2017, probe and reveal relativistic effects for the ligation of Cu + , Ag + , and Au + with NH 3 with rate coefficient measurements using our inductively-coupled selected-ion flow tube (ICP//SIFT) mass spectrometer. , These measurements tracked the reactivity of the Group 11 cations down the periodic table and revealed a clear third-row rate enhancement with Au + . Further measurements in our laboratory demonstrated the third-row enhancement of the ligation rate of the coinage metal cations with a substantial number of other ligands, including O 2 (see Figure ).…”

“…Furthermore, since the magnitude of the rate coefficient for ligation is determined by the binding energy of the intermediate encounter complex, an enhanced ligation energy due to relativistic ef fects should be manifested by an enhanced rate of ligation. 4,5 This means that laboratory measurements of rates of atomic coinage metal cation ligation down Group 11 on the periodic table should serve as a probe of relativistic effects.…”