Gas-phase oon-molecule reactions of transition metal complexes: The effect of different coordination spheres on complex reactivity

Abstract

Using a modified quadrupole ion trap mass spectrometer, a series of metal complex ions have been reacted with acetonitrile in the gas phase. Careful control of the coordination number and the type of coordinating functionality in diethylenetriamine-substituted ligands enable the effects of the coordination sphere on metal complex reactivity to be examined. The association reaction kinetics of acetonitrile with these pentacoordinate complexes are followed in order to obtain information about the starting complexes and the reaction dynamics. The kinetics and thermodynamics of acetonitrile addition to the metal complex ions are strongly affected by the chemical environment around the metal center such that significant differences in reactivity are observed for Co(II) and Cu(II) complexes with various coordination spheres. When thiophene, furan, or benzene moieties are present in the coordination sphere of the complex, addition of two acetonitrile molecules is readily observed. In contrast, ligands with better donors react mainly to add one acetonitrile molecule. Among the ligands with good donors, a clear trend in reactivity is observed in which complexes with nitrogen-containing ligands are the least reactive, sulfur-containing complexes are more reactive, and oxygen-containing complexes are the most reactive. In general, equilibrium and reaction rate constants seem to be consistent with the hard and soft acid and base (HSAB) principle. Interestingly, the presence of certain groups (e.g., pyridine and imidazole) in the coordination sphere clearly can change the acid character of the metal as seen by their effect on the binding properties of other functional groups in the same ligand. Finally, we conclude that because complexes with different coordination spheres react to noticeably different extents, ion-molecule (I-M) reactions may be potentially useful for obtaining coordination structure information for transition metal complexes. Along with collision-induced dissociation (CID), I-M reactions can also be tools that provide structural information in a mass spectrometric experiment [5][6][7]. I-M reactions are advantageous as structural probes for several reasons. They are highly selective, efficient, and fast. They are also relatively simple, and there are numerous possible combinations of ions and neutrals that can be analytically useful [7][8][9]. Finally, I-M reactions are inherently softer than CID methods, which require "heating up" ions to induce dissociation.CID of metal complexes has been studied by several investigators but mainly in order to determine the binding strengths of ligands to monovalent metals [10]. Studying the dissociation dynamics of metal complex ions from a structural elucidation standpoint, however, has received less attention. Brodbelt and co-workers have studied the dissociation patterns of polyether, crown ether, and polypyridyl complexes of singly- [11,12] and doubly-charged transition metal ions [13,14]. Details about the effect of ligand flexibility and metal type on dissociation...

Ions generated from uranyl nitrate solutions by electrospray ionization (ESI) and detected with fourier transform ion-cyclotron resonance (FT-ICR) mass spectrometry

“…Ion-molecule reactions in the gas-phase have been used extensively to gain information on the chemistry and reactivity of metals in coordination complexes, as well as the structures of these metal-ligand complexes [25][26][27][28][29][30][31][32][33][34]. In our studies, D 2 O and adventitious CD 3 OD were used as neutral reaction partners with several of the more abundant ions in Figure 1c to assess the degree of coordinative unsaturation of the uranyl in each of the selected species.…”

Ion-molecule reactions of gas-phase chromium oxyanions: CrxOyHz− + O2

“…This suggested that the initially formed adducts were not particularly sensitive to small changes in the He pressure. The reactions behaved as apparent bimolecular processes [41,42], and hence the rate constants are reported as such.…”

Elucidation of the collision induced dissociation pathways of water and alcohol coordinated complexes containing the uranyl cation

“…To gain a better understanding of the intrinsic interactions between different uranyl species and solvent, we have begun an investigation of uranyl-anion complexes in the gas phase using ion-trap mass spectrometry (IT-MS). Several recent reports have demonstrated that intrinsic metal and metal complex chemistry can be investigated by the (controlled) addition of reagent gas to an ion trap [12][13][14][15][16][17][18][19][20][21][22], or by way of the presence of H 2 O and other small molecule contaminants within the He bath gas used to collisionally cool ions and improve trapping efficiency [23][24][25]. The reactions of uranium ions in the gas phase have been the subject of several earlier investigations.…”