Effect of the carboxylate shift on the reactivity of zinc complexes in the gas phase.

The effect of different modes of the carboxylato ligands on the reactivity of gaseous zinc-acetate complexes is reported. Using infrared multiphoton dissociation spectroscopy, it is demonstrated that the coordination of acetate in [(Imi)(n)Zn(CH(3)COO)](+) complexes (Imi = imidazole, n = 1-3) changes from bi- to monodentate upon coordination of the third imidazole ligand. This so-called carboxylate shift substantially influences the reactivity of the zinc-acetate complexes in comparison to complexes with monodentate counterions. The differences in reactivities are demonstrated on the ligand exchange reactions of [L(n)ZnX](+) (n = 2 or 3,; L = imidazole or pyridine; X = OH, Cl, CH(3)COO, and CH(3)CONHO).

Direct observation of triple ions in aqueous solutions of nickel(II) sulfate: a molecular link between the gas phase and bulk behavior.

Electrospray ionization of an aqueous solution of nickel(II) sulfate provides direct experimental evidence for the formation of triple ions of the type [Ni(2)(SO(4))(H(2)O)(n)](2+) and [Ni(SO(4))(2)](2-), whose existence in aqueous solution has previously been proposed based on relaxation spectroscopy [Chen et al. J. Sol. Chem. 2005, 34, 1045]. Formally, these triple ions are formed by aggregation of the solvated ions Ni(2+) and SO(4)(2-), respectively, with the neutral ion pair NiSO(4). In addition, also higher adducts are observed, e.g. the "pentuple ions" [Ni(3)(SO(4))(2)(H(2)O)(n)](2+) (n = 7-9) and [Ni(2)(SO(4))(3)](2-), of which the dicationic is extensively hydrated, whereas the anionic is not. The structures of the dinuclear nickel clusters are derived from ab initio calculations and their infrared spectra are compared with experimental data obtained for the gaseous ions [Ni(2)SO(4)(H(2)O)(5)](2+) and [Ni(2)(SO(4))(3)](2-), respectively. The calculations show that the structures are crucially controlled by the degree of solvation of nickel ion. Explicit consideration of solvating water molecules within the first coordination sphere suggest that the dicationic triple ion [Ni(2)SO(4)](aq)(2+) is bent and thus bears a permanent dipole moment, whereas the [Ni(SO(4))(2)](aq)(2-) dianion tends to be quasi-linear. The experimental and theoretical data for the gaseous ions thus support the elegant, but indirect, deductions previously made based on solution-phase studies.

Comparative study of mono- and dinuclear complexes of late 3d-metal chlorides with N,N-dimethylformamide in the gas phase.

Mono- and binuclear complexes of N,N-dimethylformamide (DMF) with chlorides of the divalent, late 3d metals M = Co, Ni, Cu, and Zn are investigated by means of electrospray ionization (ESI). Specifically, ESI leads to monocations of the type [(DMF)(n)MCl](+) and [(DMF)(n)M(2)Cl(3)](+), of which the species with n = 2 and 3 were selected for in-depth studies. The latter include collision-induced dissociation experiments, gas-phase infrared spectroscopy, and calculations using density functional theory. The mononuclear complexes [(DMF)(n)MCl](+) almost exclusively lose neutral DMF upon collisional activation with the notable exception of the copper complex, for which also a reduction from Cu(II) to Cu(I) concomitant with the release of atomic chlorine is observed. For the dinuclear clusters, there exists a competition between loss of a DMF ligand and cluster degradation via loss of neutral MCl(2) with decreasing cluster stability from cobalt to zinc. For the specific case of [(DMF)(n)ZnCl](+) and [(DMF)(n)Zn(2)Cl(3)](+), ion-mobility mass spectrometry indicates the existence of two isomeric cluster ions in the case of [(DMF)(2)Zn(2)Cl(3)](+) which corroborates parallel theoretical predictions.

Comparison of 2,2'-bipyridine and 2,2'-bipyridyl-N,N'-dioxide as ligands in zinc complexes.

The complexation abilities of 2,2'-bipyridine (bipy) and 2,2'-bipyridyl-N,N'-dioxide (bipydiox) toward zinc(II) and the influence of these ligands on the properties and reactivities of the investigated complexes are compared by means of mass spectrometry, IR multiphoton dissociation spectroscopy, and theoretical calculations. The binding energy of bipydiox to zinc is slightly smaller than that of bipy, namely, by 0.1 eV in the mixed complex [(bipy)(bipydiox)ZnCl](+). Accordingly, the differences in the properties and reactivities of the complexes of zinc(II)/bipydiox and zinc(II)/bipy are only minor. The mechanism of decarboxylation of [(L)Zn(CH(3)COO)](+) (L = bipy or bipydiox) is investigated in detail. The substantial difference between the ligands stems only from the possibility of oxygen transfer from bipydiox, which is here, however, observed only as a high-energy channel in the fragmentation of complexes [(bipydiox)Zn(CH(3)COO)](+).

Ligand effects on the [Cu(PhO)(PhOH)]+ redox active complex.

Under gas phase conditions, the [Cu(PhO)(PhOH)](+) complex is composed of copper(I), a phenoxy radical bound via the oxygen atom, and a phenol bound via the aromatic ring. Effects of additional ligand coordination on the molecular and electronic structure of the complex [Cu(PhO)(PhOH)](+) are investigated by mass spectrometric and quantum chemical means for [Cu(PhO)L](+) (L = H(2)O, CH(3)OH, tetrahydrofuran, NH(3), pyridine, imidazole, 1,2-dimethoxyethylene, N,N,N',N'-tetramethylethylenediamine, pyrrole, and thiophene) and [Cu(PhO)(PhOH)L(n)](+) (L = H(2)O, NH(3), and 4-methylimidazole) models. The nature and number of additional ligands critically influences the spin distribution in the complex, which is sensitively reflected by the phenoxy CO stretching mode.

The interaction of zinc(II) and hydroxamic acids and a metal-triggered Lossen rearrangement.

The structure and reactivity of a complex of zinc(II), water, acetic acid, and acetohydroxamic acid, in which one of the acids is deprotonated, is investigated by means of mass spectrometry, labeling studies, and density functional calculations to unravel the exceptional binding properties of hydroxamic acids towards zinc-containing enzymes at the molecular level. It is shown that acetohydroxamic acid is deprotonated in the complex, whereas acetic acid is present in its neutral form. The binding energies of the ligands towards zinc increase in the following order: water