Electrospray ionization studies of transition‐metal complexes of 2‐acetylbenzimidazolethiosemicarbazone using collision‐induced dissociation and ion‐molecule reactions

Abstract

The complexes of transition-metal ions (M2+, where M = Fe, Co, Ni, Cu, Zn, Cd, and Hg) with 2-acetylbenzimidazolethiosemicarbazone (L) are studied under electrospray ionization (ESI) conditions. The ESI mass spectra of Fe and Co complexes showed the complex ions corresponding to [M+2L-2H]+, and those of Ni and Zn complexes showed [M+2L-H]+ ions, wherein the metal/ligand ratio is 1:2 and the oxidation state of the central metal ion is +3 in the case of Fe and Co and +2 in the case of Ni and Zn. The Cd and Cu complexes showed preferentially 1:1 complex ions, i.e., [M+L-H]+ or [M+L+Cl]+, whereas Hg formed both 1:1 and 1:2 complex ions. During formation of the above complex ions one or two ligands are deprotonated after keto-enol tautomerism, depending on the nature and oxidation state of central metal ion. The structures and coordination numbers of the metal ions in the complex ions were studied by their collision-induced dissociation spectra and ion-molecule reactions with acetonitrile or propylamine in the collision cell. Based on these results it is concluded that Fe, Co, Ni and Zn form stable octahedral complexes, whereas tetrahedral or square planar complexes are formed preferentially for other metals. In addition, the Cu complex showed a [2L+2Cu-3H]+ ion with a Cu-Cu bond.

Structural analysis of organometallic compounds with soft ionization mass spectrometry

“…ESI-MS is ideally suited for the analysis of polar and ionic organometallic compounds, the characterization of their hydrolysis mechanisms (Henderson & Taylor, 1996;Lintschinger, Schramel, & Kettrup, 1998;, their biological studies (e.g., metal interactions with biomolecules) (Yan et al, 2005), and even to screen short-lived reactive intermediates involved in organometallic catalytic reactions (Plattner, 2001;Chen, 2003;Moreno-Manas et al, 2003;Guo et al, 2005;Pla-Quintana & Roglans, 2005;Chevrin et al, 2007;Santos, 2008). The soft character of ESI permits one to analyze organometallic complexes with weakly bound ligands (Bhaskar et al, 2005), and the possibility of cold-spray ionization techniques is offered for very labile compounds (Henderson & McIndoe, 2005). Mass spectra are relatively poor in fragment ions, which can be supported with in-source dissociation or tandem MS experiments (Traeger, 2000).…”

Mass Spectrometry in India

“…100,101 They used MS/MS and ligand attachment to determine the structures of the metal complexes observed under ESI and MALDI. 102,103 They showed that information about the oxidation state and coordination number of the metal ion can be obtained in these experiments.…”

Matrix-Assisted Laser Desorption/Ionization Studies on Transition Metal Complexes of Benzimidazole Thiosemicarbazones

“…[8][9][10][11][12][13] Recently, we reported the ESI studies of transition metal complexes of 2-acetylbenzimidazolethiosemicarbazone, in which the structures and coordination numbers of the metal ions in the complex ions were studied by their collision-induced dissociation (CID) spectra and ion-molecule reactions with acetonitrile and propylamine in the collision cell. 14 MALDI was originally developed for analyzing large biomolecules and other synthetic macromolecules. MALDI and laser desorption ionization (LDI) techniques are widely applied in a variety of analytical chemistry fields, including the study of cationization or complexation of metals with different compounds of relatively large molecular weight such as cyclodextrins, oligosaccharides, peptides and proteins.…”