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

Abstract

The transition metal (M=Fe, Co, Ni, Cu, Zn, Cd and Hg) complexes of 2- acetylbenzimidazolethiosemicarbazone (L(1)) and 1-methyl 2-acetylbenzimidazole-thiosemicarbazone (L(2)) are analyzed by MALDI using HCCA, THP, MMNPD and DMN as the matrices. All the MALDI spectra are clean without any contribution from the complex ions resulted by multiple proton addition/removal. All the complexes, except Cu, irrespective of the matrix used, show 1:2 complex ions wherein two ligands (neutral or deprotonated) complex with the metal ion depending on the nature and stable oxidation state of the central metal ion viz., [M + 2L - 2H](+) ion for Fe and Co complexes (+3 oxidation state) and [M + 2L - H](+) ion for Ni, Zn, Cd and Hg (+2 oxidation state). The Cu complex show 1:1 complex ion corresponding to [2M + 2L - 2H](+) ions. When HCCA is used as a matrix, the complex ions due to ligand exchange by matrix are also found, and this process is relatively more if a neutral ligand is bound to the metal ion in the original complex ion. The type of complex ions found under MALDI experiments are similar to those found under ESI experiments. However, the complex ions due to reduction of Cu are found only in the MALDI analysis of Cu complexes.

Synthesis and Characterization of Cu(II) and Mixed-Valence Cu(I)Cu(II) Clusters Supported by Pyridylamide Ligands

“…For instance, the spectrum of complex 5 shows a fully reduced pentanuclear Cu­(I) with two ppda 2+ ligands at m / z 951.1, which could be attributed to the reduction of the original Cu II 3 Cu I 2 cluster. Previous studies of MALDI-MS of transition-metal complexes showed the reduction of metal centers due to either matrices as reducing agents or free electrons present in the MALDI plume. − Since matrices were not used in our measurement, free electrons captured by copper center(s) might be the main reason for their reduction in the gas phase. In fact, a stainless steel metal plate was used as the sample well.…”

MALDI‐TOFMS analysis of coordination and organometallic complexes: a nic(h)e area to work in

“…Since 2005 many other systems have been investigated. These include, but are not limited to, porphyrins and phthalocyanines,26–37 other nitrogen heterocycles,26, 38–46 other nitrogen ligands,47–53 metallocenes/aryl ligands,26, 54–60 phosphorus ligands,26, 44, 57, 59, 61–63 hydrazones,64 carboxylates,51, 54, 65 thiophenes,66, 67 acetylacetonates,59, 68 ethers,69, 70 polyynes/cumulenes,71 acetohydrazides,72 octreotate,73 tripsalen,74 thiols75 and quinolates 76. Successfully characterised compounds have contained, but are not limited to, magnesium,37 the first‐row transition metals in general,63, 68 specifically vanadium,59 chromium,74 manganese,28, 74 iron,26, 35, 40, 54, 59, 60, 63, 66, 74 cobalt,28, 29, 31, 33, 34, 40, 42, 64, 72 nickel,29, 33, 40, 64, 67, 72 copper,26, 29, 31, 33, 34, 39, 52, 64, 71, 72 zinc,26, 28, 29, 31–34, 40, 45, 48, 55, …”

“…Successfully characterised compounds have contained, but are not limited to, magnesium,37 the first‐row transition metals in general,63, 68 specifically vanadium,59 chromium,74 manganese,28, 74 iron,26, 35, 40, 54, 59, 60, 63, 66, 74 cobalt,28, 29, 31, 33, 34, 40, 42, 64, 72 nickel,29, 33, 40, 64, 67, 72 copper,26, 29, 31, 33, 34, 39, 52, 64, 71, 72 zinc,26, 28, 29, 31–34, 40, 45, 48, 55, 64, 65, 72 gallium,26, 42 the Group 4 metals,58 ruthenium,26, 44, 46, 53, 57, 73 rhodium,26 palladium,28, 41, 49, 50, 53, 55, 61–63, 67 silver,28, 29, 52, 71 cadmium,40, 43, 47, 72 indium,42 tin,38, 51, 54, 69, 70 rhenium,26 osmium,26 iridium,39, …”

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.…”