Dissociative electron attachment to coordination complexes of chromium: chromium(0) hexacarbonyl and benzene-chromium(0) tricarbonyl

Abstract

Here we report the results of dissociative electron attachment (DEA) to gas-phase chromium(0) hexacarbonyl (Cr(CO)6) and benzene-chromium(0) tricarbonyl ((η6-C6H6)Cr(CO)3) in the energy range of 0–12 eV. Measurements have been performed utilizing an electron-molecular crossed beam setup. It was found that DEA to Cr(CO)6 results (under the given experimental conditions) in the formation of three fragment anions, namely [Cr(CO)5]−, [Cr(CO)4]−, and [Cr(CO)3]−. The predominant reaction channel is the formation of [Cr(CO)5]− due to the loss of one CO ligand from the transient negative ion. The [Cr(CO)5]− channel is visible via two overlapping resonant structures appearing in the energy range below 1.5 eV with a dominant structure peaking at around 0 eV. The peak maxima of the fragments generated by the loss of two or three CO ligands are blue-shifted and the most intense peaks within the ion yield curves appear at 1.4 eV and 4.7 eV, respectively. (η6-C6H6)Cr(CO)3 shows a very rich fragmentation pattern with decomposition leading to the formation of seven fragment anions. Three of them are generated from the cleavage of one, two or three CO ligand(s). The energy of the peak maxima of the [(C6H6)Cr(CO)2]–, [(C6H6)Cr(CO)]–, and [(C6H6)Cr]− fragments is shifted towards higher energy with respect to the position of the respective fragments generated from Cr(CO)6. This phenomenon is most likely caused by the fact that chromium–carbonyl bonds are stronger in the heteroleptic complex (η6-C6H6)Cr(CO)3 than in homoleptic Cr(CO)6. Besides, we have observed the formation of anions due to the loss of C6H6 and one or more CO units. Finally, we found that Cr−, when stripped of all ligands, is generated through a high-energy resonance, peaking at 8 eV.

Low-energy electron interaction and focused electron beam-induced deposition of molybdenum hexacarbonyl (Mo(CO)6)

“…As also observed for W(CO) 6 [15,19,20], but in contrast to Cr(CO) 6 [16,17,19,20] and Fe(CO) 5 [51], the series of CO loss is not complete [19,20] and there is no formation of the bare metal anion. The intensities of the DEA curves in Figure 1 reflect the relative efficiencies of these reaction channels [15][16][17]19,20]. This is shown in Table 1 along with the peak maxima observed in the ion yields for individual fragments in the current study and those reported by Winters and Kiser [19] and by Pignataro and co-workers [20].…”

“…Resonant electron capture at threshold is clear in the electron transmission spectra from Giordan et al [18] indicating that in the study by Winters and Kiser [19] this might be an artifact rooted in lack of low-energy electrons from the ionization source of the mass spectrometer used in their study. This is further supported by the fact that the peak maxima for single CO loss from other metal carbonyls reported by Winters and Kiser are all close to 2 eV, while more recent studies [15][16][17] and the study by Pignataro and co-workers [20] report single CO loss from these compounds close to 0 eV. A further indication is in the relative abundance ratios of 100:65 reported by Winters and Kiser [19] for [Mo(CO) 5 ] − vs [Mo(CO) 4 ] − , while these are closer to 20:1 in the current study.…”

“…The four dissociation channels describe the series of loss of the CO ligand. As also observed for W(CO) 6[15,19,20], but in contrast to Cr(CO) 6[16,17,19,20] and Fe(CO) 5[51], the series of CO loss is not complete[19,20] and there is no formation of the bare metal anion. The intensities of the DEA curves in Figure1reflect the relative efficiencies of these reaction channels…”

“…In the context of the role of low-energy electron-induced processes in FEBID several studies on DEA and DI of metal carbonyl precursors, including Fe(CO) 5 , W(CO) 6 and Cr(CO) 6 have been reported in recent years [14][15][16][17]. Earlier studies on the low-energy electron interaction with metal carbonyls include an electron transmission spectroscopy study [18] on W(CO) 6 , Cr(CO) 6 and Mo(CO) 6 from the early 1980s, dissociative electron attachment studies on Fe(CO) 5 , W(CO) 6 , Cr(CO) 6 and Mo(CO) 6 , from Winters et al (1966) [19], Pignataro et al (1965) [20] and George et al (1982) [21] as well as a number of dissociative ionization studies from the same periods [22][23][24].…”

Chemistry for electron-induced nanofabrication

“…This expectation is met by a novel fluorinated silver carboxylate precursor that yields deposits with so far unprecedented silver content including 3D structures [ 15 – 16 ]. However, given a favorable structure, even large organic ligands may be removed more easily than previously anticipated, as exemplified by the electron-induced dissociation of benzene–Cr(CO) 3 [ 17 ] and by FEBID using the fluorine-free precursor Cu(tbaoac) 2 [ 18 ]. The most elegant approach to precursor design yet is to use a bimetallic molecular structure to predefine, through the precursor stoichiometry, the composition of an alloy to be deposited by FEBID.…”