The role of low-energy electron interactions in cis-pt(Co)2 br2 fragmentation

Funding Information: Funding: This project was conducted within the framework of ELENA, a Horizon 2020 research and innovation program under Marie Sklodowska-Curie Innovative Training Network, under the grant agreement No. 722149. M.C. and O.I. acknowledge support from the Icelandic Center of Research (RANNIS), grant no. 13049305(1−3). M.C. acknowledges a doctoral grant from the University of Iceland Research Fund. H.L. and L.M.-W. thank the National Science Foundation for support under grants CHE-1607547 and CHE-1904802. F.F.d.S. acknowledges the Portuguese National Funding Agency for Science Research and Technology (FCT-MCTES), through the research grants PTDC/FIS-AQM/31215/2017 and UIDB/00068/2020 (CEFITEC). Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Platinum coordination complexes have found wide applications as chemotherapeutic anticancer drugs in synchronous combination with radiation (chemoradiation) as well as precursors in focused electron beam induced deposition (FEBID) for nano-scale fabrication. In both applications, low-energy electrons (LEE) play an important role with regard to the fragmentation pathways. In the former case, the high-energy radiation applied creates an abundance of reactive photo-and secondary electrons that determine the reaction paths of the respective radiation sensitizers. In the latter case, low-energy secondary electrons determine the deposition chemistry. In this contribution, we present a combined experimental and theoretical study on the role of LEE interactions in the fragmentation of the Pt(II) coordination compound cis-PtBr2 (CO)2. We discuss our results in conjunction with the widely used cancer therapeutic Pt(II) coordination compound cis-Pt(NH3)2 Cl2 (cisplatin) and the carbonyl analog Pt(CO)2 Cl2, and we show that efficient CO loss through dissociative electron attachment dominates the reactivity of these carbonyl complexes with low-energy electrons, while halogen loss through DEA dominates the reactivity of cis-Pt(NH3)2 Cl2.publishersversionpublishe

The Role of Low-Energy Electron Interactions in cis-Pt(CO)2Br2 Fragmentation

Platinum coordination complexes have found wide applications as chemotherapeutic anticancer drugs in synchronous combination with radiation (chemoradiation) as well as precursors in focused electron beam induced deposition (FEBID) for nano-scale fabrication. In both applications, low-energy electrons (LEE) play an important role with regard to the fragmentation pathways. In the former case, the high-energy radiation applied creates an abundance of reactive photo- and secondary electrons that determine the reaction paths of the respective radiation sensitizers. In the latter case, low-energy secondary electrons determine the deposition chemistry. In this contribution, we present a combined experimental and theoretical study on the role of LEE interactions in the fragmentation of the Pt(II) coordination compound cis-PtBr2(CO)2. We discuss our results in conjunction with the widely used cancer therapeutic Pt(II) coordination compound cis-Pt(NH3)2Cl2 (cisplatin) and the carbonyl analog Pt(CO)2Cl2, and we show that efficient CO loss through dissociative electron attachment dominates the reactivity of these carbonyl complexes with low-energy electrons, while halogen loss through DEA dominates the reactivity of cis-Pt(NH3)2Cl2

Low energy electrons in nanotechnology and cancer therapy

The interaction of low-energy electrons (LEEs) with neutral molecules plays an important role in various applications. In focused electron beam induced deposition (FEBID), a direct-write 3D nanofabrication technique, a high-energy focused electron beam is used to induce nanostructured deposition from precursor molecules (usually organometallic complexes) adsorbed onto a surface. At the current stage, this technique faces some challenges in regard to deposit purity and resolution. These limitations are mainly attributed to the low-energy secondary electrons generated by the impact of the primary electron beam on the surface. They are emitted with a large spatial distribution and can initiate electron-induced reactions that lead to incomplete fragmentation of the precursor molecules. Low-energy electron interactions are expected to play an important role also in chemoradiotherapy, i.e., concomitant chemotherapy and radiotherapy. In this cancer treatment, radiosensitizing agents are used to sensitize cancer cells to radiation. It has been shown that LEEs, generated by the interaction of ionizing radiation with biological tissues, can interact with a radiosensitizer producing radicals that can induce DNA damage. In order to improve the performance of FEBID precursors and radiosensitizers, it is important to study the energy dependence of the electron-induced processes. Low-energy electrons (LEEs) can induce fragmentation through four distinct processes: dissociative electron attachment (DEA), dissociative ionization (DI), dipolar dissociation (DD) and neutral dissociation (ND). Low-energy electron interactions are commonly investigated in gas phase experiments, under single electron-molecule collision conditions, with crossed molecular/electron beam instruments. In this Ph.D. project, the LEE-induced decomposition of FEBID precursors and some model compounds for application in chemoradiotherapy was investigated in the gasphase, specifically focusing on DEA and DI processes. The FEBID precursors that have been selected for this work are (η 3 -C3H5)Ru(CO)3Br and cis-Pt(CO)2Br2. For (η 3 -C3H5)Ru(CO)3Br , an extensive DI study was conducted as a follow-up of previous studies of this compound. For cis-Pt(CO)2Br2, both DEA and DI were investigated, with more emphasis on DEA, and the results were compared with previous gas-phase DEA studies on cis-Pt(CO)2Cl2 and cis-Pt(NH3)2Cl2, with surface studies on cis-Pt(CO)2Cl2 and with FEBID experiments on cis-Pt(CO)2Br2 and cis-Pt(CO)2Cl2. With the aim of enhancing the susceptibility of radiosensitizers towards LEEs, extensive DEA studies on the model compounds pentafluorothiophenol, 2-fluorothiophenol and pentafluorobenzoic acid, were conducted, where we explored the perfluorination and neutral HF formation as potential means to promote DEA reactions. The results were compared with previous work on DEA to pentafluorophenol and benzoic acid

HF Formation through Dissociative Electron Attachment—A Combined Experimental and Theoretical Study on Pentafluorothiophenol and 2-Fluorothiophenol

In chemoradiation therapy, dissociative electron attachment (DEA) may play an important role with respect to the efficiency of the radiosensitizers used. The rational tailoring of such radiosensitizers to be more susceptive to DEA may thus offer a path to increase their efficiency. Potentially, this may be achieved by tailoring rearrangement reactions into the DEA process such that these may proceed at low incident electron energies, where DEA is most effective. Favorably altering the orbital structure of the respective molecules through substitution is another path that may be taken to promote dissociation up on electron capture. Here we present a combined experimental and theoretical study on DEA in relation to pentafluorothiophenol (PFTP) and 2-fluorothiophenol (2-FTP). We investigate the thermochemistry and dynamics of neutral HF formation through DEA as means to lower the threshold for dissociation up on electron capture to these compounds, and we explore the influence of perfluorination on their orbital structure. Fragment ion yield curves are presented, and the thermochemical thresholds for the respective DEA processes are computed as well as the minimum energy paths for HF formation up on electron capture and the underlying orbital structure of the respective molecular anions. We show that perfluorination of the aromatic ring in these compounds plays an important role in enabling HF formation by further lowering the threshold for this process and through favorable influence on the orbital structure, such that DEA is promoted. We argue that this approach may offer a path for tailoring new and efficient radiosensitizers

Dissociative ionization of the potential focused electron beam induced deposition precursor

Here we present a combined theoretical and experimental study on dissociative ionization of (η3-allyl)Ru(CO)3Br, a potential precursor for focused electron beam induced deposition. Experimental appearance energies are determined by electron impact ionization and relative cross sections for selected fragmentation channels are presented from their respective thresholds to about 70 eV incident electron energy. Threshold energies for individual fragmentation channels are computed at the hybrid density functional and coupled cluster level of theory and compared to the respective experimental appearance energies

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

Shih P-Y, Cipriani M, Hermanns CF, et al. Low-energy electron interaction and focused electron beam-induced deposition of molybdenum hexacarbonyl (Mo(CO)(6)). Beilstein Journal of Nanotechnology . 2022;13:182-191.Motivated by the potential role of molybdenum in semiconductor materials, we present a combined theoretical and experimental gas-phase study on dissociative electron attachment (DEA) and dissociative ionization (DI) of Mo(CO)(6) in comparison to focused electron beam-induced deposition (FEBID) of this precursor. The DEA and DI experiments are compared to previous work, differences are addressed, and the nature of the underlying resonances leading to the observed DEA processes are discussed in relation to an earlier electron transmission study. Relative contributions of individual ionic species obtained through DEA and DI of Mo(CO)(6) and the average CO loss per incident are calculated and compared to the composition of the FEBID deposits produced. These are also compared to gas phase, surface science and deposition studies on W(CO)(6) and we hypothesize that reductive ligand loss through electron attachment may promote metal-metal bond formation in the deposition process, leading to further ligand loss and the high metal content observed in FEBID for both these compounds

Dissociative ionization and electron beam induced deposition of tetrakis(dimethylamino)silane, a precursor for silicon nitride deposition

Shih P-Y, Tafrishi R, Cipriani M, et al. Dissociative ionization and electron beam induced deposition of tetrakis(dimethylamino)silane, a precursor for silicon nitride deposition. Physical Chemistry, Chemical Physics. 2022.Motivated by the use of tetrakis(dimethylamino)silane (TKDMAS) to produce silicon nitride-based deposits and its potential as a precursor for Focused Electron Beam Induced Deposition (FEBID), we have studied its reactivity towards low energy electrons in the gas phase and the composition of its deposits created by FEBID. While no negative ion formation was observed through dissociative electron attachment (DEA), significant fragmentation was observed in dissociative ionization (DI). Appearance energies (AEs) of fragments formed in DI were measured and are compared to the respective threshold energies calculated at the DFT and coupled cluster (CC) levels of theory. The average carbon and nitrogen loss per DI incident is calculated and compared to its deposit composition in FEBID. We find that hydrogen transfer reactions and new bond formations play a significant role in the DI of TKDMAS. Surprisingly, a significantly lower nitrogen content is observed in the deposits than is to be expected from the DI experiments. Furthermore, a post treatment protocol using water vapour during electron exposure was developed to remove the unwanted carbon content of FEBIDs created from TKDMAS. For comparison, these were also applied to FEBID deposits formed with tetraethyl orthosilicate (TEOS). In contrast, effective carbon removal was achieved in post treatment of TKDMAS, while his approach only marginally affected the composition of deposits made with TEOS