Dissociative electron attachment to gold(I)-based compounds: 4,5-dichloro-1,3-diethyl-imidazolylidene trifluoromethyl gold(I)

With the use of proton-NMR and powder XRD (XRPD) studies, the suitability of specific Au-focused electron beam induced deposition (FEBID) precursors has been investigated with low electron energy, structure, excited states and resonances, structural crystal modifications, flexibility, and vaporization level. 4,5-Dichloro-1,3-diethyl-imidazolylidene trifluoromethyl gold(I) is a compound that is a uniquely designed precursor to meet the needs of focused electron beam-induced deposition at the nanostructure level, which proves its capability in creating high purity structures, and its growing importance in other AuImx and AuClnB (where x and n are the number of radicals, B = CH, CH3, or Br) compounds in the radiation cancer therapy increases the efforts to design more suitable bonds in processes of SEM (scanning electron microscopy) deposition and in gas-phase studies. The investigation performed of its powder shape using the XRPD XPERT3 panalytical diffractometer based on CoKα lines shows changes to its structure with change in temperature, level of vacuum, and light; the sensitivity of this compound makes it highly interesting in particular to the radiation research. Used in FEBID, though its smaller number of C, H, and O atoms has lower levels of C contamination in the structures and on the surface, it replaces these bonds with C–Cl and C–N bonds that have lower bond-breaking energy. However, it still needs an extra purification step in the deposition process, either H2O, O2, or H jets.


Introduction
The increased importance in the pharmaceutical drug development and cancer studies, the gold(i) compounds are developed from synthesis step to quantum simulations and molecular dynamics analysis, as in our case, or for catalysed reactions and reductive elimination/migratory insertion reactions [1] .The most worth mentioning application of the gold(i) compounds is the inhibition of bacteria such as Escherichia Coli [6], through bonding of the DHFR to the C, F or P of the gold compound, where a high reduction in the level of DHFR in solution with gold(i) compared to non-gold(i) is observed.A level of reduction of 0.1 from 2.2 to 2.1 of denaturated DHFR and 1.2 to 1 of the native DHFR is observed with inhibitory constants of 2.25μM, 1.1μM and 8.63μM for 4-benzoic acid-diphenyl-phosphene gold(i) chloride, 2-benzoic acid-diphenyl-phosphane gold(i)-chloride and 4,5dichloroimidazolato-N-triphenylphosphine-gold(i) extending the use of the gold(i) compounds to the treatment of inflammatory infections, pneumonia, E. Coli and cancer.
Through the use of velocity map imaging technique and DEA mass spectroscopy studies, employed for multiple analysis involving Au compounds or compounds on gold substrates, we determine the fragmentation pathways with implications to focused electron beam deposition.At 157nm, the velocity map imaging study of diatomic gold in combination with DFT and ab initio calculations brings insight to the dynamics of the Au -Au vibrational and excitations modes, bonding between species with d-electrons valence, as well as the branching ratios for Au 5d 9 6s 2 ( 2 D3/2) and Au 5d 9 6s 2 ( 2 D5/2) [1].The optical absorption spectrums of Au in vapour form shows the allowed transition states between 211 -229nm from 1 Πu(II) to X 1 Σg + , and isolates two dissociation processes, first one at a photon energy of 2.301 -2.311eV for Au 5d 10 6s 2 ( 2 D5/2) and the second one at 3.437 -3.447eV for Au 5d 10 6s 2 ( 2 S1/2) + Au 5d 9 6s 2 ( 2 D5/2), showing particularity for gold cluster processes and the presence of the 6s orbitals combined with the relativistic effects of the s electrons.For nanotechnology applications, the assisted deposition of Au compounds has been done successfully by Schawrav et al [28] with H2O as oxidative enhancer resulting pure Au nanostructures with a resistivity of 8.8μΩcm and 91 at.% purity of the structure.The Au content of the nanostructures resulting from the focused electron beam induced deposition of Me2Au(tfac) was improved to reach values of 72 at.% through the refining of the electron beam parameters, and further to hit high purity levels of ~90 at.% through the plasma assisted structure post-processing in Ref. [29].Chien et al [30] reports carbon content up to 60% in their Au deposited nanostructures through their newly developed localized surface plasmon resonance measurement (built to enhance structure content reading) and a reduction down to 20% of the carbon content through the H2O treatment of the nanostructures.
In the normal non-assisted deposition of CF3 -Au containing compounds [31], [32] values of Au content in the deposits of 22at% in the case of CF3AuCNMe and 14at% for CF3AuCNBu [32] were obtained with values of decomposition and sublimation temperatures of the two compounds evaluated of 51°C and 80°C (CF3AuCNMe) and, 39°C and 126°C (CF3AuCNBu) respectively.CF3 -Au containing precursors are known to have very good sublimation and decomposition temperatures becoming highly sought precursors for FEBID deposition, though the lower levels of Au content and high C contamination (>60at%) are indications of the need of a postprocessing treatment or assisted deposition.The Me2Au(Acac) presents comparable results when deposited and annealed at 100 -300°C forming structures close to 14nm [33], but at the same time reducing the carbon content at 300°C under H2 jet to almost 0 at% and removing it out of the lattice through heating.Gruber et al [34] report the growth of AuCx nanopillars results of the FEBID of Me2Au(acac) with a height of 2 µm for the development of the 3D plasmonic gold nanoantennae, as one of the many applications of the induced chemistry at the nanoscale.The focus is indeed on the composition of the nanopillars that are further annealed (to 300°C) and purified using H2O jets at room temperature.The growth of nanoantennae and nanopillars have put the basis of a new lithographic method based on FEBIP using cooling to lower than 0°C of the substrate and thin films and further irradiated using e-beams to form structures [35], or, more sophisticated methods as GIS (gas injection systems) and computer assisted deposition for the creation of highly complex and accurate 3D nanostructures [36].The same methods have been applied to growing carbon nanotubes [37], carbene nanostructures [38] and cold ice organic nanostructures [35].Nanostructures have been printed in [39] using Au based compounds in reactive atmospheres [40] with very successful outcomes.

Experimental Section
VsMI/Mass Spectroscopy.The experimental equipment consists of a high-vacuum chamber with pressures in the range of 10 -9 mbar helped by a SCROLLVAC SC5D scroll pump and a gas-line oil pump Edwards RV3 with pressures in the range of 10 -3 mbar.An electron gun is mounted on the top flange of the chamber intersecting at 90° the molecular beam and in-line to the electron gun, a three-plate Chevron pattern MCP detector.A puller, pusher and flight tube assembly are connected to the detector for guiding the negatively charged ions to the phosphor screen.A CCD industrial camera is used for capturing the ions accelerated to different velocities.A pair of Helmholtz coils is placed on the top and bottom of the chamber with the purpose of creating a magnetic field with values up to 50Gauss that controls the guide path of the particles (ions/molecular fragments, electrons).The simple assembly: electron gun, the detector assembly, the flight tube guiding the ions to the phosphor screen and a CCD camera for capturing the negative fragments, is helped by a Behlke 100ns to 25ns slicer, that would physically select a certain time length slice of the Newton sphere of ions that would further be imaged by the camera and detected by the MCP data acquisition modules for mass discrimination.Similar setups [8], [9], [10] have been used at Tata Institute, India for imaging of negative ions.

Fig 2. MCP VsMI detector assembly
The increase in the number of detector's plates, reduces the aberration of the equipment, and improves the energy range.The VsMI in the Fig 2 assembly uses an energy range of 0 -50eV specifically for low electron energy applications.The phosphor screen is employing a thin tungsten with >98% transmission rate foil mounted on a brass ring.The detection of the negative ions is calibrated against a system of two molecules, O2 at 6.5eV and SO2.The kinetic energies spectrum and angular distribution follow the same rules and should be less than 0.1% to the O2 and SO2 spectrums.

XRD (X-ray Powder Diffraction).
To determine the structural characteristics of the crystalline sample XRD measurements were employed using a XPERT 3 Panalytical diffractometer based on CoKα with a time step of 150s/step and a step size of 0.0167.The angle of diffraction is 5 -80deg at a rate of 40kV and 40mA.The measurements were acquired over the duration of 1 1/2 hours.The diffraction specific wavelength is set to a value of 1.5406Å.

NMR (Nuclear Magnetic Resonance
).The proton NMR data acquisition was done using a JEOL ECS 400MHz NMR spectrometer at 25⁰C with a sensitivity of 280 (0.1% ethyl benzene) for 1 H and 19 F, with an automatic Bruker SampleXpress sample charger run by a 500MHz electric DC motor having a 60 sample carousel controlled by ICON-NMR software and equipped with barcode reader registration, with the samples kept at a temperature between 5 -30⁰C and a separate cryo-fit mounting kit for sample cooling.The sample charger and sample unit were both controlled by the Bruker Avance III 400MHz controller unit.

Results and Discussion
Structure characterization.The 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) is a gold compound synthesized by the Chemistry Department of the University of Oslo.The linear formula of the compound is C8H10Cl2N2AuF3, and it has a mass of 459.05amu.The schematic of the compound is presented in  A very important characteristic to our molecular dynamic simulations and cross-checking of our experimental results is the bond distance to C, Cl, N and H and bond angles to C, Cl, N and H. Multiple sources on trifluoromethyl gold(i) [2], [3], [4], present the bond distances for the gold(i) compounds as 0.05Å higher than gold(ii) compounds.In the study of Gil-Rubio and Vicente [1], the bond distances for the most common gold(i) compounds are experimentally determined with values in the range of ~2.04Å presented in Table 1   characteristic to the methyl radicals in our compound are 106.02deg(<HCH) to 112.71deg (<CCH).The bond lengths and angles of 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) are presented in Table 2.We report a bond distance of C -Au of 2.065Å from C7 -Au8 and a second bond distance to CF3, Au8 -C9 of 2.076Å, the affinity to CF3 being higher than to CN2 in our case.Lower bond distances of Au -C ligands have been reported in [5] with values declared for the Au -CF3 bond of all gold(i) trifluoromethyl complexes to be

Type of bond Bond lengths (Å)
Table 2. Bond lengths and angles from B3LYP/Def2TZVPP calculations The highest values of the Au8 -C7 bonds are for the B3LYP/CEP-121 basis set of 2.066Å, 0.001Å higher than the calculations at B3LYP/Def2TZVPP level of theory, 0.002Å higher than the calculations at B3LYP/QZVP and 0.014Å; the highest discrepancy is obtained using SDD basis set with the lowest bond length value of 2.052Å.

Liu, Xiong, Diem Dau et al (2013) and Benitez et al (2009).
The accuracy of MP2 methods compared to the one of B3LYP and HF is very low for very complex molecules containing a high number of atoms or organic parts (peptides, alanine) [64].Kaminsky et al (2008) [64] calculates the error of the MP2 methods with the basis set as being 20 to 30 kJ/mol in the electronic energy calculations; the values we report for the MP2 with QZVP basis set are the shortest distances Au8 -C7 to the Cl2-phenyl ring; the calculations, results of Def2TZVPP have values higher with 0.007Å of the Au8 -C7 distance.
All MP2 level calculations for all basis-sets have shorter bond length values, the MP2/SDD Au8 -C7 has a value of 2.038Å, while the MP2/CEP-121G has a value slightly higher of 2.045Å, but still lower than B3LYP calculations with the same basis set with values of 2.052Å and 2.066Å, respectively.

X-ray powder diffraction data (XRD).
A set of eight experiments at different temperatures and pressure have been run using powder X-ray diffraction method [71], [72], [73] to determine the crystallinity and structure of the sample.For the characterization of nanomaterials and deposited complexes at the nanoscale, combinations of tools such as TEM, EXAFS and XRD [75], [76] are run to obtain particle size distributions and interlayer plane distances using TEM for the localized nanostructure size and powder XRD for an average nanostructures size.
Further measurements can be done for structural characterization of the as deposited nanomaterials using synchrotron radiation (XANES, XSAS e.g.) [76], [77].A crystallinity of up to 55% is expected, with the grain size limited to an average of 41nm, and the highest grain of 82.86nm, rather small compared to a grown crystal structure or multiple grown crystals in the powder structure, the complex is in amorphous phase mixed with small grains in the form of nanostructures.trifluoromethyl gold(i), as the only anions that contain a metal atom, found in the dissociative electron attachment process of the compound.The two higher mass fragments, C5H10N2F2AuCl2 -and C7H10N2FAuCl2 -, are rather noisy with low cross sections, with highest peak values lower than 1-2cnts.The C5H10N2F2AuCl2 -ion with a mass of m/z 403amu has a maximum peak at 7.7eV, while the higher mass fragment (m/z 408amu) C7H10N2FAuCl2 -presents three resonances peaking at 0.86eV, 7.4eV and 11.8eV, all with widths in the range of ~1eV.Lower mass fragments, C7H10N2AuCl2 -and C5H9NFAuCl -, both have two resonances, with the first resonance peaking before 1eV and the second one after 5eV.With higher cross-section value, the C7H10N2AuCl2 - anion has an average value of count of 150cnts for the maximum resonance falling at an energy of 0.88eV with a width of the resonance peak of 2.03eV, while the second resonance peak is found at an incident electron energy of 7.3eV.The smoothness of the resonance shape comes with the high value of the cross-section as well.A lower value of the cross-section with maximum counts of 2cnts is characteristic to the anionic fragment C5H9NFAuCl -(m/z 334amu) but presenting similar shape to the higher mass ion at m/z 389amu.The electron energy characteristic to the two resonances of the ion (m/z 334amu) are 0.84eV (with a width of 1.81eV) and 5.6eV (with a width of 7.2eV).the range of ~2-3eV, with values of 1.53eV (0.9eV), 3.38eV (4.7eV) and 3.3eV (9.2eV).The smaller mass anion of the six gold(i) containing ions is H4N2F2Au -characterized by the presence of nitrogen and fluoride atoms in its composition, and high cross-section.The peak of the highest resonance is found at 0.82eV with a maximum of the peak of 32cnts and a width of 1.67eV.The smaller amplitude resonance falls at 4.6eV having a width of 8eV and a number of counts lower than 2cnts.After the metal containing anions, the precursor fragments in negatively charged organic fragments.The Cl -ion corresponding to a m/z of 35 presents a resonance peak at 0.85eV with high cross-section values, making it the most abundant anion result of the fragmentation of the precursor at 70eV.A shoulder corresponding to the same peak is observed at 1.8eV, while a wider resonance peak with a width of almost 4eV is observed at 5.3eV.Another very abundant anion is the C2H6NCl -ion having only one resonance peak at 0.84eV with a width of 1.7eV and 24 counts and relative high cross-section compared to the rest of the ions that present values under 10 counts at the height of their peak.The fragmentation of 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) follows the steps in relation (1) with the result of chloride anion and of a higher mass neutral fragment C8H10Cl2N2AuF3 + e - →C8H10ClN2AuF3 + Cl -(1).Xuan et al [12] presents the fragmentation of the 1,2-dichlorobenzene at low energy DEA studies using ion mass spectroscopy, time-of-flight ions and VMI on the fragmentation of the compound and resultant negative ion of Cl -at two resonances, 1.2eV and 6eV, the latter being a wider resonance of the anion possibly corresponding to the two isotopes of chloride 35 Cl -and 37 Cl -.Chloride anion is not an atypical ion in the fragmentation of the compounds containing Cl, the majority of them forming the chloride anion as a product of reaction in the induced chemistry at the interaction of the molecule with electrons.Typical to the fragmentation of diatomic molecules, the 1,2-dichlorobenzene (1,2 -C6H4Cl2) undergoes a transition from σ to σ* that further initiates the fragmentation of the molecule with the resulting fragments of C6H4 -Cl + Cl -; and the chloride anion in the 1 ∑g* excited state and Oh geometry.A study of four chlorine containing compounds (CCl4, CH2Cl2, CH3Cl and CHCl3) [13] was presented to DEA fragmentation, each of them exhibiting the presence of the chloride anion at energies close to 0eV.The positions of the resonances of the four anions are presented in Table 5.Each of the ions has the highest amplitude peak close to 0eV at an electron energy of 0.0 ± 0.05eV and the second resonance peak between 6eV and 8eV.The Cl -from CCl4 has a shoulder of the first resonance of chloride falling at 0.75 ± 0.05eV, with a value of the bond dissociation energy of C -Cl ligand of 3.3 ± 0.3eV and a characteristic electron affinity of EA(Cl2) = 2.35 ± 0.1eV; the electron affinity reported by NIST Database is in good agreement with the values reported by Scheunemann et al [13] of 2.5 ± 0.2eV.The two lower in value crosssection fragments, CF3 -and C4H9N2Cl2 -lacking the presence of any metal atom, have amplitudes in the range of ~2 -5 counts, with the highest amplitude peak for C4H9N2Cl2 -falling at 0.81eV having a width of 1.26eV, while the second peak of the same resonance has its maximum at 3.2eV with the width of the peak of 2.16eV.The CF3 -anion has its maximum amplitude of the first resonance peak at 0.88eV with a width of 1.5eV and the second peak maximum at 7.2eV characterized by a width of 6.6eV.These four lower mass fragments are particularly interesting through the lack of any metal atom in their composition, depositing and releasing as a result of collision and ionization in the interaction with a secondary electron only volatile fragments and organic material, increasing the level of contamination of the FEBID structures.2) with resulting values in the range of 2.9 -3.9eV (see Table 5).The electron affinities of the products have been calculated at room temperature (298.15K), the zero-point energy corrections being highly sensitive to the input temperature.The highest value of the electron affinity is obtained for mass m/z 267 corresponding to H4N2F2Au -with an EA value of 3.90094eV (~0.143357Hartree).

Manaa (2017) in
Lower electron affinity values are calculated for Cl -ion and C7H10N2AuCl2 -with values of 3.315709eV (~0.12185 Hartree) and 3.03271eV (~0.11145Hartree), respectively.The VEA (vertical electron affinities) values from our Gaussian 16 simulations at B3LYP/LANL2DZ level of theory are calculated using the natural bond orbital populations (NBO) and pole p3+ calculations are presented for reference in Table 5.The vertical electron affinities (VEA) [67], [68] are calculated for each ion with high cross-sections values ranging from 0.506eV to 1.090eV.The VEA of the 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) has a value of 0.242eV, 0.146eV higher than the excited anion parent with a value of the VEA of 0.096eV; similar to other compounds containing C -H bonds; example of CH3 -, SiH3 -, and CHCH2 -in [69].The anion parent was not determined experimentally as being present due to a short-lived life and being unstable in the 2 A1' state, characteristic to the form of a temporary negative ion (TNI).In the fragmentation of the 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) two pathways are possible, described by the relations (4) and ( 5), one of the fragmentation paths results in the formation of CF3 -(m/z 69) anion with C7H10Cl2N2Au as neutral fragment, while the second fragmentation pathway results in the formation of C7H10N2Cl2Au -(m/z 389) anion and CF3 as a neutral fragment: C8H10N2Cl2AuF3 + e -→ C7H10N2Cl2Au -+ CF3 (4) and C8H10N2Cl2AuF3 + e -→ C7H10N2Cl2Au + CF3 - (5).While the CF3 in neutral state is in its ground state 2 A1 C3v, for the CF3 -anion the symmetry point group conserves (C3v), but the excited state of the anion transitions to 1 A1 presents two peaks of the resonance, at 0.88eV and 7.2eV; other higher excited states correspond to E"1 and E"2.Similar behaviour of the CF3 -anion to CF3 -from 4,5-dichloro -1,3-diethylimidazolylidene trifluoromethyl gold(i) is observed for the 5-trifluoromethanesulfonyl-uracil [16] compound used extensively in cancer therapy as a radiosensitizer reducing the amount of radiation needed for the treatment of the cancer cells.Defined by an electron affinity of EA = 1.69eV, the fragmentation of 5-trifluoromethanesulfonyl-uracil (OTfU) [16] in a neutral fragment and CF3 -takes place at an electron energy characterized by four resonance peaks at 0eV, 2.35eV, 4.75eV and 8.45eV with the dissociation of the S -CF3 group ligand.The CF3 -ion in the hexafluoroacetone azine ((CF3)2C = NN = C(CF3)2) [17] reaction has its resonances falling at higher energies representing typically a bond cleavage with the fragmentation of a C -CF3 -, a C bond to a CF3 having a lower bond dissociation energy than the Au -CF3 bond cleavage for 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i).Values of 1.61eV are reported for the affinity of the CF3 -in [17] with the DEA resonance peaking at two energies, 3.8eV with the highest amplitude and 7.3eV resonance with lower amplitude, in the range of <10 counts.Calculations of the vertical electron affinities (VEA) and bond dissociation energies show a higher bond strength of the Au -CF3 ligand compared to the organic ligands for the ImCl2EtCF3Au.

Ions
Proton NMR stability measurements.The proton NMR measurements and water NMR measurements are rather simple measurements used often in the pharmacology industry for stability analysis of complex drugs and compounds and degradation study of these compounds in specified conditions (pressure, temperature, luminosity).The applications of the proton NMR studies are not limited to only stability analysis but have implications to the study of the structure and bonding of complex compounds to certain proteins (RNA signal assignment and validation [55], probing metallic-aromaticity [53]) or to structural changes (n-membrane lactones isomerism [54]).The most common example of the use of this type of measurement is the proton NMR studies to proteins [52] in different storage, transportation and daily-use conditions.The proton NMR and water NMR offer in these circumstances a comprehensive view on the stability of the compound and the time it

CDCl3 solution
Gibbs Free Energy of Reaction.The Gibbs free energy of formation and reaction has been used multiple times to analyse the suitability of different complexes and organic or protein material for drug resistance [22], equilibrium calculations of emulsion systems [21], enthalpy of DNA formation [41], calculations of different minerals formation [42] and nanolithography (the present study).The Gibbs free energy of a compound is explained in terms of enthalpy (ΔH), temperature (T) and entropy (S) by the relation: ΔG = ΔH -TΔS.The values of the enthalpy and entropy are taken from simulation data for each of the products and reactants.For a reaction the Gibbs free energy is obtained [42] from relation (4) ΔG = G(products) -G(reactants), while for molecular complexes the relation ( 5) ΔG = G(species) -∑G(elements) suffices.The Gaussian software works with calculating the corrections to the enthalpy and entropy of formation or reaction based on total energy and contributions from vibrational, rotation, translational or electronic motion; according to this the enthalpy correction is explained by the relation ( 6) HCorr = Etot + kBT [43], where the Etot is the total energy.In a similar manner, the entropy is defined by Stot = St + Se + Sv + Se (7).
Materials in powder form are usually analysed for moisture content mostly in food industry [57 -59] and to obtain the dissolution rates of complexes [56] through the calculation of the Gibbs free energy, but the use of Gibbs free energy still remains the means to determine the stability of a compound using simulation obtained values of entropies and enthalpies.In order to analyse the suitability of the Cl2ImEtCF3Au precursor, the Gibbs free energy from DFT calculations has been used.More industrial oriented applications to pipeline transport industry (water, gas, oil, steam) [60] are by the analysis of Gibbs free energy of solid-state CO2 in the transport of CO2 in carbon capture and storage (CCS).The Gibbs free energy is the entity that defines the probability of a reaction to take place, the volatility and stability of the compound.The values of ε0, εZPE, HCorr and GCorr are calculated from the thermochemistry of Cl2ImEtCF3Au at DFT level using B3LYP with a Def2TZVPP basis set, where ε0 is the electronic energy, εZPE is the zero-point energy, HCorr is the enthalpy correction and GCorr is the Gibbs free energy correction.The sum of the electronic and enthalpy energy, sum of the electronic and Gibbs free energy and sum of the electronic and zero-point energy are used as ε0 + HCorr, ε0 + GCorr and ε0 + εZPE.The calculated thermochemistry values are presented in Table 6 with the values obtained from the Gaussian Calculations of Gibbs free energy at atomistic level with great results to modelling of crystal defects are reported by Cheng and Ceriotti [61], though at defect sites the model predicts energies 300% higher than evaluated, and at non-defect sites 10% higher than reported for the evaluated model.The higher defect estimated value of the Gibbs free energy is presented as a result of the anharmonicity at the defect sites with the transition at higher temperatures (>298K).The BDE and BDFE are calculated for the chemical reaction The results of the calculations are presented in  [23].The value reported from our calculations of -424.47kcal/mol is specific for an exogenic process releasing energy, though is not characterized by high cross-section value for the elimination of the Au -CF3 ligand.Lower ΔfG would mean that the molecule is unstable making it hard to work with and to be transferred from the vial through the gas line inside the vacuum chamber.Values as low as +16.5 kcal/mol for ClAuPF3 have been reported in [23] rendering the ClAuPF3 compound as one of the compounds with low vaporization pressure.Not stable in air and at room temperature, the Cl2ImEtCF3Au has similar behaviour to AuCF3CO [23], [24] that darkens in the presence of heat and light, a sign of the oxidation process.
The Cl2ImEtCF3Au is not to be kept at temperatures higher than 5degC as it spontaneously breaks ligands and degrades, while the presence of air would intensify the process of degradation and oxidation.
Synthesis of the gold(i) compound.Gold(i) NHC complexes are a class of compounds that is widely known and studied in chemistry for their versatility, among others in catalysis [44], biomedicine [45] and photochemistry [46].The most important characteristic of the NHC ligand is the carbene carbon, which is stabilized by two neighboring nitrogen atoms.[47] Due to their popularity, several ways for the synthesis of gold(i) NHC complexes have been reported [48], which makes these systems easily accessible and adaptable to required needs.The gold(i) NHC complex [38] investigated in this work was synthesized following a reported literature procedure which is presented in Fig 15 .Starting from 4,5-chloroimidazole the desired NHC ligand precursor was obtained as a salt in a yield of 94 % through two sequential alkylation reactions using ethyl iodide.[49] By reacting the NHC ligand precursor with silver oxide, the respective silver complex was formed in-situ which underwent a trans-metalation reaction upon the addition of one equivalent of the gold precursor Au(SMe2)Cl.
[50] The resulting gold NHC chloride complex was isolated in a yield of 92%.In the last step, the title compound was synthesized through another silver mediated trans-metalation reaction.The active silver species AgCF3 is formed in situ from the reaction of silver fluoride with Me3SiCF3 and exchanges the chloro-ligand with a CF3 group when Au(NHC)Cl is added, yielding the desired Au(NHC)CF3 complex as a colourless solid (66 %).[51] Fig 15 .Synthesis route for 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) Computational details.The simulations of the structure of C8H10Cl2N2AuCF3 have been run at DFT/B3LYP level making use of the full orbital populations and natural bond orbitals using a B3LYP/Def2TZVPP basis set.The excited states calculations have been run using TDDFT.The crystal structure and slab for XRD simulations were built using Vesta and Avogadro software.

Conclusions
The 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) was analysed to its suitability as a FEBID precursor.As a newly designed compound specifically for deposition of nanoscale structure, its vaporization pressure, stability in air and volatility have been studied using proton NMR and Gibbs free energy of reaction.
A good volatility value was obtained for the compound and a high stability in air with very low modifications of the structure during exposure.Its fragmentation, resonances and anions at low electron energies and DEA have been obtained using Velocity Map Imaging studies with great success.The structure, packing, orientation of the planes and grain size have been run making use of powder XRD diffractometer data and the VESTA simulation software has offered reliable insights into the crystalline vs amorphous structure of the compound.

Fig 4 .
Fig 4. HOMO/LUMO orbitals of 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) (F yellow, C pink, H blue, N orange, Cl green, Au magenta) : (a) HOMO (b) LUMO The bond distances calculated using B3LYP/Def2TZVPP are longer than the free methyl radical bond distances, and more imbalanced ranging from 1.087Å to 2.076Å.The three C atoms of the methyl radical have the bond lengths of 1.089/1.090Å,equally spaced in all directions with an angle <HCH of 108.1deg.The angles

between 2 .
031Å and 2.046Å.Both the bond distances to CN2, C3 -N5 and C4 -N6 have values of 1.384Å and angles to axial plane of 125.3deg, while the C3 -Cl1 and C4 -Cl2 bond distances are 1.702Å set at equally spaced angles of 129deg.All C -F bond lengths (Table 2) from CF3 have values of 1.372Å balanced with an angle of 104.6deg, longer than in the free trifluoromethyl radical with distances of the C -F bond of 1.318Å and an angle of 110.76deg, 6.16deg lower than in our calculations.The simple ethyl radicals C13 -H25 and C13 -H19 have bond lengths of 1.087Å, and 1.089Å, respectively.

Fig 6 :
Fig 6: (a) Crystal structure of 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(I) complex, ellipsoids have been drawn at 50% probability.Packing and interlayer distance (b) viewed along an axis, (c) b axis and (d) the c axis has been shown Detailed investigation of the packing of the crystal structure (Fig 6b, c and d) revealed presence of various weak non-covalent interactions that exist between adjacent rows of molecules.Apart from aurophilic interactions, each molecule engages with four surrounding molecules via four different Van der Wall's interactions which are summarized in Table 4.Among these interactions, each molecule engages with two adjacent molecules in the same row via F2•••H4A and Cl1•••H4B VW interactions and two molecules in the next row via Au1•••H5B and H5C•••H5C interactions.Interestingly, one Au centre engages with another nearby Au centre via well-known

Fig 7 .
Fig 7. XRD of the Au compound under vacuum condition and at room temperature and atmospheric pressure.The two graphs show very small differences under the two different conditions, highest changes are observed between 30 -35 2θ(°).

Fig 11 .
Fig 11.Anions of 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) m/z 267 to m/z 408 At m/z 300amu an anion without nitrogen or fluoride in its composition is found, though characterized by very low cross-section value.The three peak resonances of the C5H8AuCl -anion are at electron energies of 0.9eV, 4.7eV and 9.2eV, with high characteristic widths and noisier shape.The widths of the three resonances are in

[ 62 ]
defines the value of the calculated electron affinity from Gaussian 4 simulations at CCSD(T) level of theory as the sum of the values of the energy Ee for the neutral and the anion with added zeropoint corrections of the two values (2): EA = [Ee(optimized neutral) + ZPE(neutral)] -[Ee(anion) + ZPE(anion)].A similar relation is used for the cation ionization potential at ZPE (3): IP = [Ee(cation) + ZPE(cation)] -[Ee(optimized neutral) + ZPE(optimized neutral)].In the DEA Gaussian calculations run at DFT level, the values of the transitions from the HOMO to the LUMO orbitals are related to excitation energies with the formation of a temporary negative ion (TNI).The electron affinity and electronegative potential (absolute electronegativity or absolute hardness) of the anions results of the DEA process of 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) follow (

Fig 13 .Fig 14 .
Fig 13.Chemical shift of 4,5-dichloro -1,3-diethyl -imidazolylidene trifluoromethyl gold(i) in CDCl3 solutionThe sample (~5 mg) was dissolved in 1cm 3 wet CDCl3 under air; no special precautions were taken other than calculations.The calculations have been done at a temperature of 298.15K and a pressure of 1 x 10 -4 Pa.The reaction with the result of an anion and a neutral fragment formation follows the pathway Cl2ImEtCF3Au * → Cl2ImEtAu -(m/z 389) + CF3 (m/z 69) for which the reaction energy and enthalpy are calculated to obtain the bond dissociation energy (BDE) and bond dissociation free energy (BDFE) of the reactants into products of reaction.

. Compound d(Au -C) /Å, X = F
result of a transition from Au 6s/5d hybrid partially occupied to the highest energy level occupied HOMO orbital.For our standard compound we obtain the HOMO and LUMO orbital as orbitals 76 and

Table 3
. Bond lengths of ImEtAuCl2CF3 optimized at multiple levels of theory The chlorine atoms to the phenyl ring bond lengths range from 1.685Å calculated at MP2/QZVP to 1.793Å at MP2/CEP-121G, both Cl atoms being placed symmetrically at a 129.22deg angle to the C3 and C4 atoms of the phenyl ring.Overall the structure is balanced at the central symmetry plane formed by the two C atoms and the Au, C7 -Au8 -C9, while a 110.83deg to C (in CH2) and 90deg to the symmetry plane is obtained for the two ethyl -methyl groups.

Table 4 .
List of bond lengths, bond angles, torsional angles, Van der Wall's interactions and short contact obtained from single crystal XRD structural analysis

Table 6 .
Free Gibbs energy correction, enthalpy correction and zero-point corrections of Cl2ImEtCF3Au -, Cl2ImEtAu -and CF3, products of formation and products of reaction The metal -ligand bond between Au(I) and CF3 presents higher BDE for Cl2ImEtCF3Au (189.15kcal/mol)than for Au(I) -CF3 in CF3AuCO of 151.4kcal/mol,Au(I) -Cl in ClAuPMe3 of 77.9kcal/mol or Au(I) -Me in MeAuPMe3 of 43.4kcal/mol reported by Marashdeh et al