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C: Surfaces, Interfaces, Porous Materials, and Catalysis

Adsorption and Reaction Pathways of 1H-Pyrazole on Cu(100) and O/Cu(100) Jyun-Yi Jhuang, Szu-Han Lee, Shang-Wei Chen, Yun-Hsien Chen, YouJyun Chen, Jong-Liang Lin, Yaw-Wen Yang, and Chia-Hsin Wang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b00042 • Publication Date (Web): 05 Mar 2018 Downloaded from http://pubs.acs.org on March 11, 2018

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The Journal of Physical Chemistry

Adsorption and Reaction Pathways of 1H-Pyrazole on Cu(100) and O/Cu(100)

Jyun-Yi Jhuanga, Szu-Han Leea, Shang-Wei Chena, Yun-Hsien Chena, You-Jyun Chena, Jong-Liang Lina*

a

Department of Chemistry, National Cheng Kung University, 1 Ta Hsueh Road, Tainan, Taiwan, Republic of China

Email (Lin, J.-L.): [email protected] Phone: 886 6 2757575 ext. 65326

Chia-Hsin Wangb and Yaw-Wen Yangb*

b

National Synchrotron Radiation Research Center,

101 Hsin-Ann Road, Hsinchu, Taiwan, Repubic of China

Email (Yang, Y.-W.): [email protected] Phone: 886 3 5780281 ext. 7314 Jyun-Yi Jhuang and Szu-Han Lee have an equivalent contribution to this article.

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Abstract Temperature-programmed reaction/desorption (TPR/D), reflection-absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) have been employed, with the aid of density functional theory calculations, to investigate the adsorption and reaction mechanisms of 1H-pyrazole on Cu(100) and oxygen-precovered Cu(100) (O/Cu(100)). On Cu(100), the adsorbed 1H-pyrazole molecules interact with each other through hydrogen bonding, exhibiting broad infrared absorptions between ~2750 and ~3300 cm-1, but without the N-H stretching peak detected. Near a monolayer coverage, heating the surface to ~200 K induces a change in the adsorption layer structure and generates upright or near upright 1H-pyrazole molecules attaching to the surface through the imine nitrogens. The 1H-pyrazole undergoes N-H bond cleavage first to evolve H2 (~230 K) and leaves pyrazolate on the surface. This intermediate is proposed to be adsorbed perpendicularly via the two nitrogen atoms, which are close to two surface atop sites. The pyrazolate decomposes by simultaneous C-H bond scission and ring opening with preferential bond breaking steps at ~550 K. The C-H dissociation, particularly at the 4C-H, is the main origin for the H2 formation from the pyrazolate. In the ring opening process of the pyrazolate, cleavage of the two C-N bonds produces N2, while concomitant dissociation of the N-N and 3C-4C bonds leads to the formation of HCN and CH3CN. A small amount of the pyrazolate may recombine with hydrogen to evolve 1H-pyrazole. As 1H-pyrazole is adsorbed on O/Cu(100) at 120 K, it dissociates into adsorbed H2O and dehydrogenated 1H-pyrazole species. Further reaction of the dehydrogenated species at 480 K produces adsorbed NCO and pyrazolate, and gaseous H2, H2O, HCN, CO and CO2, with other products of CH2=CHNH2 at 515 K and NH3 at 535 K. The remaining pyrazolate decomposes at 550 K to generate H2, N2, HCN, and CH3CN. 1


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Introduction Studies on adsorption of heterocyclic molecules and interactions of these molecules on metal surfaces are not only for fundamental interest but are also important for a wide range of applications. Nitrogen-containing aromatic molecules or intermediates can play a role in tuning surface properties or building two-dimensional supramolecular networks through surface functionalization or self-assembled monolayer formation. For example, 3(5)-(9-anthryl)pyrazole (ANP) molecules assemble into a chessboard-like supramolecular structure on Au(111), consisting of basic units of tetramers with planar ANP molecules and N-H⋯N hydrogen bonds.1 In the study of self-assembled monolayer of bis(pyrazol-1-yl)pyridine-substituted thiol on Au(111), being related to spin switching, it is found that the adsorbed thiolates are tilted significantly with the two pyrazole rings as the most protruded groups from the surface.2 Adsorption of adenine (a DNA base molecule containing purine ring) on copper single crystal surfaces has been studied, concerning biocatalysis and biosensors.3,4 Adenine is adsorbed parallelly on Cu(110) at a submonolayer coverage. On Cu(111), the adenine molecules form self-assembled suprastructures via hydrogen-bonded dimers. Pyrazole-based molecules or pyrazole derivatives have been used as corrosion inhibitors for metals, such as copper and iron.5-9 The high corrosion inhibition efficiency has generally been considered to be due to the energetics of the frontier orbitals of the inhibitor molecules, hardness/softness and electron transfer.5,6,8 Pyrazole-based ligands have attracted much attention and there are ample studies of pyrazole-copper complexes.10-18 The pyrazole rings coordinated to the copper ions in these reported complexes can be divided into two types. One is through the imine nitrogen (-N=) to form the HN-N→Cu coordination, while the other one involves the Cu←N-N→Cu coordination, with the pyrazole ring as a bridging unit after 2



deprotonation of the amine (-NH-) group (i.e., after breakage of the N-H bond).10-18 In some cases, these two coordinations can occur in a pyrazole-based copper complex.18 Adsorption of benzene, pyridine and pyrrole on copper single crystals has been investigated, particularly on their interactions with the surfaces. Benzene lies flat on Cu(100) and Cu(111), weakly bonding to the surfaces via the π system.19,20 On Cu(100), pyridine is adsorbed with its C2 axis tilted away from or perpendicular to the surface.21 The pyridine interacts with the surface through the nitrogen lone pair. However for pyrrole, it is weakly π-bonded to Cu(100) and the molecular plane is parallel to the surface.22,23 The different adsorption geometries for pyridine and pyrrole on Cu(100) are related to the nitrogen bonding characteristics, i.e., –N= for pyridine and –NH– for pyrrole. Benzene, pyridine and pyrrole are all adsorbed reversibly on Cu(100), without thermal decomposition. To the best of our knowledge, adsorption and reaction of 1H-pyrazole have not been investigated on single crystal metal surfaces. Scheme 1 shows the structures of 1H-pyrazole and pyrazolate from N-H bond cleavage. 1H-pyrazole demonstrates high thermal stability and the activation energy of its pyrolysis is estimated to be 71.3 kcal·mol-1.24 The products from 1H-pyrazole thermal dissociation are N2 and propyne (CH3C≡CH), with vinylcarbene (CH2=CH–CH:) proposed as the reaction intermediate. The present research of 1H-pyrazole/Cu(100) is motivated by several reasons. Although pyrazole-containing self-assembled structures have been prepared and analyzed, the studies for their thermal stability have been lacking. For using pyrazole-based molecules as copper corrosion inhibitors, the bonding of the pyrazoles on copper that should play the key role has not been fully revealed. In view of the existing pyrazole-containing copper complexes prepared and explored for their structures, it is intriguing to study the surface counterpart of 1H-pyrazole-copper in adsorption and bonding geometry. Besides, 1H-pyrazole itself possesses both imine 3


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group (–N=) and amine (–NH–) groups, their competing role in determining the bonding orientation of 1H-pyrazole on copper is worth studying. In the reaction respect, it would be interesting to show the effect of copper surface on 1H-pyrazole thermal decomposition pathway. 1H-pyrazole decomposition on metal substrates deserves attention, because it is a potential single-source precursor for making carbon nitride films. This possibility is examined in the present copper study. In general, the copper surfaces under protection with pyrazole-based corrosion inhibitors are partially or locally oxidized, therefore, the oxygen effect on the reaction pathway of 1H-pyrazole on Cu (100) is investigated as well in the present research.

Experimental Section The ultrahigh-vacuum chamber used for the TPR/D and RAIRS experiments was maintained at a base pressure of approximately 2 × 10−10 Torr. The quadrupole mass spectrometer used for TPR/ D studies was capable of detecting ions up to 300 amu and acquiring 20 different masses in a single desorption experiment. The TPR/D experiments were conducted in line-of-sight mode, with the Cu(100) surface positioned ~ 1 mm from an aperture (3 mm in diameter) leading to the mass spectrometer, at a heating rate of 2 K/s. The thermal reaction products of 1H-pyrazole on Cu(100) were identified on the basis of their parent ions or cracking patterns. In the RAIRS study, the incidence IR beam was focused at a grazing angle of 85° through a KBr window onto the Cu(100) in the UHV chamber and the reflected beam was refocused on a mercury−cadmium−telluride (MCT) detector. An air scrubber was used to remove carbon dioxide and water present in the entire beam path. All the IR spectra were taken at a temperature about 115 K, with 1000 scans and a 4 cm−1 resolution. The Cu(100) single crystal (1 cm in diameter) could be cooled with liquid nitrogen to 110 K and resistively heated to 1100 K. The surface temperature was measured by a 4



chromel−alumel (K-type) thermocouple inserted into a hole on the edge of the crystal. Prior to each experiment, cleaning of the surface by cycles of Ar+ ion sputtering and annealing was carried out until no impurities were detected by Auger electron spectroscopy. 1H-pyrazole (98%), purchased from Aldrich, was subjected to several cycles of freeze−pump−thaw before introduction of its vapor into the vacuum chamber. The XPS and NEXAFS experiments were carried out at the National Synchrotron Radiation Research Center of ROC. In the XPS measurements, a photon energy of 620 eV was used. The photoelectrons were collected at an angle of 50° from the surface normal. The total instrumental resolution was estimated to be better than 0.3 eV. The XPS spectra presented in this article were first normalized to the photon flux by dividing the recorded XPS signal by the photocurrent derived from a gold mesh situated in the beamline. The binding energy scale was referenced to the bulk Cu2p3/2 peak at 75.10 eV. Some of the X-ray photoelectron spectra obtained were fitted with Gaussian−Lorentzian functions based on a nonlinear least-squares algorithm after Shirley background subtraction. Polarization-dependent carbon K-edge NEXAFS measurements were performed in terms of total electron yield (TEY) method. The photon energy scale was referenced to the intense 1s → π* transition of HOPG at 285.38 eV. The X-ray absorptions were first normalized to the photon flux, measured from the current of a freshly evaporated gold mesh positioned in front of the Cu(100) surface, to form a so-called I0-normalized spectrum. The presented X-ray absorption spectra of adsorbed species were obtained by dividing the I0-normalized TEY spectrum of an adsorbate-covered Cu(100) surface by the I0-normalized TEY spectrum of a clean Cu(100) surface. In the present study, the oxygen-precovered Cu (100) was prepared by exposing the clean surface at 500 K to 30 L O2 and the coverage of oxygen atoms was assumed to be ~0.2 monolayer.

5


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Computational Method In our theoretical cluster model calculations for the optimized bonding geometries of 1H-pyrazole and pyrazolate, two slabs with a total of 41 Cu atoms fixed at their lattice positions were used to represent the Cu(100) surface. All of the calculations in the framework of density functional theory were performed using the program package Cerius2 -DMol3 and the generalized gradient approximation with Perdew and Wang exchange-correlation functional (GGAPW91) was employed. A double-numeric quality basis set with polarization functional (DNP) was used for the all-electron calculations including relativistic effect for the core electrons. The geometry optimization convergence threshold for energy change, maximum force, and maximum displacement between optimization cycles were 0.00001 Ha, 0.001 Ha/Å, and 0.0005 Å, respectively. No scaling factor has been used for the computational frequencies reported in this article. The mode assignments for the frequencies calculated were based on the animated molecular vibrations.

Results and Discussion In presenting the experimental results of 1H-pyrazole/Cu(100), we start with the temperature-programmed reaction/desorption spectra to show its adsorption and thermal reaction behavior, followed by spectroscopic spectra to identify the surface species or intermediates and their adsorption orientation. Additional theoretical results are shown to assist in the experimental analysis. The experimental results for O/Cu(100) are presented in a similar order.

Adsorption of 1H-Pyrazole on Cu(100) Shown in Figure 1 are the TPD spectra, represented by the molecular ion (C3N2H4+, m/z 68), after adsorption of 1H-pyrazole on Cu(100) (~120 K) at the 6



indicated exposures. The relative 1H-pyrazole desorption yields as a function of exposure are shown in the inset. At 0.3 L, 1H-pyrazole starts to evolve at ~200 K. This result indicates that 1H-pyrazole molecules can decompose at the dosing temperature or during the linear temperature ramp in the TPD experiments. In the 0.7 L trace, the desorption peak appears at ~210 K. This 210 K state grows linearly with the increasing exposures from 0.7 to 3.0 L, without reaching a saturation level, which can be attributed to multilayer desorption. The fitting line in the inset suggests that the saturation of first layer is approximately at 0.3 L. However, a zero-order kinetics is not followed for the1H-pyrazole multilayer desorption, as revealed by (1) that the desorption peak (~210 K) doesn’t seem to shift toward higher temperature with increasing of exposure, and (2) that the leading edges of the desorption traces do not overlap (Figure S1). Adsorption of 1H-pyrazole molecules on Cu(100) is likely to form multilayer islands, due to hydrogen bonding interactions between the adsorbates. Besides, the number and/or total area of the islands may increase with the adsorption amount that would cause coverage-dependent desorption rates, without showing zero-order desorption behavior. Deviation from zero-order multilayer desorption kinetics has been seen for adsorbates with hydrogen bonding interactions, for example, in the system of CH3OH/HOPG.25 In terms of the Redhead equation of first-order desorption kinetics, ∆H/RTp2 = (ν/β) e-∆H/RTp, where ∆H = adsorption energy, Tp = desorption peak temperature, ν = preexpotential factor, and β = heating rate, the peak temperature of 1H-pyrazole at 210 K corresponds to an adsorption energy of 54.0 kJ·mol-1, in the case of ν = 1013 s-1 and β = 2 K·s-1.26 This estimated adsorption energy for the 1H-pyrazole multilayers on Cu(100) is smaller than the reported sublimation energy of 1H-pyrazole by ~35 kJ·mol-1.27 The crystal structure of 1H-pyrazole has been analyzed previously, with a close-packed array comprising groups of four hydrogen-bonded 1H-pyrazole 7


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molecules.28 The smaller desorption energy of 1H-pyrazole from the multilayers on Cu(100), as compared to the sublimation energy, can be attributed to different molecular packings of 1H-pyrazole in the multilayers and in the crystal that affect the binding strength between molecules.

Reaction of 1H-Pyrazole on Cu(100) 1H-pyrazole possesses C-H and N-H groups, which would show different reaction kinetics in dehydrogenation. The H-loss process may compete with the aromatic ring rupture in the 1H-pyrazole reaction on Cu(100). Besides, various bond dissociation possibilities in the pyrazole ring, such as the breakage of C-C, C-N and/or N-N bonds, would result in different distributions of the reaction products and intermediates. These focal points in the thermal decomposition of 1H-pyrazole on Cu(100) deserve to be explored. Figure 2 shows the temperature-programmed reaction/desorption spectra of 1H-pyrazole (0.3 L) on Cu(100). H2 (m/z 2), N2 (m/z 14 and 28), HCN (m/z 26 and 27), CH3CN (m/z 39, 40 and 41) and 1H-pyrazole (m/z 68) are produced in the 1H-pyrazole decomposition. These are the only products found in the mass survey from 1 to 200 amu and are identified by the parent ions and/or fragmentation patterns, being consistent with those collected in the NIST database. As shown in Figure 2, H2 evolves at two very different temperatures of 231 and 557 K, showing a large discrepancy in the dissociation energy of the C-H and N-H bonds in 1H-pyrazole on Cu(100). Besides, the former state has a larger area. It is well known that recombination of H atoms on Cu(100), evolving H2, occurs at ~300 K.29 Therefore, the hydrogen self-coupling cannot be the formation mechanism for the H2 at 231 K. 1H-pyrazole is found to desorb at ~210 K and 529 K. The low temperature feature is due to direct molecular desorption. However, the 529 K state must be resulted from 1H-pyrazole further reaction, because 8



dehydrogenation of 1H-pyrazole occurs to form H2 at 231 K. The other three products of N2, HCN and CH3CN are from the pyrazole ring decomposition and appear at 557 K, as the high-temperature state of H2. The formation of 1H-pyrazole at 529 K strongly suggests that the pyrazole ring still remains intact, without opening, prior to ~490 K, the onset temperature of the 1H-pyrazole evolution. Up to this point, it can be briefly concluded that 1H-pyrazole undergoes dehydrogenation on Cu(100) first, followed by ring breakage. The more detailed reaction pathways of 1H-pyrazole on Cu(100) is discussed later, together with the surface intermediates involved. A similar thermal evolution behavior is observed at 1.0 L of 1H-pyrazole on Cu(100) (Figure S2).

Spectroscopic Studies of the Adsorption Structure and Reaction Intermediates of 1H-Pyrazole on Cu(100) Infrared and photoelectron spectroscopies have been employed to study the temperature-dependent surface species following 1H-pyrazole adsorption on Cu(100), which can reveal the bonding structures and surface reaction mechanism of 1H-pyrazole. Shown in Figure 3 are the RAIR spectra, varying with the briefly annealing temperatures, of 1.0 L of 1H-pyrazole on Cu(100). This exposure can render a multilayer adsorption as shown in Figure 1. In Figure 3, four different infrared absorption patterns are measured at 180 K, 200 K, 250 K and 580 K, indicating changes in the adsorption state of 1H-pyrazole molecules on Cu(100) in the ranges of 180-200 K, 200-250 K and 450-580 K. In the 120 K spectrum, the infrared peaks appear at 763, 837, 885, 918, 941, 981, 1035, 1053, 1137, 1153, 1359, 1400, 1475, 1550, 2820, 2866, 2883, 2901, 2934, 2986, 3065 and 3163 cm-1, which are partially listed in Table 1 and compared to the vibrational frequencies of 1H-pyrazole in the gas and solid phases.30-32 In the fingerprint region, 700-1600 cm-1 in this case, the observed peak positions in the 120 K spectrum are similar to the previously reported 1H-pyrazole infrared absorptions 9


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and can be assigned to three types of vibrations, 763, 837 and 885 cm-1 to out-of-plane C-H bending modes; 918 and 941 cm-1 to ring deformations; the peaks in the range of 981-1550 cm-1 to stretching vibrations of the bonds in the pyrazole ring in couple with in-plane N-H and/or C-H bending modes. Because the out-of-plane and in-plane C-H bending modes are concomitantly detected, the 1H-pyrazole molecules are adsorbed neither parallel nor perpendicular to the Cu(100) surface, according to the RAIRS dipole selection rule. This rule states that only the vibrational modes with nonzero dynamic dipole moments perpendicular to the surface are infrared active.33 The adsorbed 1H-pyrazole molecules show a complex, broad and poorly-resolved absorption behavior between 2750 and 3300 cm-1 in the 120 K spectrum. In particular, the N-H stretching mode, which is found at 3523 cm-1 in the previous gas study, is not detected, similar to the case of the solid phase (Table 1). The missing N-H stretching peak is ascribed to hydrogen bonding between the adsorbates. Several vibrational factors may contribute to the complexed infrared absorptions in the range of 2750-3300 cm-1, including C-H stretching modes, softened N-H stretching modes due to the hydrogen bonding interactions, and combination/overtone bands. As shown in Figure 3, the adsorbed layer structure of 1H-pyrazole formed at 120 K is still stable as the surface is heated to 180 K, with an unvaried absorption pattern. Upon heating to 200 K, near the onset temperature of 1H-pyrazole and H2 desorption, the infrared absorptions are similar to those shown in the 120 K spectrum, but with stronger band intensities and a better spectral resolution in general. The 200 K spectrum is due to the predominantly adsorbed 1H-pyrazole molecules, because the main multilayer desorption and H2 evolution from 1H-pyrazole dehydrogenation do not occur yet at 200 K. However, a small contribution to the 200 K spectrum from dehydrogenated 1H-pyrazole cannot be completely ruled out. The spectroscopic transformation in such a small temperature difference, from 180 K to 200 K, can be 10



attributed to a structure change of the 1H-pyrazole adsorption layer toward a more orderly molecular arrangement, resulting in the observed enhancement in band intensity and resolution. Formation of crystalline CH3OH from the multilayers adsorbed at 98 K has been reported previously as a result of temperature increase.25 In the 250 K spectrum, the infrared absorptions from 1H-pyrazole are no longer observable due to the multilayer desorption at 210 K. Since H2 evolves at ~230 K in the 1H-pyrazole reaction on Cu(100) (Figure 2), the peaks located at 981, 1029, 1255 and 1475 cm-1 in the spectra of 250-520 K should be associated with 1H-pyrazole dehydrogenation. The surface species from the 1H-pyrazole dehydrogenation is further confirmed to be pyrazolate from the N-H bond scission, with the XPS evidence shown later. This pyrazolate intermediate still exists at 520 K with its characteristic peaks at 981 and 1255 cm-1, but disappears at 580 K due to its decomposition at ~550 K to generate H2, HCN, N2, CH3CN and 1H-pyrazole, as shown in Figure 2 and Figure S2. Figure 4 shows the temperature-dependent RAIR spectra measured following adsorption of 0.3 L of 1H-pyrazole on Cu(100). At this exposure, the 1H-pyrazole desorption around 200 K is barely detectable. The infrared absorption behavior shown in the 120 K and 180 K spectra is similar to that observed in Figure 3 (1.0 L exposure of 1H-pyrazole). This result suggests that H-bonding interactions between adjacent 1H-pyrazole molecules also exist at a lower coverage and the adsorption layer doesn’t form a highly-ordered structure. However, upon heating to 200 K, the infrared absorptions dramatically change, with the main peak at 1043 cm-1. The 200 K spectrum is attributed to adsorbed 1H-pyrazole molecules with a preferential adsorption orientation. The disappearance of the relatively strong out-of-plane C-H bending mode at 760 cm-1 strongly suggests that the aromatic rings of the adsorbed 1H-pyrazole molecules are perpendicular or near perpendicular to the surface. In this adsorption geometry, the hydrogen bonding interactions between adjacent 1H-pyrazole molecules 11


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seem to be suppressed and therefore lead to the missing broad absorptions in the range 2750-3300 cm-1 in the 200 K spectrum. As the surface temperature is increased to 250 K, the absorption peaks are similar to those of the 1.0 L of 1H-pyrazole in Figure 3, which are due to pyrazolate and completely disappear at 580 K. Figure 5 shows the RAIR spectra as a function of temperature for a 0.5 L of 1H-pyrazole, with the existence of the first- and second-layer molecules at the adsorption temperature. The spectral features observed in the 120 K and 180 K spectra are similar to those shown in Figures 3 and 4 (1.0 L and 0.3 L), due to adsorbed 1H-pyrazole. Upon heating to 200 K, the peak intensities decrease in general, but with a higher intensity ratio of 1045 cm-1/ 763 cm-1. This result can be explained by the change in the adsorption geometry of 1H-pyrazole molecules in the first layer and desorption of partial second layer molecules. At higher temperatures up to 520 K, only pyrazolate peaks are detected. More evidence regarding the surface reaction mechanism of 1H-pyrazole on Cu(100) is further obtained from the XPS experiments. Figure 6 shows the temperature dependent XP spectra of 0.3 L of 1H-pyrazole on Cu(100). The C1s and N1s binding energies of 1H-pyrazole and phenyl-substituted 1H-pyrazole have been measured previously, as shown in Table 2.34,35 These reported results demonstrate the resolvable amine (-NH-,1N) and imine (-N=, 2N) groups, with a difference of ~1.2 eV in N1s binding energy. Besides, the two carbon atoms (3C and 5C) adjacent to the nitrogen atoms have higher 1s binding energies than the 4C atom. In the 120 K spectrum, the broad N1s and C1s emission signals are fitted with two deconvoluted peaks, respectively, at 400.5 and 401.6 eV for the N1s and at 285.7 and 286.7 eV for the C1s. The CO adsorption on Cu(100) from the background, which is observed as desorption peak at ~175 K in the TPR/D experiments, may partially contributes to the 286.7 eV peak. The C1s binding energy has been found to be 286.6 eV for CO adsorbed on Cu(100).36 At 12



120 K, 1H-pyrazole is adsorbed in a molecular form, without dissociation, on Cu(100), as evidenced by the RAIRS study (Figures 3-5). The amine group is expected to have a higher N1s binding energy, as compared to that of the imine. However, the N1s binding energies for these two nitrogen-containing groups of the adsorbed 1H-pyrazole molecules can be affected by the intermolecular interactions, i.e., hydrogen bonding, and by the interaction of the adsorbates with the substrate. For the latter case, the surface attaching group, -NH- or -N=, can induce a chemical shift in the N1s binding energy. In the N1s spectra of Figure 6, the 401.6 eV fitted peak decreases in company with the growth at 400.2 eV, as the surface is heated from 120 K to 200 K. At 200 K, the spectrum shows two peaks at 400.1 and 401.6 eV with a similar intensity. In the 0.3 L RAIR spectra (Figure 4), there is also a distinct change in infrared absorption behavior in this temperature range, which is related to a variation in the adsorption layer structure. After heating the surface to 200 K, the adsorbed 1H-pyrazole molecules can change adsorption geometry to an upright orientation. The theoretical calculations (shown later) predict that a 1H-pyrazole molecule is bonded to Cu(100), via the imine nitrogen, with the ring plane perpendicular to the surface. Therefore the 400.1 and 401.6 eV peaks in the 200 K nitrogen spectrum are ascribed to the -N= and -NH- of 1H-pyrazole on Cu(100), respectively. The 1.5 eV difference is consistent with those of 1H-pyrazole and phenyl-substituted 1H-pyrazole reported previously (Table 2). In the C1s case, the 286.7 eV peak slightly decreases in intensity from 120 K to 200 K, probably due to CO desorption. The two C1s fitted peaks for the 200 K spectrum appear at 285.5 and 286.6 eV, with the area ratio of 285.5 eV/286.6 eV approximately at 2. Since the 5C atom connecting to the -NH- has a higher C1s binding energy than those of the other two carbon atoms for 1H-pyrazole (Table 2),34 the 286.6 eV peak is attributed to the 5C atom and the 285.5 eV peak to the 3C and 4C atoms for the adsorbed 1H-pyrazole molecules on Cu(100). This assignment is consistent with the observed 13


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peak area ratio. In Figure 6, noticeable changes occur in the transition from 200 K to 250 K. Only one N1s peak is found to be at 400.0 eV in the 250 K spectrum. Note that H2 evolution from 1H-pyrazole reaction on Cu(100) has already taken place prior to 250 K. At 250 K, the N1s splitting peaks are no longer observable, indicating that the two nitrogen atoms of the adsorbed 1H-pyrazole have the same or a similar bonding environment. In view of the H2 evolution, dehydrogenation of the 1H-pyrazole via N-H bond scission to form a surface-bound pyrazolate can explain the N1s change from 200 K to 250 K. The chemical environments for the two N atoms in pyrazolate are the same. The theoretical work (shown later) indicates that pyrazolate is adsorbed on Cu(100) via the two chemically equivalent nitrogen atoms. In the 250 K C1s spectrum of Figure 6, only one peak is measured at 285.2 eV, which indicates that the three carbon atoms of pyrazolate on Cu(100) are indifferentiable by C1s photoelectron emission. Note that the RAIRS studies also reflect a chemical evolution of 1H-pyrazole on Cu(100) in the temperature of 200 K-250 K (Figures 3-5). The surface pyrazolate remains intact on Cu(100) at 450 K, but it disappears upon heating the surface to 580 K, due to its decomposition to form the gaseous products (Figure 2). No N1s signals are found in the 980 K spectrum, but with a small amount of carbon left on the surface (Figure 6).

Calculated Adsorption Structures and Vibrational Frequencies of 1H-Pyrazole and Pyrazolate on Cu(100). The optimized adsorption structures of 1H-pyrazole and pyrazolate on Cu(100) are illustrated in Figures 7 and 8, with the listed structural parameters (bond length and angle). 1H-pyrazole is theoretically predicted to be adsorbed at atop site, via the imine nitrogen, with the aromatic ring perpendicular to the surface. In general, the C-N bond lengths are smaller than those of the C-C bonds. Moreover, the 2N-3C bond is shorter 14



than the 1N-5C by 0.01 Å; the 4C-5C is shorter than the 3C-4C by 0.015 Å. The ∠5C1N2N and ∠2N3C4N have larger angles at 112.1° and 110.7°. The distance between the imine nitrogen atom and the surface is 2.103 Å (d(2N-Cu(s))). After the N-H bond cleavage, the pyrazolate is bonded to the surface, near two atop sites, through the two equivalent nitrogen atoms. The pyrazolate plane is at an upright orientation, in which the ∠3C4C5C is 104.8°, the smallest angle, compared to the other four bond angles of 108-109 Å in the ring. The N-Cu(s) distance (1.994 Å) is smaller than the d(2N-Cu(s)) of the 1H-pyrazole by 0.109 Å, exhibiting that pyrazolate is more strongly bonded than 1H-pyrazole on Cu(100). In parallel, the N-N length (1.365 Å) of the pyrazolate is longer than that of the 1H-pyrazole (1.353 Å). Due to the adsorption symmetry the pyrazolate, it has equivalent bond lengths of d(3C-4C)=d(4C-5C)=1.400 Å and d(5C-1N)≈d(2N-3C)=1.348 Å, and bond angles of ∠1N2N3C≈∠5C1N2N=108.5° and ∠2N3C4C=∠4C5C1N=109.1°. The equivalent bond lengths suggest that the π electrons are more evenly distributed over the 3C-4C-5C atoms for the pyrazolate, compared to those of the 1H-pyrazole, similarly also in the regions of 5C-1N and 2N-3C. Table 3 shows the experimentally and theoretically obtained infrared frequencies of 1H-pyrazole and pyrazolate on Cu(100), with vibrational mode assignments. The 1H-pyrazole and pyrazolate on Cu(100) have been theoretically shown to be adsorbed vertically. In such a geometry, the C-H out-of-plane bending modes of the two surface species cannot be observed by RAIRS according to the surface dipole selection rule. Indeed, no peaks in the theoretically predicted range (< ~900 cm-1) for the C-H out-of-plane bending vibrations are measured in the 200 K and 250 K spectra of Figure 4. This result strongly suggests that 1H-pyrazole at 200 K and the pyrazolate generated at 250 K adopt an upright or near upright adsorption geometry on Cu(100).

Study of Near-Edge X-ray Absorption Fine Structure on Adsorption Orientation 15


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On the basis of the RAIRS and calculated results, 1H-pyrazole (200 K) and pyrazolate (250 K) on Cu(100) are shown to have a near perpendicular or perpendicular adsorption orientation to the surface. NEXAFS experiments have been conducted to further investigate the adsorption geometry of the 1H-pyrazole and pyrazolate. Shown in the (a) and (b) panels of Figure 9 are the near carbon-K edge X-ray absorption fine structure spectra, measured at the indicated incidence angles (θ), of 0.3 L of 1H-pyrazole dosed at 110 K and then briefly heated to 200 K and 350 K. As already known, 1H-pyrazole exists at 200 K and pyrazolate at 350 K. In the 200 K case, the main absorption appears at 286.4 eV, but is shifted to 286.1 eV upon heating to 350 K. They are attributed to the transition of C1s→π*.37 Furthermore, the peak intensity in both cases grows with increasing incidence angle that excludes the possibility for parallelly adsorbed 1H-pyrazole and pyrazolate on Cu(100). For the two sets of the spectra (200 K and 350 K), the normalized peak intensities are plotted as a function of incidence angle and shown in Figure 9c and Figure 9d, together with the fitting curves using the equation: I(θ,α)≈P(sin2αsin2θ+2cos2αcos2θ)+(1-P)sin2α, where I is the normalized peak intensity, θ is the light incidence angle with respect to the surface, α is the angle of the ring of the adsorbed 1H-pyrazole or pyrazolate with respect to the surface, and P is the degree of linear polarization of the synchrotron radiation.19,38 The tilting angles of the aromatic ring planes of phenyl, pyridyne and benzene have been estimated using a similar method.19,39,40 For the 1H-pyrazole on Cu(100) the fitting result roughly indicates that the ring plane is away from the surface by ~70°, and the pyrazolate in the range 70°-90°. The NEXAFS results are approximately consistent with those from the RAIRS and DFT studies.

Reaction Pathway of 1H-Pyrazole on Cu(100) 1H-pyrazole decomposes on Cu(100), generating H2 at ~230 K and a surface 16



intermediate of pyrazolate. This intermediate further reacts to form H2, HCN, N2, CH3N and 1H-pyrazole at ~550 K. The atom source of the H2 evolution at 230 K is from the NH group of 1H-pyrazole. However, the H2 desorption cannot be attributed to recombination of surface hydrogen atoms, which occurs at ~300 K,29 instead the H2 could be due to the reaction between the N-H groups of the adsorbed 1H-pyrazole molecules and/or the reaction between the N-H group of one 1H-pyrazole and a H atom from N-H bond scission of another 1H-pyrazole, as shown in Scheme 2. The gas products found at ~550 K in the reaction of pyrazolate on Cu(100) reveal the bond breaking processes in the pyrazole ring decomposition. The H2 formation is from C-H bond breakage, possibly mainly from the 4C-H groups. The simultaneous dissociation of the two C-N bonds results in the N2 product. Note that self-coupling of nitrogen atoms to evolve N2 from Cu(111) occurs mainly at 677 and 768 K.41 The N-N bond cleavage occurring together with the 3C-4C breakage can lead to the formation of HCN and CH3CN. The CH3CN evolution must also involve hydrogenation and/or hydrogen transfer steps. The reaction pathway of the 1H-pyrazole is summarized in Scheme 3. Using the Redhead first-order kinetics equation, with an assumed preexponential factor of 1013 s-1, the ring opening of the pyrazolate at 550 K is estimated to have a reaction barrier of ~146.5 kJ·mol-1, which is much less than that (71.3 kcal·mol-1) of 1H-pyrazole gas phase reaction.24

Reaction of 1H-Pyrazole on O/Cu(100) Figure 10 shows the temperature-programmed reaction/desorption spectra of 1H-pyrazole on oxygen-precovered Cu(100). As compared to the reaction on the oxygen-free surface, no H2 desorption at 230 K is observed, instead, H2O evolves at 165 K (m/z 17 and 18), with a broad ~250 K shoulder. The H2 from 1H-pyrazole reaction on Cu(100) is due to N-H scission. On O/Cu(100), the H2O formation 17


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without H2 suggests that the primary 1H-pyrazole decomposition step may also occur at the N-H bond. Other reaction products of 1H-pyrazole/O/Cu(100) appear at temperatures higher than 400 K. The products detected at 467 K include H2, H2O, HCN (m/z 27), CO (m/z 28) and CO2 (m/z 44), but their formation temperature is lower than the decomposition temperature of pyrazolate on Cu(100) at 550 K (Figure 2 and Scheme 3). The preadsorbed oxygen atoms can promote the pyrazole-ring decomposition and generate the oxidized species of H2O, CO and CO2. At 555 K, the desorption products observed are H2, HCN, N2 (m/z 14, 28) and CH3CN (m/z 41). Interestingly, the product distribution and evolution temperature of this reaction channel are similar to those of pyrazolate on Cu(100), implying the formation of this intermediate on the O/Cu(100) surface. Between 467 K and 555 K, there are small peaks for the ions of m/z 16 and 17, which could be ascribed to NH3, and for m/z 29 and 43 possibly due to vinylamine (CH2=CHNH2) with a molecular mass of 43 amu.

Spectroscopic Studies of the Reaction Intermediates of 1H-Pyrazole on O/Cu(100) Shown in Figure 11 are the temperature-dependent X-ray photoelectron spectra of C1s, N1s and O1s measured before and after adsorption of 0.6 L of 1H-pyrazole on O/Cu(100) at 120 K. The O/Cu(100) surface, before being exposed to 1H-pyrazole, shows a major O1s peak at 529.7 eV assignable to adsorbed O (O(ad)), with a small shoulder at 531.3 eV, which is due to adsorbed OH (OH(ad)) from background water adsorption on the O/Cu(100).42 After adsorption of 1H-pyrazole at 120 K, the O(ad) emission is largely diminished and a new H2O(ad) peak appears at 533.0 eV. For H2O on Cu(100) and Ni(110), its O1s binding energy has been reported to be at 533.2 eV.42,43 This spectral change indicates that the O(ad) takes part in the dehydrogenation of 1H-pyrazole to form waters. This water feature decreases considerably at 180 K, corresponding to the desorption of H2O at 165 K observed in the TPR/D spectrum 18



(Figure 10), and continues to decrease, becoming very small at 220 K. In the 220 K spectrum of O1s, the main oxygen-containing surface species is OH groups at 531.3eV. Heating the surface to 280 K induces the decrease of OH(ad), but enhancing the O(ad) emission at ~529.6 eV. This change can be interpreted by the reaction of 2 OH(ad) H2O(g) + O(ad). The O(ad) is still present on the surface at 400 K, however disappears at 480 K. The O1s(ad) is consumed in the reaction with 1H-pyrazole and is responsible for the oxidized products of H2O, CO and CO2 at 467 K observed in Figure 10. In the 480 K spectrum of O1s, there is a tiny peak at 532.7 eV, showing the presence of other oxygen-containing species, different from the adsorbed O, OH and H2O. Above 480 K, O1s emission becomes negligible. In the case of N1s, the 120 K spectrum is decomposed into three peaks at 399.8, 400.3 and 401.3 eV. According to N1s assignment for the 1H-pyrazole/Cu (100) (Figure 6), the later two peaks are attributed to 1H-pyrazole. The 399.8 eV is attributed to dehydrogenated 1H-pyrazole, which is consistent with the formation of H2O(ad). The N1s peaks (400.3 and 401.3 eV) of adsorbed 1H-pyrazole vanish at 220 K, due to its molecular desorption and possibly further dissociation. The dehydrogenated 1H-pyrazole remains on the surface from 220 K to 400 K, with the N1s peak at ~399.5 eV. However, the N1s peak is slightly shifted to 399.9 eV and decreases in peak area from 400 K to 480 K. The diminished N1s peak intensity agrees with the partial product evolution occurring at 467 K, involving O(ad). Further heating to 560 K causes the disappearance of the 399.9 eV peak and formation of a small N1s feature at 398.4 eV, which could be due to adsorbed nitrogen, N(ad). This atomic N surface species is stable at 750 K, but no longer exists at 980 K, likely due to recombination to form N2.41 In the C1s analysis, the 120 K spectrum is deconvoluted with two peaks at 285.4 and 286.1 eV. Adsorbed 1H-pyrazole, including its dehydrogenated form, and CO 19


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from background adsorption contribute to the C1s emission peaks. The higher binding-energy peak is no longer observed at 220 K due to 1H-pyrazole and CO desorption. However, the C1s peak at 284.8 eV from dehydrogenated 1H-pyrazole doesn’t have much change from 220 K to 400 K, but is shifted to 285.2 eV at 480 K, with a smaller intensity. The C1s and N1s spectra show a similar changing behavior in peak position and intensity between 400 K and 480 K, reflecting partial product evolution and possible structure change of the surface species in this temperature range. Structural transformation of the surface intermediates is also observed with infrared spectroscopy (shown later). The C1s peak becomes very small at 560 K in Figure 11, presumably due to further evolution of reaction products. A small amount of carbon is left on the surface of 980 K. Figure 12 shows the temperature-dependent reflection-absorption infrared spectra of O/Cu(100) after adsorption of 0.7 L of 1H-pyrazole at 120 K. The peaks observed in the 120 K and 180 K spectra indicate the presence of adsorbed 1H-pyrazole, as shown in the case of Cu(100). Note that dehydrogenated 1H-pyrazole species can exist on the surface in this temperature range, according to the XPS study (Figure 11), however, probably due to their small peak intensities and/or peak overlapping with those of 1H-pyrazole, no peaks can be definitely assigned to dehydrogenated 1H-pyrazole in these two low temperature spectra. Heating the surface to 280 K removes the adsorbed 1H-pyrazole and produces two infrared peaks at 1024 and 1479 cm-1. A similar spectrum is obtained at 440 K. Interestingly, no pyrazolate from the N-H bond breakage, with its characteristic peaks of 980 and 1257 cm-1, is detected, between 280 and 400 K, a result different from the 1H-pyrazole reaction on Cu(100). In terms of the XPS result of Figure 11, the observed 1024 and 1479 cm-1 peaks are ascribed to dehydrogenated 1H-pyrazole species, other than pyrazolate. However, pyrazolate appears in the 480 K spectrum, as evidenced by the 20



appearance of the peaks at 982 and 1256 cm-1, with an additional strong 2169 cm-1 peak. The latter peak is attributed to adsorbed isocyanate (-NCO(ad)), which has been observed in the reaction of ICH2CN on O/Cu(100).44 These surface pyrazolate and isocyanate vanish after heating the surface to 560 K. -NCO(ad) can also be formed on Pd(100) by HNCO dissociation, with a NCO stretching band in the range of 2183-2246 cm-1.45

Reaction Pathway of 1H-Pyrazole on O/Cu(100) As revealed by the TPR/D, XPS and RAIRS results (Figures 10-12), the reaction pathway of 1H-pyrazole on O/Cu(100) is summarized in Scheme 4. Dissociative adsorption of 1H-pyrazole on O/Cu(100) occurs at 120 K, producing H2O and dehydrogenated 1H-pyrazole surface species (C3N2HX), which is not pyrazolate and is likely to be in a didehydrogenated form. The surface dehydrogenated 1H-pyrazole species is stable at 400 K, however decomposes to form adsorbed isocyanate and pyrazolate and gaseous H2, H2O, HCN, CO and CO2 after heating the surface to 480 K. The pyrazolate formation could be due to hydrogenation of didehydrogenated 1H-pyrazole surface species. The infrared peaks of 1024 and 1479 cm-1 observed in the 400 K spectrum (Figure 12) are not attributed to surface species from ring rupture of 1H-pyrazole, because it is unlikely that they can recyclize into the pyrazolate. Decomposition of the pyrazolate generates its typical products of H2, N2, HCN and CH3CN at 555 K. Note that O(ad) is already not present on Cu(100) at 480 K, therefore no oxidized products, such as H2O and CO2, are detected in the pyrazolate decomposition. Other products of CH2=CHNH2 at 513 K and NH3 at 532 K are also measured in the reaction of 1H-pyrazole on O/Cu(100).

Conclusions 21


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1H-pyrazole molecules adsorbed on Cu(100) at ~120 K have hydrogen bonding interactions. Heating to ~200 K can cause a change in the adsorption layer structure and generate upright or near upright 1H-pyrazole attaching to the surface via the imine nitrogen. Decomposition of 1H-pyrazole proceeds primarily by N-H bond scission to form H2 (~230 K) and surface pyrazolate. This intermediate is proposed to be perpendicularly adsorbed via the two chemically equivalent nitrogen atoms and further decomposes by ring-opening and C-H bond cleavage at ~550 K, to evolve H2, N2, HCN, CH3CN and 1H-pyrazole. On O/Cu(100), 1H-pyrazole is dissociatively adsorbed at 120 K, forming adsorbed water and dehydrogenated 1H-pyrazole surface species (likely in a didehydrogenated form). At ~470 K, further reaction of the dehydrogenated species generates adsorbed NCO and pyrazolate and gaseous H2, H2O, HCN, CO and CO2. Other products of CH2=CHNH2 and NH3 are also observed at 515 K and 532 K, respectively. The reaction mechanisms of 1H-pyrazole on Cu(100) and O/Cu(100) are summarized in Scheme 5.

Supporting Information The supporting information is available free of charge on the ACS Publications website at DOI: Multilayer desorption of 1H-pyrazole from Cu(100) (Figure S1) and TPR/D spectra of 1.0 L of 1H-pyrazole on Cu(100) (Figure S2).

Acknowledgments This research was financially supported by the Ministry of Science and Technology of the Republic of China (MOST 105-2113-M-006-002).

References (1) Dou, R.; Yang, Y.; Zhang, P.; Zhong, D.; Fuchs, H.; Wang, Y.; Chi, L. Building

22



Chessboard-Like Supramolecular Structures on Au(111) Surfaces. Nanotechnology 2015, 26, 385601. (2) Shen, C.; Haryono, M.; Grohmann, A.; Buck, M.; Weidner, T.; Ballav, N.; Zharnikov, M. Self-Assembled Monolayers of a Bis(Pyrazol-1-yl) Pyridine-Substituted Thiol on Au(111). Langmuir 2008, 24, 12883-12891. (3) Furukawa, M.; Yamada, T.; Katano, S.; Kawai, M.; Ogasawara, H.; Nilsson, A. Geometrical Characterization of Adenine and Guanine on Cu(110) by NEXAFS, XPS, and DFT Calculation. Surf. Sci. 2007, 601, 5433-5440. (4) Furukawa, M.; Tanaka, H.; Kawai, T. The Role of Dimer Formation in the Self-Assemblies of DNA Base Molecules on Cu(111) Surfaces: A Scanning Tunneling Microscope Study. J. Chem. Phys. 2001, 115, 3419-3423. (5) Yadav, M.; Gope, L.; Kumari, N.; Yadav, P. Corrosion Inhibition Performance of Pyranopyrazole Derivatives for Mild Steel in HCl Solution: Gravimetric, Electrochemical and DFT Studies. J. Molec. Liq. 2016, 216, 78-86. (6) Sudheer, S.; Quraishi, M. The Corrosion Inhibition Effect of Aryl Pyrazolo Pyridines on Copper in Hydrochloric Acid System: Computational and Electrochemical Studies. RSC Adv. 2015, 5, 41923-41933. (7) Cang, H.; Shi, W.; Shao, J.; Xu, Q. Study on the Pyrazole Corrosion Inhibition and Synergistic Effect for Copper in Alkaline Solution. Int. J. Electrochem. Sci. 2012, 7, 5626-5632. (8) Ma, H.; Chen, S.; Liu, Z.; Sun, Y. Theoretical Elucidation on the Inhibition Mechanism of Pyridine–Pyrazole Compound: A Hartree Fock Study. J. Molec. Struct.: THEOCHEM 2006, 774, 19-22. (9) Chetouani, A.; Hammouti, B.; Benhadda, T.; Daoudi, M. Inhibitive Action of Bipyrazolic Type Organic Compounds towards Corrosion of Pure Iron in Acidic Media. Appl. Surf. Sci. 2005, 249, 375-385. 23


Page 24 of 49

Page 25 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(10) Yang, F.; Zhu, G.; Liang, B.; Shi, Y.; Li, X. Assembly of Dinuclear Copper(II) Complexes Based on a Tridentate Pyrazol–Pyridine Ligand: Crystal Structures and Magnetic Properties. Polyhedron 2017, 128, 104-111. (11) Cheng, M.; Sun, L.; Han, W.; Wang, S.; Liu, Q.; Sun, X.; Xi, H. Effect of N Ancillary Ligands on the Structure, Nuclearity and Magnetic Behavior of Cu(Ⅱ)–Pyrazolecarboxylate Complexes. New J. Chem. 2016, 40, 10504-10511. (12) Ahmed, B.; Mezei, G. From Ordinary to Extraordinary: Insights into the Formation Mechanism and Ph-Dependent Assembly/Disassembly of Nanojars. Inorg. Chem. 2016, 55, 7717-7728. (13) Naik, K.; Nevrekar, A.; Kokare, D.; Kotian, A.; Kamat, V.; Revankar, V. Pyrazole Bridged Dinuclear Cu(II) and Zn(II) Complexes as Phosphatase Models: Synthesis and Activity. J. Molec. Struct. 2016, 1125, 671-679. (14) Chen, J.; Guo, Z.; Yu, H.; He, L.; Liu, S.; Wen, H.; Wang, J. Luminescent Dinuclear Copper(I) Complexes Bearing 1,4-Bis(Diphenylphosphino)Butane and Functionalized 3-(2′-Pyridyl)Pyrazole Mixed Ligands. Dalton Trans. 2016, 45, 696-705. (15) Wu, F.; Tong, H.; Wang, K.; Zhang, X.; Zhang, J.; Wong, W.; Zhu, X. Synthesis, Crystal Structure and Photophysical Study of Luminescent Three-Coordinate Cuprous Bromide Complexes Based on Pyrazole Derivatives. J. Coord. Chem. 2016, 69, 926-933. (16) Feng, C.; Zhang, D.; Chu, Z.; Zhao, H. Dimeric Complexes of Transition Metal Based on Azole Nucleating Ligands Involving Hydrogen Bonding Interactions. Polyhedron 2016, 115, 288-296. (17) Świtlicka, A.; Czerwińska, K.; Machura, B.; Penkala, M.; Bieńko, A.; Bieńko, D.; Zierkiewicz, W. Thiocyanate Copper Complexes with Pyrazole-Derived Ligands – Synthesis, Crystal Structures, DFT Calculations and Magnetic 24



Properties. CrystEngComm 2016, 18, 9042-9055. (18) Carlotto, S.; Casarin, M.; Lanza, A.; Nestola, F.; Pandolfo, L.; Pettinari, C.; Scatena, R. Reaction of Copper(II) Chloroacetate with Pyrazole. Synthesis of a One-Dimensional Coordination Polymer and Unexpected Dehydrochlorination Reaction. Cryst. Growth & Des. 2015, 15, 5910-5918. (19) Yang, M. X.; Xi, M.; Yan, H.; Bent, B. E.; Stevens, P.; White, J. M. NEXAFS Studies of Halobenzenes and Phenyl Groups on Cu(100). Surf. Sci. 1995, 341, 9-18. (20) Xi, M.; Yang, M. X.; Jo, S. K.; Bent, B. E.; Stevens, P. Benzene Adsorption on Cu(100): Formation of Stable Bilayer. J. Chem. Phys. 1994, 101, 9122-9131. (21) Dougherty, D. B.; Lee, J.; Yates, J. T., Jr. Role of Conformation in the Electronic Properties of Chemisorbed Pyridine on Cu(100): An STM/STS Study. J. Phys. Chem. B 2006, 110, 11991-11996. (22) Sexton, B. A Vibrational and TDS Study of the Adsorption of Pyrrole, Furan and Thiophene on Cu(100): Evidence for Π-Bonded and Inclined Species. Surf. Sci. 1985, 163, 99-113. (23) Gaudioso, J.; Ho, W. Single-Molecule Vibrations, Conformational Changes, and Electronic Conductivity of Five-Membered Heterocycles. J. Am. Chem. Soc. 2001,123, 10095-10098. (24) da Silva, G. Thermal Decomposition of Pyrazole to Vinylcarbene + N2: A First Principles/RRKM Study. Chem. Phys. Lett. 2009, 474, 13-17. (25) Burke, D.; Brown, W. Ice in Space: Surface Science Investigations of the Thermal Desorption of Model Interstellar Ices on Dust Grain Analogue Surfaces. Phys. Chem. Chem. Phys. 2010, 12, 5947-5969. (26) Redhead, P. A. Thermal Desorption of Gases. Vacuum 1962, 12, 203-211. (27) NIST, Sublimation Energy and Mass Spectrum of 1H-Pyrazole. 25


Page 26 of 49

Page 27 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


http://webbook.nist.gov/cgi/cbook.cgi?Name=1H-pyrazole&Units=SI&cTP=on& cMS=on (accessed Sep. 15, 2017). (28) Ehrlich, H. W. W. The Crystal and Molecular Structure of Pyrazole. Acta Cryst. 1960, 13, 946-952. (29) Chorkendorff, I.; Rasmussen, P. Reconstruction of Cu(100) by Adsorption of Atomic Hydrogen. Surf. Sci. 1991, 248, 35-44. (30) Durig, J. R.; Bergana, M. M.; Zunic, W. M. Fourier Transform Raman Spectrum of Polycrystalline Pyrazole, Vibrational Assignment and ab initio Calculations. J. Raman Spectrosc. 1992, 23, 357-363. (31) Majoube, M. Vibrational Spectra of Pyrazole and Deuterium-Substituted Analogues. J. Raman Spectrosc. 1989, 20, 49-60. (32) El-Azhary, A. A. A Coupled-Cluster Study of the Structure and Vibrational Spectra of Pyrazole and Imidazole. Spectrochim. Acta A 2003, 59, 2009-2025. (33) Fan, J.; Trenary, M. Symmetry and the Surface Infrared Selection Rule for the Determination of the Structure of Molecules on Metal Surfaces. Langmuir 1994, 10, 3649-3657. (34) Clark, D. T.; Lilley, D. M. J. Molecular Core Binding Energies for Some Five Membered Ring Heterocycles as Determined by X-Ray Photoelectron Spectroscopy. Chem. Phys. Lett. 1971, 9, 234-237. (35) Katrib, A.; El-Rayyes, N. R.; Al-Kharafi, F. M. N1S Orbital Binding Energies of Some Pyrazole and Pyrazoline Compounds by XPS. J. Elec. Spectrosc. Rel. Phenom. 1983, 31, 317-321. (36) Isa, S. A.; Joyner, R. W.; Roberts, M. W. Adsorption of Carbon Monoxide on Cu(100) at 295 K, Characterized by Photoelectron Spectroscopy. J. C. S. Chem. Comm. 1977, 377-378. (37) Jagst, E. Surface Functional Group Characterization Using Chemical 26



Derivatization X-ray Photoelectron Spectroscopy (CD-XPS), der Freien Universität, Berlin, 2010. (38) Stöhr, J.; Outka, D. A. Determination of Molecular Orientations on Surfaces from the Angular Dependence of Near-Edge X-Ray-Absorption Fine-Structure Spectra. Phys. Rev. B: Condens. Matter Mater. Phys. 1987, 36, 7891-7905. (39) Lin, J.-L.; Ye, C.-H.; Lin, B.-C.; Li, S.-H.; Yang, Z.-X.; Chiang, Y.-H.; Chen, S.-W.; Wang, C.-H.; Yang, Y.-W.; Lin, J.-C. Thermal Reaction of 2,4-Dibromopyridine on Cu(100). J. Phys. Chem. C 2015, 119, 26471-26480. (40) Lee, A. F.; Wilson, K.; Lambert, R. M.; Goldeni, A.; Baraldi, A.; Paolucci, G. On the Coverage Dependent Adsorption Geometry of Benzene Adsorbed on Pd{111}: A Study by Fast XPS and NEXAFS. J. Phys. Chem. B 2000, 104, 11729-11733. (41) Berkó, A.; Solymosi, F. Adsorption of Nitrogen Atoms on Cu(111), Rh(111) and Pt(110) Surfaces. Appl. Surf. Sci. 1992, 55, 193-202. (42) Vesselli, E.; De Rogatis, L.; Baraldi, A.; Comelli, G.; Graziani, M.; Rosei, R. Structural and Kinetic Effects on A Simple Catalytic Reaction: Oxygen Reduction on Ni(110). J. Chem. Phys. 2005, 122, 144710. (43) Sexton, B. A.; Hughes, A. E. A Comparison of Weak Molecular Adsorption of Organic Molecules on Clean Copper and Platinum Surfaces. Surf. Sci. 1984, 140, 227-248. (44) Lin, J.-L.; Kuo, C.-W.; Yang, C.-M.; Lin, Y.-S.; Wu, T.-S.; Chao, P.-Y. Adsorption and Reactions of ICH2CN on Cu(100) and O/Cu(100). J. Phys. Chem. C 2013, 117, 19916-19926. (45) Nemeth, R.; Kiss, J.; Solymosi, F. Surface Chemistry of HNCO and NCO on Pd(100). J. Phys. Chem. C 2007, 111, 1424-1427.

27


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Page 29 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1: Comparison of the infrared frequencies (cm-1) of 1H-pyrazole 1.0 L, on Cu(100) 120 K 763

200 K

solida

gasb

modec

778

745

ω(CH)

835

833

ω(CH)

879

ω(CH)

908

ring def.

924

ring def.

1046

1009

ν(N-N)+ρ(CH)

250 K

763 775

837

842

885

885 906

912

918

918

941

941

981

981

981

1035

1035

1029

1053

1053

1056

1054

ν(C-C)+ρ(CH)

1137

1137

1144

1121

ν(C-N)+ν(C-C)+ρ(CH)

1153

1153

1152

1159

ν(N-N)+ν(C=C)+ρ(CH)

1260

1254

ν(N=C)+ρ(NH)+ρ(CH)

1255

1255

1359

1359

1357

1358

ν(N=C)+ρ(NH)+ρ(CH)

1400

1400

1398

1395

ν(C-C)+ν(C=C)+ρ(CH)

1475

1469

1471

1447

ν(C-N)+ρ(NH)

1550

1531

1536

1531

ν(C=C)+ν(N=C)+ρ(NH)+ρ(CH)

1475

1570 2820

2816

2986

2978

3065

3055

3114

3126

ν(CH)

3126

3124

3137

ν(CH)

3159

3145

3155

ν(CH)

3523

ν (NH)

3163

a: ref. 30, b: ref. 31, c: ref. 32 ω: wagging (out-of-plane bending), def: deformation, ν: stretching, ρ: rocking (in-plane bending)

28



Table 2: C1s and N1s binding energies (eV) of 1H-pyrazole and its derivative 1N

2N

3C

4C

5C

source

402.4

401.1

286.3

285.5

287.1

1H-pyrazolea

400.8

399.7

3,5-diphenyl-1H-pyrazoleb

N

C

0.3 L 1H-pyrazole on Cu(100)c

401.6

400.5

286.7

285.7

120 K

401.6

400.1

286.6

285.5

200 K

400.0

285.2

250 K

a: ref. 34; b: ref. 35; c: this work

29


Page 30 of 49

Page 31 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 3: Comparison of the experimentally and theoretically obtained infrared frequencies of 1H-pyrazole and pyrazolate on Cu(100) 0.3 L 1H-pyrazole

Calculated

on Cu(100), 200 K

1H-pyrazole

941

1043

mode

0.3 L 1H-pyrazole

Calculated

on Cu(100), 250 K

pyrazolate

mode

571

ring def.

617

ω(CH)

626

ring def.

642

ring deformation

683

ω(NH)

708

ω(CH)

746

ω(CH)+ω(NH)

796

ω(CH)

827

ω(CH)+ω(NH)

837

ω(CH)

882

ω(CH)

904

δ(CCC)

899

ρ(CCC)

932

ρ(CH)+ring def.

923

ρ(CH)+ ρ(1N2NC)

980

1006

ρ(CH)+ ν(NN)

1021

ρ(CH)+ ν(NN)

1032

1047

ρ(CH)+ νa(CCC)

1044

ρ(CH)+ρ(NH)+ ν(3C4C)+

1119

ρ(CH)+ring bre.

1142

ρ(CH)+ ν(CN)

1259

ρ(NN)+

ν(1N5C) 1131

ρ(CH)+ρ(NH)+ ν(1N2N3C)+ νa(2N1N5C)

1145

ρ(CH)+ring bre.

1257

ν(CN)+ρ(CH) 1255

ρ(CH)+ρ(NH)+

1341

ρ(CH)+ νa(NCC)

1397

ρ(CH)+ νa(CCC)

1450

ρ(CH)+ νa(NCC)

3185

ν(CH)

3206

ν(CH)

3213

ν(CH)

νa(1N2N3C)+ νa(2N1N5C) 1348

1343

ρ(CH)+ρ(NH)+ νa(1N2N3C)

1398

1411

ρ(CH)+νa(CCC)+ρ(NH)+

1475

ν(1N2N3C) 1456

1467

1475 1516

ρ(NH)+ρ(CH)+ ν(1N5C)+ ν(3C4C5C)

1510

ρ(NH)+ρ(CH)+ ν(1N2N3C)+ ν(4C5C)

3156

ν(CH)

3309

ν(NH)

ω: wagging (out-of-plane bending), def: deformation, ν: stretching, ρ: rocking (in-plane bending), bre.: breathing

30



TOC Graphic

31


Page 32 of 49

Page 33 of 49

210 K

Rel. Yield

1.0

0.5

0.0 0.0

Ion (m/z 68) Intensity (a. u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.0 2.0 Exposure (L)

3.0

3.0L

2.0L

1.0L 0.7L 0.3L 0.05L 200

300

400

Temperature (K)

Figure 1: Temperature-programmed desorption spectra, represented by the molecular ion (m/z 68), from 1H-pyrazole adsorbed on Cu(100).



0.3L 1H-Pyrazole/Cu(100) 231K

20000

557K m/z 2

Intensity (a. u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 49

x3

14 28

26

27 x3

39 40 41 529K

x10

68 200

400

600

800

Temperature (K)

Figure 2: Temperature-programmed reaction/desorption spectra of 0.3 L of 1H-pyrazole on Cu(100), showing the evolution of H2 (m/z 2), N2 (m/z 28), HCN (m/z 26, 27), CH3CN (m/z 39, 40, 41) and 1H-pyrazole (m/z 68).


Page 35 of 49

1.0L 1H-Pyrrole/Cu(100) 580K 981

1255

520K 1475

450K

1029

350K 250K

Absorbacne

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.005

2914 2878 3159 2864 3126 2930 2978 3055 2816

941 1400 1469

200K

180K

2986 2901 3163 2883 2934 3065 2866 2820

1570

1359

1137 1035 1053 1153

1531

775 763 918 906 885 842

837

1550

150K 120K

3500

3000

1500

1000

-1

Wavenumber (cm )

Figure 3: Temperature-dependent reflection absorption infrared spectra of 1.0 L of 1H-pyrazole on Cu(100). All of the spectra were measured at ~115 K. The 1H-pyrazole molecules were adsorbed at 115 K, followed by progressively heating the surface to the temperatures indicated.



0.3L 1H-Pyrazole/Cu(100) 580K 980 1257

1475

520K

1032

0.002

450K

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 49

350K

1529

250K 1516

200K 180K

1038 1043 1051 1155 1140

1456 1398 1348

2988 2939 2900 3165 3067 2887 2868 2814

1364

931 941

912 760

120K

3500

3000

1500

1000

-1

Wavenumber (cm )

Figure 4: Temperature-dependent reflection absorption infrared spectra of 0.3 L of 1H-pyrazole on Cu(100). All of the spectra were measured at ~115 K. The 1H-pyrazole molecules were adsorbed at 115 K, followed by progressively heating the surface to the temperatures indicated.


Page 37 of 49

0.5L 1H-Pyrazole/Cu(100) 982

0.002

1256

1481

520K

1030

450K

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


350K 250K 200K

2976 2937 2904 3161 3058 2864

1400 1359

2987

1035 1045 1139 1153

939 920 763 908 775 889

1051 2819

180K 120K 3500

3000

1500

1000

Wavenumber (cm-1) Figure 5: Temperature-dependent reflection absorption infrared spectra of 0.5 L of 1H-pyrazole on Cu(100). All of the spectra were measured at ~115 K. The 1H-pyrazole molecules were adsorbed at 115 K, followed by progressively heating the surface to the temperatures indicated.



0.3L 1H-Pyrazole/Cu(100) C1s

N1s 980K 580K

285.2

Intensity (a. u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 49

450K 400.0

285.5 400.1

250K 401.6

286.6

200K 285.7 400.5

286.7

120K 406

404

402

400

398

Binding energy (eV)

396 294

292

290

288

286

284

282

280

Binding energy (eV)

Figure 6: Temperature-dependent X-ray photoelectron spectra of 0.3 L of 1H-pyrazole on Cu(100). All of the spectra were measured at ~120 K. The 1H-pyrazole molecules were adsorbed at ~120 K, followed by progressively heating the surface to the temperatures indicated.


Page 39 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Bond length (Å)

∠ N N3C

105.4

1.343

∠NCC

110.7

1.405

∠CCC

105.1

1.390

∠CCN

106.6

1.353

∠CNN

112.1

1.087

∠ C NCu

132.6

N-H

1.034

∠Cu N N

121.9

N–Cu(s)

2.103

2

N– N

2

3

N– C

3 4 5

4

C– C 5

C– C 1

C– N C-H

2

Bond angle (°)

1.353

1

1

2

3

4

5

3

2

3 4

4 5

5 1

1

2

2

2

1

Figure 7: Calculated adsorption structure of 1H-pyrazole with two viewing angles and tabulated structural parameters.



Bond length (Å) 1

N–2N

2

N–3C

Page 40 of 49

Bond angle (°)

1.365

∠1N2N3C

108.5

1.348

∠2N3C4C

109.1

3

C–4C

1.400

∠3C4C5C

104.8

4

C–5C

1.400

∠4C5C1N

109.1

C–1N

1.347

∠5C1N2N

108.4

C–H

1.084

∠Cu1N2N

107.8

N-Cu(s)

1.994

∠Cu2N1N

107.0

5

Figure 8: Calculated adsorption structure of pyrazolate with two viewing angles and tabulated structural parameters.


Page 41 of 49

350K

200K 286.4

(a)

286.1

(b) 90°

Intensity (a. u.)

Intensity (a. u.)

90° 70° 55° 40°

70° 55° 40°

30° 280

290

300

310

320

30° 280

330

290

Photon energy (eV) 2.4

2.4

(c)

30°

300

310

320

330

75

90

Photon energy (eV)

2.0

(d)

30°

2.0

40°

40°

1.6

1.6

50°

1.2

I θ/I55°

I θ/I55°

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60°

0.8

70° 0.4 90°

1.2

50°

0.8

60° 70°

0.4

90°

0.0 0

15

30

45

θ (°)

60

75

90

0

15

30

45

θ (°)

60

°

Figure 9: Near-edge X-ray absorption fine structure spectra of 0.3 L of 1H-pyrazole on Cu(100) ((a) and (b)). All of the spectra are measured at ~120 K. The 1H-pyrazole molecules are adsorbed at 120 K, followed by progressively heating the surface to 200 K and 350 K. (c) and (d) show the normalized peak intensities of 286.4 eV and 286.1 eV as a function of the light incidence angle and the fitting curves.



0.3L 1H-Pyrazole/O/Cu(100) m/z

467K

532K

x3

2

x5

14

x5

16

x5

17

x5

18

165K

Intensity (a. u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 49

250K 555K

27 28 x5

29

x5

43

x5

41

515K

44 x10 68 200

300

400

500

600

700

800

900

Temperature (K)

Figure 10: Temperature-programmed reaction/desorption spectra of 0.3 L of 1H-pyrazole on O/Cu(100).


Page 43 of 49

0.6L 1H-Pyrazole on O/Cu(100) O1s C1s

980K 750K 560K

N

1s 980K 750K

980K 750K 560K

532.7

480K

Intensity (a. u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


398.4 560K

285.2

399.9

480K

529.6

400K

284.8

280K

480K 531.3

399.5

400K

220K

280K

180K

400K

220K

533.0

280K 285.7

180K 150K 120K

220K 529.7

180K

150K

286.1

285.4

150K

400.3

531.3 BG

120K BG

120K BG

536

534

532

530

Binding energy (eV)

528

290

288

286

284

Binding energy (eV)

399.8

401.3

404

402

400

398

Binding energy (eV)

Figure 11: Temperature-dependent X-ray photoelectron spectra of 0.6 L of 1H-pyrazole on O/Cu(100). All of the spectra were measured at ~120 K. The 1H-pyrazole molecules were adsorbed at ~120 K, followed by progressively heating the surface to the temperatures indicated.



0.7L 1H-Pyrazole/O/Cu(100) 560K 2169

982

0.001 1256 1479

480K

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 49

1024

400K 280K 2936 2902 2885 2866 2822

2990 3165

3060

180K

941 1398 1035 1362 1051 1137 1155

760 891 837

120K 3600

3400

3200

3000

2800

2000

1600

1200

-1

Wavenumber (cm ) Fig.12 Temperature-dependent reflection absorption infrared spectra of 0.7 L of 1H-pyrazole on O/Cu(100). All of the spectra were measured at ~115 K. The 1H-pyrazole molecules were adsorbed at 115 K, followed by progressively heating the surface to the temperatures indicated.


800

Page 45 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1 H 4 C C

-C

C

H

3

H

H

H

5

1 2

N

N

C

C

H

H

N

N

The structure of 1H-pyrazole. Pyrazolate can be generated by N-H bond scission.



Scheme 2

Proposed H2 formation mechanism at 230 K from 1H-pyrazole reaction on Cu(100)


Page 46 of 49

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Scheme 3

Reaction pathway of 1H-pyrazole on Cu(100)



Scheme 4

Reaction pathway of 1H-pyrazole on O/Cu(100)


Page 48 of 49

Page 49 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 5

Proposed reaction mechanisms of 1H-pyrazole on Cu(100) and O/Cu(100)


Adsorption and Reaction Pathways of 1H-Pyrazole ... - ACS Publications

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