Comprehensive View of the LigandâGold Interface from First Principles

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A Comprehensive View of the Ligand-Gold Interface from First Principles Qing Tang, and De-en Jiang Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.7b02297 • Publication Date (Web): 25 Jul 2017 Downloaded from http://pubs.acs.org on July 27, 2017

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Chemistry of Materials

A Comprehensive View of the Ligand-Gold Interface from First Principles Qing Tang and De-en Jiang* Department of Chemistry, University of California, Riverside, CA 92521, USA *To whom correspondence should be addressed. E-mail: [email protected].

Abstract A large number of ligands have been used to stabilize and functionalize the gold surfaces and nanoclusters, but there has been no systematic comparison about their binding strengths with gold. In this work, we studied the interaction between 27 ligands of six different types (thiolates, phosphines, amines, aryl radicals, alkynyls, and N-heterocyclic carbenes) with the model Au surfaces by first principles density functional theory (DFT). On the perfect Au(111), we found the order of binding strengths to be: bulky N-heterocyclic carbenes (NHCs) ≈ alkynyls > thiolates ≈ phosphines > aryls ≈ less sterically bulky NHCs > alkylamines. The much stronger interaction of bulky carbenes to Au than the less sterically bulky NHCs arises from the van der Waals (vdW) attraction of bulky side groups with gold surface via the short Au…HCH2R contact. Further, we showed that the presence of a gold adatom on Au(111) leads to enhanced binding and a similar order for most of the ligands examined. Overall, bulky NHCs and alkynyl groups form the strongest interaction to both Au(111) and Auad-Au(111). This suggests that NHCs can be employed as alternatives to the currently widely used thiolates and the emerging alkynyl ligands for the preparation of more stable SAM structures on metal surfaces. Further, this insight allowed us to design viable magic-number gold clusters with NHCs as the protecting ligands.

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Introduction Ligands play an important role in the stabilization and functionalization of Au nanostructures that find applications in microelectronics,1 electrochemistry,2 sensing,3 drug delivery,4 photovoltaic devices,5 and catalysis.6,7 Thiols have been the most popular ligands for stabilizing gold surfaces and nanoparticles, due to the ease of preparation and the relatively high stability of such systems mediated by the strong S-Au bonds.8-10 The Au-thiolate interface and the Au-S bonding characteristics have been well characterized and understood11 as the building blocks of self-assembled monolayers (SAMs) on the planar surfaces and the protective layer for thiolated Au nanoparticles and nanoclusters.12 Thiol-derived SAMs tend to degrade when exposed to ambient conditions (air, light) or immersed in organic solvents and aqueous solutions for prolonged periods.13-15 Thus, improving the chemical and thermal stability of thiolate-Au SAM systems has been a key challenge for their broader applications in ambient and aqueous environments. As such, it would be highly desirable to develop new ligands that yield stronger covalent bonds between metal surfaces and the ligands. Phosphines and alkylamines have been used in the past on gold surfaces and nanoparticles.16-19 The phosphine and amine groups interact with the gold surface via the dative bond of the P/N lone pair to the Au atom.20 Organogold interfaces have been developed recently. For example, aryl radicals derived from the diazonium salts can functionalize the metal surface.21,22 More recently, the alkynyl groups (RC≡C-) have been used to functionalize Au surfaces and particles.23 By using a biphasic ligand exchange of phenylacetylene (PA-H) with the preformed polyvinylpyrrolidone (PVP)-stabilized Au clusters, Tsukuda and coworkers reported the first synthesis of phenylethynyl-capped organogold clusters with atomic precision, e.g., Au34(PA)16, Au43(PA)22, Au54(PA)26.24,25 Major breakthroughs have been made in the totalstructure determination of a series of atomically precise alkynyl-protected gold nanoclusters.26-29


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The PhC≡C-Au-C≡CPh and PhC≡C-Au-C≡C(Ph)-Au-C≡CPh motifs were observed in these new gold nanoclusters, where the terminal C≡C groups from the alkynyl ligands can function as both σ and π donors in coordination to gold, thereby providing more diverse interfacial binding motifs.30 The alkynyl ligands could also form SAMs on gold surfaces.31 From the σ and π bonding perspective, N-heterocyclic carbenes (NHCs) are of particular interest due to their high σ-donating ability and variable π-accepting property.32,33 The tendency of NHCs to form fairly robust bonds with most metals of the periodic table has inspired researchers to use them for surface modification.34 To date, there have been only a few experimental reports on the reaction between flat Au surfaces and stable NHCs. In 2011 Siemeling and his colleagues prepared NHC-based SAMs on planar gold substrate with 1,3diethylbenzimidazol-2-ylidene (BIEt) as the ligands.35 In 2013, Johnson and colleagues developed addressable NHCs that enabled modification of the properties of the NHC-coated Au surfaces.36 Then in 2014, Crudden, Horton and colleagues showed that planar NHC-Au monolayers could outperform thiol-based SAMs in stability when exposed to various conditions such as high temperatures, boiling water, organic solvents and pH extremes.37 More recently, Crudden et al. prepared the assembled NHC films on Au(111) by vapor-phase deposition and described the use of these films in surface plasmon resonance-type biosensing.38 Besides the planar surfaces, NHCs have also been recently used for functionalization of gold nanoparticles and nanocrystals.39-43 Despite the increasing number of organic groups capable of stabilizing gold in addition to the popular thiolate ligands, to our knowledge there has been no systematic comparison of these ligands regarding their binding strength to gold. The ultimate utility of SAM-derived gold nanosystems for their technological applications will be critically dependent on their stability and


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the integrity of the ligand-gold interface. Thus, there is a clear need to explore the binding strengths of various stabilizing agents with gold to facilitate the future experimental design of promising ligands for gold surfaces, nanostructures, and nanoclusters. The goal of the present work is to provide a comprehensive view of the ligand-gold interface that will be useful to establish a trend among all popular ligands and to guide the synthesis of more stable SAMs and new gold nanoparticles and nanoclusters. Results and discussion We aim to study the influence of ligand types and groups on their binding strengths to the gold surfaces with both perfect and adatom-decorated Au(111) surfaces as the substrates. Six types and 27 ligands are investigated (Figure 1), including six thiolates, three phosphines, three alkylamines, two aryl groups, two alkynyls, and 11 NHCs. Most of these groups have been used in preparing gold nanosystems or SAMs, for example, NHC-9, NHC-10 and NHC-11 are used for creation of ultrastable SAMs on gold.36,37 Overall trend of ligand binding on the flat Au(111) surface. We considered four types of binding sites on Au(111): ontop, bridge, fcc and hcp hollow sites. After relaxation, we found that thiolates and alkynyls favor the fcc hollow sites where each S or C headgroup binds to three gold atoms. For phosphines, alkylamines, aryl radicals, and NHCs, the most stable binding mode is the ontop site via a single Au-L (L=P, N, C) bond. Figure 2 presents the relaxed Au-L geometry for a selection of ligands on Au(111). One can see that the Au atom bonded to the adsorbed ligands is found to slightly protrude from the surface layer, indicating strong chemisorption of these organic groups on the Au(111) surface. The calculated Au-L (L=S, P, N, C) bond lengths for the binding complexes are in the range of 2.43~2.45 Å (Au-thiolate interface), 2.35~2.41 Å


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(Au-phosphine interface), 2.34~2.48 Å (Au-amine interface), 2.08~2.09 Å (Au-aryl interface), 2.24~2.25 Å (Au-alkynyl interface), and 1.96~2.15 Å (Au-NHC interface).

Figure 1. Ligands compared for protecting the gold surface. To be consistent with the way we computed the interfacial bonding, thiolates, aryls, and alkynyls are in their radical states.


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Figure 2. The relaxed bonding geometry of thiolate-3 (a), phosphine-3 (b), alkylamine-2 (c), aryl-2 (d), alkynyl-1 (e), NHC-6 (f), NHC-9 (g), NHC-10 (h), and NHC-11 (i) on Au(111). Here only the top two layers of Au(111) surface are shown. See Figure 1 for the ligand number label.

Figure 3 plotted the calculated binding energies on Au(111) for all the 27 ligands from Figure 1, as defined by the energy needed to desorb the neutral ligand from the surface to the gas phase; in other words, we computed the homolytic bond-dissociation energies in the case of thiolates, aryls, and alkynyls, where the desorbed ligands are in their neutral radical states (Figure 1), while in the case of NHCs, amines, and phosphines, we computed the heterolytic bond-dissociation energies, where the lone pairs remain on the desorbed ligands (Figure 1). One can see that NHCs with bulkier substituents and alkynyls stand out, forming stronger bonds to gold as compared to other groups; the bond strengths corresponding to NHC-9, NHC-10, alkynyl-1, and alkynyl-2 on Au(111) are approximately 2.41 eV, 2.33 eV, 2.27 eV and 2.37 eV,


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respectively. The overall order of the ligand/Au(111) binding strength is roughly: bulky carbenes (NHC-9, NHC-10) ≈ alkynyls > thiolates (alkanethiolates > aromatic thiolates) ≈ phosphines (PCy3 > PPh3 > PMe3) > aryl radicals ≈ less sterically bulky carbenes (from NHC-1 to NHC-8) > alkylamines. Below we analyze the trend in detail.

Figure 3. The calculated binding energies of different classes of organic ligands on Au(111) at the DFTPBE-D3 level with scaling (see the method section). The serial numbers for each type of ligand correspond to those marked in Figure 1.

Analysis of the NHC-Au(111) binding. Figure 3 shows that the NHCs with the simple methyl substituents (from NHC-1 to NHC-8) have relatively weaker bond strengths (in the range of 0.7 eV ~ 1.4 eV), compared with alkynyls, thiolates or phosphines. The significant increase in the binding energy of more bulky NHCs (NHC-9 to NHC-11) is due to contributions from the van der Waals (vdW) attraction between the bulkier side groups (1,3,5-trimethylbenzene or phenyl


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substitutes) and the Au(111) surface. We found that the vdW interaction accounts for over 75% of the total binding energy for bulky NHCs including NHC-9, NHC-10, and NHC-11. This difference in binding between bulky and less bulky NHCs can be clearly seen in their structures on Au(111): Figure 2g-i (bulky) versus Figure 2f (less bulky). Among the three strongly bonded NHCs, NHC-9 and NHC-10 turn out to have greater binding energies than NHC-11 by about 0.6 eV. So 1,3,5-trimethylbenzene groups on NHC-9 and NHC-10 offer stronger vdW interactions with the gold surface than the phenyl groups on NHC-11. By examining the optimized structures, we observed that surface Au atoms and the H atoms from the –CH3 groups in 1,3,5-trimethylbenzene substituent (Figure 4) are interacting at short distances, within 2.4~2.8 Å. Note that the vdW radii for Au and H are 1.86 Å and 1.2 Å, respectively. So the short Au…H distances between the Au surface and the -CH3 groups of NHC9 and NHC-10 shown in Figure 4 is a type of the Au…H-X hydrogen bonding (X=C, N, O) reviewed previously44 and contribute to the interfacial binding strength.


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Figure 4. The Au…H interactions between the -CH3 groups and the surface Au atoms in the optimized structures of NHC-9 (a) and NHC-10 (b) on Au(111). See Figure 1 for molecular structures of NHC-9 and NHC-10.

Comparison of thiolates on Au(111). The thiolates strongly adsorb on Au(111), with binding energy varying from 1.53 to 2.01 eV. In the stronger binding cases, the thiolates are of the alkyl, cycloalkyl or substituted alkyl types (e.g., tert-butyl, cyclohexyl, phenylethyl, 4-tert-butylbenzyl), while in the weaker cases they are of the aromatic types (e.g., phenyl or 4-tert-butylphenyl) where the electronic effect from the conjugation of the aromatic rings with the S atom’s lone-pair electrons might account for the weakening of the Au-S bond. This conjugation is manifested in the higher acidity of PhSH (pKa = 6.6) than PhCH2SH (pKa = 9.4),45 due to stabilization of the PhS- group. Phosphines and amines on Au(111). The phosphine groups primarily function as a Lewis base, interacting with gold predominantly through donation of the lone-pair electron of P to Au surface (strong σ donor) and back donation from Au to P-C σ* anti-bonding orbital (weak π acceptor). Figure 3 shows that the Au-P binding energies for the bulkier PPh3 and PCy3 ligands (phosphine2 at 1.65 eV and phosphine-3 at 1.86 eV) are stronger than that for the simpler PMe3 ligand (phosphine-1 at 1.23 eV). PCy3 is the most Lewis-basic ligand of the three due to the presence of more donating cyclohexyl groups, leading to higher nucleophilicity on P and higher binding energy with Au. Alkylamines and phosphines demonstrate similar bonding and coordination characteristics, but the Au-amine interactions (binding energy of 0.47, 0.73 and 0.84 eV for amine-1, -2 and -3, respectively) are much weaker than their phosphine counterparts. In fact, amines are also the weakliest bound ligands among all the 27 groups examined here. The


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stronger Au-P bonds than the Au-N bonds can be explained by the hard-soft acid-base theory, since phosphines are a softer base than amines while Au is a soft acid. Organogold interfaces based on aryl and alkynyl groups. In the case of aromatic aryl radicals, the interaction energies of phenyl and nitrophenyl groups with Au(111) are 1.27 eV and 1.29 eV, respectively, comparatively weaker than thiolates, phosphines and alkynyls, and about half as strong as NHC-9. Similar to the all-aromatic thiolates (benzenethiol or 4-tert-butylbenzenethiol), the presence of aromatic rings in the phenyl and nitrophenyl radicals tends to weaken the Au-C covalent bonding. The Au-C≡CR σ bond at the alkynyl-gold interface is much stronger than the Au-C6H5 σ bond at the aryl-gold interface, indicating stronger σ-donating and π-back-bonding ability of the alkynyl group. The vdW contribution to the binding of the alkynyl-1 (phenylethynyl) and alkynyl-2 (1-hexynyl) groups to Au(111) is about 12.8% and 13.9%, respectively. Therefore, the strong adsorption of alkynyl groups to Au is mainly contributed by the chemisorption of the terminal R-C≡C- group. Overall trends of ligands on Au-adatom-decorated Au(111) surface. Au-adatoms are easily available on the Au(111) surface at elevated temperatures or facilitated by ligand adsorption.46 This is especially motivated by the fact that the adatom-mediated linear RS-Auad-SR12 and PhC≡C-Auad-C≡CPh staple motifs28 are the common interfacial structures observed in thiolateand phenylethynyl-capped gold nanoclusters. So for a complete comparison, we also examined the ligands on a Au-adatom-decorated Au(111), denoted as Auad-Au(111). We found that like thiolates and alkynyls, aryls and less sterically bulky NHCs (NHC-1 to NHC-8) prefer the staple motif bonding with two ligands sharing one adatom, while phosphines, amines and bulky NHCs species prefer the onefold-coordinated upright geometry on top of the Au adatom due to the steric repulsion of bulky side groups with the gold surface. The


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resulting bonding geometries of several representative ligands on Auad-Au(111) are shown in Figure 5. For the thiolate-Auad-thiolate (Figure 5a) and aryl-Auad-aryl motifs (Figure 5d), each S or C head group is bonded to two Au atoms (Auad and a surface Au) via σ-type bonding, with Auad shifting to the bridge site. In the PhC≡C-Auad-C≡CPh motif (Figure 5e), the C≡C bond forms π-type bonds with the surface Au in addition to the σ bonds of the terminal C to the adatom. In the case of less sterically bulky NHCs (Figure 5f), the two NHCs are joined by the adatom forming a linear NHC-Auad-NHC complex, with no chemical bonding to the Au(111) surface. Here we note that both the NHC-Au adatom and the NHC-Auad-NHC dimer complex have been observed by scanning tunneling microscopy (STM) recently.47 Experimentally, bisand mono-NHC complexes of Au can be observed in solution due to etching away Au atoms from the surface.33 Based on our computational models of the interface, simulations of the etching process can be done via reactive-force-field-based molecular dynamics and explicit inclusion of solvent molecules to further shed light on this issue. Phosphines, amines and bulky NHCs (Figure 5b, 5c, 5g, 5h and 5i) are found to adsorb directly on top of the Au adatom at the surface hollow site, leading to a shortened Au-L (L=P, N, C) bond than on the perfect Au(111). Here we note that the binding of NHC-10 on the adatom surface (Figure 5h) has been calculated in a previous study which reported an identical Au-C binding length (2.03 Å).36


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Figure 5. Bonding geometry of selected ligands on Au-adatom-decorated Au(111) surface: (a) thiolate-3; (b) phosphine-3 (b), alkylamine-2 (c), aryl-2 (d), alkynyl-1 (e), NHC-6 (f), NHC-9 (g), NHC-10 (h) and NHC-11 (i).

Figure 6. The calculated binding energies of different classes of ligands on Auad-Au(111) at the DFT-PBE-

D3 level with scaling. The serial numbers for each type of ligand correspond to those marked in Figure 1.


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Figure 6 shows the calculated ligand binding energy of different functional groups on Auad-Au(111). For the less sterically bulky NHCs, their binding is greatly enhanced after forming the linear NHC-Auad-NHC complexes driven by the vdW interaction between the flatlying NHC molecules and the Au surface. The binding energies of the eight less sterically bulky NHCs range from 1.43 to 1.99 eV, averaging about 30% increase in binding from on Au(111) to on Auad-Au(111); among them, NHC-6 possesses the strongest interaction on Auad-Au(111) due to the added contribution of the benzene ring/surface vdW interaction (Figure 5f). Moreover, the Au-H distance between the surface Au and H from the -CH3 side group of NHC-6 is about 2.74 Å, again suggesting the Au⋅⋅⋅H–R hydrogen bond. The presence of adatom also leads to stronger binding of bulky NHCs to gold, reflected in bond strength increase at 11.6%, 10.7%, and 21.3% for NHC-9 (from 2.41 to 2.69 eV), NHC10 (from 2.33 to 2.58 eV), and NHC-11 (from 1.78 to 2.16 eV), respectively, from on Au(111) to on Auad-Au(111). The vdW interaction in the adatom case contributes to about 40% of the binding stability of these bulky NHCs to Auad-Au(111), which is indeed a significant decrease from the non-adatom case. Formation of RC≡C-Auad-C≡CR staple motif increases the binding energy by 22% for alkynyl-1 (phenylethynyl) and 11% for alkynyl-2 (1-hexynyl). The aryl groups also prefer the aryl-Auad-aryl motif by about 0.50 eV per aryl group in terms of the binding energy on AuadAu(111) than on Au(111). The change in binding energy is relatively small for phosphines, amines, and thiolates on Auad-Au(111) than on Au(111).


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Charge state of Au atoms. To understand the charge transfer between the Au surfaces and the ligands, we analyzed the Bader charges on the Au atoms. We found that the Au atoms on Au(111) bound to thiolates, amines, aryl groups, alkynyl groups and NHCs carry a positive charge in the range of +0.02 ~ +0.12 |e|, while the Au atoms bound to phosphines carry a negative charge of 0.03 ~ -0.15 |e|. On Auad-Au(111), the Au adatoms bound to amines and bulky NHCs are positively charged in the range of +0.08 ~ +0.11 |e|, while the Au adatoms bound to phosphines are negatively charged (-0.05 ~ -0.14 |e|). In the case of thiolates, aryl groups, alkynyl groups and less sterically bulky NHCs, we found that the Au adatoms in the staple motifs carry more positive charge (+0.13 ~ +0.27 |e|) than the ligand-bound surface Au (+0.04 ~ +0.06 |e|) since the former is coordinated to two ligands while the latter is only coordinated to one ligand. So the phosphines are electron-donating, while the other ligands are electron-withdrawing on the Au surfaces and the Au adatoms can enhance the charge transfer via the staple motifs. NHC-protected gold clusters. The results above show the unique strength of bulky NHC groups in interacting with gold. Inspired by the thiolate-protected gold nanoclusters and the recently emerging alkynyl-protected nanoclusters, we wonder if magic-number gold clusters can be created using NHCs as the protecting ligands. To test this idea, we hypothesize that an icosahedral-based Au13 core can be capped by NHCs. To satisfy the electron count, we can use the chloride ions to tune the charge.48,49 We estimate that the maximum number of less sterically bulky NHC ligands can be allowed on the icosahedral cluster is about 12. This number can be further reduced by using chloride to maintain an 8-electron count. The viable compositions are, for example, Au13(NHC-6)12]5+, [Au13(NHC-6)10Cl2]3+, [Au13(NHC-6)8Cl4]1+, and [Au13(NHC6)7Cl5]0. For the larger NHC-9 ligand, the Au13 cluster can only accommodate a maximum of four ligands, the remaining eight Au are stabilized by Cl. We optimized these structures (Figure


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7) with DFT and found that they all have a large HOMO-LUMO gap from 1 to 2 eV, indicating that they are potentially viable structures. Among these hypothesized Au13 clusters, we selected [Au13(NHC-6)10Cl2]3+ to calculate its frontier orbitals (Figure 8). We found that the frontier orbitals have the characters of superatomic orbitals, where the three nearly degenerate HOMO-2, HOMO-1 and HOMO have the 1P-orbital characters, while the nearly doubly degenerate LUMO and LUMO+1, and the triply degenerate LUMO+2, LUMO+3 and LUMO + 4 have the 1Dorbital characters. It would be interesting to compare the stability of the proposed clusters in Figure 7 with other well-known Au13-based clusters such as Au25(SR)18- and [Au13(PR3)10Cl2]3+, but that is still computationally challenging. Recent advances have been made to compare the stability of nanoclusters of the same family, such as Aun(SR)m.50 We plan to address the stability of nanoclusters of different compositions, ligands, and charge states in future by using chemical reactions to relate the clusters in question and also including a solvation model to take into account the solvation effect.


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Figure 7. Optimized structures of Au13 clusters capped by NHCs and chloride; the composition and the calculated HOMO-LUMO gap are shown under each cluster. Yellow, Au; black, N; green, Cl.

Figure 8. Frontier orbitals of the [Au13(NHC-6)10Cl2]3+ cluster.

Conclusions In summary, the adsorption and binding strengths of different types of ligands (27 in total) on perfect and adatom-decorated Au(111) surfaces were studied by dispersion-corrected DFT. It is found that on flat Au(111), ligand binding strength follows the order: bulky NHCs ≈ alkynyls > thiolates ≈ phosphines > aryl radicals ≈ less sterically bulky NHCs > alkylamines. Compared to the less sterically bulky NHCs, bulky NHCs have much greater vdW attraction to the gold surface. With the involvement of Au adatom, thiolates, alkynyls, aryls and less sterically bulky NHCs form the linear ligand-Auadatom-ligand staple motif where each headgroup of the ligand is coordinated to two gold atoms: one to the adatom and another to the lattice gold on Au(111).


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Phosphines, amines and bulky NHCs species prefer to be ontop of the gold adatom. The gold adatom leads to enhanced binding stability for most protecting groups, and the ligand binding energies follows the similar order as on perfect Au(111). Among all the types of ligands investigated in this work, bulky NHCs and alkynyl groups form the strongest bonds to both the perfect and adatom-decorated Au(111) surfaces. This suggests that NHCs and alkynyls may outperform the traditional ligands (e.g., thiolates, phosphines, amines, aryl radicals) in producing more stable SAMs structures on gold. In addition, several viable gold nanoclusters with the NHC ligands were proposed, having a Au13 icosahedral core and the magic number of 8 free-electron count. The current work offers useful theoretical guidelines and insights for future selection of appropriate ligands as chemical tools to functionalize gold surfaces.

Computational method DFT computations were performed to examine the structural features and binding energies of different organic ligands on the Au (111) surface by using the Vienna ab initio simulation package (VASP).51 The ion-electron interaction is described with the projector augmented wave (PAW) method.52 Electron exchange-correlation is represented by the functional of Perdew, Burke and Ernzerhof (PBE) of generalized gradient approximation (GGA).53 A cutoff energy of 400 eV was used for the plane-wave basis set. To construct the surface slab, the fcc unit cell of bulk gold with optimized lattice parameter of a = 4.17 Å was employed. The Au(111) surface slab was modeled in a rectangular 3×2 3 unit mesh (with lateral dimensions of a=15.3 Å and b=17.7 Å) with four-layer thickness. During all the computations, the bottom two substrate layers were kept fixed at the optimized bulk positions, and only the top two layers with the coordinated organic ligands were allowed to relax. The thickness of the vacuum layer was set to


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be 17 Å. The Brillouin zone was sampled by a Monkhorst-Pack k-point mesh of 3×3×1 grid. The convergence threshold for structural optimization was set to be 0.02 eV/Å in force. We used the recently developed DFT-D3 method to take into account long-range dispersion interactions in our calculations.54 The binding energy (eV per ligand) is defined as the energy needed to desorb the organic groups into isolated neutral molecules in the gas phase. It is known that the PBE-D3 functional usually overestimates the binding energies of adsorbates on metal surfaces.55-58 In Figure S1 in the Supporting Information (SI), we compared the calculated binding energy with the available experimental values17,38,59,60 for six different adsorbates on Au(111), and obtained a scaling factor of 0.67 and an offset of -0.10 eV between the PBE-D3 value and the experimental measurement. This scaling relationship has been applied in the binding energies reported in the main text; the original PBE-D3 binding energies are provided in Figures S2 and S3 in the SI.

Supporting Information •

Scaling relationship between the experimental and PBE-D3 adsorption energies of some organic groups on Au(111);

•

PBE-D3 binding energies without scaling for the 27 ligands examined in this work.

Acknowledgements.


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This work was supported by University of California, Riverside. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy.

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Comprehensive View of the LigandâGold Interface from First Principles

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Comprehensive View of the LigandâGold Interface from First Principles