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Manipulating Stabilities and Catalytic Properties of Trinuclear Metal Clusters through Tuning the Chemical Bonding: H Adsorption and Activation 2

Cong-Qiao Xu, Deng-Hui Xing, Hai Xiao, and Jun Li J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b00081 • Publication Date (Web): 14 Feb 2017 Downloaded from http://pubs.acs.org on February 20, 2017

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The Journal of Physical Chemistry

Manipulating Stabilities and Catalytic Properties of Trinuclear Metal Clusters through Tuning the Chemical Bonding: H2 Adsorption and Activation Cong-Qiao Xu, Deng-Hui Xing, Hai Xiao*, and Jun Li* Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China ABSTRACT: Chemical bonding involving metal-metal (M-M) and metal-ligand (M-L) interactions provides opportunity to tune the stabilities and catalytic properties of metal clusters. We report here the electronic and bonding properties of a series of trinuclear clusters [M3X3(PR3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I; R = H) to explore the electronic effect on the adsorption and activation of H2 and other small molecules. The bonding model of M3 is discussed in details, and the formal +4/3 oxidation state of metal element in the M3 cluster is proposed. Metallic -aromaticity is also found in the trinuclear clusters. We have shown that the stability and the catalytic activity of the trinuclear clusters can be tuned by altering the energies and compositions of M-M and M-L chemical bonding orbitals. The performance of H2 dissociative adsorption on these clusters can be explained by the orbital interactions. Relativistic effects also play a significant role in determining the activity of H2 adsorption. This finding provides an example for controlling catalytic properties through tuning chemical bonding of metal clusters.

INTRODUCTION Heterogeneous catalysts are widely used in laboratory and industries, but they are usually composed of non-uniformly sized nanoparticles, which prevents precise control of the reaction pathways and detailed understanding of the catalytic mechanisms. In contrast, many naturally occurring biocatalysts, such as Mo-Fe-S nitrogenase and Fe-S dehydrogenase,1-2 contain welldefined metal clusters that are surrounded by proteins. In these systems, the metal clusters serve as the active centers, and the intra-cluster interactions, ligands and biological environment dictate the catalytic activity and efficiency through synergetic effects. These metal clusters thus provide an effective platform to precisely control catalytic performance. Our study suggests that tuning the chemical bonding between metal clusters and ligands can manipulate the catalytic property of the metal clusters, which can serve as a model for understanding the catalytic performance of large metal clusters, nanoparticles and surfaces with well-defined absorbates. Understanding of the chemical bonding can shed light on the stabilities and catalytic activities of the clusters.3-5

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For decades, triangular metal clusters, especially those of group 10, have been widely studied due to their broad applications in synthesis and catalysis.6-17 For example, previous experimental work by Li and coworkers has shown that the triangular tripalladium sandwich complex [Pd3(C7H7)2(MeCN)3](BF4)2 is an efficient catalyst for the cycloisomerization of 2phenylethynylaniline to form 2-phenylindole.10 Recent experimental work also indicates that [Pd3Cl(PPh2)2(PPh3)3]+[SbF6]− cluster is an excellent catalyst for the Suzuki-Miyaura cross C-C coupling of a variety of aryl bromides and aryl boronic acid under ambient aerobic conditions.13 The Ptn− (n = 3-7) clusters also were found to efficiently catalyze the oxidation of CO to CO2 by N2O or O2.14 Moreover, the formation of benzene from cyclotrimerization of acetylene on Pd3 cluster supported on MgO(100) films was also achieved at 300 K.15 The palladium cluster Pd3(dppm)3(CO)2+

(dppm

=

bis(diphenylphosphino)methane)

is

also

an

efficient

electrochemically assisted Lewis acid catalyst for the fluorination and alcoholysis of acyl chlorides.16 A series of tri-nuclear metal sandwich clusters with cycloheptatrienyl and monocyclic group-15 ring ligands [M3L2(CO)3]q (M = Ni, Pd, Pt; L = C7H7, P5, P6, As5, As6; q = 2+, 0, or 2−) were proposed theoretically to possess high stability and aromatic characters.18 Indeed, trinuclear clusters of M(0), such as [Pt3(CO)3(P(C6H11)3)4],19 [M3(CO)3L3] (M = Pd, L = P(t-Bu)3, PPh(tBu)2; M = Pt, L = PPh(t-Bu)2),20 [Pt3(SO2)3(PPh3)3]21, and [Pt3(CN-t-Bu)6] were characterized and investigated a long time ago. [Pt3(PPh3)2(PPh2)3(Ph)] with two short Pt-Pt bonds (2.79 Å) and the nonbonding Pt-Pt of 3.63 Å was synthesized from [Pt(PPh3)4]22 and reported to have a mixed oxidation states with two Pt(I) and one Pt(II).23-24 Palladium cluster [Pd3Cl(PPh2)2(PPh3)3][BF4] with Pd in an oxidation state other than zero was also well-characterized by Dixon and coworkers.25-26 Besides, previous works have shown that M3 can act as either Lewis base or Lewis acid, which enables the formation of the “open face” (or half-sandwich) or the “full face” (or sandwich) structure by interacting with H+, MPH3+, Tl+, and Cd2+ ions.6, 27-32 The electronic structures and chemical bonding of trinuclear metal clusters had attracted extensive interest since the early days when Cotton proposed the concept of atomic cluster. In 1964, Cotton and Haas presented the empirical Cotton-Haas (CH) method as a model for metalmetal bonding of d-orbitals in trinuclear metal clusters.33 Since then, the CH method has been widely used in electronic structure analysis of triangular metal clusters.34-40 Bursten et al. extended this type of analysis to M312+ (M = Mo, W) clusters.34 However, despite the success of the empirical CH method, detailed bonding analysis of trinuclear metal clusters based on modern quantum chemical calculations is still noteworthy. In this paper, we investigate thoroughly the bonding character of the trinuclear metal clusters M3 of group-10 elements (M = Ni, Pd, Pt), as well as their interactions with the bridging and terminal ligands in a series of [M3X3(PH3)3]+ (M = 2


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Ni, Pd, Pt; X = F, Cl, Br, I) compounds. By comparing the interactions between M3 and different bridging halogen ligands, we have concluded that the stability of triangular metal clusters can be modified by altering the peripheral ligands. In addition, the metal-metal and metal-ligand interactions are also essential for evaluating the potential of trinuclear clusters as catalysts.

COMPUTATIONAL DETAILS The [M3X3(PPh3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I) clusters were chosen as the models based on the widely studied structure of [Pd3Cl(PPh2)2(PPh3)3]+ and other similar tri-metal clusters.13, 2226

In order to simplify the orbital interactions and to save time for calculations, we used phosphine

(PH3), instead of bulky triphenylphosphine (PPh3) used in experiments, as the terminal ligand. All the monovalent bridging ligands were modeled by the halogen atoms to maintain the high symmetry for subsequent chemical bonding analysis. Theoretical calculations were performed using Density Functional Theory (DFT) as implemented in the Amsterdam Density Functional (ADF 2016.101) program.41-43 The generalized gradient approximation (GGA) with the PBE exchange-correlation functional44 was used, together with the TZ2P Slater basis sets.45 Frozen core approximations were applied to the inner shells [1s2] for F, [1s2-2p6] for Ni, P, Cl, [1s2-3p6] for Br, [1s2-3d10] for Pd, [1s2-4p6] for I, and [1s2-4d10] for Pt. The scalar relativistic (SR) effects were taken into account by the zeroorder-regular approximation (ZORA).46 All the geometries were optimized under C3v group symmetry and vibrational frequencies were also calculated to confirm that they are true local minima. Natural bond orbital (NBO) analysis47-49 was performed by using the NBO 6.0 package as implemented in the ADF program. Energy decomposition analysis with natural orbitals for chemical valency (EDA-NOCV)50-52 calculations were carried out to examine the energy contributions of the main orbital interactions. Nucleus independent chemical shift (NICS) analyses53-56 were obtained by calculating the magnetic shielding tensors of a series of ghost atoms along the z-direction perpendicular to the M3 ring center. The electron localization functions (ELFs)57-58 plots were computed with all-electron Slater basis sets at the PBE/TZ2P level of theory. In order to explore the effects of metal-ligand interactions on the chemisorption, calculations of H2 adsorption at the metal clusters were performed using the PBE, B3LYP59 and M0660 functionals implemented in the Gaussian 09 program package.61 Double- basis sets (LanL2DZ) with the effective core potentials for I, Pd and Pt62 and the standard 6-311G(d,p) Gaussian basis sets for the other atoms (denoted here by 6-311G**~dz) were employed. The geometries were

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fully optimized and analytical frequency calculations were obtained to characterize the nature of the stationary points.

RESULTS AND DISCUSSION Structures and Stability The structures of [M3X3(PH3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I) systems were optimized with the C3v symmetry at the PBE/TZ2P level of theory, as shown in Figure S1 and Table S1 of the Supporting Information. Pd-Pd bond distances lie in the range of 2.69 Å to 3.06 Å, below the sum of the van der Waals radii (3.26 Å).63 Increasing bond lengths of Pd-X and Pd-Pd are observed as the bridging halogen goes from F to I, which can be attributed to the growing atomic radii of X and the decreasing Pd-Pd interactions. For Pd3 compounds, the energy gap (EHL) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) decreases as halogen changes from F, Cl to Br to I in the group, with [Pd3Cl3(PH3)3]+ having the largest HOMO-LUMO gap and the most stable structure. Calculations of [Ni3Cl3(PH3)3]+ and [Pt3Cl3(PH3)3]+ are also performed to compare the structures and bonding properties with the Pd3 clusters. The HOMO-LUMO energy gap increases as the trinuclear center changes from Ni to Pt, with Pt3 clusters showing the highest stability. Note that all the M-M distances are larger than the sum of the covalent radii but smaller than that of the van der Waals radii, while all the M-P interactions are characterized as single bonds and the M-P bond distance increases from Ni to Pd and then decreases slightly for Pt, consistent with the general trend of relativistic effects.64 M-X bond distances are larger than the sum of the covalent radii, indicating that M-X belongs to weak covalent single bond. Thus both the metal-metal and metal-ligand interactions play an important role in manipulating the stabilities of the trinuclear clusters. Electronic and bonding properties The chemical bondings of metal complexes and metal-metal-bonded diatomic systems were well established.65 In order to understand the molecular orbitals of the trinuclear metal clusters, MOs formed with d-AOs are representatively divided into three types: , , . Meanwhile, the clusterskeletal MOs can be classified as radial (r), tangential (t), vertical (v) according to the orientation of the AOs relative to the M3 triangle. Besides, MOs are composed of bonding and antibonding orbitals. Based on an overall consideration of these points, ten types of MOs are defined: 0r, 0t, 1r*, 1t*; 0r, 0t, 1r*, 1t*; and 0v, 1v*, where asterisk indicates the antibonding MOs. Here MOs composed of both radial and tangential AOs are symbolically given as radial or tangential based on the main character. Following the CH method,33 we use a right-handed local coordinate system (LCS) at each metal atom in which the z-axis on each metal atom points to the center of the 4


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triangle, with the x-axis lying in the plane of the triangle and the y-axis perpendicular to the plane. Therefore, the d-type group orbitals of metal atoms can be classified as dx2-y2, dz2, dxz, dyz, dxy, with their transformation properties under D3h symmetry shown in Table S2, which illustrates the specific ways how the ten types of MOs are derived from AOs. The MO energy levels of Pd1, Pd2 and Pd34+ are shown in Figure 1 and the MO contours of Pd34+ are shown in Figure 2. In constructing Figure 1, a variety of electronic states of Pd34+ (see Table S3) were studied to explore the most stable electronic state. A triplet state of Pd34+ was found to be lowest in energy with the electron configuration of (5e)2(6e)4(3e)4(1a1)2(2a2)0, which was used in further fragment analysis. In order to gain better understanding of the metalmetal bonding within this triatomic cluster, we plot the d orbital interactions of Pd34+ correlated with Pd2, as shown in Figure 1. As is well known, the d orbital manifold of Pd2 consists of bonding and antibonding combinations of orbitals with ,  and  symmetry. Similarly, it is easier to analyze chemical bonding of triatomic systems with bonding models defined specifically in the local coordinate system. Indeed in previous work, Boldyrev et al. analyzed the orbital forms of triatomic and tetratomic systems, which led to the clear picture of bonding involving aromaticity.66 Our previous work has also shown the s- and p-orbital bonding patterns of triangular metal clusters.67-68 Herein we further studied the bonding model with regard to d atomic orbital (AO) of triatomic systems M34+ (M = Ni, Pd, Pt).

Figure 1. Orbital energy-level correlation diagram of Pd34+ clusters from Pd and diatomic fragment (Pd2). The inset on the right shows the MO contours (isovalue = 0.03 a.u.) of Pd2. Energies of the Pd34+ orbitals are shifted to align the middle of  orbital manifold with that of Pd2.

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Figure 2. MO contours (alpha spin) of M34+ (M = Ni, Pd, Pt) with the most stable triplet states at the SR-ZORA PBE/TZ2P level of theory (isovalue = 0.03 a.u.). The M34+ geometry is fixed at the core structure of [M3Cl3(PH3)3]+, respectively.

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As can be seen from Table S3 and Figure 2, M34+ formed by metals of group 10 show similar electronic structures and bonding characters. A triplet state with electron configuration of (1v*)2(1r*)4(1r*)4(1t*)2(1t*)0 is most stable for M34+ (M = Ni, Pd, Pt). In all cases of M34+ (M = Ni, Pd, Pt), the antibonding orbital 1t* is unoccupied and only two electrons are located at the doubly degenerate orbital 1v* with weak antibonding character, making triplet state the most stable. The lowest-lying MO is a radially completely bonding orbital (0r) while the highest-lying MO is a tangentially completely antibonding orbital (1t*), with weaker bonding and antibonding orbitals distributed in the middle. The bonding orbitals, 0r and 0v, are higher in energy than 0r due to weak overlaps of AOs. As the interactions between Pd and Pd2 fragments of Pd34+ have shown (Figure 1), complicated mixing of the MOs of Pd2 are observed in MOs of Pd34+ because the coordinate systems of orbitals are transformed from along or perpendicular to Pd-Pd bond to radial, tangential, and vertical to Pd3 triangle. MO contours of Pd2 and Pd3 in Figures 1 and 2 can help better understand the bonding model evolution. As an illustrating example, Figure S2 presents the molecular orbital (MO) energy-level correlation diagram of [Pd3Cl3(PH3)3]+ from analyzing the fragment interactions. The MO contours are shown in Figure S3 for visualizing the orbital interactions. It can be seen that the HOMO (16e) is a doubly occupied degenerate  orbital, while the LUMO (17e) is a degenerate  orbital. The LUMO is an antibonding orbital arising from the interactions between higher-energy 6e (*) orbital of Pd3, lower-energy 2e (t) orbital of Cl3, and lower-energy 4e (r*) orbital of (PH3)3. The LUMO arises mainly from the * orbital of Pd3, implying that the formal oxidation state of Pd3 cluster is +4 or of Pd is +4/3. Meanwhile, all the 3p orbital interactions of Cl atoms are found to mainly contribute to the MOs below the LUMO, consistent with the Cl-1 oxidation state in [Pd3Cl3(PH3)3]+ cluster. In the case of Cl33- and (PH3)3, MOs composed of p-AOs are also defined upon trinuclear bonding models, with r, t, r*, t*; and v, v* components, which have been discussed in our previous works.67-68 To elucidate how the trinuclear cluster and the ligand determine the stability and the bonding properties of [M3X3(PH3)3]+, various bridging ligands formed by halogen (X = F, Cl, Br, I) and different metals (M = Ni, Pd, Pt) are investigated. The orbital energy-level correlation diagrams of all the other systems except for [Pd3Cl3(PH3)3]+ are present in Figure S4, with only the main MO correlations displayed for clarity. The corresponding MO contours of [M3X3(PH3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I) are shown in Figure S5. Similar to [Pd3Cl3(PH3)3]+, it is found that the LUMOs for all these systems are mainly composed of 1r*(M34+), indicating that four d electrons of M3 are oxidized to form a stable M34+ cluster core.

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The metal-metal bonding is significantly affected by the ligand effects. We will take the Pd3 clusters as examples. Except for the cluster with three F bridging ligand, the HOMOs of all the other systems are the same as that of [Pd3Cl3(PH3)3]+, which is dominated by (Pd34+) and mixed with *(Cl33-). In contrast, the HOMO of [Pd3F3(PH3)3]+ is composed of 1v*(Pd34+), which can be explained by the lower-lying energies of F33- fragment that results in weak orbital overlaps between (Pd34+) and *(F33-). As the HOMO and HOMO-1 of [Pd3F3(PH3)3]+ are much more stabilized than those of [Pd3Cl3(PH3)3]+, the LUMO of [Pd3F3(PH3)3]+ is also stabilized with a small energy decrease of orbital energy, leading to similar HOMO-LUMO gaps for these two clusters. Overall, orbital energies and components of the LUMOs do not change much as the halogen bridging ligands change, because these orbitals are mainly correlated with Pd34+ and (PH3)3 fragment orbitals that are close in energy. However, the HOMOs are remarkably affected by the bridging ligands as they are mainly formed with (Pd34+) and v*(X33-). As the bridging halogen changes from F to I, the orbital energies of X33- fragment increase, triggering enhancing orbital overlaps in HOMOs. Consequently, HOMO becomes less stable as the halogen becomes heavier. We can thus conclude that the HOMO-LUMO gap decreases from Cl to I because of the raised HOMO energies. In addition to the -interactions discussed above, MOs with large (Pd34+) distributions also present orbital interactions between the trinuclear cluster and the ligands. Orbital interactions of [M3Cl3(PH3)3]+ (M = Ni, Pt) clusters are also shown in Figure S4, with the MO isosurfaces shown in Figure S5. They have the same number of valence d bonding orbitals, similar shapes and symmetries as the Pd analogues [Pd3X3(PH3)3]+ (X = F, Cl, Br, I). As can be seen, the LUMOs are composed of similar types of fragment orbital distributions, revealing that four d valence electrons are also oxidized in M3 (M = Ni, Pt). Compared to Pd34+, the valence d band of Ni34+ is higher in energy while Pt34+ shows similar d band energy (Figure S4). Therefore, 1r*(6e) of Ni34+ is less destabilized than Pd34+ because of an antibonding interaction with (PH3)3 4e-type orbitals, resulting in a smaller HOMO-LUMO gap, while the largest HOMO-LUMO gap is observed for [Pt3Cl3(PH3)3]+. Overall, the stability of [M3X3(PH3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I) clusters can be engineered by replacing the metal atoms and the bridging ligand. Meanwhile, the terminal ligand can also control the stability of the cluster as the bridging ligand does. In the present work, the most destabilized LUMO can be achieved when 1r*(M34+) and r*((PH3)3) become close in energy, while the HOMO is mainly controlled by tuning the energy difference between 0t(2e, M34+), 1r*(3e, M34+) and v*(1e, X33-). This understanding paves the way for designing tri-metal

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clusters with desired orbital features for practical applications in homogeneous or heterogeneous catalysis. Table 1. EDA-NOCV analysis of M34+ + [X3(PH3)3]3-  [M3X3(PH3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I) at the PBE/TZ2P level of theory a Eorbb

M = Ni

M = Pt

X=F

X = Cl

X = Br

X=I

X = Cl

X = Cl

Eorb

844.5

936.6

-954.3

994.5

993.7

1183.8

Eorb1

186.3

220.1

228.5

247.3

181.6

233.8

(22.1%)

(23.5%)

(23.9%)

(24.9%)

(18.3%)

(19.7%)

186.3

220.1

228.5

247.3

181.6

233.8

(22.1%)

(23.5%)

(23.9%)

(24.9%)

(18.3%)

(19.7%)

85.3

90.3

91.1

94.8

142.0

171.3

(10.1%)

(9.6%)

(9.5%)

(9.5%)

(14.3%)

(14.5%)

43.3

38.2

37.2

36.5

40.1

71.2

(5.1%)

(4.1%)

(3.9%)

(3.7%)

(4.0%)

(6.0%)

43.3

38.2

37.2

36.5

40.1

71.2

(5.1%)

(4.1%)

(3.9%)

(3.7%)

(4.0%)

(6.0%)

300.0

329.7

331.8

332.1

408.3

402.5

(35.6%)

(35.2%)

(34.7%)

(33.4%)

(41.0%)

(34.0%)

Eorb2 Eorb3 Eorb4 Eorb5 Eorb a

M = Pd

rest

The valence electronic structures of M34+ are (4e)2(6e)4(3e)4(1a1)2(2a2)0 (M = Ni), and

(5e)2(6e)4(3e)4(1a1)2(2a2)0 (M = Pd, Pt). Singlet state of [X3(PH3)3]3- (X = F, Cl, Br, I) is used. b

Orbital interactions can be split into five major components Eorb1Eorb5 and the rest part

(Eorbrest), with the relative proportions to the total orbital interactions given in parentheses. Energies are in kcalmol1. To further investigate the charge and energy contribution to the orbital interactions, EDA-NOCV calculations are carried out, and the results are shown in Table 1 and Figure S6. According to the interactions between trinuclear metal cluster and the ligands, molecular fragments M34+ with completely unoccupied 1r* orbital and [X3(PH3)3]3- (X = F, Cl, Br, I) with singlet state are used in the EDA-NOCV calculations. Five main contributions (Eorb1Eorb5) of the orbital interactions (see Table 1) are considered, with the corresponding deformation densities (orb1orb5) presented in Figure S6. Two degenerate contributions with orbital terms Eorb1 9



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and Eorb2 are the major components, which are -donation [X3(PH3)3]3-M34+ from bridging ligands and the terminal ligands. These two components refer to the degenerate LUMO in the MO contours. It is found that the charge flow in this channel increases with heavier halogen ligand and metal. The [X3(PH3)3]3-M34+ -donation components that correspond to the HOMO of [Pd3F3(PH3)3]+ and HOMO-1 of [M3X3(PH3)3]+ (M = Ni, Pd, Pt; X = Cl, Br, I) are shown with orbital energy Eorb3. Both inflow (density accumulation in red) and outflow (density depletion in blue) are found for the metal cluster in orb3 due to non-negligible s-d hybridization and the orbital contributions from -orbitals of M34+. Eorb4 and Eorb5 indicate weak -backdonation [X3(PH3)3]3-M34+, which contributes less to the total orbital interactions. Table S4 shows the results of NBO population analysis at the PBE/TZ2P level of theory. The natural atomic charges indicate that the triangular cluster cores are positively charged while the halogen ligands are negatively charged. Meanwhile, charge transfer to the Pd3 core decreases as the atomic number of the halogen ligand increases, arising from decreasing electronegativity of the halogen atom. The charge of M decreases from Ni to Pd to Pt, due to less covalent bonding for 3d orbitals than from 4d, 5d orbitals. Therefore, the charge of the M3 core depends on the cluster and the ligands. Besides, s-d hybridizations of Ni, Pd and Pt can be observed from the natural electron configurations, especially for Pt, due to the strong relativistic effects. Bonding characters of the trinuclear clusters are further illustrated by the various calculated bond orders of M-M, M-X and M-P (see Table S5). It is found that the metal-metal bond is rather weak, consistent with the large M-M bond distances in Table S1. As the bond distance of M-M increases with heavier halogen, the bond order reduces slightly. The M-PH3 dative bonds with bond lengths in the range of covalent bonds show larger bond orders compared to the metallic MM bonds. The spatial electron localization of [M3X3(PH3)3]+ clusters can be visualized with the electron localization function (ELF) maps in Figure S7. The lone pairs and core electrons are shown as deep blue area. Large probabilities of electron pairs are found between bonded P and H atoms. The regions between M and P correspond to 0.2 < ELF < 0.3 with white or light purple color. It is less favorable for electron pairs to localize at M-M and M-X bonds when comparing with Pd-PH3 and P-H bonds, which agrees well with the bond lengths and the bond order analysis. Moreover, it is noteworthy that the electron pairs are also localized in the trinuclear center, which implies 3c-2e bonding and metallic aromaticity in the trinuclear clusters, consistent with AdNDP results.13 Indeed, in the LCS bonding analysis, the 0r bonding orbital of M3 are occupied by two electrons, whereas the 1r* antibonding orbitals are empty, giving rise to net radial bonding interaction.

10


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Aromaticity We reported aromaticity of the trinuclear early transition metals (Mo3, W3, Nb3, Ta3, etc.) clusters in the early 1990s.37-40, 69 Since then, significant progress has been made by Boldyrev, Wang and others with numerous works on the metallo-aromatic properties of triangular metal clusters, such as Li3+,70 M3O9- (M = W, Mo),71 Ta3O3-,72 Nb3On (n = 0-8),73-74 [Tc3(μ-X)3X6]0/1-/2- (X = F, Cl, Br, I),75 [Re3X9]0/2- (X = Cl, Br),76-79 Hf3,80 La33-,81 and so on.82-87 To investigate the plausible aromaticity of the trinuclear metal clusters, nucleus-independent chemical shift (NICS) analyses are performed, and the results are shown in Table 2. In our study, the NICS values at the ring centers, NICS(0), are all considerably negative, indicating aromatic metal triangle in [M3X3(PH3)3]+ (M = Ni, Pd, Pt) clusters. These NICS values of the M3 clusters are larger than benzene but smaller than cyclopropane in the ring center. NICS values are also calculated at 1 Å above the metal triangle (NICS(1)) and they are all larger than those of benzene and cyclopropane. Table 2. The NICS values (in ppm) of [M3X3(PH3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I), benzene, and cyclopropane calculated at the geometrical ring center , NICS(0), and 1 Å above the ring center, NICS(1), at the SR-ZORA PBE/TZ2P level of theory Molecule

NICS(0)

NICS(1)

[Pd3F3(PH3)3]+

-31.5

-10.0

+

-32.5

-15.0

+

[Pd3Br3(PH3)3]

-31.4

-15.3

[Pd3I3(PH3)3]+

-30.5

-15.3

[Ni3Cl3(PH3)3]+

-30.2

-13.2

+

[Pt3Cl3(PH3)3]

-34.9

-15.1

Benzene, C6H6

-7.3

-9.7

Cyclopropane, C3H6

-43.3

-8.6

[Pd3Cl3(PH3)3]

It is worth mentioning that although NICS is a simple and inexpensive calculated index often used to characterize aromaticity of cyclic systems, there are discrepancies between results from NICS approaches and other methods in some cases.75, 79, 88-89 For example, negative NICS indices erroneously suggest an aromatic character of neutral Re3X9 (X = Cl, Br) and Tc3X9 (X = F, Cl, Br, I) clusters,77-79 while the AdNDP analysis does not identify such aromaticity, suggesting that NICS values alone should be used carefully to discuss aromaticity. In our studies, the electronic properties and ELF plots are additional evidence supporting the -aromaticity of the trinuclear 11



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clusters. As discussed in the last section, the 1r* orbitals of M3 are oxidized in the tri-metal cluster compounds while the 0r orbital is occupied by two electrons, which renders the trinuclear clusters as being -aromatic. Interestingly, the NICS(0) values of the cluster shows the same trend as HOMO-LUMO gaps, which is consistent with the understanding that the high stability of M3 is ascribed to -aromaticity.83 Catalytic activity The bonding analyses of the M3 clusters show that the orbital energies and characters of the metal centers can be manipulated by changing the metals and/or the bridging and terminal ligands. The catalytic properties of the metal active center can therefore be tuned via coordination chemistry. We have selected the adsorption of hydrogen, oxygen, and carbon monoxide molecules on these clusters to study the potential catalytic performance of [M3X3(PH3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I). The calculations show that chemical adsorptions of O2 and CO on these clusters are endothermic. We will thus focus on the adsorption of H2, with the calculated results shown in Figure S8 and Table 3. Two types of adsorption structures are found, shown as STR-A and STRB in Figure S8. From the dissociative adsorption energies (Ead) of H2 at the trinuclear clusters (STR-A) using B3LYP, M06 and PBE functionals (Table 3), we can see that Ead values from PBE calculations are appreciably smaller than those from the hybrid functional calculations, while they are similar between different hybrid functionals. B3LYP results are thus used in the further discussion. The dissociative adsorption of H2 at palladium clusters are all endothermic, with Ead at [Pd3I3(PH3)3]+ cluster the lowest. Furthermore, H2 dissociative adsorptions at nickel and platinum clusters are more favorable than at the palladium clusters, with H2 adsorption at [Pt3Cl3(PH3)3]+ cluster being exothermic. Among the two kinds of adsorption structures (STR-A and STR-B) for H2@[M3X3(PH3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I), STR-A of H2@[Pd3F3(PH3)3]+, H2@[Pd3Cl3(PH3)3]+, H2@[Pt3Cl3(PH3)3]+ are found to be more stable while the others prefer STR-B. With H2 adsorption at the trinuclear clusters, there is a change in the shape of the clusters, where the Cl atoms (STR-A) or the P atoms (STR-B) are not in the same plane as the metal atoms. In the case of STR-A systems, two Cl atoms close to the active metal atom and the H atoms are distributed at the opposite side of the metal triangle (Figure S8). H2 molecule dissociates into two H atoms (H…H distance > 1.8 Å) and forms two Ma-H single bonds with the active M site (Ma). Meanwhile, Ma-X bonds are stretched by more than 0.20 Å. In this case, the M-X bond is activated and can act as an active site for catalytic reactions, which is consistent with the recent study of [Pd3Cl(PPh2)2(PPh3)3]+ by Li et al., where the Cl ligand is substituted by the OH ligand in the Suzuki-Miyaura reaction.13 As for STR-B structures, one H atom is located at the top site of 12


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one M atom (Mt), resulting in the neighboring PH3 moving to the other side and the Mt-P distance elongated by ~0.1-0.2 Å. The other H atom situates at the bridge site of two M atoms (Mb), where the Mb-H distance is smaller than Mt-H. Table 3. The adsorption energies of H2 (Ead) at [M3X3(PH3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I) and optimized bond lengths of H2@[M3X3(PH3)3]+ a,b Bond length/Å c

Ead/eV

STR-A B3LYP

M06

PBE

Ma-X

Mn-

Ma-H

H-H

Ma-Mn Mn-Mn

X +

[Pd3F3(PH3)3]

0.91

1.05

0.47

2.28

2.02

1.51

1.90

2.72

2.65

[Pd3Cl3(PH3)3]+

0.87

1.03

0.46

2.59

2.36

1.52

1.88

2.74

2.82

[Pd3Br3(PH3)3]+

0.80

0.85

0.37

2.70

2.48

1.53

1.90

2.74

2.90

+

[Pd3I3(PH3)3]

0.45

0.51

-0.02

2.90

2.68

1.57

2.00

2.75

3.08

+

[Ni3Cl3(PH3)3]

0.21

0.11

-0.45

2.38

2.15

1.46

1.86

2.34

2.77

[Pt3Cl3(PH3)3]+

-0.24

-0.05

-0.60

2.61

2.38

1.54

2.05

2.80

2.80

STR-B [Pd3Br3(PH3)3]+ +

[Pd3I3(PH3)3]

+

[Ni3Cl3(PH3)3] a

Bond length/Å d

Ead/eV B3LYP

Mt-P

Mb-P

Mt-H

Mb-H

H-H

Mt-Mb

Mb-Mb

0.71

2.54

2.35

1.52

1.75

2.38

3.10

2.96

0.27

2.53

2.34

1.53

1.77

2.32

3.13

3.06

0.02

2.35

2.23

1.44

1.62

1.94

2.63

2.60

The adsorption energy (Ead) is calculated as : Ead = E(AB)  E(A)  E(B). bAll bond lengths are

based on calculations at the B3LYP level of theory. cMa is the active site of the metal and Mn represents the non-active metal site of STR-A. dMt is the metal with H adsorbed at the top site and Mb represents the metal with H adsorbed at the bridge site. For the palladium clusters, the Ead value decreases as the halogen atom changes from F, Cl to Br to I, which can be explained by the decreasing stability of the [M3X3(PH3)3]+ cluster. The adsorption energy of H2 at [Pd3I3(PH3)3]+ cluster is the lowest with Ead = 0.27 eV due to its vulnerable structure destabilized by the strong interactions between Pd34+ and I33- fragments, as discussed in the orbital energy-level correlation diagram. H2 adsorption at [Ni3Cl3(PH3)3]+ cluster is found to be more favorable compared to the palladium clusters, which results from the lowest HOMO-LUMO gap because of weak orbital overlaps between Pd34+ and (PH3)3 fragments. Thus the nickel cluster can be easily reconstructed with H2 adsorption. Unlike [Pd3Cl3(PH3)3]+ cluster, 13



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[Pt3Cl3(PH3)3]+ cluster with the highest stability can activate H2 via dissociative adsorption with an exothermic energy of -0.24 eV. As shown in Figure S9 and Table S6, the distributions and components of the MO maps of [Pd3Cl3(PH3)3]+ and [Pt3Cl3(PH3)3]+ can be used to elucidate this energetic difference. From Figure S9, the bonding orbital formed by H atoms and the cluster is HOMO-24 for Pd3 cluster and HOMO-31 for Pt3 cluster, while the LUMO and LUMO+1 are also mainly composed of 1r* orbital of M3, where antibonding interactions between H atoms and the clusters are observed in LUMO+1. The HOMO-31 is highly stabilized because of the strong interactions between  orbital of H2 and s-type AOs of Pt atoms. Strong relativistic effects of Pt atoms lead to contracted and stabilized 6s-AO, which facilitates the orbital overlaps between H2 and the cluster. However, the interactions between the cluster and the H2 are much weaker for [Pd3Cl3(PH3)3]+ cluster, due to weaker relativistic effects for Pd. To further confirm that this difference is due to the relativistic effects, we compare the components of the bonding orbital under non-relativistic (NR) and scalar relativistic (SR) calculations (see Table S6). Increased s-AO components are found for bonding orbitals of both Pd3 and Pt3 clusters upon considering the relativistic effects, while it is much more so for Pt3 cluster, where the 6s-AO contribution grows from 10% (NR) to 28% (SR). This result indicates that relativistic effects play a significant role in the H2 activation reaction at Pt3 clusters. We recently reported that relativistic effects can sometimes break the periodicity of chemical bonding in the nonrelativistic domain.90 The present results provide a further example.

CONCLUSIONS In this study, the geometry and electronic structures, stabilities, and bonding characters of the trinuclear clusters [M3X3(PH3)3]+ (M = Ni, Pd, Pt; X = F, Cl, Br, I) are studied via DFT calculations to explore how to manipulate the active centers for catalytic process. We report herein a bonding model of triangular clusters M3 with d-type atomic orbitals. The d-AOs based MOs of M3 are divided into ten types: 0r, 0t, 1r*, 1t*; 0r, 0t, 1r*, 1t*; and 0v, 1v*. The M-M bond strength decreases as the bridging halogen becomes heavier and also decreases from Ni-Ni to Pd-Pd and Pt-Pt. The average formal oxidation state of the group-10 metal atoms in M3 clusters is +4/3. We find that the stability and the catalytic property of the trinuclear clusters are dependent on the interactions between the triangular cores, the bridging ligands and the terminal ligands. The LUMO is mainly composed of 1r*(M34+) and r*((PH3)3) interactions while the HOMO is controlled by orbital overlaps between 0t(2e, M34+), 1r*(3e, M34+) and v*(1e, X33-) orbitals, which provides opportunity to tune the orbital features of these frontier orbitals in catalysis. Furthermore, from energy decomposition analysis, the major contributions to the orbital 14


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interactions arise from the -donation [X3(PH3)3]3-M34+ from bridging ligands and the terminal ligands. We also show that the trinuclear clusters have  aromaticity due to oxidizing of four electrons of 1r*(M3) orbitals and the doubly occupied 0r orbital, which can account for the stability of the clusters. Changing the metallic cores can also tune the bonding and properties. H2 dissociative adsorptions at the clusters show distinct performances for different halogen bridging ligands. Consequently, the highest stability and activity of the trinuclear clusters can be achieved with a rational choice of bridging and terminal ligands. Relativistic effects are also found to affect the H2 adsorption. Our findings provide insight into manipulating the energies and components of the frontier orbitals of metal clusters through the chemical bonding with other metals and ligands. These results can help to understanding of the adsorption and reaction mechanisms of chemical species absorbed on trinuclear clusters, nanoparticles, and surfaces.

ASSOCIATED CONTENT Supporting Information Additional information on the optimized geometries, transformation properties of the d-type orbitals, electron configurations, MO contours, energy-level correlation diagrams, deformation density plots of the NOCV pairs, NBO population analysis, bond orders, ELFs of the trinuclear clusters and structures, MO contours as well as the AO distributions in the bonding MOs of H2 adsorption at the clusters are given. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (H.X.); [email protected] (J.L.). Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by the NKBRSF (Grant No. 2013CB834603) and National Natural Science Foundation of China (Nos. 21590792, 91645203 and 21521091). The calculations were performed on supercomputers at Tsinghua National Laboratory for Information Science and Technology, at the Supercomputing Center, Computer Network Information Center of the Chinese Academy of Sciences, and at the Computational Chemistry Laboratory of Department of Chemistry, Tsinghua University. 15



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REFERENCES (1) Averill, B. A. Fe-S and Mo-Fe-S Clusters as Models for the Active Site of Nitrogenase. In Copper, Molybdenum, and Vanadium in Biological Systems. Structure and Bonding Book Series; Springer: Berlin, 1983; Vol. 53, pp 59-103. (2) Boyington, J. C.; Gladyshev, V. N.; Khangulov, S. V.; Stadtman, T. C.; Sun, P. D. Crystal Structure of Formate Dehydrogenase H: Catalysis Involving Mo, Molybdopterin, Selenocysteine, and an Fe4S4 Cluster. Science 1997, 275, 1305-1308. (3) Dai, D.; Balasubramanian, K. Potential Energy Surfaces for Platinum (Pt3) + Hydrogen Atom and Palladium (Pd3) + Hydrogen Atom Interactions. J. Phys. Chem. 1992, 96, 3279-3282. (4) Cabria, I.; López, M. J.; Fraile, S.; Alonso, J. A. Adsorption and Dissociation of Molecular Hydrogen on Palladium Clusters Supported on Graphene. J. Phys. Chem. C 2012, 116, 2117921189. (5) Ong, S. V.; Khanna, S. N. Theoretical Studies of the Stability and Oxidation of Pdn (n = 1– 7) Clusters on Rutile TiO2(110): Adsorption on the Stoichiometric Surface. J. Phys. Chem. C 2012, 116, 3105-3111. (6) Imhof, D.; Venazi, L. M. Trimetallic Units as Building Blocks in Cluster Chemistry. Chem. Soc. Rev. 1994, 23, 185-193. (7) Kovala-Demertzi, D. Synthesis and Reactivity of Tripalladium Clusters. In Metal Clusters in Chemistry. Book Series; Wiley-VCH: Weinheim, 1999; pp 399-416. (8)

Puddephatt, R. J.; Manojlovic-Muir, L.; Muir, K. W. Coordinatively Unsaturated

Tripalladium and Triplatinum Clusters: Models for Reactions on Metal Surfaces. Polyhedron 1990, 9, 2767-2802. (9) Burrows, A. D.; Mingos, D. M. P. The Chemistry of Group 10 Metal Triangulo Clusters. Coordin. Chem. Rev. 1996, 154, 19-69. (10) Lv, C.; Cheng, H.; He, W.; Shah, M. I. A.; Xu, C.; Meng, X.; Jiao, L.; Wei, S.; Li, J.; Liu, L., et al. Pd3 Cluster Catalysis: Compelling Evidence from in Operando Spectroscopic, Kinetic, and Density Functional Theory Studies. Nano Res. 2016, 9, 2544-2550. (11) Santana, J. A.; Rösch, N. Metal-Supported Metal Clusters: A Density Functional Study of Pt3 and Pd3. J. Phys. Chem. C 2012, 116, 10057-10063. (12) Zhang, J.; Zhang, M.; Han, Y.; Li, W.; Meng, X.; Zong, B. Nucleation and Growth of Palladium Clusters on Anatase TiO2(101) Surface: A First Principle Study. J. Phys. Chem. C 2008, 112, 19506-19515. 16


Page 16 of 24

Page 17 of 24

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


(13) Fu, F.; Xiang, J.; Cheng, H.; Cheng, L.; Chong, H.; Wang, S.; Li, P.; Wei, S.; Zhu, M.; Li, Y. A Remarkably Robust and Efficient Pd3 Cluster Catalyst for the Suzuki Reaction and Its Odd Mechanism. ACS Catal. 2017, in press (doi: 10.1021/acscatal.6b02527). (14) Böhme, D. K.; Schwarz, H. Gas-Phase Catalysis by Atomic and Cluster Metal Ions: The Ultimate Single-Site Catalysts. Angew. Chem., Int. Ed. 2005, 44, 2336-2354. (15)

Watanabe, Y. Atomically Precise Cluster Catalysis Towards Quantum Controlled

Catalysts. Sci. Technol. Adv. Mater. 2014, 15, 063501. (16) Lemaître, F.; Lucas, D.; Mugnier, Y.; Harvey, P. D. The Pd3(dppm)3(CO)2+ Cluster: An Efficient Electrochemically Assisted Lewis Acid Catalyst for the Fluorination and Alcoholysis of Acyl Chlorides. J. Org. Chem. 2002, 67, 7537-7540. (17) Luo, P.; Karsenti, P.-L.; Brisard, G.; Marsan, B.; Harvey, P. D. Electron-Transfer Kinetics within Supramolecular Assemblies of Donor Tetrapyrrolytic Dyes and an Acceptor Palladium Cluster. Inorg. Chem. 2016, 55, 1894-1904. (18) Jin, P.; Li, F.; Chen, Z. Theoretical Design of Novel Trinuclear Sandwich Complexes with Central M3 Triangles (M = Ni, Pd, Pt). J. Phys. Chem. A 2011, 115, 2402-2408. (19) Albinati, A.; Carturan, G.; Musco, A. X-Ray Structure of the Trinuclear Metal Cluster Pt3[P(C6H11)3]4(CO)3. Inorg. Chim. Acta 1976, 16, L3-L4. (20)

Yoshida, T.; Otsuka, S. Reactions of Two-Coordinate Phosphine Platinum(0) and

Palladium(0) Compounds. Ligand Exchange and Reactivities toward Small Molecules. J. Am. Chem. Soc. 1977, 99, 2134-2140. (21)

Moody, D.; Ryan, R. Pyramidal Metal-Sulfur Dioxide Coordination. Chemistry of

Pt(SO2)2(PPh3)2 and Synthesis and Molecular Structure of Pt3(SO2)3(PPh3)2×C7H8×SO2. Inorg. Chem. 1977, 16, 1052-1055. (22) Taylor, N. J.; Chieh, P. C.; Carty, A. J. Platinum Cluster Compounds: X-Ray Structures of Phosphido-Bridged Bi- and Tri-Nuclear Complexes with Strong Metal-Metal Bonds Derived from [Pt(PPh3)4]. J. Chem. Soc., Chem. Commun. 1975, 448-449. (23) Bender, R.; Braunstein, P.; Tiripicchio, A.; Camellini, M. T. Skeletal Isomerization of the [Pt3(μ-PPh2)3Ph(PPh3)2] Cluster by Recrystallization in Various Solvents. Angew. Chem., Int. Ed. Engl. 1985, 24, 861-862. (24) Bender, R.; Braunstein, P.; Dedieu, A.; Ellis, P. D.; Huggins, B.; Harvey, P. D.; Sappa, E.; Tiripicchio, A. Synthetic, Structural, Spectroscopic, and Theoretical Studies of Structural Isomers of the Cluster Pt3(μ-PPh2)3Ph(PPh3)2. A Unique Example of Core Isomerism in Phosphine Phosphido-Rich Clusters. Inorg. Chem. 1996, 35, 1223-1234.

17



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(25) Dixon, K. R.; Rattray, A. D. Trinuclear Palladium Clusters: Synthesis and Phosphorus-31 Nuclear Magnetic Resonance Spectra of [Pd3Cl(PPh2)2(PPh3)3][BF4] and Related Complexes. Inorg. Chem. 1978, 17, 1099-1103. (26) Cartwright, S. J.; Dixon, K. R.; Rattray, A. D. Studies of Trinuclear Palladium Clusters by Phosphorus-31 NMR Spectroscopy: Reactivity of [Pd3Cl(PPh2)2(PR3)3][BF4] Complexes (R = Ethyl or Phenyl) and the Synthesis of [Pd3(PPh2)3(PR3)3][BF4]. Inorg. Chem. 1980, 19, 11201124. (27) Mendizabal, F.; Donoso, D.; Burgos, D. Theoretical Study of the Protonation of [Pt3(μL)3(L)3](L = CO, SO2, CNH; L = PH3, CNH). Chem. Phys. Lett. 2011, 514, 374-378. (28) Donoso, D.; Mendizabal, F. Theoretical Study of the Interaction between Pt(0) and MPH3+ Fragments in Complexes of the [Pt3(μ-CO)3(PH3)3]–MPH3+ (M= Cu+, Au+, Ag+) Type. Theor. Chem. Acc. 2011, 129, 381-387. (29) de Silva, N.; Fry, C. G.; Dahl, L. F. Phosphine-Ligated Induced Formation of Thallium (I) “Full” Pt3TlPt3 Sandwich Versus “Open-Face” TlPt3 Sandwich with Triangular Pt3(μ2-CO)3(PR3)3 Units: Synthesis and Structural/Spectroscopic Analysis of Triphenylphosphine [(µ3-Tl)Pt3(μ2CO)3(PPh3)3]+ and Its (μ3-AuPPh3)Pt3 Analogue. Dalton Trans. 2006, 1051-1059. (30) Tanaka, K.; Tanabe, M.; Ide, T.; Osakada, K. Cationic Hydridotriplatinum Complex with Bridging Germylene Ligands. Organometallics 2014, 33, 2608-2612. (31) Underwood, D. J.; Hoffmann, R.; Tatsumi, K.; Nakamura, A.; Yamamoto, Y. Triangular Platinum and Nickel Clusters: The "Tinker-Toy" Construction of Chains with High Nuclearity. J. Am. Chem. Soc. 1985, 107, 5968-5980. (32)

Tsipis, A. C.; Gkekas, G. N. Shedding Light on the Bonding, Photophysical and

Magnetotropic Properties of Triangular Pt3 Complexes and Their "Open-Face" TlPt3 HalfSandwiches. Dalton Trans. 2013, 42, 2201-2212. (33) Cotton, F. A.; Haas, T. E. A Molecular Orbital Treatment of the Bonding in Certain Metal Atom Clusters. Inorg. Chem. 1964, 3, 10-17. (34) Bursten, B. E.; Cotton, F. A.; Hall, M. B.; Najjar, R. C. Survey of the Bonding in Several Structural Types of Trinuclear Molybdenum and Tungsten Cluster Compounds. Inorg. Chem. 1982, 21, 302-307. (35) Cotton, F. A.; Stanley, G. G. Ground State Electronic Structures of Some Metal Atom Cluster Compounds. Chem. Phys. Lett. 1978, 58, 450-453. (36) Bursten, B. E.; Cotton, F. A.; Green, J. C.; Seddon, E. A.; Stanley, G. G. Electronic Structures and Photoelectron Spectra of the Metal Atom Cluster Species Tri-.Mu.-Chloro-

18


Page 18 of 24

Page 19 of 24

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


Hexachlorotrirhenium,

Tri-.Mu.-Bromo-Hexabromotrirhenium,

and

Tri-.Mu.-Chloro-

Nonachlorotrirhenate(3-). J. Am. Chem. Soc. 1980, 102, 955-968. (37) Li, J.; Liu, C.-W.; Lu, J.-X. Electronic Structures and d-pπ Bonding of Some M3X44+ Cluster Compounds. Polyhedron 1994, 13, 1841-1851. (38) Li, J.; Liu, C.-W.; Lu, J.-X. Quantum Chemical Studies on the Bonding Characteristics of Some M3X4 Transition-Metal Halogenide Clusters. J. Clust. Sci. 1994, 5, 505-521. (39)

Li, J.; Liu, C.-W.; Lu, J.-X. Ab Initio Studies of Electronic Structures and Quasi-

Aromaticity in M3S4-nO4+n (M = Mo, W; n = 0-4) Clusters. J. Chem. Soc., Faraday Trans. 1994, 90, 39-45. (40) Li, J.; Liu, C.-W.; Lu, J.-X. Theoretical Studies of (d-p)ρ Bonding, Electronic Spectra, and Reactivities in Homo- and Heterometallic Clusters: [Mo3-nWnX4(H2O)9]4+ ( X = O, S, Se, Te; n = 0-3). J. Clust. Sci. 1996, 7, 469-500. (41) ADF 2016.101. http://www.scm.com. (42) te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; Fonseca Guerra, C.; van Gisbergen, S. J. A.; Snijders, J. G.; Ziegler, T. Chemistry with ADF. J. Comput. Chem. 2001, 22, 931-967. (43) Fonseca Guerra, C.; Snijders, J. G.; te Velde, G.; Baerends, E. J. Towards an Order-N DFT Method. Theor. Chem. Acc. 1998, 99, 391-403. (44)

Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made

Simple. Phys. Rev. Lett. 1996, 77, 3865-3868. (45) Van Lenthe, E.; Baerends, E. J. Optimized Slater-Type Basis Sets for the Elements 1–118. J. Comput. Chem. 2003, 24, 1142-1156. (46)

Lenthe, E. v.; Baerends, E. J.; Snijders, J. G. Relativistic Regular Two-Component

Hamiltonians. J. Chem. Phys. 1993, 99, 4597-4610. (47) Foster, J.; Weinhold, F. Natural Hybrid Orbitals. J. Am. Chem. Soc. 1980, 102, 7211-7218. (48) Reed, A. E.; Weinstock, R. B.; Weinhold, F. Natural Population Analysis. J. Chem. Phys. 1985, 83, 735-746. (49) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Intermolecular Interactions from a Natural Bond Orbital, Donor-Acceptor Viewpoint. Chem. Rev. 1988, 88, 899-926. (50)

Mitoraj, M.; Michalak, A. Natural Orbitals for Chemical Valence as Descriptors of

Chemical Bonding in Transition Metal Complexes. J. Mol. Model. 2007, 13, 347-355. (51)

Mitoraj, M.; Michalak, A. Donor–Acceptor Properties of Ligands from the Natural

Orbitals for Chemical Valence. Organometallics 2007, 26, 6576-6580. (52) Mitoraj, M. P.; Michalak, A.; Ziegler, T. A Combined Charge and Energy Decomposition Scheme for Bond Analysis. J. Chem. Theory Comput. 2009, 5, 962-975. 19



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

(53) Elser, V.; Haddon, R. C. Icosahedral C60: An Aromatic Molecule with a Vanishingly Small Ring Current Magnetic Susceptibility. Nature 1987, 325, 792-794. (54) Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; Hommes, N. J. R. v. E. NucleusIndependent Chemical Shifts: A Simple and Efficient Aromaticity Probe. J. Am. Chem. Soc. 1996, 118, 6317-6318. (55) Chen, Z.; Corminboeuf, C.; Heine, T.; Bohmann, J.; Schleyer, P. v. R. Do All-Metal Antiaromatic Clusters Exist? J. Am. Chem. Soc. 2003, 125, 13930-13931. (56) Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer, P. v. R. NucleusIndependent Chemical Shifts (NICS) as an Aromaticity Criterion. Chem. Rev. 2005, 105, 38423888. (57) Becke, A. D.; Edgecombe, K. E. A Simple Measure of Electron Localization in Atomic and Molecular Systems. J. Chem. Phys. 1990, 92, 5397-5403. (58) Savin, A.; Jepsen, O.; Flad, J.; Andersen, O. K.; Preuss, H.; von Schnering, H. G. Electron Localization in Solid-State Structures of the Elements: The Diamond Structure. Angew. Chem., Int. Ed. Engl. 1992, 31, 187-188. (59) Becke, A. D. Density‐Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648-5652. (60) Zhao, Y.; Truhlar, D. G. Density Functionals with Broad Applicability in Chemistry. Acc. Chem. Res. 2008, 41, 157-167. (61) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A., et al. Gaussian 09, Revision C.01; Gaussian, Inc.: Wallingford, CT, 2010. (62) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for K to Au Including the Outermost Core Orbitals. J. Chem. Phys. 1985, 82, 299-310. (63) Bondi, A. Van Der Waals Volumes and Radii. J. Phys. Chem. 1964, 68, 441-451. (64) Xu, C.-Q.; Xiong, X.-G.; Li, W.-L.; Li, J. Periodicity and Covalency of [MX2]– (M = Cu, Ag, Au, Rg; X = H, Cl, Cn) Complexes. Eur. J. Inorg. Chem. 2016, 2016, 1395-1404. (65) Cotton, F. A.; Murillo, C. A.; Walton, R. A. Multiple Bonds between Metal Atoms, 3rd ed.; Springer: New York, 2005. (66) Sergeeva, A. P.; Averkiev, B. B.; Boldyrev, A. I. All-Transition Metal Aromaticity and Antiaromaticity. In Metal-Metal Bonding. Structure and Bonding Book Series; Parkin, G., Ed; Springer: Berlin, 2010; Vol. 136, pp 275-305.

20


Page 20 of 24

Page 21 of 24

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


(67) Pan, F.-X.; Xu, C.-Q.; Li, L.-J.; Min, X.; Wang, J.-Q.; Li, J.; Zhai, H.-J.; Sun, Z.-M. A Niobium-Necked Cluster [As3Nb(As3Sn3)]3- with Aromatic Sn32-. Dalton Trans. 2016, 45, 38743879. (68) Li, W.-L.; Xu, C.-Q.; Hu, S.-X.; Li, J. Theoretical Studies on the Bonding and Electron Structures of a [Au3Sb6]3- Complex and Its Oligomers. Dalton Trans. 2016, 45, 11657-11667. (69) Chen, Z.-D.; Li, J.; Liu, C.-W.; Lu, J.-X. Localized Molecular Orbital Studies of the Electronic Structures of a Typical [Mo3S4]4+ Cluster and Its Addition Products [Mo3S7]4+ and [Mo3CuS4]5+. Prog. Nat. Sci. 1991, 1, 133-144. (70) Alexandrova, A. N.; Boldyrev, A. I. σ-Aromaticity and σ-Antiaromaticity in Alkali Metal and Alkaline Earth Metal Small Clusters. J. Phys. Chem. A 2003, 107, 554-560. (71) Huang, X.; Zhai, H.-J.; Kiran, B.; Wang, L.-S. Observation of d-Orbital Aromaticity. Angew. Chem., Int. Ed. 2005, 44, 7251-7254. (72) Zhai, H.-J.; Averkiev, B. B.; Zubarev, D. Y.; Wang, L.-S.; Boldyrev, A. I. δ Aromaticity in [Ta3O3]−. Angew. Chem., Int. Ed. 2007, 46, 4277-4280. (73) Zhai, H.-J.; Wang, B.; Huang, X.; Wang, L.-S. Probing the Electronic and Structural Properties of the Niobium Trimer Cluster and Its Mono- and Dioxides: Nb3On− and Nb3On (n = 0−2). J. Phys. Chem. A 2009, 113, 3866-3875. (74) Chen, W.-J.; Zhai, H.-J.; Zhang, Y.-F.; Huang, X.; Wang, L.-S. On the Electronic and Structural Properties of Tri-Niobium Oxide Clusters Nb3On− (n = 3−8): Photoelectron Spectroscopy and Density Functional Calculations. J. Phys. Chem. A 2010, 114, 5958-5966. (75) Weck, P. F.; Sergeeva, A. P.; Kim, E.; Boldyrev, A. I.; Czerwinski, K. R. Chemical Bonding and Aromaticity in Trinuclear Transition-Metal Halide Clusters. Inorg. Chem. 2011, 50, 1039-1046. (76)

Alvarado-Soto, L.; Ramírez-Tagle, R.; Arratia-Pérez, R. Spin–Orbit Effects on the

Aromaticity of the Re3Cl9 and Re3Br9 Clusters. Chem. Phys. Lett. 2008, 467, 94-96. (77)

Alvarado-Soto, L.; Ramírez-Tagle, R.; Arratia-Pérez, R. Spin−Orbit Effects on the

Aromaticity of the Re3X92− (X = Cl, Br) Cluster Ions. J. Phys. Chem. A 2009, 113, 1671-1673. (78) Sergeeva, A. P.; Boldyrev, A. I. The Chemical Bonding of Re3Cl9 and Re3Cl92- Revealed by the Adaptive Natural Density Partitioning Analyses. Comments Inorg. Chem. 2010, 31, 2-12. (79) Vásquez-Espinal, A.; Pino-Rios, R.; Alvarez-Thon, L.; Rabanal-León, W. A.; TorresVega, J. J.; Arratia-Perez, R.; Tiznado, W. New Insights into Re3(μ-Cl)3Cl6 Aromaticity. Evidence of σ- and π-Diatropicity. J. Phys. Chem. Lett. 2015, 6, 4326-4330. (80) Averkiev, B. B.; Boldyrev, A. I. Hf3 Cluster Is Triply (σ-, π-, and δ-) Aromatic in the Lowest D3h, 1A1 State. J. Phys. Chem. A 2007, 111, 12864-12866. 21



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

(81) Ivanov, A. S.; Zhang, X.; Wang, H.; Boldyrev, A. I.; Gantefoer, G.; Bowen, K. H.; Černušák, I. Anion Photoelectron Spectroscopy and CASSCF/CASPT2/RASSI Study of Lan– (n = 1, 3–7). J. Phys. Chem. A 2015, 119, 11293-11303. (82)

Blanchard, S.; Fensterbank, L.; Gontard, G.; Lacôte, E.; Maestri, G.; Malacria, M.

Synthesis of Triangular Tripalladium Cations as Noble-Metal Analogues of the Cyclopropenyl Cation. Angew. Chem., Int. Ed. 2014, 53, 1987-1991. (83) King, R. B. Metal Cluster Topology. 21. Sigma Aromaticity in Triangular Metal Carbonyl Clusters1. Inorg. Chim. Acta 2003, 350, 126-130. (84) Boldyrev, A. I.; Wang, L.-S. Beyond Organic Chemistry: Aromaticity in Atomic Clusters. Phys. Chem. Chem. Phys. 2016, 18, 11589-11605. (85) Galeev, T. R.; Boldyrev, A. I. Recent Advances in Aromaticity and Antiaromaticity in Transition-Metal Systems. Annu. Rep. Prog. Chem., Sect. C: Phys. Chem. 2011, 107, 124-147. (86) Zubarev, D. Y.; Averkiev, B. B.; Zhai, H.-J.; Wang, L.-S.; Boldyrev, A. I. Aromaticity and Antiaromaticity in Transition-Metal Systems. Phys. Chem. Chem. Phys. 2008, 10, 257-267. (87) Boldyrev, A. I.; Wang, L.-S. All-Metal Aromaticity and Antiaromaticity. Chem. Rev. 2005, 105, 3716-3757. (88) Torres-Vega, J. J.; Vásquez-Espinal, A.; Caballero, J.; Valenzuela, M. L.; Alvarez-Thon, L.; Osorio, E.; Tiznado, W. Minimizing the Risk of Reporting False Aromaticity and Antiaromaticity in Inorganic Heterocycles Following Magnetic Criteria. Inorg. Chem. 2014, 53, 3579-3585. (89) Islas, R.; Martínez-Guajardo, G.; Jiménez-Halla, J. O. C.; Solà, M.; Merino, G. Not All That Has a Negative NICS Is Aromatic: The Case of the H-Bonded Cyclic Trimer of HF. J. Chem. Theory Comput. 2010, 6, 1131-1135. (90) Wang, Y.-L.; Hu, H.-S.; Li, W.-L.; Wei, F.; Li, J. Relativistic Effects Break Periodicity in Group 6 Diatomic Molecules. J. Am. Chem. Soc. 2016, 138, 1126-1129.

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