Deviation from the trans-Effect in Ligand-Exchange Reactions of

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Cite This: J. Phys. Chem. A 2018, 122, 1209−1214

Deviation from the trans-Effect in Ligand-Exchange Reactions of Zeise’s Ions PtCl3(C2H4)− with Heavier Halides (Br−, I−) Gao-Lei Hou,† Niranjan Govind,*,‡ Sotiris S. Xantheas,*,§,∥ and Xue-Bin Wang*,† †

Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, MS K8-88, Richland, Washington 99352, United States ‡ Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, MS K8-91, Richland, Washington 99352, United States § Advanced Computing, Mathematics and Data Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, MS K1-83, Richland, Washington 99352 United States ∥ Department of Chemistry, University of Washington, Seattle, Washington 98195, United States S Supporting Information *

ABSTRACT: Four new Zeise’s family ions with mixed-halide ligands, i.e., PtClnX3−n(C2H4)− (X = Br, I; n = 1, 2), were synthesized via ligand-exchange reactions of KX salts with KPtCl3(C2H4) in aqueous solutions, and were detected in vacuum via electrospray ionization mass spectrometry. Their photoelectron spectra reveal a series of well-resolved spectral peaks with their electron binding energies (EBEs) decreasing with increasing halide size, with I having a much stronger effect than Br, i.e., 4.57 (−Cl3) > 4.56 (−Cl2Br) > 4.53 (−ClBr2) > 4.34 (−Cl2I) > 4.30 eV (−ClI2). Ab initio electronic structure calculations including spin−orbit coupling (SOC) predict that the cis- and trans-isomers are nearly isoenergetic with the cisisomer for −Cl2X and the trans-isomer for −ClX2 slightly favored, respectively. Excited-state spectra calculated with time-dependent density functional theory (TDDFT), and their comparison with the observed ones, suggest that for each species both the cis- and trans-configurations coexist in the experiments and contribute to the observed spectra, a fact that clearly deviates from the prediction of the widely accepted trans-effect, which suggests that only one isomer would have formed.

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INTRODUCTION The trans-effect, a widely accepted and practical concept in the fields of synthetic inorganic and organometallic chemistry, especially for square-planar metal complexes, describes how an existing ligand affects the kinetics of an incoming ligand to substitute its trans-ligand.1−4 This term had been also used in earlier studies to delineate the properties of a trans-ligand− metal bond, and the thermodynamics, to which a closely related notion of trans-influence is preferred nowadays.1−4 The first discovery of the trans-effect (influence) was made by Chernyaev in platinum(II) complexes in the 1920s, when he observed a weakening of the bond in the trans-position of electronegative groups.4 Later, this effect was also found in other metal complexes, such as in palladium(II) and Pt(IV) complexes.1,2,4 One of the most famous examples of the application of the trans-effect is the synthesis of cisplatin,3 the most important and widely used anticancer drug in treating various tumors.5 To date, the underlying physics of the transeffect is still intriguing. Two main theories based on σ- and πbonding scenarios have been suggested to qualitatively explain this effect.1,2,6−8 Accordingly, a ligand (L) with strong πaccepting ability will exhibit a strong trans-effect, making its trans-positioned ligand (X) more labile and easily substitutable by another incoming ligand (Y).1,2 © 2018 American Chemical Society

It has previously been reported that ethylene (C2H4) is a ligand showing the strongest trans-effect,6 and therefore, Zeise’s salt, K[PtCl3(C2H4)]·H2O, a square-planar Pt(II) complex containing a C2H4 ligand, should be a prototypical compound9−13 illustrating this effect. This has been documented for Zeise’s ion using infrared (IR) spectroscopy and kinetic measurements, showing that labilization of ethylene can weaken the bond in the trans-position (trans-influence) and, consequently, affect the ligand substitution rate and product configuration (trans-effect).6,7,14 However, no consensus has been reached for the trans-effect (influence) in Zeise’s ion. For example, whether the trans-Pt−Cl bond is indeed longer than the cis-one is still controversial.15−18 Recently, as part of our previous study of homogeneoushalide Zeise’s ions PtX3(C2H4)− (X = Cl, Br, I),18 we have also synthesized mixed-halide Zeise’s ions PtClnX3−n(C2H4)− (X = Br, I) in solution and observed them in our mass spectrometer. A natural question to ask was whether these mixed halides follow the trans-effect, namely whether only one configuration is preferentially formed for each species. The answer to this Received: November 1, 2017 Revised: January 12, 2018 Published: January 16, 2018 1209

DOI: 10.1021/acs.jpca.7b10808 J. Phys. Chem. A 2018, 122, 1209−1214

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The Journal of Physical Chemistry A question, as suggested from our detailed spectroscopic and high-level theoretical studies described below, is a surprising “no!” We note that an earlier study by Pearson19 has pointed out that soft trans-ligands are susceptible to attack by hard ligands (antisymbiotic behavior),20 while both Br and I (incoming ligands) are softer ligands compared to Cl (being the substituted ligand) in the formation of the mixed-halide Zeise’s ion complexes.21 In this article, we present our detailed spectroscopic and theoretical studies on four Pt(II) complexes that strongly suggest that the widely accepted trans-effect in ligand-exchange reactions of Br−/I− with PtCl3(C2H4)− to produce mixed-halide Zeise’s ions PtClnX3−n(C2H4)−, is not entirely true, leading to the coexistence of two isomers for each of the four species. We also present a discussion of the underlying reasons that are responsible for this deviation.

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EXPERIMENTAL AND THEORETICAL METHODS Experimental Details. The experiments were performed using the Pacific Northwest National Laboratory (PNNL) negative ion photoelectron spectroscopy (NIPES) setup for size-selective clusters, equipped with a cryogenic ion trap and electrospray ionization (ESI) source.22 Four mixed-halide Zeise’s ions, PtClnX3−n(C2H4)−, were produced via ligandexchange reactions of K[PtCl3(C2H4)]·H2O with KBr or KI in acetonitrile/water (3/1 volume ratio) solutions, and were transferred into the gas phase via ESI. All ions, produced by ESI, were guided by two RF-only quadrupoles and a 90° bender into a cryogenically controlled ion trap set at 20 K, where they were accumulated and cooled via collisions with a cold buffer gas of ∼0.1 mTorr (20% H2 balanced in helium) for 20−80 ms, before being pulsed out into the extraction zone of a time-offlight (TOF) mass spectrometer with a 10 Hz repetition rate. The low temperature serves to eliminate hot bands and to improve the energy resolution in the spectra. During each experiment, the desired cryogenic ions were mass selected and maximally decelerated before being interacted with a laser beam of 193 nm (6.424 eV) from an ArF excimer laser or 157 nm (7.867 eV) from an F2 excimer laser in the photodetachment zone of a magnetic-bottle photoelectron analyzer. The laser was operated at a 20 Hz repetition rate with the ion beam off at alternating laser shots, enabling for shot-by-shot background subtraction. Photoelectrons were collected at nearly 100% efficiency by the magnetic bottle and analyzed in a 5.2 m long electron flight tube. TOF photoelectron spectra were recorded and converted to kinetic energy spectra, calibrated by the spectra of I− and Cu(CN)2− taken at similar conditions. The electron binding energy spectra were obtained by subtracting the kinetic energy spectra from the detachment photon energies. The electron energy resolution (ΔE/E) was about 2%, i.e., ∼20 meV for 1 eV kinetic energy electrons. Theoretical Methods. All calculations were performed with the NWChem computational chemistry suite.23 All density functional theory (DFT)/time-dependent density functional theory (TDDFT) calculations were performed using the optimized geometries obtained at the MP2 level of theory.24 Harmonic frequency analysis has been performed to confirm there were no imaginary frequencies at the optimized structures. The adiabatic detachment energy (ADE) was calculated as the energy difference between the neutral and anion species at their respective optimized geometries with zero-point energy (ZPE) corrections, while the first vertical detachment energy (VDE) was calculated as the energy

Figure 1. The 20 K photoelectron spectra of PtClnX3−n(C2H4)− (X = Br, I; n = 1, 2) at 157 (red) and 193 nm (blue), respectively. Vertical bars denote the excited states of the neutral species, calculated with TDDFT for the cis- (pink bars) and trans-configurations (black bars) of each species. The calculated first VDEs are aligned to the X peak in each spectrum.

difference between the neutral and anion, both at the anion’s geometry. During the structure optimization, we have considered both the trans- and cis-configurations. The excited state calculations were performed using TDDFT25 with the CAM-B3LYP functional.26 The attenuation parameter (γ) was set to 0.33, which has been previously shown to yield excitation energies that are in excellent agreement with high-level coupled-cluster calculations.18,27 For the MP2 and DFT calculations, the aug-cc-pVTZ basis set was used for the C, H, and Cl atoms,28−32 while the aug-ccpVTZ-PP basis set and effective core potentials (ECPs) were used for Pt, Br, and I atoms,33−38 respectively. Ground state spin−orbit (SO) effects were included via SO ECPs associated with the ECPs used in the calculations, and were performed with the two-component SO-DFT module in NWChem. All ECPs and basis sets were obtained from the EMSL Basis Set 1210


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The Journal of Physical Chemistry A

Table 1. Experimentally Measured ADEs and VDEs of PtClnX3−n(C2H4)− (X = Br, I; n = 1, 2); Calculated ADE Values and Theoretical Excitation Energies for Excited States from TDDFT Calculationsa PtCl2Br(C2H4)− theor

PtCl2I(C2H4)− c

PtClBr2(C2H4)− c

theor

theor

PtClI2(C2H4)− c

theorc

exptb

trans

cis

exptb

trans

cis

exptb

trans

cis

exptb

trans

cis

4.56

4.43

4.40

4.34

4.22

4.32

4.53

4.41

4.39

4.30

4.27

3.93

X A B B′ C

4.70 4.96 5.31 5.39 5.56

4.70 4.85 5.24 5.32 5.43

4.70

4.40 4.74 4.92

4.40 4.93 5.02

4.40

4.65 5.05 5.42

4.65 4.82 5.27

4.36 4.43 4.88

4.36 4.70 5.00

4.36 4.64

4.92

4.65 4.95 5.30

5.63

5.31

5.27 5.34

5.61

5.54

5.16

5.07

5.30

5.10

D E F G

6.17 6.74 7.01 7.26

5.47 6.04 6.72 7.04

5.57 6.20 6.43 7.08

6.05 6.47 6.79 7.12

6.16 6.40 6.65 7.26

5.41 5.82 6.14 6.52

5.56 5.90 6.05

5.59

6.91 7.16

6.30 6.64 6.84 7.26

H

7.70

7.52

7.3

7.37

6.83

7.02

ADE VDE

7.71 7.76

7.65

6.24 6.72 7.03 7.15 7.71

6.17 6.58 6.79

6.38 7.00

a

Presented as vertical bars in Figure 1. bThe experimental uncertainty of ADEs and VDEs is 0.02 eV. cThe calculated ADE includes both zero-point energy (ZPE) and spin−orbit coupling (SOC) corrections with the values in bold denoting the most stable isomers. The calculated VDEs have been aligned to the first peak (X) in the experimental spectra by the amount of ∼0.1 eV (see Table S1 in the Supporting Information).

Exchange,39 while the corresponding SO ECPs were obtained from the Stuttgart/Köln web page.40 Minimum energy paths for the SN2-like reactions of Br− ion attacking PtCl3(C2H4)− ion to produce either the trans- or cisPtCl2Br(C2H4)− complex were calculated using the nudged elastic band (NEB) module41 as implemented in NWChem. To compare the excitation energies calculated using TDDFT with experiment (Figure 1), we only considered the dominant singly excited determinants (with amplitudes greater than 0.8) to identify the occupied and unoccupied orbitals involved in the transitions within a single-particle picture. These orbitals were also used to estimate the SO corrections to the excitation energies as follows:

corresponding neutrals estimated from the fast rising onset threshold of each spectrum, and the vertical detachment energies (VDEs) measured from the peak of each spectral feature, are summarized in Table 1. It can be seen that the species with heavier halides tend to have lower ADEs, and the iodine ligand has stronger effects than bromine in reducing the ADE; i.e., 4.57 (−Cl3) > 4.56 (−Cl2Br) > 4.53 (−ClBr2) > 4.51 (−Br3) > 4.34 (−Cl2I) > 4.30 (−ClI2) > 4.18 eV (−I3) (Table 1 and ref 18). In fact, this trend in the ADEs follows the decreasing electronegativity of halogen from Cl to Br to I along the periodic table.42 The calculated highest occupied molecular orbitals (HOMOs) tend to localize more on Pt and the heavier halide ligands (Figure S1). The natural population analysis (NPA) (Figure S2) shows progressively less positive charge on Pt(II) with increasing halide size; additionally, the trans-Pt−X bond is also more ionic than the cis- one. Previous studies on homogeneous-halide Zeise’s ions suggested that MP2 was a reliable method to predict structures that were in good agreement with experiments.16,18 We therefore carried out geometry optimization for these mixedligand species at this level of theory (Table S1). Figure 2 shows that all of these complexes adopt the Dewar−Chatt− Duncanson (DCD) bonding scheme, i.e., the C2H4 molecule interacts perpendicularly with the nearly planar PtClnX3−n− moiety via the dative η2 Pt−C bonds, similar to the cases for PtX3(C2H4)− (X = Cl, Br, and I).18,43,44 Two isomers are expected for each PtXY2(C2H4)− complex (X, Y = Cl, Br, I): the trans-/cis-isomers, where X is at the trans-/cis-positions relative to C2H4, respectively (Figure 2). The relative stability of these trans- and cis-configurations changes with different halide ligand combinations. Specifically, for the Cl/Br case, the trans- and cis-structures are nearly degenerate in energy (within 0.1−0.2 kcal/mol), while for the Cl/I case the energy difference is slightly larger (0.6−1.2 kcal/mol). The cis- is the most stable isomer for −Cl2Br and −Cl2I, whereas the trans- becomes more stable for −ClBr2 and −ClI2; namely, the heavier halogens appear to always favor the cis-position. Such a stability variation may be qualitatively rationalized based on the increased

ΔTDDFTSO ≈ ΔKSSO + CORR

where ΔKSSO represents Kohn−Sham orbital energy differences from ground state SO calculations and CORR is the response corrections from scalar TDDFT calculations.

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RESULTS AND DISCUSSION The four mixed-halide Zeise’s ions, PtClnX3−n(C2H4)− (X = Br, I; n = 1, 2), were synthesized by the ligand-exchange reactions of K2PtCl3(C2H4) with KBr or KI in water/acetonitrile solutions. They were further transferred into the gas phase via ESI, detected in a time-of-flight mass spectrometer, and characterized by NIPES.22 Their 20 K photoelectron spectra, measured with 157 and 193 nm photons and presented in Figure 1, show well-resolved sharp features for each species. These features correspond to the electronic transitions from the anion ground state to the ground and excited states of the neutral, and can be viewed as originating from successive oneelectron removal from the occupied molecular orbitals in the anion ground state configuration within the single particle approximation, directly reflecting the electronic structure and bonding nature of these anionic species. The adiabatic detachment energies (ADEs) of PtClnX3−n(C2H4)−, or the electron affinities (EAs) of the 1211


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reagents in various catalytic and asymmetric synthesis processes.46−49 According to the widely accepted trans-effect, one would have expected only one isomer for each PtXY2(C2H4)− complex to be formed via the ligand-exchange reactions of PtCl3(C2H4)− with Br−/I−, i.e., the trans-isomer for −Cl2Br/I and the cis-isomer for −ClBr2/I2, in particular considering the fact that C2H4 is a prototypical strong trans-ligand in squareplanar Pt(II) complexes.1,2 On the contrary, our calculations (shown in Figure 2) indicate that the expected structure from the trans-effect is in fact always the higher of the two isomers for each case, albeit with relatively small energy differences, suggesting a clear deviation of the trans-influence from the trans-effect. On the other hand, the trans-effect originates from kinetic reasons. We therefore explored the Br− + PtCl3(C2H4)− reaction path (Figure S3). The calculated (at the MP2 level of theory) reaction barriers to form the cis- and trans-PtCl2Br(C2H4)− products are 28.0 and 29.0 kcal/mol, respectively, suggesting similar kinetic probabilities. These energetic and kinetic analyses indicate that the trans-effect does not hold for the Br−/I− + PtCl3(C2H4)− reactions, at least in predicting the exclusive formation of a single isomer. In other words, this raises the question of whether both isomers coexist and contribute to the observed spectra. Table 1 shows that the calculated ADEs for the cis- and transconfigurations of −Cl2Br and −ClBr2 are almost identical, being ∼0.1 eV lower compared to the experimental values. For −Cl2I and −ClI2, the calculated ADE values for the most stable isomers, i.e., the cis- for the former and the trans- for the latter, are in excellent agreement (within 0.03 eV) with the experimental values, whereas the calculated ADEs for the other isomer (trans- for −Cl2I and cis- for −ClI2) are lower by 0.10 and 0.37 eV, respectively. We further compared the calculated excitation energies from TDDFT calculations with the experimental spectra (vertical bars in Figure 1 and VDEs listed in Table 1). Apparently, it is essential to include both the trans- and cis-configurations to account for the all observed spectral features. This comparison strongly suggests that both cis- and trans-isomers coexist in the experiments and contribute to the measured spectra.

Figure 2. Optimized structures of PtClnX3−n(C2H4)− (X = Br, I; n = 1, 2) ions at the MP2 level of theory (Pt, brown; Cl, green; Br, pink; I, purple; C, gray; H, white). The relative energies (kcal/mol) including both ZPE and SOC corrections and the bond lengths (Å) are indicated.

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CONCLUSIONS In summary, four Zeise’s family of ions with mixed-halide ligands, PtClnX3−n(C2H4)− (X = Br, I; n = 1, 2), were synthesized in solutions. Their cryogenic NIPE spectra were obtained, showing well-resolved spectral peaks for each species and a general trend in decreasing ADE by substituting chloride with heavier halides. Through a detailed spectroscopic and theoretical study, we demonstrated that the widely accepted trans-effect predictions of isomer formation may not be always true, in particular for the cases where a hard ligand is substituted by a softer one.2,19 Both cis- and trans-isomers for each species are needed to account for the observed photoelectron spectra. The coexistence of different isomers is consistent with the fact that these isomers are theoretically predicted to have similar stabilities and formation barriers.

polarizabilities and sizes from Cl to Br and to I:45 the more polarizable and larger halides tend to stay farther away in order to reduce the electrostatic repulsion between ligands. In addition, the relative stability of the three different isomers of PtClBrI(C2H4)− follows the polarizability trend mentioned above, in which the more polarizable Br and I occupy the two cis-positions in the most stable structure (Table S2). For each structure, the trans-Pt−X bond is longer by 0.02− 0.04 Å than the one in the cis-position, the CC bond is elongated by ∼0.1 Å compared to that of free C2H4 (1.339 Å),18 and the average Pt−C bond length increases following the size of the halide ligand (Figure 2 and Table S1). The ethylene molecule is significantly activated in all these species as indicated by the elongated CC bond, as well as the position of the hydrogen atoms that bend away. The intramolecular interaction between C2H4 and the platinum trihalide part weakens upon substituting Cl with heavier halides, particularly by replacing the trans-Cl, and can be tuned by 7.6 kcal/mol via the trihalide combination (Table S3). Therefore, these mixedligand complexes expand the potential of the family of Zeise’s ions to become more efficient catalysts and more versatile

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpca.7b10808. 1212


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(15) Black, M.; Mais, R. H. B.; Owston, P. G. The Crystal and Molecular Structure of Zeise’s Salt, KPtCl3·C2 H4·H2 O. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1969, B25, 1753−1759. (16) Love, R. A.; Koetzle, T. F.; Williams, G. J. B.; Andrews, L. C.; Bau, R. Neutron Diffraction Study of the Structure of Zeise’s Salt, KPtCl3(C2H4)·H2O. Inorg. Chem. 1975, 14, 2653−2657. (17) Forniés, J.; Martín, A.; Martín, L. F.; Menjón, B.; Tsipis, A. AllOrganometallic Analogues of Zeise’s Salt for the Three Group 10 Metals. Organometallics 2005, 24, 3539−3546. (18) Hou, G.-L.; Wen, H.; Lopata, K.; Zheng, W.-J.; Kowalski, K.; Govind, N.; Wang, X.-B.; Xantheas, S. S. A Combined Gas-Phase Photoelectron Spectroscopic and Theoretical Study of Zeise’s Anion and Its Bromine and Iodine Analogues. Angew. Chem. Int. Ed. 2012, 51, 6356−6360. (19) Pearson, R. G. Antisymbiosis and The trans Effect. Inorg. Chem. 1973, 12, 712−713. (20) Chatt, J.; Heaton, B. T. The Hydrolysis of Monochlorophosphine and Monochloroarsine Complexes of Platinum(II): Bridging Phosphinato- and Arsinato-Groups. J. Chem. Soc. A 1968, 2745−2757. (21) In the theory of hard and soft acids and bases (HSAB) developed by Ralph G. Pearson, “hard” refers to species that are small, have high charge states, and are weakly polarizable, and “soft” refers to species that are large, have low charge states and are strongly polarizable. (22) Wang, X.-B.; Wang, L.-S. Development of a Low-Temperature Photoelectron Spectroscopy Instrument Using an Electrospray Ion Source and a Cryogenically Controlled Ion Trap. Rev. Sci. Instrum. 2008, 79, 073108. (23) Valiev, M.; Bylaska, E. J.; Govind, N.; Kowalski, K.; Straatsma, T. P.; Van Dam, H. J. J.; Wang, D.; Nieplocha, J.; Apra, E.; Windus, T. L.; et al. NWChem: A Comprehensive and Scalable Open-Source Solution for Large Scale Molecular Simulations. Comput. Phys. Commun. 2010, 181, 1477−1489. (24) Head-Gordon, M.; Pople, J. A.; Frisch, M. J. MP2 Energy Evaluation by Direct Methods. Chem. Phys. Lett. 1988, 153, 503−506. (25) Runge, E.; Gross, E. K. U. Density-Functional Theory for TimeDependent Systems. Phys. Rev. Lett. 1984, 52, 997−1000. (26) Yanai, T.; Tew, D. P.; Handy, N. C. A New Hybrid Exchange− Correlation Functional Using the Coulomb-Attenuating Method (CAM-B3LYP). Chem. Phys. Lett. 2004, 393, 51−57. (27) Kowalski, K.; Krishnamoorthy, S.; Villa, O.; Hammond, J. R.; Govind, N. Active-Space Completely-Renormalized Equation-ofMotion Coupled-Cluster Formalism: Excited-State Studies of Green Fluorescent Protein, Free-Base Porphyrin, and Oligoporphyrin Dimmer. J. Chem. Phys. 2010, 132, 154103. (28) Dunning, T. H., Jr. Gaussian Basis Sets for Use in Correlated Molecular Calculations. I. The Atoms Boron Through Neon and Hydrogen. J. Chem. Phys. 1989, 90, 1007−1023. (29) Woon, D. E.; Dunning, Jr. Gaussian Basis Sets for Use in Correlated Molecular Calculations. IV. Calculation of Static Electrical Response Properties. J. Chem. Phys. 1994, 100, 2975−2988. (30) Kendall, R. A.; Dunning, T. H., Jr.; Harrison, R. J. Electron Affinities of The First Row Atoms Revisited. Systematic Basis Sets and Wave Functions. J. Chem. Phys. 1992, 96, 6796−6806. (31) Woon, D. E.; Dunning, Jr. Gaussian Basis Sets for Use in Correlated Molecular Calculations. III. The Second Row Atoms, Al-Ar. J. Chem. Phys. 1993, 98, 1358−1371. (32) Balabanov, N. B.; Peterson, K. A. Systematically Convergent Basis Sets for Transition Metals. I. All-Electron Correlation Consistent Basis Sets for The 3d Elements Sc-Zn. J. Chem. Phys. 2005, 123, 064107. (33) Peterson, K. A. Systematically Convergent Basis Sets with Relativistic Pseudopotentials. I. Correlation Consistent Basis Sets for The Post-d Group 13 - 15 Elements. J. Chem. Phys. 2003, 119, 11099− 11112. (34) Peterson, K. A.; Figgen, D.; Goll, E.; Stoll, H.; Dolg, M. Systematically Convergent Basis Sets with Relativistic Pseudopotentials. II. Small-Core Pseudopotentials and Correlation Consistent Basis

Frontier molecular orbitals; NPA charge distributions; SN2-like reaction paths for Br− + PtCl3(C2H4)− to form cis- and trans-PtCl2Br(C2H4)− products; comparison between theory and experiment; optimized three PtClBrI(C2H4)− configurations and their relative stabilities; intramolecular interaction energies between C2H4 and the platinum trihalide part; Cartesian coordinates (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (X.-B.W.). *E-mail: [email protected] (N.G.). *E-mail: [email protected] (S.S.X.). ORCID

Gao-Lei Hou: 0000-0003-1196-2777 Sotiris S. Xantheas: 0000-0002-6303-1037 Xue-Bin Wang: 0000-0001-8326-1780 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, and performed in EMSL, a national scientific user facility sponsored by DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory, which is operated by Battelle Memorial Institute for the DOE.

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REFERENCES

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Deviation from the trans-Effect in Ligand-Exchange Reactions of

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