Theoretical and Synthetic Study on the Existence, Structures, and

Article pubs.acs.org/IC

Theoretical and Synthetic Study on the Existence, Structures, and Bonding of the Halide-Bridged [B2X7]− (X = F, Cl, Br, I) Anions Philipp Bertocco,† Christoph Bolli,†,‡ Bruno A. Correia Bicho,† Carsten Jenne,*,† Berrin Erken,† Risto S. Laitinen,§ Helene A. Seeger,† and Teemu T. Takaluoma*,†,§ †

Fakultät für Mathematik und Naturwissenschaften, Anorganische Chemie, Bergische Universität Wuppertal, 42119 Wuppertal, Germany § Laboratory of Inorganic Chemistry, University of Oulu, P.O. Box 3000, 90014 Oulu, Finland S Supporting Information *

ABSTRACT: While hydrogen bridging is very common in boron chemistry, halogen bridging is rather rare. The simplest halogen-bridged boron compounds are the [B2X7]− anions (X = F, Cl, Br, I), of which only [B2F7]− has been reported to exist experimentally. In this paper a detailed theoretical and synthetic study on the [B2X7]− anions is presented. The structures of [B2X7]− anions have been calculated at the MP2/ def2-TZVPP level of theory, and their local minima have been shown to be of C2 symmetry in all cases. The bonding situation varies significantly between the different anions. While in [B2F7]− the bonding is mainly governed by electrostatics, the charge is almost equally distributed over all atoms in [B2I7]− and additional weak iodine···iodine interactions are observed. This was shown by an atoms in molecules (AIM) analysis. The thermodynamic stability of the [B2X7]− anions was estimated in all phases (gas, solution, and solid state) based on quantum-chemical calculations and estimations of the lattice enthalpies using a volume-based approach. In the gas phase the formation of [B2X7]− anions from [BX4]− and BX3 is favored in accord with the high Lewis acidity of the BX3 molecules. In solution and in the solid state only [B2F7]− is stable against dissociation. The other three anions are borderline cases, which might be detectable under favorable conditions. However, experimental attempts to identify [B2X7]− (X = Cl, Br, I) anions in solution by 11B NMR spectroscopy and to prepare stable [PNP][B2X7] salts failed.

1. INTRODUCTION While hydrogen bridging (e.g., B−H−B) is very common in boron chemistry,1 halogen bridging (e.g., B−X−B; X = F−I) is much less known. The simplest boron compounds containing a bridging halogen atom are the heptahalodiborate [B2X7]− ([X3B−X−BX3]−; X = F−I) anions. Thus far, only the fluoro anion [B2F7]− has been known experimentally. Its existence was predicted in the mid 1960s in parallel investigations by Harris2a and Brownstein and Paasivirta2b based on vapor pressure measurements and infrared spectroscopy. In 1975 the presence of [B2F7]− as a fluorine-bridged compound in solution at −155 °C was demonstrated by NMR spectroscopy.3 The structure was eventually confirmed in 1999 by X-ray diffraction.4 To date the number of crystal structures containing the [B2F7]− anion has still been small. In most cases the anion possesses Cs symmetry,5 but a C2-symmetric structure has also been observed (Scheme 1).6 In contrast to the fluoro anion [B2F7]− no reports on the related [B2X7]− anions, containing the other halogens chlorine, bromine, and iodine, can be found in the literature. In this contribution quantum-chemical calculations to access the structure of the unknown [B2X7]− anions are reported in order to understand their bonding situations and to estimate their thermodynamic stabilities. In addition, attempts to © XXXX American Chemical Society

Scheme 1

experimentally access the unknown [B2X7]− anions are presented.

2. RESULTS AND DISCUSSION 2.1. Structural and Bonding Properties. 2.1.1. Structures. The structural properties of the [B2X7]− (X = F, Cl, Br, I) anions Received: January 15, 2016

A

DOI: 10.1021/acs.inorgchem.6b00118 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Structural Properties of the [B2X7]− (X = F, Cl, Br, I) Anions Computed on the MP2/def2-TZVPP Levela bond length [Å] angle [deg] [B2F7]− [B2Cl7]− [B2Br7]− [B2I7]− a

bridging

terminal

intramolecular distance [Å]

X2−B1−B5−X8

B1−X9−B5

B1−X9

B1−X3

B1−X2

B1−X4

X2−X8

X3−X8

43.8 34.9 34.3 33.8

132.2 115.6 113.6 111.6

1.564 2.012 2.139 2.309

1.366 1.805 1.965 2.179

1.369 1.815 1.976 2.193

1.373 1.829 1.993 2.213

3.226 3.659 3.869 4.166

3.127 3.740 3.973 4.284

See Figures 1 and 2 for the numbering scheme.

were calculated to estimate their relative stabilities and to understand their bonding situations. Optimizations of the structures on the MP2/def2-TZVPP level of theory led to C2symmetric structures for all halogens.7 The Cs-symmetric structures are 1−4 kJ mol−1 higher in energy (lowest for X = F) and are transition states according to vibrational analyses. At room temperature this small energy barrier allows free rotation about the bridging B−X bonds. In the solid state, however, packing forces determine the actual crystal structures.4−6 The computed structural properties of the C2-symmetric [B2X7]− anions are listed in Table 1. The bond lengths increase with the increasing size of the halogen atoms. As expected, the B−Xbridging (B−Xb) distances are significantly longer than the B−Xterminal (B−Xt) distances. The difference between the bridging and the terminal B−X bonds decreases when going from fluorine to iodine. In [B2F7]− the terminal B−F bond is about 14% shorter than the bridging B−F bond (B−Xb 1.564 Å, av. B−Ft 1.369 Å), while this difference is only 5% for [B2I7]− (B−Ib 2.309 Å, av. B−It 2.195 Å). The variations in the B−Xt bond lengths increase down the group. For [B2F7]−, the terminal B−F bonds are within a narrow range of 1.366−1.369 Å, while in [B2I7]− the B−I terminal bonds range from 2.179 to 2.213 Å. This indicates that, depending on the halogen, significantly different bonding situations occur (see section 2.1.3). With increasing halogen size the bridging B−X bonds become longer, which gives the BX3 groups more space to rotate. This allows a relaxation of the B1−X9−B5 angle, which decreases from fluorine to iodine (132.2°, 115.6°, 113.6°, and 111.6° for X = F, Cl, Br, and I, respectively). In a purely electrostatic model the dihedral X2−B1−B5−X8 angle would be maximized (about 45°). In [B2F7]−, the BF3 groups orient themselves at a dihedral angle of 43.8°, which is close to the maximal value expected for a purely electrostatic interaction between the BF3 groups. The angles of the heavier halogen derivatives are significantly smaller (33.8−34.9°) (Figure 1). 2.1.2. Charge Distribution. To get an idea on the importance of the electrostatic interactions the atomic partial charges were calculated based on an atoms in molecules (AIM) analysis (Table 2). While in [B2I7]− the charge is more equally distributed over all atoms leaving only a small negative partial charge on the terminal and the bridging iodine atoms, in [B2F7]− large negative partial charges are located on the fluorine atoms while the boron atoms carry high positive partial charges. The calculated charge distribution is in very good agreement with a consideration based on Pauling electronegativities. In [B2F7]− the electron density is equally distributed over terminal and bridging fluorine atoms (−0.87 vs −0.85), while in [B2I7]− the electron density is shifted to the terminal iodine atoms (−0.35 vs −0.13). The charge distribution in the chloro and the bromo derivative is in between that of [B2F7]− and [B2I7]−. Equal charge distribution over all

Figure 1. Illustration of the X2−B1−B5−X8 dihedral angle for the [B2F7]− (left) and [B2I7]− anions (right).

Table 2. Atomic Partial Charges for the [B2X7]− Anions Based on an AIM Analysis B1/B5 X2/X7 X3/X8 X4/X6 X9

F

Cl

Br

I

2.539 −0.871 −0.870 −0.871 −0.852

2.050 −0.745 −0.742 −0.745 −0.636

1.525 −0.601 −0.597 −0.603 −0.452

0.545 −0.326 −0.304 −0.348 −0.130

atoms plays an important role for the stability of main group compounds, which has already been shown, for example, for chalcogen halides.8 2.1.3. Atoms in Molecules Analysis of the Bonding. Depending on the halogen the calculated structures discussed above already indicate significantly different bonding situations in all four anions. With increasing size of the halogen, polarization and nonelectrostatic interactions start to play a more important role. A detailed AIM analysis of the electron density of the [B2X7]− (X = F, Cl, Br, I) anion was performed to better understand the nature of bonding in these compounds. According to AIM theory, a bonding interaction between two atoms is related to a ridge of electron density maximum called the bond paths. The electron density minimum at the bond path between two atoms is the bond critical point (BCP). The electron density value at this BCP is a measure for the strength of the bond. Although the bonding interaction derived from AIM theory should not be directly equaled with the (somewhat vague) concept of a chemical bond, it still serves as a useful tool for understanding atomic interactions.9−11 The AIM partial charges and the electron density at the bond critical points were used for the AIM analysis of the bonding in the [B2X7]− anions. Bond critical points were found to connect all the atomic centers where a strong bond could be expected (illustrated in Figure 2). In addition to strong bonding interactions, weak interactions were also detected for [B2X7]− (X = Cl, Br, I). B

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K(r) is generally positive for electron-sharing interactions and negative for dispersive interactions. The delocalization index (DI) gives a qualitative estimation for the amount of electron density exchange between atoms. For purely covalent bonds, for instance, in hydrocarbons, the DI correlates well with the chemical bond order, whereas for more ionic interactions it only describes the covalent part of the interaction and does not include the electrostatic contribution to the bond. Thus, for anions like [B2X7]− (X = F, Cl, Br, I) the DI is mainly useful to get a measure for the relative strengths of the covalent interactions in the molecules. On the basis of the DI values, the covalent part of the strength of the B−Xb bonds relative to the terminal B−Xt bonds increases down the periodic series from 57% for F to 77% for I. Thus, while the chemical bonds in [B2I7]− are weakest in the series (B1−F2 has a ρ(r) of 0.181, whereas that of B1−I2 is 0.105), this anion has the relatively strongest bridging interactions. The relative strength of the bridging B−Xb bond increases the resistance against B−Xb bond cleavage. 2.2. Thermodynamic Estimations and Experiments. 2.2.1. Thermodynamic Stability in the Gas Phase. To the best of our knowledge, to date only the fluoro anion [B2F7]− has been known experimentally.2−6 We calculated the thermodynamic stability of all [B2X7]− anions in the gas phase based on eq 1, which represents the formation of [B2X7]− from BX3 and [BX4]−.

Figure 2. Atoms in molecules representation of the bond critical points (red circles) in the [B2X7]− (X = F, Cl, Br, I). Strong covalent bonds are indicated by solid lines, while dotted lines represent weak halogen− halogen contacts. For [B2I7]− the formation of three weak I···I interactions can be seen.

BX3 + [BX4]− → [B2X 7]− (X = F, Cl, Br, I)

Table 3 summarizes the bonding information obtained from the AIM analysis for the [B2X7]− (X = F, Cl, Br, I) anions. From the descriptors12 in Table 3 it can be seen that B−F bonds are strong and polarized covalent or borderline ionic bonds (bold values in Table 3), whereas the strong B−X (X = Cl, Br, I) bonds are predominatly covalent. The observed halogen−halogen interactions are weak van der Waals interactions (italic values in Table 3).13 These weak interactions explain why the [B2X7]− (X = Cl, Br, I) anions do not maximize the X2−B1−B5−X8 dihedral angle (see Figure 1 and Table 1). Net repulsive X−X interactions would favor larger dihedral angles than observed. The electron density value at the bond critical point ρ(r) is a qualitative indicator for the strength of the chemical bond. ∇2ρ(r) is the second derivative of the electron density and qualitatively describes either the covalent (negative value) or the ionic (positive value) nature of the interaction. The descriptor

(1)

The reaction energies for eq 1 are shown in Table 4. It can be seen that the heavier halide derivatives [B2Cl7]−, [B2Br7]−, and [B2I7]− follow a trend of increasing stability (Figure 3). This trend follows the decreasing electronegativity of the halogens and thus an increasing charge delocalization over the entire molecule. In contrast, the [B2F7]− anion shows an out-of-trend surprisingly high stability and is predicted to be even more stable than the iodine analog. With increasing halogen size the B1−X9−B5 angle decreases and the bridging B−X bonds become longer, which gives the BX3 groups more space. This allows relaxation of the B1−X9−B5 angle (see section 2.1.1 for detailed discussion). This most likely is one of the main reasons for the observed stability trend for [B2X7]− (X = Cl, Br, I). This effect would also predict a very high

Table 3. AIM Analysis of the Bond Critical Points for the [B2X7]− Anionsa ρ(r) (10−1) F B1 B1 B1 B1 bridging vs terminal B−X X2 X3

B1 B1 B1 B1 X2 X3 a

X2 X3 X4 X9 X8 X8

X2 X3 X4 X9 X8 X8

1.81 1.83 1.79 0.98 54% N/A N/A

Cl 1.37 1.40 1.33 0.87 64% 0.06 N/A K(r) (10−1)

∇2ρ(r) Br

I

F

1.25 1.27 1.20 0.87 70% 0.06 0.05

1.05 1.08 1.01 0.83 79% 0.06 0.05

1.02 1.02 1.01 0.47 N/A N/A

Cl −0.09 −0.08 −0.09 −0.06 0.02 N/A DI (10−1)

Br

I

−0.26 −0.27 −0.25 −0.12

−0.13 −0.14 −0.13 −0.09

0.19 0.17

0.02 0.01

F

Cl

Br

I

F

Cl

Br

I

1.30 1.30 1.30 0.60 N/A N/A

1.40 1.43 1.37 0.76 −0.01 N/A

1.16 1.20 1.12 0.63 −0.01 −0.01

0.60 0.62 0.58 0.44 −0.01 −0.01

2.40 2.43 2.37 1.37 N/A N/A

4.13 4.19 4.01 2.90 0.48 N/A

5.64 5.73 5.47 4.19 0.61 0.45

7.59 7.74 7.28 5.84 0.81 0.58

Bridging vs terminal illustrates that the relative strength of the bridging B−X bond becomes stronger on going down the series. C

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temperatures. Indeed, mixtures of [BI4]− and BI3 show a 11B NMR signal, which is indicative of the formation of [B2I7]− (Figures S.15 and S.16 in the Supporting Information). Unfortunately, a low-temperature NMR study is hampered by the low solubility of BI3, which completely precipitates. Nevertheless, the [B2X7]− anion may still be experimentally accessible in the solid state, when partnered with a large and weakly coordinating countercation, which minimizes lattice energy differences. Such a cation is the bis(triphenyl-λ5phosphanylidene)ammonium cation ([Ph3PNPPh3]+, abbreviated [PNP]+), which has been used by us before to stabilize only very weakly bound anions in the solid state.14

Table 4. Calculated (MP2/def2-TZVPP) Reaction Enthalpies and Gibbs Free Energies [in kJ mol−1] for the Reaction According to Eq 1 ΔH(gas) ΔG(gas) ΔG(CH2Cl2, 298.15 K) ΔG(CH2Cl2, 183.15 K) ΔH(solid state)a

[B2F7]−

[B2Cl7]−

[B2Br7]−

[B2I7]−

−90.0 −52.8 −5.6 −9.4 −86

−40.9 −0.5 35.1 31.0 −9

−52.8 −11.6 21.1 17.0 −12

−70.6 −28.9 1.8 −2.5 −18

a

The reaction enthalpies in the solid state have been estimated based on a volume-based approach and the Born−Haber-Fajans cycle in Figure 4. Details are given in the Supporting Information in section S.5.

BX3 + [PNP][BX4](s) → [PNP][B2X 7]− (s) (X = F, Cl, Br, I)

(2)

The reaction enthalpy for eq 2 has been estimated based on a Born−Haber−Fajans cycle (see Figure 4 for a general Born− Haber−Fajans cycle and section S.5 in the Supporting Information for details). The reaction enthalpies for the solid state (ΔH(solid state) in Table 4) clearly show that the [B2F7]− anion, when partnered with the large countercation [PNP]+, is stable in the solid state by 86 kJ mol−1 against dissociation. This is in agreement with several reports on crystal structures containing this anion.4−6 Surprisingly, the salts [PNP][B2X7] (X = Cl, Br, I) were calculated to be stable by 9−18 kJ mol−1 against dissociation. However, these values are certainly within the deviations of these estimations. Nevertheless, the [B2X7]− anions might be accessible under favorable conditions. We therefore attempted to prepare [PNP][B2X7] salts by reacting [PNP][BX4] with BX3 (X = Cl, Br, I). However, the experimental attempts were unsuccessful (see section S.1 and S.2 in the Supporting Information for details). Several crystal structures of byproducts and starting materials have been obtained in the course of these investigations (see section S.2 in the Supporting Information).15 Even though we failed to prepare salts of the [B2X7]− anions, our thermodynamic considerations indicate that it might be possible in the future to isolate compounds containing the [B2X7]− (X = Cl, Br, I) anions.

Figure 3. Free energy in solution (CH2Cl2, 298.15 K) for the reaction BX3 + [BX4]− → [B2X7]− (X = F, Cl, Br, I).

destabilization for the [B2F7]− anion, which is in contrast to experimental and theoretical findings. The fluorine analog is an anomaly to the general trend, which can be traced back to the very high electronegativity of fluorine, which makes electrostatic attraction and repulsion (staggering of the BF3 groups) governing the molecular structure. In contrast, the heavier halogen analogs follow the qualitative trend of having higher stability with increased polarizability of the halogen. 2.2.2. Thermodynamic Stability in Condensed Phase and Experimental Attempts To Access the [B2X7]− Anions (X = Cl, Br, I). The more important question is if the [B2X7]− anions could exist in the condensed phase (solution and solid state) and thus could they be experimentally accessible. To estimate their existence in solution we performed calculations of the reaction enthalpies according to eq 1 taking solvation effects into account by applying the PCM model as implemented in Gaussian 09. These calculations (Table 4) show that [B2F7]− should be present in CH2Cl2 solution even at room temperature, which is in agreement with published experimental results.3 [B2Cl7]− and [B2Br7]− should dissociate into [BX4]− and BX3, while [B2I7]− is a borderline case and might be detectable in solution at lower

3. EXPERIMENTAL SECTION Computational Details. All calculations have been performed with the program Gaussian 09.16 Møller−Plesset perturbation theory with second-order corrections (MP2) has been used for all structural optimizations and vibrational analysis.17−22 All computed structures are at local minima based on vibrational analyses. Def2-TZVPP basis sets23 have been used throughout and obtained from the EMSL basis set exchange library.24 In the case of iodine, the corresponding effective core

Figure 4. Born−Haber−Fajans cycle for the formation of [PNP][B2X7] in the solid state. D

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(9) Popelier, P. Atoms in Molecules: An Introduction; Prentice Hall: London, UK, 2000. (10) Takaluoma, T. PhD Thesis, University of Oulu, Oulu, 2013. (11) Bader, R. F. W. Atoms in Molecules: A quantum theory; Oxford Science Publications: Oxford, UK, 1990. (12) ρ(r) is the electron density at the BCP. ∇2ρ(r) and K(r) are the second derivative and the kinetic energy at the BCP. Combined these values give a qualitative description for the bond. ρ(r) ≈ 0.1−1.0 and positive K(r) signify typical strong bonds. Those interactions with positive ∇2ρ(r) are electron-sharing interactions. Negative ∇2ρ(r) indicates strong polarization usually found for ionic bonds. Low ρ(r) (∼10−3), positive ∇2ρ(r), and negative K(r) are a typical signature for weak hydrogen bonds and van der Waals-type interactions. (13) Similar intramolecular halogen−halogen interactions were observed for perhalogenated ethanes X3C−CX3 and have been described as weak but stabilizing noncovalent interactions. See for references: (a) Johansson, M. P.; Swart, M. Phys. Chem. Chem. Phys. 2013, 15, 11543−11553. (b) Yahia-Ouahmed, M.; Tognetti, V.; Joubert, L. Comput. Theor. Chem. 2015, 1053, 254−262. (14) (a) Bolli, C.; Gellhaar, J.; Jenne, C.; Keßler, M.; Scherer, H.; Seeger, H.; Uzun, R. Dalton Trans. 2014, 43, 4326−4334. (b) Correia Bicho, B. A.; Bolli, C.; Jenne, C.; Seeger, H. Acta Crystallogr., Sect. E: Struct. Rep. Online 2013, 69, o1435−o1436. (c) Gellhaar, J.; Knapp, C. Acta Crystallogr., Sect. E: Struct. Rep. Online 2011, 67, o2546. (d) Knapp, C.; Uzun, R. Acta Crystallogr., Sect. E: Struct. Rep. Online 2010, 66, o3185. (e) Knapp, C.; Uzun, R. Acta Crystallogr., Sect. E: Struct. Rep. Online 2010, 66, o3186. (15) The crystal structures of [PNP][H4BO3][I]2 (CCDC-1443849), [PNP][Cl2H]·CH2Cl2 (CCDC-1443850), [PNP][BF4] (CCDC1443851), and [PNP][BCl4] (CCDC-1443848) were obtained in the course of these investigations. Details on the crystal structure determinations are included with the Supporting Information. Note that the crystal structure of [PNP][BF4] was also reported by Reedijk et al. in a very recent publication. Folda, A.; Scalcon, V.; Ghazzali, M.; Jaafar, M. H.; Khan, R. A.; Casini, A.; Citta, A.; Bindoli, A.; Rigobello, M. P.; Al-Farhan, K.; Alsalme, A.; Reedijk, J. J. Inorg. Biochem. 2015, 153, 346−354. (16) 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.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, M. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö .; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision D.01; Gaussian, Inc.: Wallingford, CT, 2009. (17) Møller, C.; Plesset, M. S. Phys. Rev. 1934, 46, 618−622. (18) Head-Gordon, M.; Pople, J. A.; Frisch, M. J. Chem. Phys. Lett. 1988, 153, 503−506. (19) Saebø, S.; Almlöf, J. Chem. Phys. Lett. 1989, 154, 83−89. (20) Frisch, M. J.; Head-Gordon, M.; Pople, J. A. Chem. Phys. Lett. 1990, 166, 275−280. (21) Frisch, M. J.; Head-Gordon, M.; Pople, J. A. Chem. Phys. Lett. 1990, 166, 281−289. (22) Head-Gordon, M.; Head-Gordon, T. Chem. Phys. Lett. 1994, 220, 122−128. (23) Schäfer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829−5835. (24) Schuchardt, K. L.; Didier, B. T.; Elsethagen, T.; Sun, L.; Gurumoorthi, V.; Chase, J.; Li, J.; Windus, T. L. J. Chem. Inf. Model. 2007, 47, 1045−1052.

potential (ECP) was used to model the inner core electrons as defined in EMSL. Solvation corrections using CH2Cl2 as a solvent have been included based on the polarizable continuum model (PCM) as implemented in Gaussian 09.16 An analysis on the computationally obtained electron density was performed based on the atoms in molecules (AIM) theory11 developed by Richard Bader by using the AIMAll program.25

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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.inorgchem.6b00118. Experimental details, spectroscopic characterization, crystal structures, computational details, and thermodynamic estimations (PDF) (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (overall concept and experimental chemistry). *E-mail: [email protected] (theoretical calculations). Present Address ‡

C.B.: Paul Scherrer Institut, CH-5232 Villigen, Switzerland.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS C.B. thanks the Bergische Universität Wuppertal for a scholarship and T.T.T. the Inorganic Materials Chemistry Graduate Program by The Finnish Ministry of Education for financial support. Dr Harald Scherer from the University of Freiburg is thanked for helpful discussion.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.6b00118 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (25) Keith, T. A. AIMAll (Version 13.11.04); TK Gristmill Software: Overland Park, KS, 2013; aim.tkgristmill.com.

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DOI: 10.1021/acs.inorgchem.6b00118 Inorg. Chem. XXXX, XXX, XXX−XXX