Octafluorodirhenate(III) Revisited: Solid-State Preparation

May 12, 2016 - Department of Chemistry, University of Nevada Las Vegas, Las Vegas, Nevada 89154, United States. ‡ Laboratoire de Chimie des Processu...
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Octafluorodirhenate(III) Revisited: Solid-State Preparation, Characterization, and Multiconfigurational Quantum Chemical Calculations Samundeeswari Mariappan Balasekaran,*,† Tanya K. Todorova,‡ Chien Thang Pham,§ Thomas Hartmann,# Ulrich Abram,§ Alfred P. Sattelberger,†,⊥ and Frederic Poineau† †

Department of Chemistry, University of Nevada Las Vegas, Las Vegas, Nevada 89154, United States Laboratoire de Chimie des Processus Biologiques, UMR 8229 CNRS, UPMC-Paris 6, Collège de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France § Institute of Chemistry and Biochemistry, Freie Universität Berlin, D-14195 Berlin, Germany # Department of Engineering, University of Nevada Las Vegas, Las Vegas, Nevada 89154, United States ⊥ Argonne National Laboratory, Lemont, Illinois 60439, United States ‡

S Supporting Information *

ABSTRACT: A simple method for the high-yield preparation of (NH4)2[Re2F8]· 2H2O has been developed that involves the reaction of (n-Bu4N)2[Re2Cl8] with molten ammonium bifluoride (NH4HF2). Using this method, the new salt [NH 4]2[Re2 F8]·2H2O was prepared in ∼90% yield. The product was characterized in solution by ultraviolet−visible light (UV-vis) and 19F nuclear magnetic resonance (19F NMR) spectroscopies and in the solid-state by elemental analysis, powder X-ray diffraction (XRD), and infrared (IR) spectroscopy. Multiconfigurational CASSCF/CASPT2 quantum chemical calculations were performed to investigate the molecular and electronic structure, as well as the electronic absorption spectrum of the [Re2F8]2− anion. The metal−metal bonding in the Re26+ unit was quantified in terms of effective bond order (EBO) and compared to that of its [Re2Cl8]2− and [Re2Br8]2− analogues.

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In contrast to [Re2Cl8]2− and [Re2Br8]2−, no theoretical studies on [Re2F8]2− have been reported so far.1,6 The study of the electronic structure of [Re2F8]2− will allow a better understanding of ligand effects on the metal−metal bond. Because the [Re2F8]2− salts were prepared in good yield (∼70%),4 we expected that these compounds could serve as precursors to other dinuclear rhenium(III) fluoro complexes. In this context, we decided to explore the chemistry of [Re2F8]2− and started by revisiting its preparation and understanding its electronic structure. Here, we report a convenient new method for the preparation of [Re2F8]2−. Using this method, the new [NH4]2[Re2F8]·2H2O salt was prepared and characterized in solution by ultraviolet−visible light (UV-vis) and 19F NMR spectroscopies and in the solid state by infrared (IR) spectroscopy and powder X-ray diffraction (XRD). Finally, the molecular and electronic structure, as well as the electronic absorption spectrum of the [Re2F8]2− anion, were studied by multiconfigurational quantum chemical methods.

INTRODUCTION The octachlorodirhenate(III) anion, [Re2Cl8]2−, is the archetypal quadruply metal−metal bonded complex. The study of its molecular and electronic structure, and its spectroscopic properties, was key to the development of multiple metal− metal bond chemistry.1 Furthermore, [Re2Cl8]2− was widely used as a precursor for the synthesis of many other multiply bonded rhenium dinuclear species. Studies of the lighter halogen derivative, [Re2F8]2−, are sparse and since its discovery in 1979, only a few reports have been published. The (nBu4N)2[Re2F8]·4H2O salt was initially prepared from the metathesis of [Re2Cl8]2− in CH2Cl2/(n-Bu4N)F·3H2O solution.2 The compound has been characterized by X-ray absorption fine structure (XAFS) and Raman spectroscopies.3 These techniques confirmed the presence of the Re−Re quadruple bond (Re−Re = 2.22(2) Å from XAFS and 2.20 Å from Raman spectroscopy). The (n-Bu4N)2[Re2F8]·2Et2O salt was later obtained from a metathesis reaction in anhydrous CH2Cl2/(n-Bu4N)F solution, recrystallized from an acetone/ THF/Et2O mixture, and characterized by single-crystal X-ray diffraction.4 The latter reveals an [Re2F8]2− anion with an eclipsed D4h geometry and a Re−Re separation of 2.188(3) Å. Other experimental studies on [Re2F8]2− included Raman and fluorescence spectroscopy measurements under high pressure.5 © XXXX American Chemical Society

Received: February 19, 2016

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DOI: 10.1021/acs.inorgchem.6b00424 Inorg. Chem. XXXX, XXX, XXX−XXX

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THF/Et2O mixture at −30 °C.4 The authors report that a change of color from green to blue was observed and that (nBu4N)2[Re2F8]·2Et2O was obtained in 72% yield. We repeated this preparation but even under anhydrous conditions, we never observed the blue color in solution. After several unsuccessful attempts, we decided to develop a new method for the preparation of [Re2F8]2−. A survey of the literature indicates that bifluoride salts (MHF2 = NH4, K) are strong fluorinating agents and have been used for the preparation of salts containing the [MF6]2− (M = Tc, Re) anions.21−24 In those reactions, A2MX6 salts (A = K, NH4; X = Cl, Br) were treated in the molten bifluorides and the resulting A2MF6 salts were separated after washing with water. Interestingly, this method, to the best of our knowledge, has never been employed for the preparation of fluoro complexes with metal−metal bonds. The method reported here involves the reaction of excess ammonium bifluoride with (n-Bu4N)2[Re2Cl8]. The reaction of (n-Bu4N)2[Re2Cl8] with molten NH4HF2 at 150−300 °C resulted in the formation of (NH4)2[Re2F8]·2H2O. Details of the procedure are given in the Experimental Section. The preparation can be performed on the gram scale in platinum or nickel crucibles (50 mL) under air. In a typical preparation, the reagents NH4HF2 and (n-Bu4N)2[Re2Cl8] (mole ratio ∼200:1) were placed in a crucible and mixed with a plastic pipet; the crucible was placed on a hot plate and the temperature increased to ∼300 °C. A change of color from green to violet was immediately observed upon melting of NH4HF2. After 2 min of reaction, the crucible was removed from the hot plate and cooled to room temperature. Methanol was added to the crucible and the compound washed three times. After that, the precipitate was washed with H2O:MeOH mixture, and the suspension transferred into a centrifuge tube. After centrifugation, the supernate was removed and diethyl ether added in the tube and the compound washed and centrifuged. After centrifugation, the diethyl ether was removed and the violet solid dried under vacuum. The compound (NH4)2[Re2F8]·2H2O was obtained in ∼90% yield. It is assumed that the anhydrous salt is initially formed in the melt (eq 1), while the hydrated salt is obtained after washing with the H2O:MeOH mixture (eq 2).

EXPERIMENTAL SECTION

Starting Materials. (n-Bu4N)2[Re2Cl8] was prepared as described in the literature.7 Solvents and reactants (e.g., NH4ReO4, NH4HF2) were purchased from Sigma−Aldrich and used as received. Because of the evolution of gaseous HCl and the corrosive nature of molten ammonium bifluoride, the preparation must be performed in a wellventilated fume hood. Hydrofluoric acid (HF, 48%) was used and reactions with it were performed using Teflon-PFA flasks. Physical Measurements. Infrared measurements were performed on a Nicolet iS10 FT-IR system between 400 cm−1 and 4000 cm−1. Powder X-ray measurements were performed on a Bruker-AXS D8 Advanced Vario instrument. UV−vis measurements were performed on a Cary 6000i UV-vis-NIR spectrophotometer between 200 and 800 nm using 1 cm path length quartz cuvettes; deionized (DI) water was used as the baseline solvent. 19F NMR spectra were taken with Varian 400 MHz multinuclear spectrometer and chemical shifts are expressed in ppm, relative to external CFCl3. Elemental analyses were performed at the ALS Life Sciences Division, Environmental, Tucson, AZ USA. Computational Details. Quantum chemical calculations were performed using the multiconfigurational Complete Active Space SCF (CASSCF) methods,8 followed by multistate second-order perturbation theory (MS-CASPT2).9,10 Relativistic all-electron ANO-RCC basis sets of triple-ζ (VTZP) and quadruple-ζ (VQZP) quality were employed on all atoms with the following contractions: 8s7p5d3f2g1h for Re and 4s3p2d1f for F (VTZP level of contraction) and 9s8p6d4f3g2h for Re and 5s4p3d2f1g for F (VQZP level of contraction).11 Scalar relativistic effects were included using the Douglas−Kroll−Hess Hamiltonian.12 The effects of spin−orbit coupling were calculated employing the CASSCF state interaction (CASSI) method which was also used to compute the transition probabilities.13,14 In the CASSCF treatment, the complete active space contains 12 electrons in 12 active orbitals (12/12). This space comprises one 5d σ, two 5d π, and one 5d δ metal−metal (Re−Re) bonding orbitals and the corresponding antibonding orbitals, two metal-halide (Re−F) σ bonding and the corresponding antibonding orbitals. In the subsequent MS-CASPT2 calculations, orbitals up to and including the 4d for Re and 1s for F were kept frozen. The computational costs arising from the two-electron integrals were drastically reduced by employing the Cholesky decomposition (CD) technique15−17 combined with the Local Exchange (LK) screening.18 A numerical CASPT2 optimization of the Re−Re and Re−F bond distances was performed for the 1A1g ground state and the 1A2u excited state of [Re2F8]2− using the VTZP basis set and imposing D2h symmetry. The adiabatic energy difference between the 1A1g and 1 A2u electronic states was computed with the VTZP and VQZP basis sets at the VTZP optimized geometry. All calculations were performed with the MOLCAS 7.8 package19 and the molecular orbital plots were generated using the Luscus software.20 Preparation of (NH 4 ) 2 [Re 2 F 8 ]·2H 2 O. A mixture of (nBu4N)2[Re2Cl8] (0.2 mmol, 228 mg) and NH4HF2 (40 mmol, 2.28 g) were melted in a platinum crucible until the color turned violet (∼2 min). After cooling, the solid product was washed first with MeOH (3 × 3 mL) and then with several aliquots (20 × 5 mL) of MeOH:H2O mixture (4:1 by volume) and centrifuged. Finally, the solid was washed with Et2 O and dried under vacuum. Yield: 105 mg, 88%. F8H12N2O2Re2 (596.51): calcd. F, 25.48, Re, 62.43; found: F, 25.23, Re, 61.79. UV/vis (H2O): λmax: 46 375 cm−1 (ε = 3977 M−1 cm−1), 17 438 cm−1 (ε = 820 M−1 cm−1). 19F NMR (D2O): −150.5 (Re−F) ppm. IR (ν, cm−1), 3259 br, 3218 br, 3104 m, 2864 m, 1704 m, 1421 s, 938 (sh), 907 s, 527 s.

(n‐Bu4N)2 [Re2Cl8] + 4NH4HF2 → (NH4)2 [Re2F8] + 2(n‐Bu4N)Cl + 2NH4Cl + 4HCl(g ) (1)

(NH4)2 [Re2F8] + 2H 2O → (NH4)2 [Re2F8]· 2H 2O

(2)

In a similar procedure, we found that the reaction with KHF2 resulted in the formation of K2[Re2F8]. In addition, we investigated the preparation of [Re2F8]2− salts using anhydrous NH4F. The reaction between (n-Bu4N)2[Re2Cl8], and NH4F was performed following a method similar to that used with NH4HF2. However, during the reaction, no color change was observed and [Re2F8]2− was not obtained. Characterization. The (NH4)2[Re2F8]·2H2O salt was characterized in the solid state by elemental analysis, IR spectroscopy, and powder XRD and in solution by 19F NMR and UV-vis spectroscopy. Elemental analysis agrees well with the (NH4)2[Re2F8]·2H2O stoichiometry. The (NH4)2[Re2F8]· 2H2O salt is a dark violet microcrystalline powder. It is soluble in H2O and HF(aq) and insoluble in common organic solvents. Aqueous solutions of (NH4)2[Re2F8]·2H2O are stable for ∼3 h;

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RESULTS AND DISCUSSION Preparation. Historically, (n-Bu4N)2[Re2F8]·4H2O was the first compound containing the [Re2F8]2− anion to be reported.2 Its preparation was followed by that of (n-Bu4N)2[Re2F8]· 2Et2O.4 The synthesis of (n-Bu4N)2[Re2F8]·2Et2O involves the reaction of (n-Bu4N)2[Re2Cl8] with “dry” (n-Bu4N)F in anhydrous CH2Cl2, followed by treatment with an acetone/ B

DOI: 10.1021/acs.inorgchem.6b00424 Inorg. Chem. XXXX, XXX, XXX−XXX

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which is assigned to the Re−F stretching. This value is comparable to those reported for (n-Bu4N)2[Re2F8]·4H2O (Re−F: 572 cm−1)2 and (n-Bu4N)2[Re2F8]·2Et2O (Re−F: 568 (vs) cm−1).4 The bands between 3259 cm−1 and 3104 cm−1 were assigned to the N−H stretching. The water molecules exhibit stretches in the same region (3550−3200 cm−1).27 The electronic absorption spectrum of [Re2F8]2− was recorded at room temperature in H2O immediately after dissolution of (NH4)2[Re2F8]·2H2O (Figure 2). The spectrum

after that, they oxidize to colloidal ReO2. The stability of [Re2F8]2− in H2O has been monitored by UV-vis spectroscopy (see Figure S1 in the Supporting Information). Attempts to obtain (NH4)2[Re2F8]·2H2O single crystals via recrystallization from H2O or HF(aq) at room temperature, at −15 °C in a freezer, or under solvothermal conditions (150 °C in HF(aq)) in an autoclave were unsuccessful. Attempts to precipitate the tetrabutylammonium salt after dissolution of (NH4)2[Re2F8]·2H2O in HF/(n-Bu4N)F·3H2O or H2O/(nBu4N)F·3H2O (0.2 M) solutions were also unsuccessful, i.e., ReO2 formed after 1 day at room temperature and 1 week at −15 °C. Powder XRD measurements indicate the product to be single phase (see Figure S2 in the Supporting Information). The powder XRD pattern was indexed based on a body-centered orthorhombic unit cell with the following lattice parameters: a = 12.3362(4) Å, b = 6.8084(2) Å, c = 6.2366(2) Å, and V = 523.81(3) Å3 (see Table S1 in the Supporting Information). The 19F NMR spectrum (Figure 1) of the compound in D2O exhibits resonances at −150.5, −130.1, and −131.3 ppm vs

Figure 2. UV-vis spectrum of (NH4)2[Re2F8]·2H2O (0.5 mM) in H2O.

is similar to those previously recorded in CH2Cl2.2,28 It exhibits bands at 17 438 cm−1 (ε = 820 M−1 cm−1) and 46 375 cm−1 (ε = 3977 M−1 cm−1). The position of the lowest energy band is slightly dependent on the solvent: at 17 921 cm−1 for (nBu 4 N) 2 [Re 2 F 8 ]·4H 2 O in CH 2 Cl 2 2 and 17 438 cm − 1 (NH4)2[Re2F8]·2H2O in water (this work). Theoretical Studies. Molecular and Electronic Structure. The structure of the [Re2F8]2− anion in its 1A1g ground state and the 1A2u excited state as well as the nature of the metal− metal bonding have been analyzed at the CASSCF/CASPT2 level. The molecular orbitals forming the complete active space are shown in Figure 3. The electronic configuration of the 1A1g ground state is σ2π4δ2. Geometry optimization of the ground state reveals that the calculated Re−Re and Re−F distances are

Figure 1. 19F NMR spectrum of (NH4)2[Re2F8]·2H2O recorded in D2O. CFCl3 was used as the external reference.

CFCl3. The main resonance (−150.5 ppm) is assigned to [Re2F8]2−, while the one at −130.1 ppm is attributed to NH4F,25 obtained from the hydrolysis of [Re2F8]2−. The resonance at −131.3 ppm is attributed to [SiF6]2−,25 which results from the reaction of F− with the glass of the NMR tube. The (n-Bu4N)2[Re2F8]·2Et2O salt was also studied by 19F NMR in acetone-d6 and it exhibit signals at −135.06 ppm and −134.16 ppm vs CFCl3, respectively, but experimental details on the measurements and NMR spectra were not provided.4 Fluorinated quadruply M−M bonded transition-metal compounds are rare. To the best of our knowledge, only two compounds have been reported, namely, Mo2F4(PR3)4 (R3 = Me3, Me2Ph)26 The 19F NMR spectra of Mo2F4(PMe3)4 and Mo2F4(PMe2Ph) 4 were measured in C6D6 and exhibit resonances at −216 and −196.9 ppm, vs CF3C6H5. The signal of CF3C6H5 vs CFCl3 is −63.75 ppm.26 The IR spectrum (Figure S3 in the Supporting Information) of (NH4)2[Re2F8]·2H2O exhibits a strong band at 527 cm−1,

Figure 3. Active orbitals for [Re2F8]2− with their occupation numbers in the ground state. C

DOI: 10.1021/acs.inorgchem.6b00424 Inorg. Chem. XXXX, XXX, XXX−XXX

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Table 1. Re−Re and Re−X Bond Distances, Effective Bond Order (EBO), and Total Bond Order for [Re2X8]2− (X = F, Cl, and Br) Calculated at the CASPT2/VTZP Level of Theorya Bond Distance (Å)

a

Effective Bond Order, EBO

complex

Re−Re

Re−X

σ

π

δ

total

[Re2F8]2− − 1A1g [Re2F8]2− − 1A2u [Re2Cl8]2− (ref 6) [Re2Br8]2− (ref 6)

2.182 (2.188) 2.231 2.230 (2.220) 2.210 (2.218)

1.928 (1.94) 1.925 2.315 (2.34) 2.443 (2.51)

0.93 0.92 0.92 0.92

1.76 1.68 1.76 1.78

0.53 0.05 0.57 0.62

3.22 2.65 3.25 3.32

Experimental average bond distances for the (n-Bu4N) salts are given in parentheses.

in excellent agreement with the experimental values (Table 1). For comparison, the corresponding distances in the [Re2Cl8]2− and [Re2Br8]2− analogues are also presented.6 Our calculations confirm the experimental observation that the Re−Re distance is only slightly shorter in [Re2F8]2− than in the Cl and Br analogues, presumably due to less steric repulsion induced by the smaller fluoride ligands. In contrast, the Re−F distance is 1.928 Å, whereas Re−Cl and Re−Br are significantly longer (2.315 and 2.443 Å, respectively).6 The CASPT2-optimized structure of the 1A2u excited state has a slightly elongated (∼0.05 Å) Re−Re distance of 2.231 Å and an average Re−F distance of 1.925 Å, which is virtually the same as that in the ground state. The δ bond has an effective bond order of only 0.53 and is the weakest bond. Moreover, it is the weakest δ bond among the three halides, increasing in the order [Re2F8]2− < [Re2Cl8]2− < [Re2Br8]2−. The total bond order in [Re2F8]2− is 3.22, which is slightly lower than that in [Re2Cl8]2− (3.25) and [Re2Br8]2− (3.32). Hence, our calculations indicate that the Re26+ unit is slightly sensitive to the nature of the ligand. Electronic Spectroscopy. In the next step, we assess the optical transition energies and intensities, and provide assignments of the bands using the VTZP and VQZP basis sets at the VTZP optimized geometry of [Re2F8]2−. The results are presented in Tables 2 and 3. The lowest energy transition is a δ

→ δ* (1A1g → 1A2u) excitation, computed at 19 326 (VTZP) and 18 856 cm−1 (VQZP), which is ∼1900 and ∼1400 cm−1, respectively, higher than the experimental value (17 438 cm−1). The adiabatic energy for this transition, calculated from the energies of the optimized 1A1g ground state and the 1A2u excited state are 19 091 and 18 615 cm−1 with the triple-ζ and quadruple-ζ quality basis set, respectively, are in very good agreement with the experimental band at 17 438 cm−1. Note that the corresponding VTZP and VQZP excitation energies differ by only 470 cm−1, indicating that our results are converged, with respect to the basis set. Moreover, a similar difference of 1000−2000 cm−1, with respect to the measured values, has been calculated for [Re2X8]2− (X = Cl, Br).29 In the region of 20 000−40 000 cm−1, the absorption spectrum of [Re2F8]2− is characterized by a single allowed transition, which is a double excitation (δ)2 → (δ*,π*) at 30 746 cm−1 with VTZP and 30 445 cm−1 with the VQZP basis set, respectively. At ∼40 000 cm−1, the calculations predict a very weak π→ π* excitation at 39 991 cm−1 and an intense double excitation (δ,π) → (δ*)2 at 40 484 cm−1. The corresponding values with VQZP are 39 504 and 39 960 cm−1, respectively. At even lower energies, three very intense and close-in-energy transitions, computed at 45 606, 46 320, and 47 506 cm−1, account for the experimentally measured band centered at 46 375 cm−1 (see Figure 2).

Table 2. CASPT2 Excitation Energies (ΔE), Intensities, and Assignments Computed with the VTZP and VQZP Basis Sets at the VTZP Optimized Geometry of [Re2F8]2−

CONCLUSIONS In summary, a new method for the preparation of [Re2F8]2− involving the reaction of (n-Bu4N)2[Re2Cl8] with molten NH4HF2, gives the new [NH4]2[Re2F8]·2H2O in ∼90% yield. The compound was characterized in solution and in the solidstate by spectroscopic techniques. Infrared spectroscopy confirms the presence of Re−F stretching. Powder XRD indicates the compound crystallizes in the body-centered orthorhombic system. The aqueous 19F NMR spectrum of [NH4]2[Re2F8]·2H2O exhibits a main resonance attributed to F coordinated to Re and minor resonanced attributed to NH4F and SiF62−. Multiconfigurational quantum chemical calculations showed that the calculated molecular structure of [Re2F8]2− anion is in excellent agreement with the structure determined by X-ray diffraction of (n-Bu4N)2[Re2F8]·2Et2O.4 Effective bond order (EBO) analysis indicate that the σ- and π-bonds in [Re2F8]2− have the same strength as in [Re2Cl8]2− and [Re2Br8]2−, while the strength of the δ-bond follows the order [Re2F8]2− < [Re2Cl8]2− < [Re2Br8]2−. Nevertheless, the halide ligand has only a minor effect on the total bond order in the Re26+ core. Calculations reveal that the lowest energy band in the experimental spectrum is the δ → δ* transition, while the intense band at high energy is attributed to multiple intra dshell transitions within the metal−metal bond.

VTZP assignment

ΔE (cm−1)

δ → 3δ* δ → 1δ* (δ)2 → (δ*,π*) π → π* (δ,π) → (δ*)2 (δ → σ*)(π → δ*) σ → σ* (δ)2 → (σ*,π*)

3388 19 326 30 746 39 991 40 484 45 606 46 320 47 506

VQZP

intensity 0.58 0.38 0.15 0.11 0.11 0.22 0.11 0.26

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× × × × × × × ×

10−7 10−2 10−3 10−6 10−2 10−2 10−2 10−2

ΔE (cm−1) 3738 18 856 30 445 39 504 39 960 45 235 45 625 47 812

intensity 0.88 0.37 0.15 0.33 0.11 0.24 0.52 0.25

× × × × × × × ×

10−7 10−2 10−3 10−7 10−2 10−2 10−3 10−2

Table 3. Vertical (ΔEv) and Adiabatic (ΔEad) Excitation Energies Corresponding to the δ → δ* (1A1g → 1A2u) Transition Computed with VTZP and VQZP Basis Sets at the VTZP Optimized Geometry of [Re2F8]2− basis set

ΔEv (cm−1)

ΔEad (cm−1)

VTZP VQZP

19 326 18 856

19 091 18 615

D

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(15) Aquilante, F.; Malmqvist, P. A.; Pedersen, T. B.; Ghosh, A.; Roos, B. O. J. Chem. Theory Comput. 2008, 4, 694. (16) Aquilante, F.; Pedersen, T. B.; Lindh, R.; Roos, B. O.; Sanchez De Meras, A.; Koch, H. J. Chem. Phys. 2008, 129, 024113. (17) Aquilante, F.; Gagliardi, L.; Pedersen, T. B.; Lindh, R. J. Chem. Phys. 2009, 130, 154107. (18) Aquilante, F.; Pedersen, T. B.; Lindh, R. J. Chem. Phys. 2007, 126, 194106. (19) Aquilante, F.; De Vico, L.; Ferrè, N.; Ghigo, G.; Malmqvist, P.A.; Neogrády, P.; Pedersen, T. B.; Pitonak, M.; Reiher, M.; Roos, B. O.; Serrano-Andrès, L.; Urban, M.; Veryazov, V.; Lindh, R. J. Comput. Chem. 2010, 31, 224. (20) Kovacevic, G.; Veryazov, V. J. Cheminf. 2015, 7, 16. (21) Peacock, R. D. Chem. Ind. (London) 1955, 1453. (22) Peacock, R. D. J. Chem. Soc. 1956, 1291. (23) Weise, E. Z. Anorg. Allg. Chem. 1956, 283, 377. (24) Schwochau, K.; Herr, W. Angew. Chem. 1963, 75, 95. (25) Rashidi, N.; Vai, A. T.; Kuznetsov, V. L.; Dilworth, J. R.; Edwards, P. P. Chem. Commun. 2015, 51, 9280. (26) Cotton, F. A.; Wiesinger, K. J. Inorg. Chem. 1992, 31, 920. (27) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B, Applications in Coordination, Organometallic, and Bioinorganic Chemistry, 6th Edition; Wiley: Hoboken, NJ, 2009. (28) Clark, R. J. H.; Stead, M. J. Inorg. Chem. 1983, 22, 1214. (29) Poineau, F.; Sattelberger, A. P.; Conradson, S. D.; Czerwinski, K. R. Inorg. Chem. 2008, 47, 1991.

The convenient and high yield preparation of (NH4)2[Re2F8]·2H2O will contribute to the development of Re fluorine metal−metal bond chemistry. The use of molten NH4HF2 may now expand the number of dinuclear transitionmetal fluorides. Experiments are in progress and the results will be reported in due course.

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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.6b00424. UV-vis kinetic spectra, powder XRD pattern, IR spectrum of (NH4)2[Re2F8]·2H2O (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Mr. Trevor Low and Ms. Julie Bertoia for laboratory support, Ms. Wendee Johns for administrative support, and Dr. Dong-Chan Lee for assisting in the 19F NMR measurements. T.K.T. acknowledges the HPC resources from GENCI (CINES/TGCC/IDRIS) through Grant No. 2015-097343. Dr. Frederic Poineau acknowledges the Department of Chemistry and Biochemistry at UNLV for supporting his research through a startup package.

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DEDICATION Dedicated to the memory of Professor Malcolm H. Chisholm (1945−2015), The Ohio State University, a true pioneer in metal−metal multiple bond chemistry.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.6b00424 Inorg. Chem. XXXX, XXX, XXX−XXX