Synthesis and Characterization of the Aurivillius Phase CoBi2O2F4

Jul 11, 2018 - Max Planck Institute for Solid State Research, Heisenbergstrasse 1, ..... e.g., in Bi2O3(20) and the Bi–F bond distance of 2.21(1)–...
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Synthesis and Characterization of the Aurivillius Phase CoBi2O2F4 Eleni Mitoudi Vagourdi,† Silvia Müllner,‡ Peter Lemmens,‡ Reinhard K. Kremer,§ and Mats Johnsson*,† †

Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden Institute for Physics of Condensed Matter, TU Braunschweig, D-38106 Braunschweig, Germany § Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany ‡

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S Supporting Information *

ABSTRACT: The new CoBi2O2F4 compound was synthesized by a hydrothermal method at 230 °C. Single-crystal X-ray diffraction data were used to determine the crystal structure. The compound is layered and belongs to the Aurivillius family of compounds. The present compound is the first oxo-fluoride Aurivillius phase containing Co2+. Inclusion of a d-block cation with such a low oxidation state as 2+ was achieved by partially replacing O2− with F− ions. The crystal structure is best described in the tetragonal noncentrosymmetric space group I4̅ with unit-cell parameters a = 3.843(2) Å and c = 16.341(8) Å. The crystal structure consists of two main building units: [BiO4F4] distorted cubes and [CoF6] octahedra. Interestingly, since the octahedra [CoF6] tilt between four equivalent positions, the F atoms occupy a 4-fold split position at room temperature. For the investigation of the structural disorder, Raman scattering data were collected in the range from 10 K to room temperature. As the temperature decreases, sharper phonon peaks appear and several modes clearly appear, which indicates a reduction of the disorder. Magnetic susceptibility and heat capacity measurements evidence long-range antiferromagnetic ordering below the Néel temperature of ∼50 K. The magnetic susceptibility is in agreement with the Curie−Weiss law above 75 K with a Curie−Weiss temperature of θCW = −142(2) K.

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INTRODUCTION Because of their rich structural chemistry and their interesting physical properties, transition-metal oxohalide compounds consisting of a p-block cation with a lone-electron pair (L) have attracted particular interest.1 A previous investigation has shown that the effective volume of a lone pair decreases with increasing atomic number.2 L-cations of the fourth and fifth row of the periodic table, e.g., Se4+, Te4+, Sb3+, exhibit a lone pair that most often is stereochemically active and occupies a volume comparable to an O2− or a F− anion and thus help to open up the crystal structure. However, the heavier cations Pb2+ and Bi3+ of the sixth row have a lone pair that is attracted closer to the nucleus and is less or not stereochemically active. As observed, for example, with Cu 4 Te 5 O 12 Cl 4 or Cu7(SeO3)2O2Cl6,3,4 in an oxohalide environment rich in oxygen, the lighter L-cations most often bond to oxygen ions, rather than halide ions. The lone pair and the halide ion both act as chemical scissors, helping to open up the crystal structure. As a result, a layered compound that only shows van der Waals interactions between the layers is often obtained. This has been observed, e.g., in Co5(TeO3)4Cl2 and Co5(TeO3)4Br2, where both the stereochemically active lone pair on Te4+ and the Cl−/Br− ions are protruding from the layers.5 It is also common with framework compounds having nonbonding volumes, where the lone pair and the halide ion reside.6−8 Oxofluorides behave differently and the electronegative fluorine © XXXX American Chemical Society

anions, like oxygen, usually participate in building the framework.9 However, heavier L-cations, such as Pb2+ and Bi3+, are used to bond to both oxygen and halide ions without any preference between different halide ions, as has been seen, e.g., in Pb4Fe3O8X (X = Cl and/or Br) and in [Cu5Cl][Bi48O59Cl30].10,11 Most Aurivillius phases are oxides and their crystal structure consists of alternating [Bi2O2]2+ layers and n perovskite layers (n ≤ 5), as found, for example, for Bi2MoO6 and Bi4Ti3O12 with n = 1 and 2, respectively.12,13 In the present study, a new oxofluoride, CoBi2O2F4, belonging to the Aurivillius family of compounds, has been synthesized and characterized. So far, there are only three such oxofluorides described in the literature: TiBi2O4F2, NbBi2O5F, and VBi2O5F.14,15 CoBi2O2F4, to the best of our knowledge, is the first compound in the Co2+− Bi3+−O−F system constituting the first oxo-fluoride Aurivillius phase with Co2+. The crystal structure determination is based on single-crystal X-ray diffraction (XRD) data. Raman scattering in the temperature range of 10−300 K has been performed to extract information on how the disorder in the crystal structure changes with temperature. Magnetic susceptibility and heat capacity studies conclude that the compound undergoes an antiferromagnetic transition at low temperatures. Received: April 23, 2018

A

DOI: 10.1021/acs.inorgchem.8b01118 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

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EXPERIMENTAL SECTION

Table 1. Crystal Data and Refinement Parameters for CoBi2O2F4

Reddish tetragonal single crystals have been synthesized via a hydrothermal method. A mixture of 0.097 g (1 mmol) of CoF2 (Alfa Aesar, 99.9%) and 0.465 g (1 mmol) of Bi2O3 (Aldrich, 99.9%), together with 2.5 mL of deionized water and 2−3 drops of hydrofluoric acid (HF) (80 μL) were sealed in a 23 mL Teflon-lined steel autoclave. The mixture was heated to 230 °C for 3 days. The crystals were washed with deionized water, followed by ethanol, and left to dry for 24 h at room temperature. The chemical composition of the product was characterized by a scanning electron microscopy (SEM) system (JEOL, Model JSB-7000F) that was equipped with an energydispersive spectrometer. Single-crystal XRD data were collected on a Bruker D8 Venture diffractometer using Mo Kα radiation (λ = 0.710730 Å). The intensities of the Bragg reflections were integrated using the SAINT software,16 and the multiscan absorption correction was performed with the SADABS program17 supplied by the manufacturer. The structure was solved by dual space methods SHELXT using the SHELXT-2014/7 software and refined by full matrix on F2 using the SHELXL-2014/7 program.17 The heavy atoms Co and Bi were refined with anisotropic displacement parameters, whereas O and F were restrained to isotropic displacement behavior. Powder XRD patterns were collected on a Panalytical X’Pert PRO diffractometer. The purity of the multicrystal sample was confirmed by comparing the powder pattern with the simulated pattern of the crystal structure from the single-crystal data. A scanning mode between 5° and 80° with a θ step of 0.001 was selected for the data collection. The Raman experiments were performed in a quasi-backscattering geometry with a solid-state Nd:YAG laser at an excitation wavelength of λexc = 532.1 nm with a 50-fold magnification objective. In order to prevent damaging, the sample by overheating, a laser power of Pexc = 33 μW has been applied. Raman data has been collected with a microRaman spectrometer (LabRAM HR, Jobin-Yvon) with an acquisition time of 100 s accumulated eight times. A diffraction grating with 1800 grooves/mm was used. The signal has been detected with a nitrogen-cooled CCD camera (Horiba, Spectrum One). Polarization of the laser had been set to XU, indicating parallel and unpolarized light of the incident and backscattered light, respectively. This allows the observation of all A and B symmetry phonons. The crystals were cooled inside a microcryostat (KONTI, Cryovac) and in vacuum at temperatures ranging from room temperature to 10 K. The magnetization, M(T,H) versus temperature of a coarse polycrystalline sample of 28.8 mg was measured in a MPMS SQUID magnetometer (Quantum Design) in various magnetic fields. To avoid reorientation of the crystals in the external magnetic field, the sample was immersed in a minute amount of Apiezon N vacuum grease. The heat capacity of a polycrystalline sample (m = 2.55 mg) was measured with a PPMS system (Quantum Design) equipped with a 3He inset in the temperature range of 2−90 K. The sample was immersed in Apiezon N grease to ensure thermal coupling to the sapphire platform. The heat capacities of the grease and the platform were measured in a preceding run and subtracted from the total heat capacities.

parameter

value/comment

empirical formula formula weight temperature wavelength crystal system space group a b c volume Z density (calc) F(000) crystal color crystal habit crystal size theta range for data collection index ranges reflections collected independent reflections data/restraints/parameters refinement method goodness-of-fit on F2 final R indices [I > 2σ(I)]a R indices all data

CoBi2O2F4 584(1) g/mol 295(2) K 0.71073 Å tetragonal I4̅ 3.843(2) Å 3.843(2) Å 16.341(8) Å 241.33(3) Å3 2 8.049 g cm−3 490 red plate 0.2 × 0.2 × 0.1 2.493°−28.263° −5≤ h ≤ 4, −5 ≤ k ≤ 5, −21 ≤ l ≤ 21 1339 307 [R(int) = 0.039] 307/0/24 full-matrix least-squares refinement on F2 1.25 R1= 0.0216 wR2 = 0.0432 R1 = 0.0274, wR2 = 0.0449

R1 = ∑∥Fo| − |Fc∥/∑|Fo|;wR2 = {{∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]}1/2.

a

The fluorine atoms show a 4-fold split position. In a simplified structure model using the average positions of the F atoms, the two main building units are [CoF6] octahedra and [BiO4F4] distorted cubes. The [CoF6] octahedra connect by corner sharing to form [CoF4]∞ layers and the [BiO4F4] cubes connect to form [BiO2F2]∞ layers, so that the crystal structure is composed of fluoride layers and oxide layers. The layers connect via corner sharing at F atoms (see Figure 1). The oxide layers consist of zigzag cross-linked Bi−O chains, as shown in Figure 2.

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RESULTS Crystal Structure. The new compound CoBi2O2F4 crystallizes in the tetragonal space group, I4̅ with unit-cell parameters of a = 3.843(2) Å and c = 16.341(8) Å; all refinement data are summarized in Table 1. Refinement in the tetragonal space group I4, which shows the same systematic absences as I4̅ was also attempted but resulted in negative atomic displacement parameters of the anions, indicating that the structure is best described by the noncentrosymmetric tetragonal space group, I4̅. In the crystal structure, there is one crystallographically independent Bi3+ and Co2+ ion, respectively. Bond valence sum (BVS) calculations, according to Brown and Altermatt, confirm the oxidation states (see the Supportive Information).18

Figure 1. Simplified structure model of CoBi2O2F4 with one F atom at the center of the four split positions in the [CoF6] octahedra, c.f., Figure 5 (presented later in this work).

The crystal structure as obtained from single-crystal XRD is disordered so that the F atoms of the [CoF6] octahedron show a four-fold split position at room temperature with Co−F bond B

DOI: 10.1021/acs.inorgchem.8b01118 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 2. (a) Bi−O chains and (b) Bi2O2 Aurivillius layers formed by connected Bi−O chains.

Figure 4. (a) Chain of idealized nontilting [CoF6] octahedra and (b) chain of tilted octahedral due to the split.

lengths in the range of 1.99(4)−2.05(6) Å close to the Co−F distances observed in CoF2, i.e., 2.04(1)−2.05(2) Å.19 Projections of the [CoF6] octahedron along the [010] and [001] directions, showing the split positions occupied by the F atoms due to tilting-in between four equal positions, are presented in Figures 3a and 3b. For the sake of simplicity, the crystal structure is drawn so that the tilted [CoF6] octahedra are fixed to an average position (see Figures 1 and 4a). However, because of the split positions of the F atoms, the structure consists of fluoride layers comprised of [CoF6] octahedra that are tilted within the layer (see Figure 4b), and rigid oxide layers alternating along the [001] direction, as depicted in Figure 5. The Bi−O distances in the [BiO4F4] cubes amount to 2.298(4) Å and the Bi−F distances are found to be in the range of 2.40(6)−2.49(6) Å. These values agree with the Bi−O bond distance range of 2.08(3)−2.29(3) Å observed, e.g., in Bi2O320 and the Bi−F bond distance of 2.21(1)−2.50(0) Å ascertained in BiF3.21 Starting from an F atom that forms a Bi−F bond with a bond length of 2.49(6) Å, the distances from this F atom to the next three Bi atoms are significantly longer and are within the range of 2.81(6)−3.17(6) Å, as shown in Figure 3b. Such long bond lengths are the reason for the four split positions equally occupied by F atoms in order to form the desired Bi−F bond lengths with all the four neighboring Bi atoms. Therefore, each position has a 25% probability of being occupied by an F atom.

Figure 5. Overview of the CoBiO2F4 crystal structure showing the 4-fold split F atoms.

Another example of a compound showing eight-coordinated Bi3+ is BiO0.55F1.90.22 BiO0.55F1.90 crystallizes with a layered crystal structure, wherein the Bi atom is the center of a [BiO4F4]

Figure 3. (a) Representation of the [CoF6] octahedron with the 4-fold split F atoms. (b) Each split F atom show one reasonable or optimal Bi−F bond distance in the range of 2.40−2.50 Å and three too-long Bi−F distances that is the reason for the split. C

DOI: 10.1021/acs.inorgchem.8b01118 Inorg. Chem. XXXX, XXX, XXX−XXX

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number of 36 modes. At temperatures of T > 393 K, the phonon modes are expected to be similar to the modes below T < 335 K. An overview of the phonon modes at 293 and 10 K is depicted in Figure 6a. Phonons distribute over a frequency range of 50−440 cm−1. At room temperature, three broad maxima appear in the low-frequency region of 50−100 cm−1. It splits into several maxima (54, 56, 62, 66, 70, 83, 89, and 96 cm−1) at low temperature (see Figure 6b). A rather broad mode is observed at ∼165 cm−1 at high temperatures, which splits into four modes at low temperature (see Figure 6c). These modes are fitted with Lorentzians. Discussion on Phonon Analysis. The lower energy frequency modes (54−96 and 160−170 cm−1) in Figure 6 are most likely attributed to rotational modes of coordinations involving heavy atoms, i.e., [BiO4F4] or [CoF6] units. Reference data from perovskites, e.g., LaCoO3, show modes at similar frequencies (42, 50, and 86 cm−1).27−29 It is also noticeable that the modes at 160, 164, 168, and 170 cm−1 have the highest scattering intensity. This is consistent with their origin in the Bi-block of the compound, as high scattering intensities would be expected for the lone-pair Bi. This is also supported by reference data of [Bi5]3+[AlCl4]3−, where four Raman active modes appear in a similar frequency range (146, 135, 125, 119 cm−1).30 The mode at 238 cm−1 coincides with reference data of a rotational mode of an oxygen cage at 241 cm−1.28 The higher frequency modes at 424 and 385 cm−1 are attributed to distortions of the [CoF6]-building block. Reference data show modes at 439 and 440 cm−1 for KCoF3 and KCoO2, respectively.30 The transformation of the broad modes into sharp modes for decreasing temperatures indicates an order/disorder transition, attributed to a gradual freezing of rotational degrees of freedom at lower temperatures. Such a phenomenon occurs if the thermal occupation of the modes decreases strongly, which is evident from a similarity of the modes energy with the observed temperature regime of the transition. Magnetic and Thermal Properties of CoBi2O2F4. The magnetization, M(T,H) versus temperature of a coarse polycrystalline sample was measured in various external magnetic fields. To avoid reorientation of the crystals in the field, the sample was immersed in a minute amount of Apiezon N vacuum grease. Above ∼150 K, the inverse magnetic susceptibilities 1/χmol(T) = H/Mmol(T,H) of CoBi2O2F4 follow Curie− Weiss laws (see eq 1, given below), but with different slopes and Curie−Weiss temperatures for the different measuring fields H (see Figure 7). We attribute the field dependence to a minute ferromagnetic impurity, which may saturate by increasing the external field. Toward the highest measuring fields, the susceptibilities approach stable, field-independent values and for fields of 5 and 7 T, the high-temperature susceptibilities are essentially identical. Using the susceptibility data collected at 5 and 7 T above ∼150 K, Curie−Weiss behavior was fitted according to

building unit of the same type as in the present compound, with Bi−F and Bi−O bond distances in the ranges of 2.38(4)− 2.64(4) Å and 2.39(2)−2.546(8) Å, respectively. In BiOF,23 the Bi atom is also eight-coordinated with four F atoms and four O atoms forming a square antiprism with Bi−F and Bi−O bond lengths of 2.75(2) and 2.273(2) Å, respectively. In BiOF, there is a fifth fluorine, located 2.92(6) Å away from the Bi atom. There are three previously reported oxo-fluoride Aurivillius phases: NbBi2O5F, TiBi2O4F2,14 and VBi2O5F.15 In these phases, the octahedrally coordinated cation has an oxidation state of 4+ or 5+. The present compound is the first oxo-fluoride Aurivillius phase, where the octahedrally coordinated cation has such a low oxidation state as 2+. They all show similar structural disorder caused by tilting octahedra. Several fluoride Aurivillius phases containing 2+ cations have also been described: Ba2MF6 (M = Zn, Cu, Ni, Co, Fe). In those phases, however, there is no disorder originating from tilting of the octahedra.24 The difference between the present type of Bi-containing oxofluorides and oxochlorides/oxobromides is that the electronegative F participate in constituting the 3D network while Cl/ Br act as terminating species showing also a Sillén−Aurivillius intergrowth25 as in the layered compounds Bi4NbO8Cl and Bi4TaO8Cl.26 Phonon Analysis. According to the space group I4̅ (No. 82), the irreducible representation of Raman-active modes is given by ΓRaman = 4A + 7B + 8E1 + 8E2 modes, yielding a total of 27 modes. We observe 23 modes, which is in good agreement to the 27 expected modes. The 4 modes that are not observed are attributed to E modes that generally have a very small intensity. Consistent with the remaining 11 A and B modes, we observe 11 modes with medium to high scattering intensity. These modes are observed at 83, 89, 96, 160, 164, 168, 170, 238, 330, 385, and 424 cm−1, as shown in Figure 6.

χmol (T ) =

C + χ0 T − θCW

(1)

where the Curie constant (C) is given by ij μ yz C = 0.125051 cm K/mol × jjjj eff zzzz k μB {

Figure 6. (a) Overview Raman spectra of CoBi2O2F4 at 293 and 10 K. (b) Low-frequency modes with the transition from a disordered to an ordered phase toward lower temperatures. (c) The same as that described in panel (b) for the phonon at 165 cm−1.

2

3

For temperatures in the range of 335−393 K, the irreducible representation is ΓRaman = 6A + 8B + 11E1 + 11E2, with a total

and θCW the Curie−Weiss temperature. D

DOI: 10.1021/acs.inorgchem.8b01118 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 7. Inverse magnetic susceptibilities of CoBi2O2F4 measured at various magnetic fields as indicated. The solid (red) line represents the Curie−Weiss law according to eq 1, with an effective magnetic moment of 5.62 μB per Co2+ cation and a Curie−Weiss temperature of −142(2) K.

Figure 8. Magnetic susceptibilities of CoBi2O2F4 taken at magnetic fields of 5 and 7 T.

There are two terms contributing to the temperatureindependent susceptibility: the diamagnetic part from the electrons in the closed shells, and the temperature-independent paramagnetic Van Vleck susceptibility (defined as χ0 = χdia + χVV). For Co2+ ions, the latter is typically in the order of 2 × 10−4 cm3/mol.31 The diamagnetic contribution from the closed electronic shell can be estimated from Pascal’s increments: Co2+, −12 × 10−6 cm3/mol; Bi3+, −25 × 10−6 cm3/mol; O2−, −12 × 10−6 cm3/mol; and F−, −11 × 10−6 cm3/mol.32 The diamagnetic increments add up to χdia = −130 × 10−6 cm3/mol from the number of atoms per formula unit. This results in χ0 ≈ 70 × 10−6 cm3/mol. This value was fixed in the refinements. The fits of the experimental data (5 and 7 T) above 150 K converge to an effective magnetic moment of 5.62(5) μB per Co2+ cation and a Curie−Weiss temperature of −142(2) K, indicating predominant antiferromagnetic spin exchange interaction. The effective magnetic moment is consistent with that typically found for Co2+ in octahedral complexes (4.7−5.2 μB).31 Such large effective magnetic momenta for Co2+ in an octahedral or slightly distorted ligand field result from substantial orbital contributions. The ground state can be described by a fictitious angular moment J ̃ = 1/2 with a g-factor involving spin and angular contributions.33 At ∼40 K, the magnetic susceptibilities exhibit anomalies which, for small magnetic fields, resemble the development of spontaneous magnetization as seen in ferromagnets or ferrimagnets, whereas, for very high magnetic fields, a maximum develops in the susceptibility which is rather typical for long-range antiferromagnetic ordering (see Figure 8). The anomalies in the magnetic susceptibilities indicating long-range magnetic ordering are paralleled by a λ-type anomaly in the heat capacity at the same temperature (see Figure 9). The magnetic part of the total heat capacity was calculated by subtracting a lattice contribution, Clat(T), which was obtained by fitting a sum of a Debye-like heat capacity and three Einstein terms, according to

Figure 9. (a) Zero-field heat capacity and (b) magnetic susceptibilities of CoBi2O2F4 taken at various magnetic fields as indicated.

with θDeb being the Debye temperature and cDeb a weighting term. The Einstein terms, Cp,Ein(Ei,T), were calculated using the expression Cp ,Ein(Ei ,T ) = 3R(xi)2

∑ ci ,EinCp,Ein(Ei ,T ) i=1

(2)

where the Debye term, Cp, Deb(ΘDeb,T), is given by ij T yz zz Cp ,Deb(θDeb , T ) = 9R jjj j θDeb zz k {

3

∫0

ΘDeb / T

(exp(xi) − 1)2

where xi = Ei/T and Ei is the Einstein temperature of a total of three modes with weights ci, respectively. R is the molar gas constant. The experimental data, excluding the temperature range of the λ-type anomaly between 35 K and 45 K, were fitted to eq 2 by varying the Einstein temperatures Ei and the weights cDeb, ci by constraining the sum of all weights to nine, i.e., the number of atoms in the formula unit. The Debye temperature, θDeb, was fixed to 275 K to achieve convergence of the fits. The fitted Einstein temperatures amounted to 78, 158 and 612 K, with weights of 1.3, 2.2, and 3.6, respectively. The result of the fit is given in Figure 9 by the solid red line. The difference between experimental data and lattice contribution to the heat capacity represents the magnetic contribution,

3

C lat(T ) = c DebCp ,Deb(θDeb , T ) +

exp(xi)

x 4 exp(x) dx (exp(x) − 1)2

Cmag(T ) T E

=

Cp(T ) T

−

C lat(T ) T DOI: 10.1021/acs.inorgchem.8b01118 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry This emphasizes the λ-type anomaly centered at 40.9(5) K. The magnetic entropy was calculated from the magnetic contribution to the heat capacity, Cmag(T), by integrating Cmag(T)/T across the entire temperature range. The magnetic entropy amounts to ∼1.5 J/(mol K), or ∼26% of R ln 2, as expected for an effective spin S = 1/2 system. We assume that the remaining magnetic entropy has already been removed by magnetic short-range ordering, which would be in agreement with the two-dimensional character of the crystal structure.

Notes

CONCLUSIONS The new layered oxo-fluoride compound CoBi2O2F4 was synthesized utilizing a hydrothermal technique starting with CoF2 and Bi2O3. The crystal structure was determined from single-crystal X-ray diffraction data. The structure consists of two main building units: [CoF6] octahedra and [BiO4F4] distorted cubes. The [CoF6] octahedra are connected via corner sharing to form [CoF4]∞ layers, and the [BiO4F4] distorted cubes are connected via edge sharing to form [BiO2F2]∞ layers, respectively. The new compound belongs to the Aurivillius family and is the first oxo-fluoride in this family to contain a transition metal with such a low oxidation state as 2+. This became possible by introducing fluorine to replace some of the oxygen atoms. Spin exchange between the Co2+ cations in CoBi2O2F4 is predominantly antiferromagnetic leading to long-range antiferromagnetic order below ∼40 K indicated by a maximum in the magnetic susceptibility and a λ-type anomaly in the magnetic contribution to the heat capacity. The interlayer spin exchange paths which couple the magnetic CoF6 layers across the [BiO2F2]∞ interlayers may be expected to be much weaker than intralayer spin exchange. Details of the exchange paths are not known at present. As is well-established for archetypical layered magnetic systems, finite interlayer coupling eventually causes long-range ordering at low temperatures.34

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work has been realized with support from the Swedish Research Council (VR) (Grant No. 2014-3931), Deutsche Forschungsgemeinschaft (Nos. DFG LE967/16-1 and DFGRTG 1952/1), the NTH School for Contacts in Nanosystems and Quanomet. We thank E. Brücher and G. Siegle for expert experimental assistance.

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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.8b01118. Tables of atomic coordinates, bond lengths and bond valence calculations. Further details on the crystal structural investigations can be obtained from the Fachinformationszentrum Karlsruhe, Abt. PROKA, 76344 EggensteinLeopoldshafen, Germany, Depository No. CSD-434435 (fax +49-7247-808-666; E-mail: crysdata@fizkarlsruhe.de) (DOCX) Accession Codes

CCDC 1838439 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax: +44 1223 336033.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Reinhard K. Kremer: 0000-0001-9062-2361 Mats Johnsson: 0000-0003-4319-1540 F

DOI: 10.1021/acs.inorgchem.8b01118 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.inorgchem.8b01118 Inorg. Chem. XXXX, XXX, XXX−XXX