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Publicly Available Published by De Gruyter July 22, 2017

Crystal structures and thermal decomposition of permanganates AE[MnO4]2·n H2O with the heavy alkaline earth elements (AE=Ca, Sr and Ba)

  • Harald Henning , Jörg M. Bauchert , Maurice Conrad and Thomas Schleid EMAIL logo

Abstract

Reexamination of the syntheses and crystal structures as well as studies of the thermal decomposition of the heavy alkaline earth metal permanganates Ca[MnO4]2·4 H2O, Sr[MnO4]2·3 H2O and Ba[MnO4]2 are the focus of this work. As an alternative to the very inelegant Muthmann method, established for the synthesis of Ba[MnO4]2 a long time ago, we employed a cation-exchange column loaded with Ba2+ cations and passed through an aqueous potassium-permanganate solution. We later used this alternative also with strontium- and calcium-loaded columns and all the compounds synthesized this way were indistinguishable from the products of the established methods. Ca[MnO4]2·4 H2O exhibiting [CaO8] polyhedra crystallizes in the orthorhombic space group Pccn with the lattice parameters a=1397.15(9), b=554.06(4) and c=1338.97(9) pm with Z=4, whereas Sr[MnO4]2·3 H2O with [SrO10] polyhedra adopts the cubic space group P213 with a=964.19(7) pm and Z=4. So the harder the AE2+ cation, the higher its demand for hydration in aqueous solution. Consequently, the crystal structure of Ba[MnO4]2 in the orthorhombic space group Fddd with a=742.36(5), b=1191.23(7) and c=1477.14(9) pm with Z=8 lacks any crystal water, but contains [BaO12] polyhedra. During the thermal decomposition of Ca[MnO4]2·4 H2O, the compound expels up to two water molecules of hydration, before the crystal structure collapses after the loss of the third H2O molecule at 157°C. The crystal structure of Sr[MnO4]2·3 H2O breaks down after the expulsion of the third water molecule as well, but this already occurs at 148°C. For both the calcium and the strontium permanganate samples, orthobixbyite-type α-Mn2O3 and the oxomanganates(III,IV) AEMn3O6 (AE=Ca and Sr) remain as final decomposition products at 800°C next to amorphous phases. On the other hand, the already anhydrous Ba[MnO4]2 thermally decomposes to hollandite-type BaMn8O16 and BaMnO3 at 800°C.

1 Introduction

Permanganates in general and the permanganates of the heavy alkaline earth metals in particular are well characterized [1], [2], [3] and have a myriad of applications. For instance Ca[MnO4]2 is commercially available and used as a disinfectant in solution, whereas Ba[MnO4]2 commonly serves as starting material for the synthesis of other permanganates via sulfate metatheses [4].

Within the alkaline earth metal permanganates, a tendency for a declining demand of hydration with the growth of the cations can be observed. In this context, Mg[MnO4]2·6 H2O and the permanganates of calcium, strontium and barium, which are discussed in this work, have a well-established hydration grade [3], [5], [6], [7], when obtained from an aqueous solution. Contrasting to this, the water-richest hydrate of Be[MnO4]2 is proposed to have at least five water molecules of hydration [8], but remained structurally uncharacterized so far.

While revisiting the topic of permanganates in general, we have realized that the synthesis of these compounds is very challenging and has inherent risks. The Muthmann method [1] for the synthesis of Ba[MnO4]2 is over 120 years old and is widely used. For the synthesis of the calcium and the strontium compounds, a detour via the highly sensitive permanganic acid H[MnO4] (better: [MnO3(OH)]) has to be employed. To circumvent these issues, we have developed a new synthesis method utilizing an ion-exchange column to access these compounds and received virtually identical results to the classical preparations. We used this opportunity to reexamine these heavy alkaline earth metal permanganate (hydrates) and to refine their respective crystal structures.

The thermal behavior of many permanganates is known in the literature [4], but there is recent interest in their respective uses as precursors for oxidation catalysts as octahedral molecular sieves (OMS) based on porous manganese oxides [9], [10]. The importance and functionality of these OMS materials has been studied in detail by a Suib et al. for a number of years [11], [12], [13]. We failed to find any significant investigations on the thermal behavior of Ca[MnO4]2·4 H2O, Sr[MnO4]2·3 H2O and Ba[MnO4]2, and therefore our findings for these particular cases of thermal decomposition are new and presented here as well.

2 Results and discussion

2.1 Calcium permanganate tetrahydrate, Ca[MnO4]2·4 H2O

2.1.1 Crystal structure

As stated before by Nesper et al. in 2012 [5], Ca[MnO4]2· 4 H2O crystallizes in the orthorhombic space group Pccn (no. 56) with the lattice parameters a=1397.15(9), b=554.06(4) and c=1338.97(9) pm with four formula units per unit cell (Table 1). Its crystal structure offers six crystallographically distinguishable oxygen atoms, which are all localized on the general Wyckoff sites 8e (Table 2). The oxygen atoms O1–O4 form the tetrahedral coordination spheres around the Mn7+ cations within the [MnO4] anions (Fig. 1) with Mn–O distances of 159–162 pm (Table 3), whereas O5 and O6 represent the oxygen atoms of hydrating water molecules (d(O–H)=60–84 pm, ∡(H–O–H)=112–118°) for the Ca2+ cations. These oxygen atoms form a heterocubane-like surrounding about Ca2+ (Fig. 2) consisting of a tetrahedral water-shell (O5 and O6; d(Ca–O)=237–239 pm) and the corners O2 and O3 shared with four [MnO4] anions also forming a tetrahedron with d(Ca–O)=250–252 pm as interatomic distances (Table 3). This results in isolated chains of vertex-sharing cation polyhedra [CaO8]14− and [MnO4] propagating along [001], forming a

{(H2O)4Ca[MnO4]4/2} arrangement. The three-dimensional crystal structure of Ca[MnO4]2·4 H2O (Fig. 3) is solely formed via bridging hydrogen bonds with distances d(O···H)=213–285 pm between the chains along [100] and [010], with the oxygen atoms O1 and O4 of the permanganate anions connecting to all hydrogen atoms (H1–H4) of the two crystallographically different water molecules (Fig. 1).

Table 1:

Crystallographic and structure solution data for Ca[MnO4]2·4 H2O, Sr[MnO4]2·3 H2O and Ba[MnO4]2.

Empirical formulaCa[MnO4]2·4 H2OSr[MnO4]2·3 H2OBa[MnO4]2
Crystal systemOrthorhombicCubicOrthorhombic
Space groupPccn (no. 56)P213 (no. 198)Fddd (no. 70)
Lattice parameters
a, pm1397.15(9)964.19(7)742.36(5)
b, pm554.06(4)a1191.23(7)
c, pm1338.97(9)a1477.14(9)
Molar volume Vm, cm3·mol−1156.05(4)134.95(4)98.33(3)
Number of formula units, Z448
Calculated density Dx, g·cm−32.242.773.82
Wavelength (MoKα)λ=71.07 pm
Electron sum, F(000), e6967041360
hkl range (±h, ±k, ±l)18, 7, 1712, 12, 1211, 19, 23
θ range, deg2.9–28.33.0–28.33.5–35.0
Data correctionsBackground, polarization and Lorentz factors; numerical absorption correction program Habitus [14]
Absorption μ, mm−13.08.89.8
Extinction (g)0.0029(5)0.0040(6)0.00091(8)
Flack X parameter0.03(2)
Measured reflections1679155567831
Unique reflections1286747728
Rint/Rσ0.068/0.0240.084/0.0610.055/0.022
Structure solution and refinementProgram package Shelxs/l-97 [15], [16]
Scattering factorsInternational Tables, Vol. C [17]
R1/wR2 (all reflections)0.038/0.0620.112/0.0960.027/0.050
GooF (on F2)1.0280.9911.130
Residual electron densities (max/min), e/106 pm−30.40/–0.410.67/–0.721.05/–0.98
CSD numbera425408432611432412
  1. aFurther details of the crystal structure investigations may be obtained from FIZ Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (fax: +49-7247-808-666; e-mail: crysdata@fiz-karlsruhe.de) on quoting the listed deposition numbers.

Table 2:

Atomic positions and equivalent isotropic displacement parameters for Ca[MnO4]2·4 H2O.

AtomWyckoff sitex/ay/bz/cUeq/pm2
Ca4d
0.34957(3)201(1)
Mn8e0.131479(19)0.48838(5)0.097141(18)201(1)
O18e0.04849(12)0.6830(3)0.08964(11)489(4)
O28e0.19243(13)0.5326(3)0.19706(10)433(4)
O38e0.19975(12)0.5104(3)0.00083(10)373(4)
O48e0.08605(11)0.2200(3)0.10136(10)363(4)
O58e0.12626(13)0.0119(3)0.29679(13)450(5)
O68e0.11535(13)0.5190(3)0.40481(13)307(4)
H18e0.104(2)0.098(6)0.328(2)610(98)
H28e0.124(2)0.033(5)0.235(2)403(87)
H38e0.120(2)0.484(5)0.447(2)369(79)
H48e0.066(2)0.573(6)0.396(2)579(94)
Fig. 1: Environment of the permanganate anion in Ca[MnO4]2·4 H2O with its coordination modes towards the Ca2+ cations as well as its hydrogen bonds to the water molecules.
Fig. 1:

Environment of the permanganate anion in Ca[MnO4]2·4 H2O with its coordination modes towards the Ca2+ cations as well as its hydrogen bonds to the water molecules.

Table 3:

Selected interatomic distances (d/pm) in Ca[MnO4]2·4 H2O.

DistanceDistance
Mn–O1(1×)158.7(1)Ca–O2(2×)250.4(1)
Mn–O2(1×)160.5(1)Ca–O3(2×)252.1(1)
Mn–O3(1×)160.9(1)Ca–O5(2×)236.5(2)
Mn–O4(1×)161.8(1)Ca–O6(2×)239.3(2)
O5–H1(1×)71(3)O6–H3(1×)60(3)
O5–H2(1×)84(3)O6–H4(1×)76(3)
Fig. 2: Square antiprismatic coordination sphere of oxygen atoms surrounding the Ca2+ cations in Ca[MnO4]2·4 H2O.
Fig. 2:

Square antiprismatic coordination sphere of oxygen atoms surrounding the Ca2+ cations in Ca[MnO4]2·4 H2O.

Fig. 3: The crystal structure of Ca[MnO4]2·4 H2O viewed along [010].
Fig. 3:

The crystal structure of Ca[MnO4]2·4 H2O viewed along [010].

2.1.2 Thermal decomposition

During the thermal decomposition of Ca[MnO4]2·4 H2O the compound releases the first three water molecules at 37, 82 and 157°C with corresponding weight losses of 6.7, 6.6 and 7.8%, respectively, but the loss of the third H2O leads to a collapse of the crystal structure (Fig. 4, top left). The fourth water molecule and, according to the total loss in mass of 10.0%, an oxygen molecule (O2) are released in the range up until 800°C. The residue could not be clearly characterized via X-ray powder diffraction (XRPD), but its diffractogram shows reflections of CaMn3O6 [18] and orthobixbyite-type α-Mn2O3 [19], and moreover suggests the presence of additional amorphous phases (Fig. 4, top right).

Fig. 4: Thermogravimetrical curves (TG) monitoring the thermal decomposition of the alkaline earth metal permanganates AE[MnO4]2·n H2O (left) and the X-ray powder diffraction patterns (XRPD) of the final residues (right). Reflections corresponding to orthobixbyite-type α-Mn2O3 are marked with asterisks (*), whereas reflections corresponding to BaMn8O16 with hollandite-type structure are marked with plus signs (+). Additional unidentified reflections belong to recrystallized impurities of no consequence.
Fig. 4:

Thermogravimetrical curves (TG) monitoring the thermal decomposition of the alkaline earth metal permanganates AE[MnO4]2·n H2O (left) and the X-ray powder diffraction patterns (XRPD) of the final residues (right). Reflections corresponding to orthobixbyite-type α-Mn2O3 are marked with asterisks (*), whereas reflections corresponding to BaMn8O16 with hollandite-type structure are marked with plus signs (+). Additional unidentified reflections belong to recrystallized impurities of no consequence.

2.2 Strontium permanganate trihydrate, Sr[MnO4]2·3 H2O

2.2.1 Crystal structure

Sr[MnO4]2·3 H2O follows the aforementioned trend of decreasing hydration for the heavier homologues of a group of the periodic table and thus has only three water molecules of hydration per formula unit as opposed to four in the calcium compound Ca[MnO4]2·4 H2O and even six in the magnesium permanganate hydrate Mg[MnO4]2·6 H2O [3]. These water molecules are located within the coordination sphere of the Sr2+ cations. Confirming the results of Ferrari et al. from 1966 [6], but with higher accuracy, Sr[MnO4]2·3 H2O crystallizes in the cubic space group P213 (no. 198) with a=964.19(7) pm and four formula units per unit cell (Table 1). All of its cations, as well as two of the crystallographically distinguishable oxygen atoms (O11 and O21) are residing at the fourfold Wyckoff sites 4a, whereas the remaining oxygen atoms (O12, O22, and O3) occupy 12b positions (Table 4). Among these, O3 represents the oxygen atoms of the water molecules, for which we were not able to refine the exact position of their hydrogen atoms. The Sr2+ cation shows a tenfold coordination of oxygen atoms, consisting of three water molecules H2(O3), d(Sr–O3)=262.7(7) pm (3×), and seven terminally coordinated [MnO4] anions with d(Sr–O)=268–279 pm (Table 5 and Fig. 5). Within this coordination sphere, the water molecules H2(O3) form one of the triangular faces of an Edshammar polyhedron, which lies parallel to the triangular basis of the coordination polyhedron for Sr2+, formed by the O22 atoms. One of the two permanganate tetrahedra ([(Mn1)O4], d(Mn1–O)=158–161 pm) contributes all of its corners to [SrO10]18− polyhedra. The oxygen atom O21 in the tetrahedron around (Mn2)7+ (Fig. 6), however, is the only one not participating in the coordination sphere of Sr2+, but is located within the space between three polyhedra around alkaline earth metal cations. Finally, the interatomic distance between O21 and O3, d(O21···O3)=314 pm, suggests a hydrogen bond between a hydrating water molecule H2(O3) and a permanganate anion ([(Mn2)O4], d(Mn2–O)=159–161 pm). All these motifs support the crystal structure of Sr[MnO4]2·3 H2O (Fig. 7), which remains a three-dimensional framework even after the loss of all three water molecules.

Table 4:

Atomic positions and equivalent isotropic displacement parameters for Sr[MnO4]2·3 H2O.

AtomWyckoff sitex/ay/bz/cUeq/pm2
Sr4a0.97883(12)=x/a=x/a352(6)
Mn14a0.23722(19)=x/a=x/a347(9)
Mn24a0.67869(19)=x/a=x/a332(9)
O114a0.1407(9)=x/a=x/a435(37)
O1212b0.2875(8)0.1484(8)0.3660(8)468(22)
O214a0.5825(9)=x/a=x/a592(44)
O2212b0.1628(8)0.1424(8)0.8504(8)396(49)
O312b0.0529(8)0.2106(8)0.5565(8)346(51)
Table 5:

Selected interatomic distances (d/pm) in Sr[MnO4]2·3 H2O.

DistanceDistance
Mn1–O11(1×)161.2(8)Sr–O11(1×)270.3(8)
Mn1–O12(3×)158.4(7)Sr–O12(3×)278.6(7)
Mn2–O21(1×)160.8(8)Sr–O22(3×)267.7(7)
Mn2–O22(3×)159.3(7)Sr–O3(3×)262.7(7)
Fig. 5: Coordination sphere of the Sr2+ cation in Sr[MnO4]2·3 H2O shaped as an Edshammar polyhedron.
Fig. 5:

Coordination sphere of the Sr2+ cation in Sr[MnO4]2·3 H2O shaped as an Edshammar polyhedron.

Fig. 6: The two distinguishable permanganate anions [(Mn1)O4]− (top) and [(Mn2)O4]− (bottom) in the crystal structure of Sr[MnO4]2·3 H2O with coordinating Sr2+ cations. The dashed connection between O21 and O3 illustrates a possible O3–H···O21 hydrogen bond.
Fig. 6:

The two distinguishable permanganate anions [(Mn1)O4] (top) and [(Mn2)O4] (bottom) in the crystal structure of Sr[MnO4]2·3 H2O with coordinating Sr2+ cations. The dashed connection between O21 and O3 illustrates a possible O3–H···O21 hydrogen bond.

Fig. 7: The crystal structure of Sr[MnO4]2·3 H2O viewed along [100].
Fig. 7:

The crystal structure of Sr[MnO4]2·3 H2O viewed along [100].

2.2.2 Thermal decomposition

The TGA of Sr[MnO4]2·3 H2O shows a release of the first two water molecules with a weight loss of 10.7% at 50 and 68°C. The following weight loss of 6.4% at 148°C corresponds to the removal of another water molecule and the crystal structure collapses (Fig. 4, mid left). Finally at 800°C a weight loss of another 7.8% was detected, which corresponds to the release of an oxygen molecule (O2). This leads to a similar result as for the above-mentioned calcium compound, resulting in an amorphous phase (as well as inconsequential impurities), along with crystalline orthobixbyite-type α-Mn2O3 [19] and SrMn3O6 [20] (Fig. 4, mid right).

2.3 Barium permanganate, Ba[MnO4]2

2.3.1 Crystal structure

The crystal structure of Ba[MnO4]2 is already known and was first reported by Hardy and Fourré in 1971 [2] and in later work by our own group [3], [7], but its crystal structure was remeasured and is presented here. Ba[MnO4]2 crystallizes in the orthorhombic space group Fddd (no. 70) with a=742.36(5), b=1191.23(7) and c=1477.14(9) pm and eight formula units per unit cell (Table 1). As mentioned before, Ba[MnO4]2 follows the trend of dehydration of the heavier homologues by crystallizing without any water molecules in its structure (Table 6 and Fig. 8). As a result, the [MnO4] tetrahedra are more strongly involved in the coordination of the Ba2+ cations, resulting in distorted [BaO12]22− icosahedra. Each [MnO4] anion with d(Mn–O)=161–163 pm (Table 7) contributes to a total of five icosahedra with one coordination via an edge and four terminal coordination modes (Fig. 9) with d(Ba–O)=286–295 pm. This compound is the only example of the heavier alkaline earth metal permanganates with a direct connection between the coordination polyhedra of the heavy AE2+ cations, in this case via edges to four other Ba2+-centered icosahedra (Fig. 10).

Table 6:

Atomic positions and equivalent isotropic displacement parameters for Ba[MnO4]2.

AtomWyckoff sitex/ay/bz/cUeq/pm2
Ba8a
171(1)
Mn16f
0.42801(4)
171(1)
O132h0.0763(2)0.90273(13)0.03971(11)249(3)
O232h0.0450(2)0.99455(14)0.39955(12)324(4)
Fig. 8: The crystal structure of Ba[MnO4]2 viewed along [001].
Fig. 8:

The crystal structure of Ba[MnO4]2 viewed along [001].

Table 7:

Selected interatomic distances (d/pm) in Ba[MnO4]2.

DistanceDistance
Mn–O1(2×)162.6(2)Ba–O1(4×)287.4(2)
Mn–O2(2×)160.5(2)Ba–O1′(4×)295.4(2)
Ba–O2(4×)285.7(2)
Fig. 9: Distorted icosahedral coordination of the Ba2+ cations in Ba[MnO4]2 including two edge-wise via O1′ atoms coordinating permanganate anions. The other eight oxygen atoms (O1 and O2) are part of vertex-attached [MnO4]− ligands (not shown here explicitly for clarity).
Fig. 9:

Distorted icosahedral coordination of the Ba2+ cations in Ba[MnO4]2 including two edge-wise via O1′ atoms coordinating permanganate anions. The other eight oxygen atoms (O1 and O2) are part of vertex-attached [MnO4] ligands (not shown here explicitly for clarity).

Fig. 10: Coordination of a [MnO4]− anion in the crystal structure of Ba[MnO4]2 with one Ba2+ cation grafted to an edge and the remaining four being attached terminally.
Fig. 10:

Coordination of a [MnO4] anion in the crystal structure of Ba[MnO4]2 with one Ba2+ cation grafted to an edge and the remaining four being attached terminally.

2.3.2 Thermal decomposition

In contrast to the hydrated permanganates Ca[MnO4]2· 4 H2O and Sr[MnO4]2·3 H2O, Ba[MnO4]2 lacks water and thus shows a different thermal behavior. Whereas the other two compounds resulted in a mixture of AEMn3O6 (AE=Ca and Sr) and orthobixbyite-type α-Mn2O3, Ba[MnO4]2 thermally decomposes at 178°C with a weight loss of 9.5%, which points to little more than a single O2 molecule per formula unit with subsequent collapse of the crystal structure. Up to 800°C another very slow release of 5.5% in weight takes place, corresponding to an additional oxygen atom (Fig. 4, bottom left). This results in a mixture of BaMnO3 [21], BaMn8O16 with hollandite-type structure [22] and again amorphous phases (Fig. 4, bottom right) as a mixed solid residue.

3 Conclusion

In this work we have reevaluated the crystal structures of the alkaline earth metal permanganates AE[MnO4]2·n H2O (AE=Ca, Sr, Ba; n=4, 3, 0). This further supports the general trend in the periodic table to a lower degree of hydration around a cation upon increasing the cation size. For the permanganates of the alkaline earth metals discussed in this work and that of magnesium, the different coordination features of the central AE2+ cations and their respective oxygen ligands of crystal water and/or permanganate groups are summarized in Table 8. We could further demonstrate that the new synthesis method utilizing ion exchange leads to the same products as obtained by established methods and is indeed preferable in those cases, where detours via unstable intermediates were necessary up until now.

Table 8:

Motifs of coordination for the alkaline earth metal permanganates AE[MnO4]2·n H2O (AE=Mg, Ca, Sr, Ba; n=6, 4, 3, 0) with OW noting water ligands and OMn noting oxygen ligands as part of [MnO4] units.

AEnOW/OMnC.N.[MnO4] hapticity
Mg [3]66/060
Ca44/484×1
Sr33/7107×1
Ba00/12122×2 and 8×1

Finally, we have studied the thermal behavior of the three deep purple alkaline earth metal permanganates and found that the presence of water has a marked effect on the final dark brown to black decomposition products. Whereas both water-containing compounds, Ca[MnO4]2· 4 H2O and Sr[MnO4]2·3 H2O, thermally decompose to orthobixbyite-type α-Mn2O3 and the oxomanganates AEMn3O6 (AE=Ca and Sr), the thermal decomposition of Ba[MnO4]2 results in hollandite-type BaMn8O16 and BaMnO3. As intermediates along the decomposition of the hydrated samples, buserite- (AE4Mn14O6(OH)42) [23] and birnessite-type phases (AEMn4O5(OH)6) [23] as layered olation and oxolation products are highly probable. Unfortunately not with our method, but with a treatment described by Suib et al. [11], [12], [13] and Gläser et al. [10] even OMS materials can be synthesized.

4 Experimental section

4.1 Synthesis of Ba[MnO4]2

Ba[MnO4]2 was produced by the method given by Muthmann [1] as described in an earlier work [3]. As an alternative, an ion-exchange column filled with Amberlite® IR-120 (Fluka, Buchs, Switzerland) was loaded with an aqueous BaCl2 solution, and a solution of K[MnO4] in water was passed through this column afterwards. The water of this solution was removed gently with a rotary-evaporator and the product was subsequently dried over silica gel in an evacuated dessicator. It should be mentioned here, that the use of Ba[NO3]2 instead of BaCl2 should be considered, since the latter can lead to a co-crystallization product like BaCl[MnO4] [24] owing to residual Cl anions present in the solution, if the column was not washed properly.

4.2 Synthesis of Ca[MnO4]2·4 H2O and Sr[MnO4]2·3 H2O

Ca[MnO4]2·4 H2O and Sr[MnO4]2·3 H2O were synthesized by first adding an equimolar amount of sulfuric acid to a highly diluted solution of Ba[MnO4]2. Readily precipitated Ba[SO4] was removed by filtration and the remaining solution was neutralized under ice-cooling with aqueous Ca(OH)2 and Sr(OH)2 solutions, respectively. As described above, these compounds were also synthesized via an ion-exchange column by loading the column with aqueous CaCl2 and SrCl2 solutions, respectively, and afterwards passing a solution of K[MnO4] in water through it. Like the barium compound, the water of the solutions was first removed with a rotary-evaporator and subsequently over silica gel in a dessicator.

4.3 X-ray structure determinations

All single-crystal X-ray measurements were conducted on a κ-CCD diffractometer (Bruker-Nonius) utilizing a molybdenum source (λ=71.07 pm). The data sets were interpreted using the Shelxl [15], [16] as well as the Habitus [14] software packages. X-ray powder diffraction measurements were performed on a STADI-P diffractometer (Stoe) equipped with a copper source (λ=154.05 pm) and samples mounted on adhesive films. The diffractograms were further processed with the WinX POW software package by Stoe.

4.4 Thermal decomposition of the compounds

All samples were finely ground before their thermogravimetric analysis performed on a Netzsch STA 449X device with a coupled DSC/TG measuring set-up under argon atmosphere in a corundum crucible. Each sample was heated from 20 to 800°C with a rate of 1°C/min.

Acknowledgments

We would like to thank the Deutsche Forschungsgemeinschaft (DFG, Bonn) for financially supporting this work in the context of the special research topic SFB 706 “Katalytische Selektivoxidationen von C–H-Bindungen mit molekularem Sauerstoff”. Furthermore we are indebted to Dr. Falk Lissner (AOR) for the single-crystal X-ray measurements and to Christof Schneck (CTA) for the thermogravimetric investigations.

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Received: 2017-2-14
Accepted: 2017-3-31
Published Online: 2017-7-22
Published in Print: 2017-8-28

©2017 Walter de Gruyter GmbH, Berlin/Boston

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