#
M[B_{2}(SO_{4})_{4}] (M = Mn, Zn)—Syntheses and Crystal Structures of Two New Phyllosilicate Analogue Borosulfates

^{1}

^{2}

^{*}

## Abstract

**:**

_{2}∙4H

_{2}O with boric acid in oleum (65% SO

_{3}), we obtained single-crystals of Mn[B

_{2}(SO

_{4})

_{4}] (monoclinic, P2

_{1}/n, Z = 2, a = 8.0435(4), b = 7.9174(4), c = 9.3082(4) Å, β = 110.94(1)°, V = 553.63(5) Å

^{3}) and Zn[B

_{2}(SO

_{4})

_{4}] (monoclinic, P2

_{1}/n, Z = 2, a = 7.8338(4), b = 8.0967(4), c = 9.0399(4) Å, β = 111.26(1)°, V = 534.36(5) Å

^{3}). The crystal structures reveal layer-like anionic networks with alternating vierer- and zwölfer-rings formed exclusively by corner-linked (SO

_{4})- and (BO

_{4})-tetrahedra.

## 1. Introduction

_{4})-tetrahedra and is still a fascinating field of research for scientists from different disciplines. Friedrich Liebau is one of the pioneers in silicate chemistry and introduced a classification in 1985 [1]. According to this classification, silicates can be assigned to different classes: Nesosilicates reveal exclusively isolated (SiO

_{4})-tetrahedra. Isolated anionic moieties of corner-shared (SiO

_{4})-tetrahedra are predominant in sorosilicates. The anionic substructures of cyclosilicates contain ring-like anionic moieties of corner-shared (SiO

_{4})-tetrahedra with a Si:O ratio of 1:3. Inosilicates are formed by infinite anionic chains or bands. If the anionic network branches in two dimensions phyllosilicates occur, which reveal infinite anionic layers. Last but not least, silicates with 3D network like structures are called tectosilicates. The function of all previously introduced silicates is mostly related to their respective crystal structures, as well as the dimensionality of the anionic substructures [2,3,4,5].

_{4})- and (BO

_{4})-tetrahedra [12,13,14,15,16,17,18,19,20,21,22,23,24,25] or (SO

_{3}Cl)- and (BO

_{4})-tetrahedra [26,27,28] is suitable. The structural variety of neat borosulfates covers sorosilicate, inosilicate, phyllosilicate, and tectosilicate analogue materials. Furthermore, borosulfates can overcome Pauling’s rules, which is manifested by the formation of anionic substructures with S–O–S, as well as B–O–B bridges, like in M[B(S

_{2}O

_{7})

_{2}] (M = Li, Na, K, NH

_{4}) [20,21,24], M[B(SO

_{4})(S

_{2}O

_{7})] (M = Cs, H) [21] B

_{2}S

_{2}O

_{9}[22], or M

_{4}[B

_{2}O(SO

_{4})

_{6}] (M = Mn, Co, Ni, Zn) [23], to mention just a few examples.

_{3}[20,21,23,24]. However, up to now we have no evidence for the decisive factors leading to the different dimensionalities of the anionic subunits. The most prominent representatives are 0D and 1D compounds like soro- and inosilicate analogues, if we exclude compounds with S–O–S and B–O–B bridges. 2D and 3D materials are only rarely observed. Li[B(SO

_{4})

_{2}] [24] is the sole example of a borosulfate with an extended 3D network with exclusively S–O–B bridges, and phyllosilicate analogue substructures are only found for CaB

_{2}S

_{4}O

_{16}[18] and Mg[B

_{2}(SO

_{4})

_{4}] [25].

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}], with phyllosilicate analogue substructure, charge compensated by divalent subgroup metals, obtained from solvothermal synthesis in SO

_{3}-enriched sulfuric acid.

## 2. Results and Discussion

_{3}-enriched sulfuric acid in evacuated and torch sealed glass ampoules at elevated temperature (see Materials and Methods). Mn[B

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}] crystallize in the monoclinic space group P2

_{1}/n with a = 8.0435(4), b = 7.9174(4), c = 9.3082(4) Å, β = 110.94(1)° for Mn[B

_{2}(SO

_{4})

_{4}] and a = 7.8338(4), b = 8.0967(4), c = 9.0399(4) Å, β = 111.26(1)° for Zn[B

_{2}(SO

_{4})

_{4}] (see Table 1 and X-ray crystallography for further data and details according the refinement). The crystal structures exhibit layer-like anionic subunits of vertex-shared (BO

_{4})- and (SO

_{4})-tetrahedra (Figure 1) charge compensated by the respective divalent counter cations Mn

^{2+}and Zn

^{2+}. Each (BO

_{4})-tetrahedron is coordinated by four different (SO

_{4})-tetrahedra via common corners, whereas for each (SO

_{4})-tetrahedron two oxygen atoms remain terminal. The Niggli formula for the anionic substructure of both borosulfates can be described as ${}_{\infty}{}^{2}\left\{{\left[\mathrm{B}{\left({\mathrm{SO}}_{4}\right)}_{4/2}\right]}^{-}\right\}$. The B–O bond lengths range from 1.440(1) to 1.485(1) Å for Mn[B

_{2}(SO

_{4})

_{4}] and from 1.449(1) to 1.482(1) Å for Zn[B

_{2}(SO

_{4})

_{4}]. With about 1.52 Å, the S–O bonds within the S–O–B bridges are significantly elongated compared to the terminal or cation coordinating S–O bonds. The latter fall in the region between 1.4125(7) to 1.4427(7) Å for Mn[B

_{2}(SO

_{4})

_{4}] and 1.4135(7) to 1.442(7) Å for Zn[B

_{2}(SO

_{4})

_{4}].

_{4})-tetrahedra. For Mn[B

_{2}(SO

_{4})

_{4}], the O–S1–O angles range from 96.18(3) to 116.59(5)°, and the O–S2–O angles range from 102.84(3) to 116.23(4)°. The comparable tetrahedra in Zn[B

_{2}(SO

_{4})

_{4}] reveal angles between 97.64(3) to 116.16(4)° for O–S1–O and 104.18(3) to 115.70(4)° for O–S2–O. The deviations are less drastic for the (BO

_{4})-tetrahedra. These values range from 105.67(6) to 114.05(7)° and from 101.24(6) to 114.58(6)° for Mn[B

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}], respectively (a full list of bond lengths and angles with symmetry operators is given in the Supplementary Materials under Tables S3, S4, S7, and S8).

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}] are very similar. Both reveal twelve-membered (zwölfer) and four-membered (vierer) rings of vertex-shared (BO

_{4})- and (SO

_{4})-tetrahedra (Figure 2, top). Each zwölfer ring is surrounded by six further zwölfer rings. Two of those six are opposite to another and are aligned along the crystallographic b-axis. Each one shares two common (BO

_{4})-tetrahedra with the zwölfer ring. The common (BO

_{4})-tetrahedra are linked via two separate (SO

_{4})-tetrahedra, whereas each is part of one of the two zwölfer rings. As a result, a vierer ring is formed. The other four zwölfer rings share a common (BO

_{4})(SO

_{4})(BO

_{4})-fragment and spread the network along the ac-diagonal, thereby creating a phyllosilicate analogue anionic layer. Each layer is terminated exclusively by (SO

_{4})-tetrahedra (Figure 2, top). However, similarities to the borophosphates also occur. With a B:P ratio <1, compounds with condensed [B(PO

_{4})

_{4}]

^{9−}anions occur. In this form, highly charged P

^{5+}cations are located within the network as far away from each other as possible [29,30]. In the title compounds, the situation is similar. The highly charged sulfur atoms are in the center of the (SO

_{4})-tetrahedra, coordinated to the low charged boron cations forming repetitive [B(SO

_{4})

_{4}] blocks.

^{2+}and Zn

^{2+}cations. They are packed in a stacked manner parallel to the crystallographic b-axis in the middle of the channels running through the anionic substructures. The cations are exclusively located within the center of the zwölfer rings. They are coordinated by four of their terminal oxygen atoms of (SO

_{4})-tetrahedra and two oxygen atoms of terminal (SO

_{4})-tetrahedra belonging to the anionic layers above and underneath (Figure 3). Besides B

_{2}S

_{2}O

_{9}, a neutral vertex-shared (BO

_{4})-(SO

_{4})-network structure, only two rather similar structures are known, namely CaB

_{2}S

_{4}O

_{16}and Mg[B

_{2}(SO

_{4})

_{4}]. Formally, the same sum formula occurs for our new borosulfates and the known compounds. Furthermore, CaB

_{2}S

_{4}O

_{16}and Mg[B

_{2}(SO

_{4})

_{4}] also exhibit zwölfer and vierer rings similarly to Mn[B

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}]. However, the positions of the cations with respect to the anionic layers are different. Mn[B

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}] are the first representatives with the charge compensating cations exclusively in the center of the zwölfer rings. In CaB

_{2}S

_{4}O

_{16}and Mg[B

_{2}(SO

_{4})

_{4}], the respective cations are located above and underneath the zwölfer rings within the interlayer.

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}] are also not isotypical. Due to the differently rotated tetrahedra within the asymmetric unit, a structural aberration occurs between the anionic substructures of Mn[B

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}] (Figure 4), whereas the octahedral oxygen coordination to the metal cations remains. Focusing on one central zwölfer ring in both borosulfates, the adjoining vierer rings are almost congruent. The main differences occur in the tetrahedra, forming the common (BO

_{4})(SO

_{4})(BO

_{4})-edges to the next zwölfer rings. Especially strong rotated are the (S1O

_{4})-tetrahedra.

## 3. Materials and Methods

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}]: MnCl

_{2}∙4H

_{2}O (133 mg (0.67 mmol), Fluka, Seelze, Germany) or ZnO (55 mg (0.68 mmol), Merck, Darmstadt, Germany) were loaded together with H

_{3}BO

_{3}(300 mg (4.85 mmol), Carl Roth, Karlsruhe, Germany), and 1 mL oleum (65% SO

_{3}, Merck, Darmstadt, Germany) into a thick-walled glass ampoule (l = 300 mm, ∅ = 16 mm, thickness of the tube wall = 1.8 mm), respectively. The ampoules were torch sealed under reduced pressure (0.01 mbar), and placed into a block-shaped resistance furnace and heated up to 523 K within 150 min. The temperature was maintained for 48 h and finally reduced to 298 K within 96 h. A large number of colorless block-shaped crystals were obtained for both borosulfates (Figures S1 and S2), and the yield was quantitative for ZnO and almost quantitative for MnCl

_{2}∙4H

_{2}O. The latter suffered from small impurities of (H

_{3}O)[B(SO

_{4})

_{2}] (see X-ray crystallography). The crystals are very moisture sensitive and decompose immediately after exposure to air. Thus, the products were handled under strictly inert conditions.

**Caution**: Oleum is a strong oxidizer, which needs careful handling. During and even after the reaction, the ampoules might be under remarkable pressure. It is mandatory to cool down the ampoules using liquid nitrogen prior to opening.

_{2}(measurement temperature see Table 1) inside the diffractometer (Bruker D8 Quest κ, Bruker, Karlsruhe, Germany). After unit cell determination, the reflection intensities were collected. Structure solutions and refinements were conducted using the SHELX program package [31].

_{4}and dried under reduced pressure before the measurement. To fill a capillary with a solid sample was impossible due to small amounts of adhesive solvent. Finally, a flat sample was irradiated with Ge(111)-monochromatized Mo-Kα

_{1}-radiation (λ = 0.7093 Å), which was detected using a Dectris Mythen 1K detector (Dectris AG, Baden-Daettwil, Germany). Due to the fast decomposition of the sample holder matrix, the measurement had to be conducted with a scan range from 2 to 41.9°, with a step size of 2.1° and step time of 11 s. Rietveld refinement was accomplished using TOPAS4.2 [32]. Refined lattice parameters based on powder data: Mn[B

_{2}(SO

_{4})

_{4}] a = 8.082(4) Å, b =7.942(3) Å, c = 9.288(8) Å, β = 110.84(7)°, V = 557.24(4) Å

^{3}; Zn[B

_{2}(SO

_{4})

_{4}] a = 7.883(5) Å, b = 8.095(3) Å, c = 9.034(2) Å, β = 111.21(9)°, V = 537.45(8) Å

^{3}. An amount of 11.3% (H

_{3}O)[B(SO

_{4})

_{2}] could be detected as a byproduct of Mn[B

_{2}(SO

_{4})

_{4}] (Figure 5). Differences in the intensities of the experimental and simulated powder patterns might be due to preferred orientations of the crystalline material on the flat sample holder.

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}]: The crystal structures of Mn[B

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}] were solved in the monoclinic space group P2

_{1}/n. The heavy atom positions were determined by SHELXT-2014/5 [33] using Direct Methods. Further atoms could be successfully located by difference Fourier techniques during refinement with SHELXL-2017/1 [34]. Multi-scan absorption correction was applied to the data using the program SADABS-2014/5 by Bruker [35]. Finally, the structure and model of Mn[B

_{2}(SO

_{4})

_{4}] were refined to R

_{1}(all data) = 0.0271 and wR

_{2}(all data) = 0.0553 and for Zn[B

_{2}(SO

_{4})

_{4}] to R

_{1}(all data) = 0.0186 and wR

_{2}(all data) = 0.0468. Selected bond lengths and angles are presented in the Tables S3, S4, S7 and S8.

_{2}(SO

_{4})

_{4}] and CSD number 1958830 for Zn[B

_{2}(SO

_{4})

_{4}] contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from FIZ Karlsruhe via www.ccdc.cam.ac.uk/structures.

## 4. Conclusions

_{3}and boric acid in evacuated torch-sealed glass ampoules seem to be a powerful strategy to synthesize borosulfates with layer-like anionic substructures of divalent metals. As can be seen from this and our previous publications, not only the main group but also subgroup metals can be charge-compensating cations. In comparison to Mg[B

_{2}(SO

_{4})

_{4}] and CaB

_{2}S

_{4}O

_{16}, Mn[B

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}] are the first representatives of layer-like borosulfates with the cations residing in the plane of the anionic network and the center of zwölfer rings. However, it is still unclear why cations with a comparable atomic radius like Zn

^{2+}and Mg

^{2+}act differently. This problem is currently under investigation using quantum chemical calculations.

## Supplementary Materials

_{2}(SO

_{4})

_{4}] and Mn[B

_{2}(SO

_{4})

_{4}] under a polarisation microscope; Table S1: Fractional atomic coordinates (×10

^{4}) and equivalent isotropic displacement parameters (Å

^{2}× 10

^{3}) for Mn[B

_{2}(SO

_{4})

_{4}]; Table S2: Anisotropic displacement parameters (Å

^{2}× 10

^{3}) for Mn[B

_{2}(SO

_{4})

_{4}]; Table S3: Bond lengths for Mn[B

_{2}(SO

_{4})

_{4}]; Table S4: Bond angles for Mn[B

_{2}(SO

_{4})

_{4}]; Table S5: Fractional atomic coordinates (×10

^{4}) and equivalent isotropic displacement parameters (Å

^{2}× 10

^{3}) for Zn[B

_{2}(SO

_{4})

_{4}]; Table S6: Anisotropic displacement parameters (Å

^{2}× 10

^{3}) for Zn[B

_{2}(SO

_{4})

_{4}]; Table S7: Bond lengths for Zn[B

_{2}(SO

_{4})

_{4}]; Table S8: Bond angles for Zn[B

_{2}(SO

_{4})

_{4}]; the CIF and the checkCIF output files of Mn[B

_{2}(SO

_{4})

_{4}] and Zn[B

_{2}(SO

_{4})

_{4}].

## Author Contributions

## Funding

## Acknowledgment

## Conflicts of Interest

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**Figure 1.**Left: Asymmetric unit of Mn[B

_{2}(SO

_{4})

_{4}]. The thermal ellipsoids are set on a 90% probability level. Selected bond lengths [Å]: S1–O11 1.4427(7), S1–O12 1.4125(7), S1–O111 1.5263(6), S1–O112 1.5229(6), S2–O21 1.4333(6), S2–O22 1.4298(6), S2–O121 1.5240(6), S2–O122 1.5218(6), B1–O111 1.443(1), B1–O112 1.440(1), B1–121 1.483(1), B1–O122 1.485(1) (Symmetry operators

^{1}1−x,−y,1−z;

^{2}1/2+x,1/2−y,1/2+z;

^{3}1/2−x,−1/2+y,1/2−z;

^{4}3/2−x,1/2+y,1/2−z;

^{5}1−x,1−y,1−

_{Z}); Right: Asymmetric unit of Zn[B

_{2}(SO

_{4})

_{4}]. The thermal ellipsoids are set on a 90% probability level. Selected bond lengths [Å]: S1–O11 1.4442(7), S1–O12 1.4135(7), S1–O111 1.5247(6), S1–O112 1.5315(6), S2–O21 1.4329(6), S2–O22 1.4277(6), S2–O211 1.5116(6), S2–O212 1.5116(6), B1–O111 1.458(1), B1–O112 1.449(1), B1–O211 1.477(1), B1–O212 1.482(1) (Symmetry operators

^{1}1−x,−y,1−z;

^{2}−1/2+x,1/2−y,−1/2+z;

^{3}3/2−x,−1/2+y,3/2−z;

^{4}3/2−x,1/2+y,1/2−z;

^{5}1−x,1−y,1−z).

**Figure 2.**

**Top**: Top view of the infinite anionic layer of vertex-shared (BO

_{4})- and (SO

_{4})-tetrahedra in the structure of Mn[B

_{2}(SO

_{4})

_{4}]. The layers are constructed of zwölfer and vierer rings. Each zwölfer ring is coordinated to four vierer rings and six zwölfer rings. The layers are terminated exclusively by (SO

_{4})-tetrahedra;

**Bottom**: Side view of an infinite anionic layer. The charge compensating Mn

^{2+}-cations reside within the zwölfer rings. The interspace between the different anionic layers is free of cations or intercalating molecules.

**Figure 3.**The Mn

^{2+}cations are coordinated octahedrally by three crystallographically different oxygen atoms. Four of the six coordinating oxygen atoms belong to the terminal (SO

_{4})-tetrahedra of the equatorially surrounding layer, two originate from the terminal (SO

_{4})-tetrahedra above and underneath. Bond lengths [Å]: Mn1–O11

^{1}2.1388(7), Mn1–O21

^{1}2.2276(6), Mn1–O22

^{2}2.1400(6) (Symmetry operators

^{1}1−x,−y,1−z;

^{2}1/2+x,1/2−y,1/2+z).

**Figure 4.**Differently rotated zwölfer rings around Zn

^{2+}and Mn

^{2+}in the structures of M[B

_{2}(SO

_{4})

_{4}] (M = Mn, Zn).

**Figure 5.**Rietveld refinement plot for experimental and calculated data of M[B

_{2}(SO

_{4})

_{4}] (M = Mn, Zn). In the case of Mn[B

_{2}(SO

_{4})

_{4}], about 11.3% of (H

_{3}O)[B(SO

_{4})

_{2}] can be refined as a byproduct. Different intensities of experimental and calculated plots might result from the preferred orientation of the crystallites on the flat sample holder. Refined lattice parameters: Mn[B

_{2}(SO

_{4})

_{4}] a = 8.082(4) Å, b = 7.942(3) Å, c = 9.288(8) Å, β = 110.84(7)°, V = 557.24(4) Å

^{3}; Zn[B

_{2}(SO

_{4})

_{4}] a = 7.883(5) Å, b = 8.095(3) Å, c = 9.034(2) Å, β = 111.21(9)°, V = 537.45(8) Å

^{3}.

Sum formula | Mn[B_{2}(SO_{4})_{4}] | Zn[B_{2}(SO_{4})_{4}] |
---|---|---|

Formula weight | 460.80 | 471.23 |

Temperature/K | 173(2) | 183(2) |

Crystal system | monoclinic | monoclinic |

Space group | P2_{1}/n | P2_{1}/n |

a/Å | 8.0435(4) | 7.8338(4) |

b/Å | 7.9174(4) | 8.0967(4) |

c/Å | 9.3082(4) | 9.0399(4) |

β/° | 110.94(1) | 111.26(1) |

Volume/Å^{3} | 553.63(5) | 534.36(5) |

Z | 2 | 2 |

ρ_{calc}/g/cm^{3} | 2.764 | 2.929 |

μ/mm^{−1} | 2.052 | 3.189 |

F(000) | 454 | 464 |

Crystal size/mm^{3} | 0.07 × 0.055 × 0.03 | 0.5 × 0.3 × 0.11 |

Radiation | Mo-Kα_{1} (λ = 0.71073) | Mo-Kα_{1} (λ = 0.71073) |

2Θ range for data collection/° | 5.76 to 82.54 | 5.91 to 78.95 |

Index ranges | −14 ≤ h ≤ 14, −14 ≤ k ≤ 14, −17 ≤ l ≤ 17 | −14 ≤ h ≤ 13, −14 ≤ k ≤ 14, −16 ≤ l ≤ 16 |

Reflections collected | 58531 | 26941 |

Independent reflections | 3710 [R_{int} = 0.0417, R_{sigma} = 0.0169] | 3202 [R_{int} = 0.0278, R_{sigma} = 0.0151] |

Data/restraints/parameters | 3710/0/106 | 3202/0/107 |

Goodness-of-fit on F^{2} | 1.078 | 1.110 |

Final R indexes [I ≥ 2σ(I_{o})] | R_{1} = 0.0209, wR_{2} = 0.0534 | R_{1} = 0.0168, wR_{2} = 0.0460 |

Final R indexes [all data] | R_{1} = 0.0271, wR_{2} = 0.0553 | R_{1} = 0.0186, wR_{2} = 0.0468 |

Largest diff. peak/hole/eÅ^{−3} | 0.48/−0.61 | 0.64/−0.46 |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Pasqualini, L.C.; Huppertz, H.; Bruns, J.
*M*[B_{2}(SO_{4})_{4}] (*M* = Mn, Zn)—Syntheses and Crystal Structures of Two New Phyllosilicate Analogue Borosulfates. *Inorganics* **2019**, *7*, 145.
https://doi.org/10.3390/inorganics7120145

**AMA Style**

Pasqualini LC, Huppertz H, Bruns J.
*M*[B_{2}(SO_{4})_{4}] (*M* = Mn, Zn)—Syntheses and Crystal Structures of Two New Phyllosilicate Analogue Borosulfates. *Inorganics*. 2019; 7(12):145.
https://doi.org/10.3390/inorganics7120145

**Chicago/Turabian Style**

Pasqualini, Leonard C., Hubert Huppertz, and Jörn Bruns.
2019. "*M*[B_{2}(SO_{4})_{4}] (*M* = Mn, Zn)—Syntheses and Crystal Structures of Two New Phyllosilicate Analogue Borosulfates" *Inorganics* 7, no. 12: 145.
https://doi.org/10.3390/inorganics7120145