Daniela Vitzthum, Michael Schauperl, Klaus R. Liedl and Hubert Huppertz

High-pressure synthesis and crystal structure of In3B5O12

De Gruyter | 2017

Abstract

Orthorhombic In3B5O12 was synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 12.2 GPa and 1500°C. Its structure is isotypic to the rare earth analogs RE3B5O12 (RE=Sc, Er–Lu). In the field of indium borate chemistry, In3B5O12 is the third known ternary indium borate besides InBO3 and InB5O9. The crystal structure of In3B5O12 has been determined via single-crystal X-ray diffraction data collected at room temperature. It crystallizes in the orthorhombic space group Pmna with the lattice parameters a=12.570(2), b=4.5141(4), c=12.397(2) Å, and V=703.4(2) Å3. IR and Raman bands of In3B5O12 were theoretically determined and assigned to experimentally recorded spectra.

1 Introduction

Borates show a vast structural diversity due to the ability of boron to form planar BO3 groups, BO4 tetrahedra, as well as various combinations of these two building blocks. Applying high pressure offers even greater synthesis possibilities by obtaining thermodynamically metastable compounds. Over the last few decades, our group has combined the field of borate chemistry and high-pressure chemistry, which has led to numerous new borates containing cations across the whole periodic table. Neumair et al. and Sohr et al. investigated alkali metal borates and found the new high-pressure phases HP-LiB3O5 [1], HP-Na2B4O7 [2], HP-KB3O5 [3], HP-RbB3O5 [4], HP-CsB5O8 [5], and HP-Cs1−x (H3O)x B3O5 (x=0.5–0.7) [6], as well as the pseudo alkali metal borate HP-(NH4)B3O5 [7]. Furthermore, the field of transition metal borates was explored by our group, leading to the new compounds HP-MB2O4 (M=Cd, Ni) [8], [9], β-MB4O7 (M=Mn–Zn) [10], [11], [12], and M6B22O39·H2O (M=Fe, Co, Cd) [13], [14]. The isotypic series α-RE2B4O9 (RE=Sm–Ho) [15], [16], β-RE2B4O9 (RE=Dy, Gd) [17], [18], RE4B6O15 (RE=Dy, Ho) [19], [20], and RE3B5O12 (RE=Sc, Er–Lu) [21], [22] are just a few examples of the rare earth high-pressure borates we found.

Recently, we succeeded in the synthesis of an indium compound isotypic to the rare earth phases RE3B5O12 (RE=Sc, Er–Lu). In In3B5O12, the In3+ ions show an eight-fold coordination, which is quite uncommon. Since In3+ forms a distorted square antiprism in this structure, its ionic radius is comparable to those of the rare earth cations in RE3B5O12, making this formation possible. In3B5O12 is now the third known compound in the system In–B–O besides the well-known indium orthoborate InBO3 [23] and the only vaguely described compound InB5O9, which appears through dehydration of H2InB5O10 [24].

In the following, the synthesis and crystal structure of In3B5O12 are described in detail. Furthermore, IR and Raman vibrations of the title compound were calculated and recorded experimentally.

2 Experimental section

2.1 Synthesis

Regarding phase purity, the best synthesis results could be achieved with a mixture of 31.70 mg In2O3 (99.9%, ChemPUR, Karlsruhe, Germany) and 27.97 mg H3BO3 (99.5%, Carl Roth, Karlsruhe, Germany), which corresponds to an In:B ratio of 1:2. The batch was ground in an agate mortar and encapsulated in gold foil before being transferred into a crucible made of α-BN (Henze Boron Nitride Products AG, Kempten, Germany). The synthesis was carried out in a Walker-type multianvil apparatus (Voggenreiter, Mainleus, Germany) containing a 14/8 assembly. Details of the setup can be found in the literature [25], [26], [27]. For the synthesis program, first a pressure of about 12.2 GPa was built up in 334 min, and then the heating process was started. Within 8 min, a temperature of 1500°C was achieved. After 2 min at 1500°C, the electric current flow collapsed, so we stopped the heating process, which led to a quenching of the sample to ambient temperature. Subsequently, a 16-h decompression process was started. Although the melting point of gold increases dramatically under such pressure conditions, when examining the synthesis product, we found that the gold capsule was melted into a compact gold sphere, which presumably caused the breakdown of the heating. The reaction product appeared as a clean white powder and the color of the normally white BN crucible was significantly darker. Even though the BN crucible had to play a part in the reaction because of its color change, syntheses without the gold foil mainly led to InBO3. If the gold foil was replaced by metals with a higher melting point such as platinum or molybdenum, primarily InBO3 as well as elemental indium or yet unidentified byproducts occurred.

Concerning the ratio of the starting materials, when a stoichiometric ratio according to eq. 1 was used, only InBO3 was obtained. An excess of boron and H3BO3 instead of B2O3 as a starting material apparently supported the formation of In3B5O12. The synthesis of In3B5O12 was reproducible; however, to date, we were not able to obtain the compound phase pure.

(1) 3 In 2 O 3 + 5 B 2 O 3 2 In 3 B 5 O 12

2.2 X-ray structure determination

The reaction product was analyzed with a Stoe Stadi P powder diffractometer equipped with a Mythen 1K detector (Dectris, Switzerland). The measurement was carried out with Ge(111)-monochromatized MoKα1 radiation (λ=70.93 pm) in transmission geometry across a 2θ range of 2°–60°. In Fig. 1, the experimental powder pattern is compared with the calculated pattern derived from single-crystal data of In3B5O12. Aside from some yet unidentified reflections (marked with asterisks), the patterns are in good accordance. In total, we were able to index and refine 101 reflections of the experimental powder diffractogram [28]. The obtained lattice parameters fit well with those derived from single-crystal data (see Table 1).

Fig. 1: Powder diffraction pattern of the reaction product (top) compared to a simulation of a powder pattern of In3B5O12 based on single-crystal data (bottom). The reflections marked with an asterisk refer to an unidentified byproduct.

Fig. 1:

Powder diffraction pattern of the reaction product (top) compared to a simulation of a powder pattern of In3B5O12 based on single-crystal data (bottom). The reflections marked with an asterisk refer to an unidentified byproduct.

Table 1:

Crystal data and structure refinement of orthorhombic In3B5O12.

Empirical formula In3B5O12
Molar mass, g mol−1 590.50
Crystal system Orthorhombic
Space group Pmna (no. 53)
Powder data
 Powder diffractometer Stoe Stadi P
 Radiation MoKα1 (λ=70.93 pm)
a, Å 12.573(2)
b, Å 4.5154(3)
c, Å 12.380(2)
V, Å3 702.78(7)
Single-crystal data
 Single-crystal diffractometer Bruker D8 Quest Kappa
 Radiation MoKα (λ=71.073 pm)
a, Å 12.570(2)
b, Å 4.5141(4)
c, Å 12.397(2)
V, Å3 703.4(2)
Formula units per cell Z 4
Calculated density, g cm−3 5.58
Crystal size, mm3 0.18×0.09×0.05
Temperature, K 299(2)
Detector distance, mm 40
Exposure time 0.5 s per frame, 8 s per frame
Absorption coefficient, mm−1 9.9
F(000), e 1072
θ range, deg 2.3–32.5
Range in hkl ±19; ±6; ±18
Reflections total/independent 19 909/1326
Rint 0.0361
Reflections with I>2σ(I) 1239
Rσ 0.0130
Data/ref. parameters 1326/101
Absorption correction Multiscan
Final R1/wR2 [I>2σ(I)] 0.0151/0.0544
Final R1/wR2 (all data) 0.0167/0.0561
Goodness-of-fit on Fi2 0.859
Largest diff. peak/hole, e Å−3 0.80/−0.61

The colorless crystals of In3B5O12 were examined with a polarization contrast microscope and a suitable single crystal was isolated for X-ray measurements on a Bruker D8 Quest diffractometer equipped with a Photon 100 CMOS detector. The data were collected under ambient conditions and a multiscan absorption correction was performed with Sadabs 2014/5 [29]. For the structure solution and parameter refinement, the Shelxs/l-2013 [30], [31] software implemented in the program Wingx-2013.3 [32] was used. The structure data were standardized employing Structure tidy [33] as implemented in Platon [34] (version 170613). All atoms could be refined with anisotropic displacement parameters. Details of the data collection can be found in the synoptical Table 1. The positional parameters, anisotropic displacement parameters, interatomic distances, and angles are listed in Tables 25 . Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (fax: +49-7247-808-666; e-mail: crysdata@fiz-karlsruhe.de) on quoting the deposition number CSD-431955 for In3B5O12.

Table 2:

Wyckoff positions, atomic coordinates, and equivalent isotropic displacement parameters Ueq2) of In3B5O12.

Atom Wyckoff position x y z Ueq
In1 8i 0.13633(2) 0.48899(2) 0.19355(2) 0.00520(7)
In2 4f 0.36851(2) 1/2 0 0.00406(8)
B1 8i 0.2011(2) 0.0364(4) 0.6503(2) 0.0041(3)
B2 4h 0 0.0346(6) 0.1294(3) 0.0071(4)
B3 4h 0 0.0384(6) 0.3534(2) 0.0050(4)
B4 4e 0.1631(2) 0 0 0.0050(4)
O1 8i 0.09439(9) 0.1590(3) 0.64270(9) 0.0058(2)
O2 8i 0.09611(9) 0.1623(3) 0.07547(9) 0.0068(2)
O3 8i 0 0.1953(2) 0.56332(9) 0.0062(2)
O4 8i 0.29533(9) 0.2821(3) 0.15306(8) 0.0046(2)
O5 4h 0 0.1949(3) 0.2403(2) 0.0051(3)
O6 4h 0 0.2654(4) 0.4327(2) 0.0057(3)
O7 4h 0 0.7241(4) 0.1422(2) 0.0054(3)
O8 4g 1/4 0.8284(3) 1/4 0.0055(3)

Ueq is defined as one third of the trace of the orthogonalized Uij tensor (standard deviations are in parentheses).

Table 3:

Anisotropic displacement parameters (Uij in Å2) of In3B5O12.

Atom U11 U22 U33 U12 U13 U23
In1 0.0034(2) 0.0050(2) 0.0072(2) −0.00021(3) −0.00142(3) −0.00093(3)
In2 0.0034(2) 0.0045(2) 0.0043(2) 0 0 0.00028(4)
B1 0.0045(8) 0.0032(6) 0.0047(8) 0.0010(6) 0.0004(5) −0.0009(5)
B2 0.007(2) 0.007(2) 0.007(2) 0 0 −0.0001(9)
B3 0.003(2) 0.0047(9) 0.008(2) 0 0 0.0004(7)
B4 0.004(2) 0.008(2) 0.003(2) 0 0 0.0003(6)
O1 0.0029(5) 0.0035(5) 0.0111(5) −0.0004(4) −0.0010(4) 0.0005(4)
O2 0.0029(4) 0.0101(5) 0.0075(5) −0.0001(4) 0.0009(4) −0.0046(4)
O3 0.0074(5) 0.0052(5) 0.0060(5) 0.0006(4) 0.0038(4) 0.0009(4)
O4 0.0043(5) 0.0038(5) 0.0057(5) 0.0004(4) 0.0001(3) −0.0001(3)
O5 0.0051(7) 0.0051(6) 0.0053(7) 0 0 0.0001(5)
O6 0.0045(6) 0.0071(7) 0.0054(7) 0 0 −0.0023(5)
O7 0.0030(6) 0.0046(7) 0.0087(7) 0 0 0.0008(5)
O8 0.0080(7) 0.0042(6) 0.0042(6) 0 0.0033(5) 0

Standard deviations are in parentheses.

Table 4:

Interatomic distances (Å) in In3B5O12.

In1–O7 2.114(2) In2–O6 2.133(2) 2× B1–O4 1.438(2) B3–O6 1.420(3)
In1–O2 2.139(2) In2–O3 2.307(2) 2× B1–O1 1.454(3) B3–O1 1.485(2) 2×
In1–O8 2.209(2) In2–O4 2.327(2) 2× B1–O8 1.510(2) B3–O5 1.569(3)
In1–O5 2.244(2) In2–O1 2.391(2) 2× B1–O3 1.524(2) ØB3–O 1.490
In1–O4 2.262(2) ØIn2–O 2.290 ØB1–O 1.482
In1–O4 2.286(2)
In1–O3 2.486(2) B2–O7 1.411(3) B4–O2 1.456(2) 2×
In1–O1 2.631(2) B2–O2 1.497(2) 2× B4–O3 1.488(2) 2×
ØIn1–O 2.296 B2–O5 1.554(4) ØB4–O 1.472
ØB2–O 1.490

Standard deviations are in parentheses. Bold values are average values.

Table 5:

Interatomic angles (°) in In3B5O12.

O8–B1–O3 100.0(2) O2–B2–O5 102.5(2) 2×
O1–B1–O3 105.1(2) O2–B2–O2 107.7(2)
O1–B1–O8 105.9(2) O7–B2–O5 111.3(2)
O4–B1–O8 111.9(2) O7–B2–O2 115.7(2) 2×
O4–B1–O1 114.3(2) ØO–B2–O 109.2
O4–B1–O3 118.1(2)
ØO–B1–O 109.2
O1–B3–O1 106.1(2) O3–B4–O3 105.0(2)
O6–B3–O5 107.1(2) O2–B4–O3 108.11(7) 2×
O1–B3–O5 107.4(2) 2× O2–B4–O2 109.4(2)
O6–B3–O1 114.2(2) 2× O2–B4–O3 113.11(6) 2×
ØO–B3–O 109.4 ØO–B4–O 109.5

Standard deviations are in parentheses. Bold values are average values.

2.3 Vibrational spectroscopy

The FTIR-ATR (attenuated total reflection) spectra of a powder sample of the above-described reaction product were recorded. A Bruker Alpha-P spectrometer (Bruker, Billerica, USA) equipped with a 2×2 mm diamond ATR crystal and a deuterated triglycine sulfate (DTGS) detector was used. In a spectral range of 400–4000 cm−1, 320 scans of the sample were recorded and afterward corrected for atmospheric influences employing the Opus 7.2 software [35].

Raman spectroscopy was performed on an In3B5O12 single crystal using a Labram-HR 800 Raman microspectrometer (Horiba Jobin Yvon, Tulln, Austria) equipped with an Olympus 100× objective lens and a 1024×256 open-electrode charge-coupled device detector. The sample was excited with the 532-nm emission line of a frequency-doubled 100 mW Nd:YAG laser with a spot surface of about 1 μm in diameter. For the dispersion of the scattered light, an optical grating with 1800 lines mm−1 was used. After a quick scanning up to 4000 cm−1 to exclude any vibrations that could be assigned to water or other components, a detailed spectrum was recorded in a range of 100–1300 cm−1 with a spectral solution of about 0.6 cm−1. The measurements were performed under ambient conditions and a correction of the background was applied [36].

2.4 Density functional theory calculations

In addition to the experimental vibrational spectra, density functional theory (DFT) calculations of IR and Raman bands with the program Crystal14 [37], [38] were performed. The geometry of the obtained crystal structure was optimized. IR and Raman frequencies of the resulting structure were calculated within the harmonic approximation at the Γ-point. For the calculation of the exchange and correlation contributions, the frequently used B3lyp [39], [40], [41] hybrid functional was used. For oxygen and boron atoms all electron basis sets were chosen [42]. As a compromise between accuracy and speed, an effective core potential for indium was applied [42].

3 Results and discussion

3.1 Crystal structure

Orthorhombic In3B5O12 crystallizes in the space group Pmna and is isotypic to the rare earth borates RE3B5O12 (RE=Sc, Er–Lu) [21], [22]. In comparison to the scandium compound, the lattice of In3B5O12 with parameters of a=12.570(2), b=4.5141(4), c=12.397(2) Å, and a volume of V=703.4(2) Å3 is larger, but smaller than the rare earth pentaborates. A comparison of the different lattice parameters, cell volumes, and metal ionic radii is given in Table 6. Figure 2 illustrates the coherence of the ionic radii and the lattice parameters a, b, and c of In3B5O12 and all known phases RE3B5O12 (RE=Sc, Er–Lu). Like the other isotypes, In3B5O12 was formed under high-pressure conditions and contains only boron atoms with a coordination number of 4, as one would expect for high-pressure compounds. All BO4 tetrahedra are connected through their corners to three (Q3) or four (Q4) other BO4 tetrahedra forming a network consisting of vierer-, fünfer-, and achter-rings [45] in the ac plane (see Fig. 3). Viewed along b, the indium atoms are located in the middle of the fünfer- and achter-rings but are positioned in a height of ½ b (as can be seen in Fig. 4). Compared to the crystal structure data of the isotypic compounds, the unit cell is shifted by [0½0] because we standardized our data employing Structure tidy [33].

Table 6:

Comparison of the lattice parameters (Å), volumes (Å3), and ionic radii (eight-fold coordination) (Å) [43], [44] of In3B5O12 and its isotypes RE3B5O12 (RE=Sc, Er–Lu).

Compound a b c V r (M3+)
In3B5O12 12.570(2) 4.5141(4) 12.397(2) 703.4(2) 1.06
Sc3B5O12 12.454(3) 4.4346(9) 12.221(2) 675.0(2) 1.010
Er3B5O12 12.846(2) 4.619(2) 12.513(2) 742.4(2) 1.144
Tm3B5O12 12.820(3) 4.6019(9) 12.477(3) 736.1(3) 1.134
Yb3B5O12 12.774(3) 4.5864(9) 12.451(3) 729.5(3) 1.125
Lu3B5O12 12.765(2) 4.575(2) 12.442(2) 726.6(2) 1.117
Fig. 2: Illustration of the coherence of the ionic radii and the lattice parameters. All metal cations reveal an oxidation state of 3+.

Fig. 2:

Illustration of the coherence of the ionic radii and the lattice parameters. All metal cations reveal an oxidation state of 3+.

Fig. 3: Crystal structure of In3B5O12 viewed along [010]. The BO4 tetrahedra are either Q3-bonded (blue) or Q4-bonded (turquoise).

Fig. 3:

Crystal structure of In3B5O12 viewed along [010]. The BO4 tetrahedra are either Q3-bonded (blue) or Q4-bonded (turquoise).

Fig. 4: Crystal structure of In3B5O12 viewed along [100]. The BO4 tetrahedra are either Q3-bonded (blue) or Q4-bonded (turquoise). The indium atoms (yellow) are positioned in the middle of these tetrahedral layers.

Fig. 4:

Crystal structure of In3B5O12 viewed along [100]. The BO4 tetrahedra are either Q3-bonded (blue) or Q4-bonded (turquoise). The indium atoms (yellow) are positioned in the middle of these tetrahedral layers.

There are two crystallographically distinguishable In3+ positions in In3B5O12, which are coordinated by eight oxygen atoms each, forming two distorted square antiprisms (Fig. 5). The In–O distances vary between 2.114 and 2.631 Å and average out to 2.293 Å, which is somewhat larger than the average value of 2.18 Å for indium in octahedral coordination, as anticipated for eight-fold coordinated In3+ [46]. Corresponding to the size of the unit cell, the B–O distances in In3B5O12 are shorter than the B–O distances in the rare earth containing compounds (RE=Er–Lu) with average values of 1.484 vs. 1.494 (Er and Tm), 1.489 (Yb), and 1.492 Å (Lu) [22]. Sc3B5O12 shows average B–O distances of 1.479 Å for the smallest tetrahedra of all these isotypes [21]. Although the B–O–B angles vary between 100.0° and 118.1° in In3B5O12, they average out to a suitable tetrahedral angle of 109.3°.

Fig. 5: Edge-sharing InO8 square antiprisms in In3B5O12.

Fig. 5:

Edge-sharing InO8 square antiprisms in In3B5O12.

To evaluate and support the crystal structure refinement, bond valence sums and Maple values (MAdelung Part of Lattice Energy) [47], [48], [49] have been calculated. Table 7 shows the charge distribution in In3B5O12, calculated with the bond-length/bond-strength [50], [51] and the Chardi [52], [53] concepts, which both provide reasonable values. These results also confirm the oxidation state of 3+ for all indium cations in the title compound, which could be expected as there was no reducing compound present during the synthesis. In fact, it would be highly interesting to synthesize a borate with indium in a lower oxidation state, which will be one of our topics in future investigations. On the basis of Maple values, the new phase In3B5O12 was compared with the hypothetical compound “In3B5O12” obtained by the addition of the Maple values for In2O3 [54] and B2O3 [55] according to eq. 1. The comparison showed a discrepancy of only 0.33% (see Table 8).

Table 7:

Charge distribution in In3B5O12, calculated with the bond-length/bond-strength (ΣV) and Chardi (ΣQ) concept.

In1 In2 B1 B2 B3 B4 O1
ΣV 3.00 2.91 2.98 2.93 2.93 3.05 − 1.94
ΣQ 2.93 3.08 3.06 2.84 3.03 3.07 −1.94
O2 O3 O4 O5 O6 O7 O8
ΣV −2.03 −1.93 −1.88 −1.99 −1.95 −2.03 −2.25
ΣQ −2.09 −1.83 −1.92 −1.95 −2.06 −2.24 −2.19
Table 8:

Comparison of the calculated Maple value of In3B5O12 and the calculated Maple value received from the starting compounds In2O3 (corundum type) and HP-B2O3 according to the reaction equation: 3In2O3+5B2O3→2In3B5O12.

Calculated Maple value for In3B5O12, kJ mol−1 157 429
Calculated Maple value from the two educt compounds, kJ mol−1 157 943
Difference, % 0.33

3.2 Vibrational spectroscopy

The experimentally observed IR and Raman peaks were assigned based on DFT calculations. The irreducible representation of In3B5O12 yielded 240 possible vibrational modes (see eq. 2).

(2) Γ = 31 A g + 29 B 1g + 32 B 2 g + 28 B 3 g + 26 A u + 34 B 1 u + 27 B 2 u + 33 B 3 u

As the title compound has a center of symmetry, none of the observed vibrations can be Raman and IR active, due to the rule of mutual exclusion. Therefore, all modes with gerade (g) symmetry are Raman active. Vibrations with irreducible representation (B1u, B2u, B3u) are IR active, whereas all vibrations with symmetry Au are neither IR nor Raman active. Furthermore, one of each BXu (X=1, 2, 3) modes is acoustic, resulting in a total of 91 IR active vibrations and 120 Raman active modes. The experimental IR spectrum, recorded from a powder sample, is shown in the range between 400 and 4000 cm−1 (see Fig. 6) to confirm that the structure does not contain any water. It resembles the spectrum of the isotypic compound Yb3B5O12 except for the difference that the spectrum of In3B5O12 does not exhibit peaks above 1150 cm−1, which were assigned to impurities from a phase containing BO3 groups in the IR spectrum of Yb3B5O12 [22]. Figure 7 shows the experimentally observed single-crystal Raman spectrum in the range of 100–1300 cm−1 in combination with the calculated Raman band positions. Based on the analysis of the relative motions of atoms for each mode, the main vibrations were assigned. Below 400 cm−1 mainly stretching and bending movements of In–O bonds are present. In the range of 350 and 850 cm−1, the main contributions arise from bending modes of the BO4 tetrahedra. Above 700 cm−1, stretching motions of B–O bonds are found. Further analysis revealed that a distinction of Q4- and Q3-bonded borate groups in the vibrational spectra of In3B5O12 is not possible.

Fig. 6: IR spectrum of an In3B5O12 powder sample.

Fig. 6:

IR spectrum of an In3B5O12 powder sample.

Fig. 7: Experimental Raman spectrum of an In3B5O12 single-crystal and calculated band positions.

Fig. 7:

Experimental Raman spectrum of an In3B5O12 single-crystal and calculated band positions.

4 Conclusions

This report contains a detailed discussion of the synthesis and crystal structure of the new borate In3B5O12 containing eight-fold coordinated indium atoms. Furthermore, IR and Raman spectra of the title compound were experimentally recorded and their vibrational bands assigned based on DFT calculations. With the successful synthesis of In3B5O12, the series of isotypic rare earth compounds with the composition RE3B5O12 (RE=Sc, Er–Lu) could be expanded by a main group element containing phase. In3B5O12 is now the third known compound in the system In–B–O.

Acknowledgments

Special thanks go to Dr. Klaus Wurst for the recording of the single-crystal data set and Dr. Bastian Joachim for the Raman measurements. The computational results presented have been achieved in part using the HPC infrastructure of the University of Innsbruck.

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