In1.4B3O5.6(OH)1.4, tetragonal, P4̄21m (no. 113), a = 6.6969(9) Å, c = 4.4865(9) Å, V = 201.21(7) Å3, Z = 2, Rgt(F) = 0.0117, wRref(F2) = 0.0297, T = 293(2) K.
|Size:||0.138 × 0.110 × 0.040 mm3|
|Wavelength:||Mo Kα radiation (λ = 0.71073 Å)|
|Diffractometer, scan mode:||Bruker D8 Quest Kappa, Φ and ω-scans|
|2θmax, completeness:||37.9°, >99%|
|N(hkl)measured, N(hkl)unique, Rint:||12876, 595, 0.0372|
|Criterion for Iobs, N(hkl)gt:||Iobs > 2σ(Iobs), 595|
|Programs:||SHELX [1, 2] , WinGX , Diamond |
|Atom||Wyckoff||S.O.F.||x||y||z||Ueq (Uiso for H1)|
In2O3 (99.9%, ChemPUR, Karlsruhe, Germany) and H3BO3 (99.5%, Carl Roth, Karlsruhe, Germany) were weighed in to an In:B ratio of approximately 1:2, then ground and enwrapped in molybdenum foil. Subsequently, the sample was prepared for a typical high-pressure multi-anvil experiment , , . As soon as the maximum pressure of about 12.2 GPa was attained, the heating process started. 1500 °C was reached in 8 min, held for 6 min, then the heating was slowly downregulated to 1100 °C in 40 min. After the following decompression, the sample was freed from its surroundings revealing colorless crystals.
For the refinement, the acentric, achiral, tetragonal space group P4̄21m was chosen (Flack-Parsons parameter = 0.056(7) based on 235 quotients ). The hydrogen atom H1 was positioned via DFIX option of the SHELX system. A refinement with a higher occupancy factor for H1 up to 0.5 and a corresponding reduction of the In ratio to 0.5 leading to the sum formula InB2O5(OH)2 is possible but results in higher R values, GOOF and residual electron density.
By means of high-pressure synthesis, it was possible to obtain another borate compound that adopts the melilite structure. Melilite denominates a group of sorosilicates with the sum formula (Ca,Na)2(Mg,Al)1(Si,Al)2O7  although a variety of different minerals and synthetic compounds with the general constitution X2ZT2A7 (X = large cations, T and Z = smaller, tetrahedrally coordinated cations, A = anions) are counted among the melilite-family. As in the recently published first ternary melilite-type borate Sc1.67B3O7 , in In1.2B3O5.6(OH)1.4 the Z and T positions are both occupied by boron atoms, which thus center Q3 as well as Q4 tetrahedra. In the ab plane, two Q4 and three Q3 tetrahedra are corner-linked to five-membered rings resulting in a flat borate layer. Between these parallel layers in the center of the five-membered rings, the square antiprismatically coordinated indium atoms are located. Due to charge neutrality reasons, the atom sites of the formally 3+ charged indium atoms cannot be fully occupied. Empty antiprisms give space to the hydrogen atoms in In1.2B3O5.6(OH)1.4, which were determined with a site occupancy factor of 0.35.
We thank Dr. Gunter Heymann and Dr. Klaus Wurst for the recording of and the support with the single-crystal data.
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