Refined crystal structure of Ca[B₈O₁₁(OH)₄]—A synthetic calcium analog of strontioborite

Authors: Yamnova, N.; Egorov-Tismenko, Yu.; Zubkova, N.; Dimitrova, O.; Kantor, A.

Source: Crystallography Reports, Volume 50, Number 5, September 2005 , pp. 766-772(7)

Publisher: MAIK Nauka/Interperiodica

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Abstract:

A calcium analog of strontioborite, namely, Ca[B₈O₁₁(OH)₄], is synthesized under hydrothermal conditions (T = 270°C, P = 20 atm) within the framework of the study of the phase formation in the CaCl₂ · Rb₂CO₃ · B₂O₃ system. The crystal structure of the synthetic calcium borate [a = 7.4480(5) Å, b = 8.2627(5) Å, c = 9.8102(6) Å, β = 108.331(1)°, V = 573.09(6) Å³, space group P2₁, Z = 2, ρ_calcd = 2.15 g/cm³; Brucker SMART CCD automated diffractometer, 5506 reflections, λMoK _α] is refined by the least-squares procedure in the anisotropic approximation of thermal atomic vibrations to R ₁ = 0.050. The calcium borate studied has a crystal structure identical to the structure of the natural strontium borate (strontioborite) Sr[B₈O₁₁(OH)₄] and its calcium analog synthesized earlier. The crystal structure is built up of stacks consisting of skeleton layers (formed by boron-oxygen polyanions) and isolated strontium (calcium) polyhedra located in trigonal holes of the skeleton layers. Through channels that can contain H₂O molecules are formed between the stacks. The structure refinement and analysis of the IR spectrum of the synthetic calcium analog of strontioborite do not confirm the previously proposed hypothesis that water molecules are involved in the channels of the structure. A comparative crystal chemical analysis of the calcium borate under investigation and its formula analog, namely, the lead borate Pb[B₈O₁₁(OH)₄], is performed.

Document Type: Research article

DOI: http://dx.doi.org/10.1134/1.2049393

Affiliations: 1: Email: natalia_yamnova@mail.ru

Publication date: 2005-09-01