Temperature-dependent Changes of the Crystal Structure of Li2B4O7

The crystal structure of Li2B4O7 was studied by single crystal X-ray diffraction whilst the substance was cooled down from room temperature to -150 degrees C. The title compound crystallizes in the tetragonal, non-centrosymmetric space group 14(1)cd (no. 110), a = 9.475(5) angstrom (r.t.) c = 10.283(6) angstrom (r.t.) R values for seven different data sets vary from 2.6 to 2.9 %. Low-temperature single crystal examinations were combined with low-temperature powder X-ray diffraction experiments (-189 - +27 degrees C). The results are discussed in comparison with data earlier obtained Lit high temperatures (20 - 500 degrees C). No phase transitions or abrupt changes of the crystal structure were observed. The coordination sphere of the lithium ions is that of a distorted tetrahedron and remains almost unchanged, although the coordination number of the lithium ions decreases slightly with rising temperature, similarly to what was found for LiB3O5. Ail expected rigidity of the boron-oxygen groups was confirmed. The thermal deformations of the [B4O7](2-) framework occur according to the hinge mechanism. This indicates that the LiO4 chains Change their winding oil cooling. which leads to deformations along c.