The trigonal polymorph of strontium tetra-borate, β-SrB(4)O(7).

Area of Science:

• Inorganic Chemistry
• Crystal Engineering
• Materials Science

Background:

• Strontium tetraborate (SrB4O7) exists in different polymorphic forms, with distinct structural and physical properties.
• Understanding the atomic arrangement is crucial for predicting material behavior and applications.

Purpose of the Study:

• To elucidate the detailed crystal structure of the beta polymorph of strontium tetraborate (β-SrB4O7).
• To compare the structural characteristics and density of β-SrB4O7 with its alpha polymorph.

Main Methods:

• Single-crystal X-ray diffraction analysis was employed to determine the atomic positions and coordination environments.
• The structural framework was analyzed in terms of the connectivity of boron-oxygen units (BO3 triangles and BO4 tetrahedra).

Main Results:

• The asymmetric unit of β-SrB4O7 contains five Sr atoms, twelve B atoms, and 21 O atoms.
• The structure is built from an equal ratio of BO3 triangles and BO4 tetrahedra, forming linked chains that create a 3D framework with [001] channels.
• Strontium ions (Sr2+) are located within these channels, coordinated by distorted polyhedra.
• The density of β-SrB4O7 is significantly lower than that of α-SrB4O7, which exclusively contains BO4 tetrahedra.

Conclusions:

• The unique 3D framework constructed from mixed borate units in β-SrB4O7 dictates its lower density.
• The arrangement of Sr2+ ions within the framework channels influences the overall structure and properties.