Abstract

Sodium copper borate, Na₂Cu₂B₁₂O₂₁21, is a member of the Na2M2B12O (M(II) = Ni, Cu and Co) structure type. It has been synthesized by a solid-state reaction. Single-crystal XRD analysis showed that it crystallizes in the monoclinic system, I 2/a space-group with a = 17.353(1), b = 4.671(1), c = 19.672(1)Å, ß= 101.42(1)^°, Z = 4. The new anhydrous borate shows a 3-D framework crystal structure. It contains a discernible tunnel structure constructed from BO₄ tetrahedra, BO₃ trigonal units and CuO₆ octahedra. Seven-coordinate Na⁺ cations lie in the large tunnels that extend along the b axis. This structural model is validated by the charge distribution (CD) analysis.

Keywords

Na₂Cu₂B₁₂O₂₁, Crystal structure, X-ray diffraction, Charge distribution (CD)