Synthesis, crystal structure, and optical properties of a novel pentaborate, K2NaZnB5O10

A novel quaternary borate, dipotassium sodium zinc pentaborate. K2NaZnB5O10, has been prepared by high-temperature solution reaction at temperature below 780 C. Single-crystal XRD analyses showed that it crystallizes in the monoclinic C2/c group with a = 7.9244 (16) angstrom, b = 12.805 (3) angstrom, c = 18.962 (4) angstrom, beta = 99.39 (3)degrees, z = 8. The crystal structure is composed of double ring [B5O10](5-) and tetrahedral ZnO4 groups that are linked to form a two-dimensional (2)infinity [ZnB5O10](3-) layer by sharing O vertices. The layers are stacked along the c-axis, with the interlayer void spaces filled by K+ and intralayer open channels occupied by Na+ cations to balance charge. The IR spectrum further confirmed the presence of both BO3 and BO4 groups, UV-vis diffuse reflectance spectrum showed a band gap of about 3.1 eV. Solid-state fluorescence spectrum was also investigated exhibiting the maximum emission peak at around 387.4 nm. Band structure calculations indicated that the compound is an indirect semiconductor with the calculated band gap close to the observed one. (C) 2009 Elsevier B.V. All rights reserved.