Synthesis, crystal structure, and spectrum properties of a new borate Ba_4K_2Zn_5(B_3O_6)_3(B_9O_(19)) with two isolated types of blocks: 3[3Δ] and 3 [2Δ + 1T] + 3Δ + 3[2Δ + 1T]

摘要

A new barium potassium zincoborate, Ba_4K_2Zn_5(B_3O_6)_3(B_9O_(19)), has been synthesized by high-temperature solution reaction at 750 °C. Its crystal structure was established by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2i (No. 14) with cell parameters of a = 7.1620(14) A, b = 38.772(8) A, c = 12.360(3) A, /? = 90.26(3)°, V = 3432.2(12) A3, and Z = 4. It has a new structure type that features two-dimensional ~2_∞ [Zn_5(B_3O_6)_3(B_9O_(19))]~(10-) anionic layers composed of ZnO_4 tetrahedra, [B_3O_6]~(3-) rings with notation of 3[3Δ], and [B_9O_(19)]~(11-) groups with notation of 3 [2Δ + 1T] + 3Δ + 3[2Δ + 1T], where Δ and T represent BO3 triangles and BO4 tetrahedra, respectively. The zinc borate anionic layers stack along b-axis, with the intralayer open channels and interlayer void spaces filled by Ba~(2+), K~+, or Ba~(2+)/K~+ cations to compensate the negative charges of the layers. Infrared spectrum was measured, which confirms the presence of both BO_3 and BO4 groups. The optical properties were investigated in terms of diffuse reflectance and fluorescence spectra, which reveal an optical band gap of 3.18 eV as well as a broad emission band at around 515.8 nm upon laser excitation at 325 nm.