Synthesis, crystal structure, and spectrum properties of a new borate Ba4K2Zn5(B3O6)3(B9O19) with two isolated types of blocks: 3[3Δ] and 3[2Δ + 1T] + 3Δ + 3[2Δ + 1T]

• Ba4K2Zn5(B3O6)3(B9O19) has been synthesized by high-temperature solution reaction.
• It has a layered structure consisting of ZnO4 tetrahedra, [B3O6]3− rings, and [B9O19]11− groups.
• The IR spectrum confirmed the presence of both BO3 and BO4 groups.
• UV–vis diffuse reflectance spectrum revealed a band gap of about 3.18 eV.
• Solid-state fluorescence spectrum shows a broad emission band at about 515.8 nm.

A new barium potassium zincoborate, Ba4K2Zn5(B3O6)3(B9O19), 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 P21/n (No. 14) with cell parameters of a = 7.1620(14) Å, b = 38.772(8) Å, c = 12.360(3) Å, β = 90.26(3)°, V = 3432.2(12) Å3, and Z   = 4. It has a new structure type that features two-dimensional [Zn5(B3O6)3(B9O19)]∞210− anionic layers composed of ZnO4 tetrahedra, [B3O6]3− rings with notation of 3[3Δ], and [B9O19]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 Ba2+, K+, or Ba2+/K+ cations to compensate the negative charges of the layers. Infrared spectrum was measured, which confirms the presence of both BO3 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.

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