非线性光学晶体3BiCl3·7SC（NH2）2的合成及其转化过程

Synthesis and crystal conversion processes of nonlinear optical crystal 3BiCl3·7SC（NH2）2

针对金属有机配合物非线性光学晶体3BiCl3·7SC(NH2)2(DCBPB)合成过程中伴生BiCl3·3SC(NH2)2(β-BTC)的问题,以硫脲与氯化铋为原料,在甲酸-水体系中研究了溶剂配比、反应温度、反应物配比等因素对DCBPB纯度的影响,对反应条件进行了优化,并基于XRD特征峰面积标准曲线法研究了β-BTC与DCBPB之间的转化过程。结果表明,甲酸抑制氯化铋水解且选择性生成DCBPB,氯化铋与硫脲摩尔配比大于1:3时可选择性生成DCBPB。合成过程先生成β-BTC,再由β-BTC转化为DCBPB,甲酸-水体系中氯化铋水解发生在β-BTC生成过程中,且不可避免,导致基于氯化铋直接合成只能获得最高含量为89.91wt%的DCBPB晶体。β-BTC向DCBPB转化率极高且无水解,可获得DCBPB含量大于98wt%的晶体。

Semi-organic nonlinear optical(NLO) materials attract growing attention due to its balanced properties and potential applications in various fields. Thioureacoordinating metal-organic NLO material is one of the famous semi-organic systems. In our previous work, new 3BiCl3×7SC(NH2)2(DCBPB) NLO crystals which exhibits excellent fluorescence properties and better optical transmission properties than other reported complexes of thiourea and bismuth(Ⅲ) chloride were synthesized. However, during the synthesis of DCBPB, the coexistence of BiCl3·3SC(NH2)2(β-BTC) was found to be difficult to avoid. In order to improve the quality of the synthesized DCBPB crystals, the effects of solvent ratio, reaction temperature, and reagent ratio on the purity of DCBPB using thiourea and bismuth(Ⅲ) chloride as reagents in formic acid-water solvent system were investigated. The results showed that formic acid not only depressed the hydrolysis of bismuth(Ⅲ) chloride, but also improved the selectivity of DCBPB. A high selectivity of DCBPB could be achieved when the molar ratio of bismuth(Ⅲ) chloride to thiourea was larger than 1:3. The reaction temperature shouldn′t exceed 50℃ to avoid side reactions. The optimization of the synthesis indicated that the hydrolysis of bismuth(Ⅲ) chloride was inevitable and the highest purity of DCBPB was 89.91 wt%. A two-step mechanism of DCBPB synthesis was found which included the formation of β-BTC and the conversion of β-BTC to DCBPB. Furthermore, the conversion between β-BTC and DCBPB in formic acid aqueous solution was investigated based on XRD characteristic peak area correlation. The results showed that β-BTC almost completely converted to DCBPB and no hydrolysis of bismuth(Ⅲ) was detected during the conversion, a high purity of more than 98 wt% was achieved via conversion of β-BTC to DCBPB in formic acid.