离子液体1-仲丁基-3-甲基咪唑六氟磷酸盐的微波辅助合成、晶体结构及热稳定性

以具有支链结构的溴代仲丁烷作为烷基化试剂, 在微波辐射下采用两步法合成了1-仲丁基-3-甲基咪唑六氟磷酸盐(s-bmim]PF₆])离子液体. 在配比为V(水)∶V(乙醇)∶V(甲苯)=0.16∶2.84∶7的混合溶剂体系中, 培养出晶型完整的长约11 mm的离子液体大单晶体. 通过单晶体X衍射研究了s-bmim]PF₆]的晶体结构. s-bmim]PF₆]属于三斜立方晶系, 空间群为P2(1)/m, 晶胞参数为a=0.9042(4) nm, b=0.8213(3) nm, c=0.9775(4) nm, γ=116.618°(6), Z=2, V=64.909(4) nm³, D_c=1.454 g/cm³, μ=0.265 mm^-1, F(000)=292. 在s-bmim]PF₆]晶体结构中, 阴阳离子间的离子键仍然是主要的, 同时还存在氢键和阳离子-阳离子间的非键斥力作用. 研究结果表明, s-bmim]PF₆]的支化烷基结构对其晶体有效堆积、熔点、液程范围以及热分解温度等性质具有重要影响.

Microwave-Assisted Synthesis, Crystal Structure and Thermal Stability of Ionic Liquid 1-sec-Butyl-3-methylimidazolium Hexfluorophosphate

In this paper, 1-sec-butyl-3-methylimidazolium hexfluorophosphate(s-bmim]PF6]) was synthesized with the aid of microwave. Large single crystals were formed in the water-ethanol-toluene systemV(water)∶V(ethanol)∶V(toluene)=0.16∶2.84∶7]. The large single crystals are stable under the air and moisture, with the maximum length of 11 mm. The crystal structure was determined by X-ray diffraction. s-bmim]PF6] crystallizes in the monoclinic space group P21/m, with unit-cell parameters a=0.9042(4) nm, b=0.8213(3) nm, c=0.9775(4) nm, γ=116.618°(6), Z=2, V=64.909(4) nm3, Dc=1.454 g/cm3, μ=0.265 mm-1, F(000)=292, the final R=0.0998, wR=0.2656. In the structure, the cations and anions can not form neutral ion pairs owing to the interionic interactions such as the dominant Coulombic attraction, the weak hydrogen bonds and the non-chemical-bond tension of cation-cation. Moreover, it was found that introducing the sec-butyl chain could change the asymmetry of cations and inhibit the rotation of the alky chains of s-bmim]PF6]. The branched structure leads to the void space filling in the crystal stacking and high lattice energy. Finally, the thermal stability of s-bmim]PF6] was discussed.