X射线粉末衍射从头晶体结构测定: [Co(NH~3)~5Br]Br~2 配合物的晶体结构

总结了粉末衍射从头晶体结构测定中的问题与对策,并采用常规X射线粉末衍射数据,从头测定了配合物Co(NH~3)~5Br]Br~2的晶体结构。在指标化与分峰基础上,采用直接法获得含7个独立非H原子的粗结构。在10°～80°(2θ)范围内用3500个强度数据对38个参数作Rietveld精修,得到了Co(NH~3)~5Br]Br~2的晶体结构。其晶胞参数为a=1.3692(1)nm,b=1.0707(1)nm,c=0.6940(1)nm,V=1.0175(1)nm^3,Z=4。空间群:Pnma,品质因子:M~2~0=49,F~3~0=93(0.0075,43),结构吻合因子:R~p=0.066,R~w~p=0.090,R~F=0.041,R~B=0.042。

Ab initio structure determination using conventional X-ray powder diffraction: The crystal structure of [Co(NH~3)~5Br]Br~2

The crystal structure of Bromopentamminocobalt bromide (Co(NH~3) ~5Br]Br~2) has been ab initio determined from the X-ray powder diffraction data collected on a Rigaku D/MAX-rB diffractometer. The pattern was auto indexed using the trial-error and the successive- dichotomy methods. The orthorhombic unit cell and the possible space group according to extinction conditions were obtained. 329 integrated intensities were extracted by whole pattern fitting. The approximate structure with all 7 independent non-H atoms was solved by direct methods followed by interactive cycles of least-squares refinement and Fourier syntheses. The following Rietveld refinement was carried out over the angular range of 10°～80°(2θ) with 3495 intensities step and 45 parameters. The final orthorhombic unit-cell parameters are: a=1.3692(1)nm, b=1.0707(1)nm, c=0.6940(1)nm, V=1.0175 (1)nm^3, M~2~0=49, F~3~0=93(0.0075, 43), Z=4. Space group is Pnma. The structure agreement factors are: R~p=0.066, R~w~p=0.090, R~F=0.041, R~B=0.042. In this paper, the crucial steps, the difficuties and the authors' practical experience in ab initio powder diffraction crystal structure determination methods were summed up.