【求助】审稿意见中碰到的flack参数相关的问题
本人有两个晶体,解析完了以后flack参数分别是0.691(18)和0.50(2),platon检测报告有C类提示,分别是:
(1)STRVA01_ALERT_4_C Flack test results are ambiguous.
From the CIF: _refine_ls_abs_structure_Flack 0.691
From the CIF: _refine_ls_abs_structure_Flack_su 0.018
(2)STRVA01_ALERT_4_C Flack test results are ambiguous.
From the CIF: _refine_ls_abs_structure_Flack 0.500
From the CIF: _refine_ls_abs_structure_Flack_su 0.020
但审稿人提出了如下意见:
In the Cc non-centrosymmetric space group with heavy atom like Pb, one should
expect to be able to determine reliably the absolute structure, which is not the
case in this manuscript. In both structures, the value of the Flack parameter is
0.69 and 0.50 respectively with a rather large su. This large su is certainly
related to the merging of reflections in the 2/m point group which is incorrect.
The data should have been merged in the 2 point group.
In any case, the compounds are obviously twinned by inversion and this important
characteristic has been completely missed by the authors.
审稿人认为su值偏大,但我觉得应该是不大啊。另外,按照 审稿人的意见,采用2 点群重新合并数据后的flack参数基本上没有什么变化,不知道有什么问题?
谢谢指教! 返回小木虫查看更多
重新处理数据吧,那个等效点合并是错误的。
参数分别是0.691(18)和0.50(2),这样的数据根本定不了绝对构型。审稿人没有毙你,你已经很幸运了。
1. 对于需要确认绝对构型的结构是不要合并Friedel mates。
2. 这么大的Flack参数,必然是racemic twin。换句话说就是绝对构型无法确认。
既然绝对构型无法确认,那么是不是合并或者不合并Friedel mates都没有什么区别了呢
,
如果是手性空间群,最好不要合并Friedel mates。这样得到的flack参数才有意义。“flack参数有意义”并不是说能确定绝对构型。Racemic twin也是其意义的一种表现。