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zleyre

新虫 (小有名气)

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虫号: 2013314
注册: 2012-09-19
专业: 原子簇化学

[求助] 求解单晶，内详已有1人参与

金币不多，如能帮忙，另作他谢
审稿人的意见如下：
Compounds 3 and 4 were almost certainly assigned the wrong space group. The correct space group appears to be the centrosymmetric group P-1 (No. 2), not P1 (No. 1). The structure determinations are not acceptable in P1. There are poor ring geometries, strange C-C distances, abnormally non-planar six-membered rings and an obvious inversion center between the two molecules in P1. The refinement of the compound 3 dataset used 1282 restraints versus only 1173 data! Most restraints seem to have been applied to the Uij values of the displacement parameters, to prevent non-positive definite 'ellipsoids'. This is a direct consequence of the falsely low symmetry reported by the authors. For compound 4, the refinement did not reach convergence. The maximum refined parameter shift/error value is very large, 2.72. This is another effect of refining in a space group with incorrectly low symmetry. The authors clearly encountered some difficulty in solution and refinement, but these
details are not fully reported in the MS.

Data should be re-refined in the centrosymmetric space group P-1 (No. 2) and resubmitted. Alternatively, the authors should provide good reasons for adopting P1 over P-1. It would also be preferable to collect low-temperature data for 3 and 4, as was done for compound 2.

Compounds 3 and 4 can be easily transformed from P1 to P-1 with the ADDSYM-SHELX function in PLATON. The metal and Si atomic positions transform to:

Compound 3:
Mo1 0.46691  0.20722  0.65915
Si1 1.00290  0.93210  0.75930
Si2 0.73890  0.33280  0.07460

Compound 4:
W1    0.46735 -0.29233  0.65856
Si1 0.73650 -0.16862  0.07409
Si2 1.01150  0.43295  0.76276

from which the rest of the structure can be built up. Additional disorder of TIPS groups may be observed but they are already disordered and a centrosymmetric description is preferred, as shown by the refinement instabilities evident in the CIFs.

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