PLAT031 Type_4 Check need for Extinction Correction Parameter

This test checks whether a refined extinction parameter is meaningful i.e. whether its value is significantly larger than its corresponding s.u. If not, this parameter should be removed from the model and the structure refined without this meaningless additional parameter. The current default gives a warning when its value is within 3.33 s.u. SHELXL97-2 will not allow negative values leading to ill-convergence and non-zero maximum shift/error values: remove extinction parameter from the refinement.

(http://journals.iucr.org/services/cif/checking/PLAT031.html)

例：PLAT031_ALERT_4_A Refined Extinction Parameter within Range ...... 0.00 Sigma

警告原因：消光系數(shù)誤差較大，系數(shù)值小于3.33倍的誤差，消光系數(shù)無意義。

解決策略：刪除EXTI命令再精修即可。

PLAT032 Type_4 Check s.u. Flack Parameter

Check the validity of the absolute structure determination. A high s.u. indicates that the experimental data do not support the determination of the absolute structure. This will generally be the case with light atom MoKa data where f" is nearly zero.

Note: Use the TWIN & BASF 0.0 instructions in SHELXL97. The default FLACK parameter is not always reliable, in particular when strongly correlated with the position of the origin (e.g. along y in space-group P21). Please refer to Flack, H.D. & Bernardinelli, G. (1999) Acta Cryst. A55, 908-915 and (2000) J. Appl. Cryst., 33, 1143-1148.

(http://journals.iucr.org/services/cif/checking/PLAT032.html)

警告原因：檢查絕對構(gòu)型的確定結(jié)果的正確性。當Flack系數(shù)的誤差值高時表明試驗數(shù)據(jù)無法支持絕對構(gòu)型的確定結(jié)果。一般來說都是由于使用了Mo靶進行衍射試驗且分子中沒有重原子(小于Si元素)，導致誤差值過大。

解決策略：1. 如果有手性且有重原子，那在修正中加入Flack指令，修正后重新產(chǎn)生CIF。

2. 如果沒有手性，或有手性但用Mo靶做僅含小于Si元素的結(jié)構(gòu)，則可將_chemical_absolute_configuration項后面的值改成句點“.”或'unk'(或unknown)。

PLAT033 Type_4 Check Flack Parameter value

Check the relevance/validity of the absolute structure determination. Please refer to Flack, H.D. & Bernardinelli, G. (1999) Acta Cryst. A55, 908-915 and (2000) J. Appl. Cryst., 33, 1143-1148. A value of the Flack parameter that deviates significantly from zero (taking into account the associated s.u.) might indicate that the absolute structure should be inverted in case of a value closer to 1.0 than to zero. A value close to 0.5 may be indicative of an inversion twin or a missed centre of inversion. For valid absolute structure assignments, abs(x) should be less than 2 * s.u., with s.u. < 0.04. For enantiopure compounds, s.u. should be less than 0.1.

(http://journals.iucr.org/services/cif/checking/PLAT033.html)

警告原因：檢查Flack系數(shù)值的正確性，當Flack系數(shù)值遠不為0時可能表明需要將絕對構(gòu)型翻轉(zhuǎn)從而使Flack由1改變?yōu)榻咏?。當Flack系數(shù)值接近0.5時表明該晶體可能為倒反孿晶或者該模型缺失對稱中心。當Flack系數(shù)值小于2倍的誤差值，且誤差值小于0.04時，可以確定絕對構(gòu)型。當為光學純化合物時，誤差值應小于0.1.

解決策略：當Flack系數(shù)值約為1時，可以使用inv –f(Olex2中)命令翻轉(zhuǎn)構(gòu)型。當Flack系數(shù)約為0.5時，可以采用Platon升高空間群或者TWIN指令進行孿晶精修。

PLAT034 Type_1 Check for Flack parameter value specified Z>Si, non-centro

No Flack parameter value given for non-centrosymmetric structure with heaviest atom Z > Si. This might be intentional.

(http://journals.iucr.org/services/cif/checking/PLAT034.html)

警告原因：非中心對稱結(jié)構(gòu)中存在重原子，卻未給出Flack系數(shù)值。

解決策略：一般不會出現(xiàn)，重新精修生成CIF文件即可。

PLAT035 Type_1 Check for _chemical_absolute_configuration

Options are 'rm', 'ad', 'rmad', 'syn', 'unk' or '.'

rm?? : absolute configuration established by the structure determination of a compound containing a chiral reference molecule of known absolute configuration.

ad?? : absolute configuration established by anomalous dispersion effects in diffraction measurements on the crystal.

rmad : absolute configuration established by the structure determination of a compound containing a chiral reference molecule of known absolute configuration and confirmed by anomalous dispersion effects in diffraction measurements on the crystal.

syn? : absolute configuration has not been established by anomalous dispersion effects in diffraction measurements on the crystal. The enantiomer has been assigned by reference to an unchanging chiral centre in the synthetic procedure.

unk? : absolute configuration is unknown, there being no firm chemical evidence for its assignment to hand and it having not been established by anomalous dispersion effects in diffraction measurements on the crystal. An arbitrary choice of enantiomer has been made.

.??? : inapplicable.

(http://journals.iucr.org/services/cif/checking/PLAT035.html)

例：PLAT035_ALERT_1_A No _chemical_absolute_configuration info given . ?

警告原因：空間群為非對稱中心空間群，未給出絕對構(gòu)型確定的方法。確定絕對構(gòu)型的常見方法有如下方式。

rm：絕對構(gòu)型由帶有手性中心的參考分子給出。

ad：絕對構(gòu)型由反常散射效應確定。

rmad：絕對構(gòu)型由參考分子和反常散射共同確定。

syn：未通過反常散射確定，手性中心在合成過程中未發(fā)生改變。

unk：絕對構(gòu)型未知，現(xiàn)有試驗結(jié)果下無法確定絕對構(gòu)型。CIF中構(gòu)型選擇是任意的。

.：不可用。

解決策略：根據(jù)需要選擇絕對構(gòu)型的確定方式，非手性空間群改成句點。手性空間此項后改成ad，非手性空間群改成na。

PLAT036 Type_1 Check for missing Flack Parameter s.u.

No standard uncertainty found for the Flack parameter. When the structure refinement was done with SHELXL97-2, the likely reason for this is a missing BASF instruction. This applies in particular when the associated Flack parameter has the value 0.000. No valid conclusions on the absolute structure can be drawn in that case.

(http://journals.iucr.org/services/cif/checking/PLAT036.html)

警告原因：Flack值未給出誤差，此種情況下絕對構(gòu)型結(jié)果不可信。當采用ShelXL97精修時，可能是缺少了BASF命令，尤其是Flack值為0.000時。

解決策略：一般不會出現(xiàn)，重新精修生成cif文件即可。當使用TWIN指令進行精修時，需要加上BASF指令。

PLAT037 Type_1 Check _diffrn_reflns_theta_full

No information is given about the theta value for which the dataset is complete, subject to the percentage given with the dataname _diffrn_measured_fraction_theta_full.

(http://journals.iucr.org/services/cif/checking/PLAT037.html)

警告原因：CIF中缺少_diffrn_reflns_theta_full項，該項受_diffrn_measured_fraction_theta_full約束。

解決策略：一般不會出現(xiàn)，重新精修生成CIF文件即可。

PLAT038 Type_1 Check _diffrn_measured_fraction_theta_max

This fraction should be specified in combination with the theta value given with the dataname _diffrn_reflns_theta_full.

(http://journals.iucr.org/services/cif/checking/PLAT038.html)

警告原因：CIF中缺少_diffrn_measured_fraction_theta_max值。

解決策略：一般不會出現(xiàn)，重新精修生成CIF文件即可。

PLAT039 Type_1 Check _diffrn_measured_fraction_theta_full

This fraction should be specified in combination with the value for _diffrn_reflns_theta_max.

(http://journals.iucr.org/services/cif/checking/PLAT039.html)

警告原因：cif中缺少_diffrn_measured_fraction_theta_full項。

解決策略：一般不會出現(xiàn)，重新精修生成CIF文件即可。

PLAT040 Type_1 Test for H-atoms [0,1]

Alert for 'no H-atoms' in CIF. This is unusual for carbon containing compounds, but may be correct.

(http://journals.iucr.org/services/cif/checking/PLAT040.html)

警告原因：CIF文件中未找到氫原子。

解決策略：將模型加氫并精修即可。如果結(jié)構(gòu)本身不含氫原子，解釋即可。