Abstract
As described in the Introduction, we became interested in the existing literature for the crystallization behavior of (±)-[Co(en)3]I3·H2O and the absolute configuration of its enantiomers because of our project on the historical sequence of chemical studies leading Werner to formulate his Theory of Coordination Chemistry. In so doing, we discovered a number of interesting facts, including the possibility that the published “Pbca” structure of the (±)-[Co(en)3]I3·H2O was incorrect, and that it really crystallizes as a kryptoracemate in space group P212121. Other equally interesting facts concerning the crystallization behavior of [Co(en)3]I3·H2O are detailed below, together with an explanation why Platon incorrectly selects, in this case, the space group Pbca instead of the correct choice, P212121. As for the Flack parameter, (±)-[Co(en)3]I3·H2O provides an example long sought by Flack himself – a challenging case, differing from the norm. For that purpose, data sets (for the pure enantiomer and for the racemate) were collected at 100 K with R-factors of 4.24 and 2.82%, respectively, which are ideal for such a test. The fact that Pbca is unacceptable in this case is documented by the results of Second-Harmonic Generation experiments. CCDC nos: 1562401 for compound (I) and 1562403 for compound (II).
Acknowledgments
We thank Dr. Janusz Grebowitz for his running the samples at high temperature on the DSC and for his interpretation of the results of that experiment. The authors also acknowledge support by NSF-CRIF Grant No. 0443538 for part of the purchase of the X-ray diffractometer. L. Zhao acknowledges the support by NSF CAREER Grant No. DMR-1749774 and AFOSR YIP Grant No. FA9550-21-1-0065.We also thank Dr. Trevor Tyson from NJIT for his meaningful, astute discussions, and suggestions regarding this project.
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Author contributions: K.S., I.B. & R.A.L. were responsible for the preparation and X-ray studies; X.G. & L.Z. were responsible for the SHG measurements. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
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Research funding: There was no external funding for this research.
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Conflict of interest statement: The authors declare that no conflicts of interest regarding this article.
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Ethical approval: All ethical guidelines have been adhered.
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Supplementary Material
The online version of this article offers supplementary material (https://doi.org/10.1515/zkri-2022-0044).
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