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What information may be obtained from Re-determination of Crystal Structures?

Takashiro Akitsu* and Yuika Onami

What information may be obtained from re-determination of crystal structures? Besides simple reproducibility, what information may be obtained from re-determination of crystal structures? In this commentary, we would like to consider this query based on some examples of re-determination of aqua-cis-(L-valinato) copper (II) complex. As is known well, amino acids have -NH2 and -COOH groups or their charge separated species. In order to coordinate to a Cu2+ ion, they should be synthesized employing a high pH aqueous solvent to bias the equilibrium toward the -COO- side generally. In addition, when two bidentate chelate ligands are coordinated, cis- and trans- structural isomers may be produced potentially. Since the cis-form is kinetically advantageous in general, while the trans-form is a thermodynamically advantageous product. Thus a cis- form may yield in a short time of synthesis quickly. In a study in which both were isolated [1], the cis-form affords a penta-coordinated quadrangular pyramidal geometry having an apical water ligand. Additionally, even in some cases of re-determination, disorder was reported in the amino acid substituent moiety in space group C2 [2-4].