The crystal structure of a new polymorph of Vitamin B1 has recently been described (Balasubramanian et al., 2006). According to these authors, this is the third polymorphic form of this important biochemical to be identified and they note that `two different forms [were] reported previously' by Kraut & Reed (1962) and Suh et al. (1982); similar statements appear in their Abstract and elsewhere in their text. These statements about the number of polymorphs require careful examination. The reported cell dimensions summarized in Table 1 clearly fall into two groups – firstly Cambridge Structural Database (CSD, Version 1.8; Allen et al., 2002) refcodes THIAMC, THIAMC01 and THIAMC12, and then separately polymorph III (THIAMC13). In the first group, the values of a, b (unique) and unit-cell volume are very similar but the values of β and c differ, as do the assigned space groups. One immediately suspects that revised choices of β and c would give essentially the same unit cells and the same space group for all three members of the first group. This has been confirmed by transforming THIAMC12 to space group P21/c, as shown in Table 1. An alternative but equivalent method of demonstrating the equivalence of the group I structures is via the reduced cells, not reproduced here but given in the CSD. Suh et al. (1982, see p. 116) recognized that they and Kraut & Reed studied the same polymorph. For convenience, we designate the group I structure as the P21/n polymorph and the THIAMC13 structure as the P21/c polymorph; standard designations require knowledge of the thermodynamic relations between the polymorphs.
We note that the differences in cell dimensions for the various independent determinations are far larger than their reported standard uncertainties, suggesting unspecified systematic differences; dehydration (Te et al., 2003) does not appear to provide an explanation. Comparison of torsion angles (Table 2) provides some more information; it is not clear whether the differences in torsion angles for the three examples of group I are due to real structural differences. Te et al. (2003) describe the P21/n polymorph as `a nonstoichiometric solvate, a class of solvates where the water molecules occupy voids in a stable network that does not collapse after dehydration.'
†Also given as THIAMC11 (Suh & Kim, 1982)
|Refcode ||Polymorph designation ||a ||b/β ||c ||Unit cell volume ||Z ||Reported space group ||Reference |
|Group I results |
|THIAMC ||I ||6.99 (1) ||20.59 (2) 114.0 (1) ||12.73 (2) ||1673.8 ||4 ||P21/c ||Kraut & Reed (1962) |
|THIAMC01† ||II ||6.975 ||20.555 98.78 ||11.727 ||1661.16 ||4 ||P21/n ||Suh et al. (1982) |
|THIAMC12 296K ||Not given ||6.9928 (2) ||20.6631 (10) 98.699 (2) ||11.7695 (5) ||1681.0 (2) ||4 ||P21/n ||Te et al. (2003) |
|THIAMC12 reoriented to P21/c || ||6.9928 ||20.6631 114.369 ||12.775 ||1681.0 ||4 ||P21/c || |
|Group II results |
|THIAMC13 173 K ||III ||9.1437 (2) ||7.3438 (2) 92.112 (1) ||24.7447 (6) ||1660.47 (7) ||4 ||P21/c ||Balsubramanian et al. (2006) |
|Refcode ||ϕT τ(C2–N1–C7–C8) ||ϕD τ(N1–C7–C8–C9) ||ϕSα τ(S1–C1–C4–C5) ||ϕSβ τ(C1–C4–C5–O1) ||τ(C7–C8–C9–N2) |
|THIAMC ||170.8 ||76.1 ||103.4 ||53.8 ||176.8 |
|THIAMC01 ||170.6 ||74.8 ||100.8 ||50.6 ||177.2 |
|THIAMC12 ||170.9 ||75.7 ||103.1 ||53.6 ||3.5 |
|THIAMC13 ||179.2 ||79.3 ||24.2 ||63.4 ||176.4 |
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Te, R. L., Griesser, U. J., Morris, K. B., Byrn, S. R. & Stowell, J. G. (2003). Cryst. Growth Design, 3, 997–1004. Web of Science CSD CrossRef CAS
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