Volumetric measure of isostructurality

Abstract

The numerical descriptors of isostructurality are critically reviewed and to overcome their limitations a new volumetric measure is proposed. It is de®ned as the percentage ratio of the overlapping volume of molecules in the analyzed structures to the average of the corresponding molecular volumes. For the calculation of this index a numerical approach is presented, which is also capable of treating disordered structures. The use of isostructurality calculations is demonstrated using a series of examples. Homologous 9-alkylthiophenanthrenes are used as simple illustrations of the necessity and applicability of the new descriptor. The structural changes in the inclusion compounds of 5-methoxysulfadiazine with chloroform, dioxane and tetrahydrofuran are analyzed and rationalized with the aid of isostructurality indices. The diverse relationships among a series of helical tubuland diols cocrystallized with simple phenols are also characterized. The modi®cations in molecular and crystal structures are correlated with the calculated degree of isostructurality.

Halogen bonding and isostructurality in 2,4,6‐tris(2‐halophenoxy)‐1,3,5‐triazines

“…Monovalent iodine-containing organic compounds whose 3D coordinate are determined, are single-component, not disordered, and not polymeric; no errors, no ions, no powder structures, and R <0.10 were a In some cases the F derivative is also reported. Unit cell similarity index, [38], is calculated for isostructural pairs.…”

“…If the corresponding fluoro compound is known then this entry was added to Table 3. The unit cell similarity index, [38], was calculated for pairs of crystal structures. There are 56 crystal structures wherein chloro, bromo, and iodo derivative of the same compound is reported and out of these the fluoro structure is also known in 21 cases.…”

Symmetry-controlled rearrangements in Piedfort Units (PU) of 2,4,6-triaryloxy-1,3,5-triazines

“…It is worth noting that a superposition of the unit cells of POT with a relaxed, and 4-BrPOT with a perfect C 3 symmetry shows isostructurality, although their unit cells and space groups are different. They exemplify homostructurality [1], whereas 4-BrPOT, 4-IPOT (see 'Appendix') and 4-MePOT are perfectly isostructural (their unit cell similarity index [1,5] is P = 0.005).…”

“…These may bring us closer to crystal structure predictions [9]. Bearing this in mind, as a continuation of our research [10,11], the present work aims to shed more light on two questions: (i) what is the limit of a 'high degree' isostructurality which is quantified by the descriptors [5,12] such as P, I i (n) or I v and (ii) what sort of crosswalks link the 3D ? 1D forms of isostructurality (including polymorphism) described by a hypothetical family of compounds and structures.…”

“…Papers report on the isostructurality of homo- [3] or heteromolecular [4] clusters. Parallel to this, there has been an incessant effort to find better algorithms [5][6][7][8][9] to describe the forms of structural similarity. These may bring us closer to crystal structure predictions [9].…”