Conformations of calix[4]arenes — an investigation based on CSD data. Part I. Cone conformers of methylene- and heteroatom-bridged calix[4]arenes

Abstract

Conformations of calix[4]arenes -an investigation based on CSD data. Part I. Cone conformers of methylene-and heteroatom-bridged calix[4]arenesConformations of calix[4]arenes with methylene and heteroatom bridges from the Cambridge Structural Database (CSD) were investigated with the help of the previously introduced parameters α, β and δ. The usefulness of these parameters in describing the conformations of the scaffolds of the above mentioned compounds was demonstrated. The dependence of the values of these parameters on inter-and/or intramolecular interactions present in the structure was investigated in order to discover how the geometry of the calix[4]arene moiety depends on the above listed effects. Structures with C 4v symmetry in the cone group have both β and δ close to 0°. With deformation of the calix[4]arene symmetry towards C 2v (flattened cone structures), the β parameter increases. Deformation towards C s symmetry is best reflected by increase of the parameter δ. Parameter α reflects the degree of 'opening' of the calix[4]arene cavity; structures with four OH groups at the lower rim tend to have lower α and therefore more open structure.

Conformations of Calix[4]arenes. An Investigation Based on CSD Data. Part III. Calix[4]resorcinarenes

“…Duplicite hits not excluded from Table 2; seven structures with incomplete cif files, where conformations were impossible to determine, are not included in the total number in Table 2. Unlike previously discussed calix [4]arenes [7,8], there are substituents present on the methylene bridges of calix [4]resorcinarenes; the positions (axial/equatorial with regard to the macrocycle) of these groups significantly affect the geometry of the resorcinarene scaffold [1]. However, because of the presence of two hydroxyl groups at the m-positions of the upper rim (and in some cases a third hydroxyl group at the p-position of the upper rim), several substitution patterns not observed in the group of calix [4]arenes are possible with calix [4]resorcinarenes (e.g.…”

“…The group of calix [4]resorcinarenes is smaller than the group of calix [4]arenes with methylene bridges but significantly larger than the group of calix [4]arenes with heteroatom bridges (see [7,8]). There are altogether 551 cif files belonging to this group (23.2 % from the total of 2377 cif-files in [9] belonging to calix [4]arenes with methylene and heteroatom bridges and calix [4]resorcinarenes); the number of 218 cif files for calix [4]arenes with heteroatom bridges amounts to 9.2 % and for calix [4]arenes with methylene bridges (1610 cif files) to 67.7 %.…”

“…In the preceding two papers [7,8]), the previously introduced parameters α, β and δ [11,12] have been utilized to describe the geometry of the calix [4]arene base frame. Furthermore, the utility of the parameters α, β and δ to describe the influence of inter/intramolecular interactions on the geometry of the calix [4]arene scaffold in all conformers of methylene-and heteroatom-bridged calix [4]arenes was demonstrated.…”

“…In the previous two parts, of this work [7,8], influence of inter/intramolecular interactions and substitition patterns on the geometry of methylene-and heteroatom-bridged calix [4]arenes has been investigated. To enable comparison between calix [4]arene and calix [4]resorcinarene molecules, the system of ca-Вестник Карагандинского университета lix [4]resorcinarene and calix [4]arene conformations has been unified so the conformations of calix [4]resorcinarenes are reported as cone, partial cone, 1,2-alternate and 1,3-alternate.…”

“…In the group of calix [4]resorcinarenes, there is a relatively large percentage of cone-structures (over 82 %) and of symmetrically substituted structures with the exception of partial cone conformers (see Table 2). In the large number of symmetrically substituted structures, the resorcinarene group resembles the group of heteroatom-bridged calix [4]arenes described in previous papers [7,8]. Duplicite hits not excluded from Table 2; seven structures with incomplete cif files, where conformations were impossible to determine, are not included in the total number in Table 2.…”