On the Supramolecular Symmetries of the Piedfort Units Formed by 2,4,6-Triaryloxy-1,3,5-triazines

Abstract

The basic forms of supramolecular symmetries in the molecular diads (Piedfort units, PUs) observed in the crystal structures of 2,4,6-triaryloxy-1,3,5-triazines (n-RPOT, n ) 2, 3, 4, R ) halogen atoms or alkyl groups) are revisited, their extended canonical classification is given, and descriptions including symbols and graphical presentation are improved. The semirigid molecules in their column are stacked around a C 3 axis which may associate (i) with three parallel glide planes (C 3(g) ) having the angle of 120°, (ii) centers of inversion (C 3i ), or (iii) three perpendicular 2-fold axes (D 3 ) with an angle of 120°. In addition, the present work demonstrates that the columns formed by the C 3(g) -PUs (space group R3c) and C 3i -PUs (space group R3 j ) are related by noncrystallographic rotations (ncr). Similarly, the columns containing D 3 -PUs are formed from C 3i -PUs by ncr's. It is proved that the occurrence of the D 3 -PUs is inseparable from the presence of the C 3i -PUs in the crystal structures of several 3-RPOT derivatives in space group P3 j c1.

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

“…In the course of our study on semirigid 2,4,6-triaryloxy-1,3,5-triazines [18] (Scheme 1) (nR-POT; n = 2, 3, 4 and R = F, Cl, Br, I, Me) found in the literature [19][20][21][22][23][24][25], we recognised [26] a mistake in the assignment of D 3 symmetry to POT confused with relaxed form of C 3(g) found in 4-BrPOT [21]. Thus, three PU-diads (the stacked diads formed by 2,4,6-triaryloxy-1,3,5-triazines in crystalline state are called Piedfort Units [27]) can be distinguished according to their symmetries C 3(g) , C 3i and D 3 ( (ii) 4-BrPOT has a hexagonal dimorph (HEXWIQ); (iii) it is isostructural with 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (4-ClPOT, VALQEE), common space group P6 3 /m; and (iv) in clathrates via two real ncr's (180°, 60°), induced by the guest molecules, it assumes space group R 3 (Fig.…”

A Quest towards Eccentric Piedfort Pairs

“…Piedfort pairs (PPs) are dimeric assemblies of sym ‐threefold‐substituted aromatic molecules such as benzenes, 1,3,5‐triazines or 1,3,4,6,7,9,9b‐heptazines (Figure ). Molecular PPs acquired such name, as they look like two coins stuck together (Piedfort coins).…”

“…Hence, our goal is to design and synthesize 1,3,5‐triazine molecules that can form PPs with sufficient area in between monomers (two disks of PP) to accommodate a small molecule (Figure ) . However, known PPs possess distances (D Cg⋅⋅⋅Cg ) between two six membered rings in the range of 3 to 4 Å due to π⋅⋅⋅π stackings whereas to park a small molecule in between the two disks of PP at least ∼8 Å distance (D Cg⋅⋅⋅Cg ) might be required ,,,,. In order to achieve ∼8 Å of D Cg⋅⋅⋅Cg between disks of PP, we have decided to play with the substituents on the periphery of 1,3,5‐triazine rings.…”

“…A self-assembled dimer of sym-1,3,5trisubstituted six-membered aromatic rings can be seen as a sym-hexasubstituted benzene molecule. [16] Symmetrically trisubstituted molecules and PPs are of tremendous interest in the context of materials for nonlinear optics, [5][6][7][8][9][10][11][12][17][18][19][20][21][22] constructing porous materials, [23][24][25][26][27][28][29][30][31][32][33][34][35][36] building blocks for nano-scalar supramolecules, [37][38][39][40][41][42][43] self-assembling metallacycles, [44][45][46][47][48][49][50][51][52][53][54][55][56] encapsulation ...…”

“…[58] However, known PPs possess distances (D Cg···Cg ) between two six membered rings in the range of 3 to 4 Å due to p···p stackings whereas to park a small molecule in between the two disks of PP at least~8 Å distance (D Cg···Cg ) might be required. [6,9,10,57,59] In order to achieve~8 Å of D Cg···Cg between disks of PP, we have decided to play with the substituents on the periphery of 1,3,5-triazine rings.…”