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

Abstract

Crystal structures of 2,4,6-tris(2-halophenoxy)-1,3,5-triazines (halo =fluoro, chloro, bromo, iodo; 2-XPOT) are discussed in the background of 3-halophenoxy (3-XPOT) and 4-halophenoxy (4-XPOT) structures. Among interhalogen interactions, the electrostatic L-shaped type II interactions are generally shorter than the inversionrelated type I geometry in 2-halo compounds. π-Stacking of triazine rings at van der Waals separation (∼3.5 Å) makes the well-known Piedfort Unit assembly and the halogen atoms form a trimer motif. 2-FPOT and 2-ClPOT are 2D isostructural but there are differences in the complete 3D molecular packing. 2-BrPOT and 2-IPOT are a 3D isostructural pair and their isomorphous unit cells have a similarity index of 0.008. The position of the halogen atom causes structural differences in 2-, 3-, and 4-XPOT compounds, with the para-series showing guest inclusion and the ortho- and meta-compounds having single-component close-packed structures. The Cambridge Structural Database is analyzed for structural mimicry upon halogen GRoup eXchange (GRX). Chloro-, bromo-, and iodo-substituted compounds of the same molecule (56 clusters) are isostructural in 30% cases, Cl/Br are identical in 66% pairs, and Br/I in 50% examples of the subdatabase. © 2007 Wiley Periodicals, Inc.