Equivalence of Ethylene and Azo-Bridges in the Modular Design of Molecular Complexes: Role of Weak Interactions

Abstract

Structural equivalence is a general tool applied in crystal engineering for the predictable construction of molecular assemblies. In the present contribution we analyzed the equivalence of azo (-N=N-) and ethylene (-C=C-) bridges in the modular design of organic assemblies by studying 22 molecular complexes of 4,4'-azopyridine and 1,2-bis(4-pyridyl)ethene, of which 12 are novel. Unit cell similarity index (Π), as a numerical descriptor, was used to rationalize the observed equivalence/variance in the crystal packing of related complexes. A combined structural chemistry, database analysis and computational methods unveil the fact that the identity of the primary synthons alone does not ensure isostructurality; instead a concurrent effect of the contributions from both strong and weak/dispersive forces determines the structural equivalence. A statistical analysis based on a CSD survey features an apparent inverse correlation that exist between N···I and I-I bond distances; a group of data points, however, deviate from this linear relation and was accounted on the basis of electrostatic potential distribution and interaction types.

Halogen bonding in the co-crystallization of potentially ditopic diiodotetrafluorobenzene: a powerful tool for constructing multicomponent supramolecular assemblies

“…The introduction of heteroatoms between two pyridine groups does not change the binding site of halogen-bonding acceptors, such as 4-(pyridin-4-ylsulfanyl)pyridine (PySPy) [ 71 ] and 4,4'-azopyridine (APy) [ 64 ]. The sulfur atom or azo moiety is not engaged in any inter/intramolecular interaction and linear-extended halogen-bonding chains still occur between the pyridine N atom and iodine atom of 1,4-DITFB.…”

New Crystal Forms for Biologically Active Compounds. Part 1: Noncovalent Interactions in Adducts of Nevirapine with XB Donors

“…It should be noted that isomeric 1,4-diiodobenzene (1,4-DIB) is a well-known participant in the C-I•••N XBs. In most cases involving 1,4-DIB, the lengths of such contacts are in the range 2.928(4)-3.076(11) Å [23,[78][79][80][81]. Noticeably larger lengths (3.313(3)-3.462(2) Å and 3.239(3) Å, respectively) were encountered in the case of bifurcate C-I•••(N,N) contacts [82] as well as for C-I•••N≡C-R XB involving much less nucleophilic Nsp atoms [79].…”

Intermolecular Interactions in Functional Crystalline Materials: From Data to Knowledge

“…For example, tetraphenylborates of N-salicylideneanilines form isostructural series of photochromic solids due to the packing of cations within a cavity formed by phenyl groups of anions, while more dense packing in other salts gives non-photochromic solids [86]. The effect of substituents on isostructurality of compounds was widely analyzed for both rigid [87][88][89][90][91][92] and flexible molecules [93][94][95][96][97][98]. Not only long-accepted isostructurality of Cl-and Me-or -Cl, -Br, and -I substituted molecules were revealed, but also the equivalence of ethylene and azo-bridges [92], or that of azide and iodide substituents [85] were demonstrated.…”

“…The effect of substituents on isostructurality of compounds was widely analyzed for both rigid [87][88][89][90][91][92] and flexible molecules [93][94][95][96][97][98]. Not only long-accepted isostructurality of Cl-and Me-or -Cl, -Br, and -I substituted molecules were revealed, but also the equivalence of ethylene and azo-bridges [92], or that of azide and iodide substituents [85] were demonstrated. Besides the Crystal Packing Similarity tool, XPac [99] and Crycom [100] are also among the software appropriate to carry out such a comparison.…”