Abstract
The use of halogens in the crystal engineering of supramolecular porphyrin assemblies has been a topic of strong interest over the past decades. With this in mind we have characterized a series of direct meso-halogenated porphyrins using single crystal X-ray crystallography. This is accompanied by a detailed conformational analysis of all deposited meso-halogenated porphyrins in the CSD. In this study we have used the Hirshfeld fingerprint plots together with normal-coordinate structural decomposition and determined crystal structures to elucidate the conformation, present intermolecular interactions, and compare respective contacts within the crystalline architectures. Additionally, we have used density functional theory calculations to determine the structure of several halogenated porphyrins. This contrasts conformational analysis with existing X-ray structures and gives a method to characterize samples that are difficult to crystallize. By using the methods outlined above we were able to deduce the impact a meso halogen has on a porphyrin, for example, meso-halogenation is dependent on the type of alternate substituents present when forming supramolecular assemblies. Furthermore, we have designed a method to predict the conformation of halogenated porphyrins, without need of crystallization, using DFT calculations with a high degree of accuracy.
Highlights
Crystal engineering using porphyrins as a scaffolding unit has been a topic of increasing interest over the past few decades
The other motif seen is the inline interactions where layers of porphyrins are lined up with the bromine atoms pointing towards the phenyl rings in a ↑↓↑↓ repeating pattern (Figure 2C)
By comparing the density functional theory (DFT) calculated geometries with crystal structures we have found that DFT is a good approximation
Summary
Crystal engineering using porphyrins as a scaffolding unit has been a topic of increasing interest over the past few decades. In recent years there has been a strong uprising interest for substituting hydrogen-bonding motifs with their halogen-bonding counterparts This is due to their relative versatility in areas such as directionality, the tunability of the σ-hole, hydrophobicity, and donor atom size [14]. Recent studies from our group have been carried out on the use of halogens as a binding motif in cubanes [15], bicyclo[1.1.1]pentane [16], and nonplanar porphyrins [17] Another reason to investigate the effect of meso-halogenation of porphyrins is due to the potential of induced distortion of the macrocyclic core. Any general structural motif that appears consistent among the mesox-halo-substituted porphy-
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