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Imidazoporphyrins as supramolecular tectons: synthesis and self-assembly of zinc 2-(4-pyridyl)-1H-imidazo[4,5-b]porphyrinate

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Abstract

5,10,15,20-Tetramesityl-2-(4-pyridyl)-1H-imidazo[4,5-b]porphyrin (PyPor) bearing a pyridine donor site connected to the tetrapyrrolic macrocycle by a rigid imidazole linker was prepared in high yield by the condensation of the corresponding 2,3-dioxochlorin and 4-formylpyridine in the presence of ammonium acetate. After the insertion of a metal ion capable of metal–ligand axial coordination, namely Zn(II), this compound afforded self-complementary porphyrin PyPorZn which was suitable for self-assembly. In the crystals, this complex exists as a zigzag coordination polymer formed through the axial coordination of the pyridine nitrogen atom to the zinc ion of the neighbouring porphyrin molecule. The Zn atoms adopt a distorted tetragonal pyramidal environment and the pyridine rings significantly deviate from the orthogonal orientation to the mean N4 plane of the adjacent macrocycle (the Cpara–NPy–Zn angle is equal to 148°). This distortion was analysed by using DFT calculations of a zinc 5,10,15,20-tetraphenylporphyrinate–pyridine complex (TPPZn–Py). The energy and the geometry of TPPZn–Py were calculated by varying the tilt of the pyridine ligand. The change of the Cpara–NPy–Zn angle from 180° to 150° induces a small increase (within 1.5 kcal mol−1) of the total energy of the complex. Such a small increase can be easily compensated by the intermolecular CH⋯H and CH⋯π interactions in the crystals. The self-assembly of PyPorZn in non-coordinating solvents was also investigated by NMR and UV-vis spectroscopy. In contrast to the nickel complex PyPorNi, the zinc complex exists in 10−4 M solution in toluene and chloroform as a mixture of short linear oligomers. These oligomers dissociate affording monomer species upon heating, dilution or addition of a substituting ligand.

Graphical abstract: Imidazoporphyrins as supramolecular tectons: synthesis and self-assembly of zinc 2-(4-pyridyl)-1H-imidazo[4,5-b]porphyrinate

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Publication details

The article was received on 22 Nov 2018, accepted on 28 Jan 2019 and first published on 28 Jan 2019


Article type: Paper
DOI: 10.1039/C8CE01992D
Citation: CrystEngComm, 2019, Advance Article

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    Imidazoporphyrins as supramolecular tectons: synthesis and self-assembly of zinc 2-(4-pyridyl)-1H-imidazo[4,5-b]porphyrinate

    I. A. Abdulaeva, K. P. Birin, A. A. Sinelshchikova, M. S. Grigoriev, K. A. Lyssenko, Y. G. Gorbunova, A. Yu. Tsivadze and A. Bessmertnykh-Lemeune, CrystEngComm, 2019, Advance Article , DOI: 10.1039/C8CE01992D

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