Supramolecular isomers have a same chemical formula but more than one crystal structure in coordination polymers (CPs) and metal-organic frameworks (MOFs).
[1] Here we report the significant correlation of solvents, coordination environments, and photoreactivity between two Zn(II) supramolecular isomers. A 1D zigzag CP, [Zn(bpe)(adc)
2] (
1) is synthesized under solvothermal reaction of Zn(NO
3)
2·6H
2O, 1,2-bis(4-pyridyl)ethylene (bpe), and 1-adamantanecarboxylic acid (Hadc) in a mixture of dimethylacetamide (DMA) and H
2O. The mononuclear repeating unit in
1 consists of one Zn(II) atom, two bpe ligands, and two adc ligands. Zn1 atom is pseudo-tetrahedrally coordinated by two nitrogen atoms of bpe ligands and four oxygen atoms of adc ligands. On the other hand, a 1D railroad CP, [Zn(bpe)(adc)
2] (
2) is synthesized by same reaction condition except dimethylformamide (DMF) instead of DMA. The dinuclear repeating unit in
2 consists of two Zn(II) atoms, four bpe ligands, and four adc ligands. Zn1 is octahedrally coordinated by two nitrogen atoms of bpe ligands and four oxygen atoms of adc ligands. Especially, the double bonds of bpe ligands in
2 are parallelly aligned to each other at a distance of 3.6 Å. According to Schmidt’s Criteria,
[2] while the distance of olefins is within the range of 3.6-4.1 Å, olefins can be photo-dimerized by UV irradiation.
1H nuclear magnetic resonance (NMR) spectrum of the crystals obtained after irradiation of
1 under UV for 48 h showed the formation of cyclobutane peaks at 5.3 ppm. For better understanding of the irradiated crystal structure, we attempted to receive suitable single crystals for single crystal X-ray diffraction analysis (SC-XRD). The X-ray crystal structure of the photodimerized CP [Zn(
rctt-tpcb)(adc)
2] (
3,
rctt = regio, cis, trans, trans; tccb = 1,2,3,4-tetrakis(3’-carboxyphenyl)-cyclobutane) was finally confirmed by SC-XRD. To monitor the homogeneity of
1 and
2, the powder X-ray diffraction (PXRD) patterns have also been investigated. The details will be presented at the poster section.
References
[1] T. L. Hennigar, D. C. MacQuarrie, P. Losier, R. D. Rogers, M. J. Zaworotko, Angew. Chem. Int. Ed. Engl. 1997, 109, 972-973.
[2] G. M. J. Schmidt, Photodimerization in the solid state, Pure Appl. Chem., 1971, 27, 647-678.
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