Hydrogen-Bonded Supramolecular Structures of Cobalt(III) Complexes with Unsymmetrical Bidentate Ligands: mer/fac Interconversion Induced by Hydrogen-Bonding Interactions
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- 作者：Ryoji MitsuhashiTakayoshi Suzuki ; Satoshi Hosoya ; Masahiro Mikuriya
- 刊名：Crystal Growth & Design
- 出版年：2017
- 出版时间：January 4, 2017
- 年：2017
- 卷：17
- 期：1
- 页码：207-213
- 全文大小：510K
- ISSN：1528-7505
文摘
Cobalt(III) complexes with three unsymmetrical bidentate ligands containing a noncoordinating N–H bond and a phenolate-O donor as hydrogen-bond donor and acceptor, respectively, were prepared and characterized. 1H NMR spectroscopy indicated that all the tris-chelate Co(III) complexes prepared favor the mer configuration in solution. [Co(Hthp)3] and [Co(Himn)3] also possess the mer configuration in the crystals (Hthp– = 2-(1,4,5,6-tetrahydropyrimidin-2-yl)phenolate, Himn– = 2-(2-imidazolinyl)phenolate). On the other hand, [Co(Himl)3] takes the fac configuration in the crystal (Himl– = 2-(2-imidazolyl)phenolate). These Co(III) complexes showed three types of characteristic supramolecular structures: ladder, distorted hexagonal sheet, and honeycomb sheet structure, constructed by intermolecular hydrogen bonds. Heating [Co(Himn)3] and [Co(Himl)3] in methanol selectively afforded precipitates of the fac isomer due to the low solubility of the hydrogen-bonded supramolecular structures. This mer to fac isomerization upon crystallization in methanol is presumably induced by the formation of highly ordered hydrogen-bond networks via the methanol molecule. The fac isomers remained intact in dimethyl sulfoxide (DMSO) for longer than a week at room temperature. Upon heating, however, fac to mer geometrical isomerization of both fac-[Co(Himn)3] and fac-[Co(Himl)3] was observed in DMSO. Thus, mer/fac interconversion was achieved by heating in two different solvents, due to the formation of a supramolecular assembly of hydrogen-bond networks.