Abstract
Herein, we report the synthesis and the anion binding properties of a family of N,N′-diphenylureas L1-L15, bearing on the aromatic ring(s) halogens (chlorine and iodine) and/or nitro or trifluoromethyl electron-withdrawing groups. The analysis of the crystal structures obtained from single crystal X-ray diffraction experiments shows that self-assembled chains or tapes connected via N–H···O hydrogen bonds are the most commonly adopted arrangements for this type of molecules in the crystal lattice. In the presence of anion guests or solvent molecules with competing hydrogen bond donors and acceptors, other supramolecular arrangements can be observed. Solution studies conducted in DMSO-d6/0.5% H2O by means of 1H-NMR titrations show the formation of 1:1 adducts with all receptors. The different observed affinities of the receptors for the anion guests were rationalised in terms of steric hindrance of the substituents on the phenyl rings and their electron-withdrawing properties.
Highlights
The development of synthetic receptors for anion binding, sensing, catalysis and transport is one of the most active area of Supramolecular Chemistry.[1]
Solution studies conducted in DMSO-d6/0.5% H2O by means of 1H-NMR titrations show the formation of 1:1 adducts with all receptors
The different observed affinities of the receptors for the anion guests were rationalised in terms of steric hindrance of the substituents on the phenyl rings and their electron-withdrawing properties
Summary
The development of synthetic receptors for anion binding, sensing, catalysis and transport is one of the most active area of Supramolecular Chemistry.[1]. An example of simple symmetric N,N’-diphenylurea receptors para substituted with halogens and able to bind anions forming both hydrogen and halogen bonds in solution and in the solid state was reported by Das et al.[11] Inspired by these results we decided to synthesize a new family of simple asymmetric N,N’-diphenylurea receptors L1-L15 for anion recognition. These receptors are substituted on one of the phenyl ring with iodine and chlorine in various position (ortho and para for chlorine and ortho for iodine), and with nitro or a trifluoromethyl moiety on the other (Figure 1). We tested receptors L1-L 15 with a set of anions of different geometries [(Y-shape (AcO- and BzO-), spherical (Cl- and F-) and tetrahedral (H2PO4-)] by means of 1H-NMR spectroscopy and, where possible, single crystal X-ray diffraction
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