Selective recognition of sulphate in a Cu(ii) assisted 1D polymer of a simple pentafluorophenyl substituted pyridyl-urea via second sphere coordination?

Dalton Transactions Pub Date: 2013-02-05 DOI: 10.1039/C3DT32710H

Abstract

A pentafluorophenyl (–C6F5) substituted 3-pyridyl urea, L1, is explored extensively to demonstrate SO42? binding exclusively via second sphere coordination in the cavity of a 1D polymeric self-assembly of L1, selectively assisted by Cu2+. A single crystal X-ray diffraction study depicts SO42? encapsulation in the C2 symmetric cleft via nine hydrogen bonding interactions contributed by eight urea protons of four L1 moieties in [CuL14(DMF)2]SO4 (1). To revalidate the importance of Cu2+ selective anion coordination via exclusive second sphere coordination, a complex of L1 and Cu(NO3)2, i.e. [CuL14(H2O)2](NO3)2 (2), is also isolated and characterized by a single crystal X-ray diffraction study. When SO42? salts of different metal ions such as Co2+/Ni2+ are employed, the first sphere coordination of SO42? is observed in cases of complexes [CoL13(DMF)2SO4] (3) and [NiL13(DMF)2SO4] (4) respectively. These results clearly suggest the importance of Cu2+ towards anion recognition via purely second sphere coordination in the case of complexes 1 and 2. To understand the importance of (–C6F5) substitution in the design of L1 towards such recognition of SO42? in 1, the phenyl (–C6H5) analogue of L1, i.e.L2, is allowed to complex with the SO42? salt of Cu2+. Interestingly, L2 shows first sphere SO42? coordination in the complex [CuL22(DMF)(H2O)2SO4] (5). Solution state UV-Vis experiments of L1 with various copper salts such as Cu(ClO4)2, CuSO4, Cu(NO3)2, CuCl2 and CuBr2 in DMF show the formation of a binary complex corresponding to 1. Further, Cu2+ selective second sphere coordination of SO42? in solution is also demonstrated by UV-Vis studies of complexes isolated from the mixtures of various Cu2+ salts and/or SO42? salts of different metal ions.

Graphical abstract: Selective recognition of sulphate in a Cu(ii) assisted 1D polymer of a simple pentafluorophenyl substituted pyridyl-urea via second sphere coordination
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