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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.
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