First structural authentication of third-sphere coordination: [p-sulfonatocalix[4]arene]5-as a third-sphere ligand for Eu3+

Abstract
The central feature of the complicated structure of Na[Eu3(p-sulfonatocalix[4]arene)2(OH2)18(ONC5H5)3]·14 H2O is the coordination sphere of one of the three independent europium atoms. Its first coordination sphere consists of seven water molecules, the oxygen atom of a pyridine N-oxide molecule, and a sulfonate oxygen atom from one of the two independent calix[4]arenes. The second-sphere coordination consists of the second calix[4]arene which is bound to the coordinated pyridine N-oxide via hydrophobic interactions, and a second pyridine N-oxide which is hydrogen bonded to a coordinated water molecule. The third-sphere coordination consists of the binding of the second-sphere coordinated pyridine N-oxide to the cavity of the first-sphere coordinated calix[4]arene. Na[Eu3(p-sulfonatocalix[4]arene)2(OH2)18(ONC5H5)3]·14 H2O crystallizes in the monoclinic space group P21/c with a = 20.973(2), b = 18.678(2), c = 29.502(4)Å, β = 109.19(1)°, and Dc = 1.74 g cm−3 for Z = 4. Refinement based on 10,043 observed reflections led to a final R value of 0.091.

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