Cavitands Incorporating a Lewis Acid Dinickel Chelate Function as Receptors for Halide Anions
2015; American Chemical Society; Volume: 54; Issue: 8 Linguagem: Inglês
10.1021/acs.inorgchem.5b00123
ISSN1520-510X
AutoresAlexander Jeremies, Ulrike Lehmann, Sina Gruschinski, Frederik Schleife, Michel Meyer, V.E. Matulis, Олег А. Ивашкевич, Marcel Handke, K. Stein, Berthold Kersting,
Tópico(s)Supramolecular Chemistry and Complexes
ResumoThe halide binding properties of the cavitand [Ni2(L(Me2H4))](2+) (4) are reported. Cavitand 4 exhibits a chelating N3Ni(μ-S)2NiN3 moiety with two square-pyramidal Ni(II)N3S2 units situated in an anion binding pocket of ∼4 Å diameter formed by the organic backbone of the (L(Me2H4))(2-) macrocycle. The receptor reacts with fluoride, chloride (in MeCN/MeOH), and bromide (in MeCN) ions to afford an isostructural series of halogenido-bridged complexes [Ni2(L(Me2H4))(μ-Hal)](+) (Hal = F(-) (5), Cl(-) (6), and Br(-) (7)) featuring a N3Ni(μ-S)2(μ-Hal)NiN3 core structure. No reaction occurs with iodide or other polyatomic anions (ClO4(-), NO3(-), HCO3(-), H2PO4(-), HSO4(-), SO4(2-)). The binding events are accompanied by discrete UV-vis spectral changes, due to a switch of the coordination geometry from square-pyramidal (N3S2 donor set in 4) to octahedral in the halogenido-bridged complexes (N3S2Hal donor environment in 5-7). In MeCN/MeOH (1/1 v/v) the log K11 values for the 1:1 complexes are 7.77(9) (F(-)), 4.06(7) (Cl(-)), and 2.0(1) (Br(-)). X-ray crystallographic analyses for 4(ClO4)2, 4(I)2, 5(F), 6(ClO4), and 7(Br) and computational studies reveal a significant increase of the intramolecular distance between two propylene groups at the cavity entrance upon going from F(-) to I(-) (for the DFT computed structure). In case of the receptor 4 and fluorido-bridged complex 5, the corresponding distances are nearly identical. This indicates a high degree of preorganization of the [Ni2(L(Me2H4))](2+) receptor and a size fit mismatch of the receptor binding cavity for anions larger than F(-).
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