科研之友
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摘要
Dinuclear Ag(I) metallamacrocycles containing bis-N-heterocyclic carbene units and calixarene fragments [{1,1'-R-2-3,3'-CH2{(p-R-1-C6H2OMe)CH2}(m)-bisimidazol-2-ylidene}(2)-Ag-2](PF6)(2) (6a-f), (6a: m = 1, R-1 = Me, R-2 = Me; 6b: m = 1, R-1 = t-Bu, R-2 = Me; 6c: m = 1, R-1 = Me, R-2 = naphthylmethyl; 6d: m = 1, R-1 = Me, R-2 = anthrylmethyl; 6e: m = 2, R-1 = Me, R-2 = anthrylmethyl; 6f: m = 3, R-1 = t-Bu, R-2 = anthrylmethyl) were synthesized by reacting silver oxide with the corresponding bis-imidazolium salts (5a-f). Single crystal structural analyses reveal that metallamacrocycles of diverse sizes consisting of two NHC-Ag(I)-NHC units and two calixarene fragments are found in the structures of these dinuclear complexes. These complexes show different configurations with the change of the upper-rims (R-1) of the calixarene fragments or N-substituents (R-2) of the NHC rings. The two bis-NHC ligands in the complexes generally adopt trans-conformations except for the pair in 6b. Complexes 6a and 6c-d, in which R-1 are methyl groups, show rectangular cavities in their structures. Complex 6b, in which R-1 are tert-butyl groups of great steric hindrance, adopts cone conformation analogous to that of the calixarene. Interestingly, cation-pi interactions are present between Ag(I) and the pi-electron rich arene ring of R-2 in the structures of complexes 6c-f. Intermolecular C-H center dot center dot center dot F hydrogen bonds exist in the crystal packing of all these complexes. Moreover, intermolecular Ag center dot center dot center dot Ag interactions are found in complex 6a and intermolecular pi-pi interactions are observed in complexes 6c-f. These intermolecular interactions lead to the formation of 2D supramolecular layers in complex 6c and 3D supramolecular networks in complexes 6a-b and 6d-f, respectively. The fluorescent chemosensing behaviors of these metallamacrocycles were explored for some neutral molecules. The results showed that 6d can behave as an efficient fluorescent chemosensor for p-benzoquinone and 6e-f exhibit fluorescent quenching behaviors for C-60 or C-70 fullerenes.
