Tuning the Size and Geometry of Pd(II)-Based Metallacalixarenes by Varying the N-Containing Ligands: Synthesis, Structure, and Sensing Properties

Abstract

Four types of palladium­(II)-based cup-shaped structures as structural analogues of [M3L3 ]3+-type metallacalix[3]­arene, [M2L]2+-type semimetallacalix[4]­arene, [M2L2 ]4+-type metallacalix[4]­arene, and [M3L3 ]6+-type metallacalix[6]­arene have been designed and synthesized via coordination-driven self-assembly using two types of imidazole- and dithiophene-containing ligands, [4,5-bis­(2,5-dimethylthiophen-3-yl)-1H-imidazole (HL1 ) and bis­(4,5-bis­(2,5-dimethylthiophen-3-yl)-1H-imidazol-1-yl)­methane (L2 )], with four types of palladium­(II) nitrate precursors, (bpy)­Pd­(NO3)2 (M1 -NO3), (tmen)­Pd­(NO3)2 (M2 -NO3), (en)­Pd­(NO3)2 (M3 -NO3), and Pd­(NO3)2 (M4 -NO3) (bpy = 2,2′-bipyridine; tmen = tetramethylethylenediamine; en = ethylenediamine). The difference in the imidazolate ligands and palladium­(II) nitrate precursors in each complex brings about the variety of the structures and ion-encapsulating characteristics of the obtainable cavities in all the complexes. The fascinating multidimensional 2-D and 3-D highly ordered supramolecular configurations with metallacalixarenes as building blocks were constructed via π–π stacking and multiple hydrogen bonding. Furthermore, this successful strategy provides an insight into the construction of other more intricate structural analogues of metallacalixarenes and the chemistry in crystal engineering.