Metallo-macrocycles from a library of flexible linkers: 1D cobalt(II) coordination polymers and a supramolecular pipe

Abstract

Three cobalt(II) coordination polymers containing compounds {Co(3-mboba)(1,2-bix)2}n (1), {Co2(1,3-pda)(px3ampy)(H2O)2}n (2), {Co2(hfipbb)2(bpbix)2}n (3), that are formed from three different bent carboxylic acids [3,3′-methylenebis(oxy)dibenzoic acid (3-H2mboba), 2,2′-(1,3-phenylene)diacetic acid (1,3-H2pda) and 4,4′-(perfluoropropane-2,2-diyl)dibenzoic acid (H2hfipbb)] as primary ligands and three different {N,N}-donor linkers [1,2-bis((1H-imidazol-1-yl)methyl)benzene(1,2-bix), N,N′-(1,4-phenylenebis(methylene)) dipyridin-3-amine (px3ampy) and 4,4′-bis((1H-imidazol-1-yl)methyl)biphenyl (bpbix)] as secondary ligands, have been synthesized under hydrothermal conditions. Compounds 1–3 are characterized by single crystal X-ray diffraction analysis, IR spectroscopy, thermogravimetric (TG) and elemental analysis. Single crystal X-ray crystallography shows that diverse metallo-macrocycles are formed in compounds 1, 2 and 3. In the crystal structure of compound 1, two different metallo-macrocyles, 28-membered metal–acid {Co2(3-mboba)2} ring and 24-membered metal-N-linker {Co2(1,2-bix)2} ring, are formed. The alternative arrangement of these macrocylic rings leads to the formation of 1D chainlike coordination polymer (compound 1). In the crystal of compound 2, a 25-membered macrocycle ring {Co(1,3-pda)(px3ampy)} is formed from one dicarboxylic acid ligand and one {N,N}ligand, which further undergoes coordination with itself resulting in the formation of 1D chain. The {Co3(hfipbb)(bpbix)2} metallamacrocycle, observed in the crystal structure of compound 3, is more diversified in the sense that it is relatively bigger in size and this trinuclear metallo-macrocycle is formed by one dicaryboxylic acid ligand and two {N,N} donor linkers, but not in a plane. Interestingly, the inter-linking of these non-planar macrocycles results in the construction of a supramolecular pipe.