Impact of binding positions of 1,3-alternate calix[4]arene tetrabenzoic acids on geometry of coordination polymers

Abstract

In this work, calix[4]arene was used as a building block for the preparation of 1,3-alternate calix[4]arene tetrabenzoic acids. Two structural isomers, 3A and 3B were obtained which have the carboxylate groups on the para and meta positions, respectively. The reaction conditions were optimized to obtain, four coordination polymers with linkers of 3A and 3B with Zn²⁺ and Cd²⁺ in different forms. Structural analysis of the product (CU-SCRU1) from 3A with Zn²⁺ showed that it was a 1D polymeric chain. In the case of 3B with Zn²⁺ it was a 1D polymeric chain in a zig-zag shape (CU-SCRU2). The free rotation of the methylene bridge allowed the carboxylate group at the meta position of 3B to coordinate with the Zn²⁺ ion. In both cases, the carboxylate groups at each side of the organic linkers, 3A and 3B, chelated to the same metal center (Zn²⁺) which resulted in the formation of 1D coordination polymers. However, each polymeric chain extended to a 3D framework by nonclassical hydrogen bonding and intermolecular interactions for CU-SCRU1 and CU-SCRU2, respectively. The reaction of 3B and Cd²⁺ provided coordination polymers that were suitable for structural characterization. Interestingly, two products were formed in the same reaction, CU-SCRU3 and CU-SCRU4, that had different coordination structures. The structural features of these two products suggested that they exist as a 3D framework, however, the nitrogen adsorption–desorption analysis revealed that they were nonporous materials.

Graphic abstract