A three-dimensional supramolecular framework based on the interlinkage of an interpenetrating diamondoid coordination network

Abstract

In the development of coordination-driven crystalline materials, O- and N-atom donors from carboxylate and pyridyl-based ligands are widely used classes of multidentate bridging ligands composed of several terminal coordinating groups linked by either rigid or flexible spacers. The rigidity of the ligands can play a vital role in the determination of the structures formed. A new CdII supramolecular compound, namely poly[μ-adipato-κ2O1:O4-μ-adipato-κ4O1,O1':O4,O4'-diaquabis[μ-1,4-bis(pyridin-4-yl)-1,3-butadiene-κ2N:N']dicadmium(II)], [Cd2(C6H8O4)2(C14H12N2)2(H2O)2]n, (I), has been synthesized by the self-assembly of Cd(NO3)2·4H2O, adipic acid (hexane-1,6-dioic acid; H2adp) and the dipyridyl ligand 1,4-bis(pyridin-4-yl)buta-1,3-diene (1,4-bpbd) under hydrothermal conditions. Single-crystal X-ray diffraction analysis reveals that each CdII centre is located in a distorted octahedral coordination environment, coordinated by one water O atom, three carboxylate O atoms from two different adp2- ligands and two N atoms from two different 1,4-bpbd ligands. The Cd(H2O) units are interconnected by the μ2,κ2-adp2-, μ2,κ4-adp2- and 1,4-bpbd ligands, which lie across centres of inversion, to give a 66-dia network. Large cavities within a single diamondoid network permit the mutual threefold interpenetration of crystallographically equivalent frameworks. Hydrogen-bonding interactions between the coordinated water molecules and adp2- carboxylate O atoms anchor the interpenetrating networks into a unique three-dimensional supramolecular structure. Topologically, taking the coordinated water molecules and CdII centres as nodes, the whole architecture can be simplified as a binodal (3,7)-connected supramolecular framework. The identity of (I) was further characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis and powder X-ray diffraction. The solid-state photoluminescence properties of (I) were also investigated.