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

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 Cd^II supramolecular compound, namely poly[μ-adipato-κ²O¹:O⁴-μ-adipato-κ⁴O¹,O^1':O⁴,O^4'-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 Cd^II centre is located in a distorted octahedral coordination environment, coordinated by one water O atom, three carboxylate O atoms from two different adp^2- ligands and two N atoms from two different 1,4-bpbd ligands. The Cd(H₂O) units are interconnected by the μ₂,κ²-adp^2-, μ₂,κ⁴-adp^2- 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 adp^2- carboxylate O atoms anchor the interpenetrating networks into a unique three-dimensional supramolecular structure. Topologically, taking the coordinated water molecules and Cd^II 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.