Two 2D → 3D entangled coordination polymers with polycatenated and polythreaded features based on 44-sql layers

Abstract

Two fascinating 3D entangled coordination polymers, [Ni₅(pda)₅(bpp)₅]·12H₂O (1) and [Cd₂(pda)₂(1,10′-phen)₂]·4H₂O (2) (pda = phenylenediacrylate dianion; bpp = 1,3-bis(4-pyridyl)propane; 1,10′-phen = 1,10′-phenanthroline), have been successfully synthesized and characterized by single-crystal X-ray analysis. In complex 1, two 4⁴-sql nets interweave in parallel and give rise to a 2-fold interpenetrated layer (2D → 2D). In addition, each layer interlocks two other layers, one above and one below (2D → 3D). This results in an interesting 3D coordination polymer containing interpenetration and polycatenation at the same time. Complex 2 exhibits a 2D → 3D polythreaded framework based on 2D 4⁴-sql motifs with side arms. If π–π interactions are taken into account, the resulting structure displays a 2-fold interpenetrated 3D α-Po network. Interestingly, if crystals of 2 are dissolved in water and left undisturbed for about two weeks at room temperature, its supramolecular isomer [Cd₂(pda)₂(1,10′-phen)₂]·H₂O (3) is formed. On the contrary, when yellow block crystals of 3 are treated under microwave conditions, colorless plate crystals of 2 reappear. This means that there exists a reversible transformation process between 2 and its isomer 3. Furthermore, the fluorescence properties of 2 have been studied.