A Metal−Organic Bilayer Open Framework with a Dynamic Component: \nSingle-Crystal-to-Single-Crystal Transformations

Abstract

A metal−organic bilayered open framework, [Ni₂(C₂₆H₅₂N₁₀)]₃[BTC]₄·6C₅H₅N·36H₂O (<b>BOF-1</b>, <b>1</b>), has been prepared by the self-assembly of a new bismacrocyclic nickel(II) complex [Ni₂(C₂₆H₅₂N₁₀)(Cl)₄]·H₂O (<b>A</b>) and sodium 1,3,5-benzenetricarboxylate (Na₃BTC) in the mixture of water/DMSO/pyridine. The X-ray crystal structure of <b>1 </b>shows that 2D layers with the cavities of brick-wall motifs (22.6 × 14.3 Ų) are formed by the coordination of the nickel(II) complex with BTC^3- ions and that the two 2D layers are linked with the <i>p</i>-xylyl bridging groups of the bismacrocycles as pillars to generate 3D channels in the bilayered framework. The voids of the channels occupy 61% of the total volume, which are filled with pyridine and water guest molecules. When <b>1 </b>was dried at 75 °C for 1.5 h, [Ni₂(C₂₆H₅₂N₁₀)]₃[BTC]₄·4H₂O (<b>2</b>) resulted by maintaining the single-crystallinity, which exhibited a dramatic decrease in the interlayer spacing as well as changes in the cell parameters. Solid <b>2</b> differentiates various alcohols such as MeOH, EtOH, isopropyl alcohol, and benzyl alcohol in toluene. When <b>1 </b>was immersed in insoluble solvents such as pyridine and benzene, some guest molecules were exchanged with the aromatic molecules to give [Ni₂(C₂₆H₅₂N₁₀)]₃[BTC]₄·20pyridine·6H₂O (<b>3</b>) and [Ni₂(C₂₆H₅₂N₁₀)]₃[BTC]₄·14benzene·19H₂O (<b>4</b>), respectively. The guest-exchange processes also involve single-crystal-to-single-crystal transformation.