Structure and Small Molecule Binding of a Tetranuclear Iron(II) Resorc[4]arene-Based Cage Complex

Four iron(II) ions help assemble a container molecule (1), by bringing together two hemispherical resorc[4]arenes. The resorc[4]arene ligands are appended with four iminodiacetate moieties which act as ligands for the
iron atoms. X-ray crystallographic analysis of 1 shows that the iron atoms are coordinated in an N,N-cis-fac
manner and exhibit a trigonal prismatic geometry. When 1 is formed in water, six water molecules, hydrogen
bonded together, occupy its cavity. However, when 1 is formed with bromobenzene present in the water solution,
bromobenzene is trapped in the cavity. Multinuclear NMR experiments (1H, 2H, and 19F) demonstrate the pH-dependent encapsulation of various organic guest molecules by 1, e.g., substituted benzenes, alkanes, ethers, and
chlorocarbons. Complex 1 is the first iron(II)-containing cage complex that is formed by assembly of resorcinarene
molecules and that binds neutral organic molecules.