Synthesis and Crystal Structure of an Adjoined Metallacrown: An Archetypal 12-Metallacrown-4 Connected to a Collapsed 11-Metallacrown-4

The adjoined 3d–4f metallacrown (MC) molecule Dy^III₂Mn^III₆(H₂shi)(Hshi)(shi)₇(py)₉·2py·0.7H₂O, 1, where H₃shi is salicylhydroxamic acid and py is pyridine, has been synthesized and characterized by FT–IR spectroscopy and single-crystal X-ray diffraction. The core of the molecule consists of two metallacrown (MC) rings, an archetypal 12-MC-4 and a collapsed 11-MC-4, that are linked through a common ring Dy^III center. For the 12-MC-4 portion of 1, the heterobimetallic composition of the MC ring with one Dy^III and three Mn^III ions is uncommon for metallacrowns as most 12-MC-4 rings are homometallic. In addition, the 12-MC-4 binds a Dy^III cation in the central cavity of the MC. The coordination environment about the central Dy^III ion has a triangular dodecahedron shape, which again is atypical. For 12-MC-4 molecules with a central lanthanide ion, the central lanthanide ion typically adopts a square antiprism geometry. The ring Dy^III cation of the 12-MC-4, which has a biaugmented trigonal prism shape, is shared with the collapsed 11-MC-4 and serves to join both metallacrowns. The collapsed 11-MC-4 ring is also composed of three Mn^III and one Dy^III ions. For one of the ring metal–metal linkages, only an oxygen atom is present, and an eleven membered ring is generated. In addition, the Dy^III center and one of the Mn^III centers bind to ring oxygen atoms on the opposite side of the MC ring; thus, the potential cavity of the MC is collapsed, and the MC does not bind a central metal ion as is customary.

Graphical Abstract