Coordination-directed self-assembly of nano-cages: metal ion-change, ligand-extending, shape-control and transdermal drug delivery

Abstract

The combination of different pyridyl ligands and metal ions has proven to be a very reliable strategy for controlling the coordination mode of the heterometallic coordination nano-cages. Adjusting the length of the ligands could result in the selective synthesis of several heterometallic coordination nano-cages, either [8Rh + 2M]-4L, [8Rh + 2M]-5L or [8Rh + 4M]-6L cages, derived from the very same precursors (LH3tzdc) through half-sandwich rhodium self-assembly. Moreover, a series of [8Rh + 4M]-6L cages was chosen to exemplify the preparation. The rigidity of various pyridyl donor ligands caused the vertical nano-cage to be energetically preferred and was able to change the self-assembly process through ligand flexibility to selectively give the inclined nano-cage and cross nano-cage.

Scheme 1. The three modes of self-assembly of heterometallic coordination cages observed in this work, with different metal centers and ligands (pink for Rh, red for Zn, Ni, or Na; purple for Zn or Ni; yellow for Na or K, green for Cu).

Fig. 1. (a)–(e) Single-crystal structures of 1–5 (gray for C, blue for N, red for O, green for Cu, pink for Rh, orange for Na, yellow for S, fluorescent green for F; Na some hydrogen atoms and solvent molecules or anions are omitted for clarity).

Scheme 2. The synthetic routes to 1D chain structures, 2D polygons and 3D nano-cages.

Fig. 2. In vitro drug release of Febuxostat tablets with complexes.

Fig. 3. In vitro skin penetration of Febuxostat tablets released from the complexes.

Fig. 4. Biocompatibility of the complexes.