Self-Assembly of Cationic, Hetero- or Homonuclear Ruthenium(II) Macrocyclic Rectangles and Their Photophysical, Electrochemical, and Biological Studies

A series of supramolecular rectangles, including two
mixed-metal
Ru/Pt complexes, have been formed by the coordination-driven self-assembly
of a range of arene–Ru “molecular clip” acceptors
(1a–1d) with rigid dipyridyl-based
ligands (2a–2d) over the course of
10 h in solution. The isolated products were characterized by multinuclear
NMR (1H and 13C or 31P), HR-ESI-MS,
and an X-ray diffraction study to support the ascribed two-component
rectangular structures. The rectangles were further characterized
by UV–vis and fluorescence studies. The redox behaviors of
rectangles 3ca and 3da were also determined
using cyclic voltammetry. Additionally, the antitumor activities of
the suite of rectangles were determined against various human cancer
cell lines, and significant activity was shown by complexes 3ca, 3da, 3cb, 3cc,
and 3cd, with IC50 values as low as 2.65 μM.