Synthesis and Photophysical Properties of Ru Homo- and Heterodinuclear Transition Metal Complexes Bearing Tetrakispyrazolylethene as a Bridging Ligand

We report the synthesis and characterization of Ru mononuclear
(1), Ru/Pd dinuclear (2), and Ru/Ru dinuclear
(3) complexes bearing tetrakis(pyrazol-1-yl)ethene (L) as a bridging ligand. NMR analyses and single-crystal X-ray
crystallography reveal that 1 has a distorted octahedral
geometry with C1 symmetry at room temperature
and quasi-C2 symmetry upon heating, resulting
from the thermally activated motion of L. The coordination
of L to the second metal (Pd or Ru) restricts its motion.
In the case of complex 2, this restriction leads to enhanced
emission at room temperature, accompanied by the energy transfer from
the Ru unit to Pd.