Integration
of Alkyl-Substituted Bipyridyl Benzenedithiolato Platinum(II) Complexes
with Cadmium(II) Ion via Selective Dative Bond Formation
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Abstract
The
presence of lone pairs on the Pt and S atoms of [Pt(Bdt)(DTBbpy)]
(<b>1</b>) (Bdt = 1,2-benzenedithiolato and DTBbpy = 4,4′-di-<i>tert</i>-butyl-2,2′-bipyridine) and [Pt(Bdt)(C13bpy)]
(<b>2</b>) (C13bpy = 4,4′-ditridecyl-2,2′-bipyridine)
led to selective dative bond formation with Cd(II). Complexes <b>1</b> and <b>2</b> show no binding interaction with Zn(II),
while they bind selectively with Cd(II) to give a twisted trinuclear
complex, [Cd{Pt(Bdt)(DTBbpy)}<sub>2</sub>(ClO<sub>4</sub>)(H<sub>2</sub>O)](ClO<sub>4</sub>) (<b>3</b>), and a shuttlecock-shaped tetranuclear
complex, [Cd{Pt(Bdt)(C13bpy)}<sub>3</sub>(H<sub>2</sub>O)](ClO<sub>4</sub>)<sub>2</sub>·CH<sub>2</sub>Cl<sub>2</sub> (<b>4</b>), respectively, depending upon the alkyl groups substituted on the
2,2′-bipyridine. The two platinum moieties in <b>3</b> are connected to the seven-coordinated Cd atom through Pt →
Cd (2.7331(7) and 2.7936(7) Å) and S → Cd (2.690(3), 2.940(3),
and 3.067(3) Å) dative bonds, while the three moieties in <b>4</b> are connected to the tetrahedral Cd atom only by S →
Cd (2.552(4) Å) dative bonds. These structural variations found
in <b>3</b> and <b>4</b> are caused not only by steric
hindrance of the <i>t</i>-Bu groups but also by the microsegregation
effect derived from the tridecyl chains. The three platinum moieties
in <b>4</b> align so as to form a parallel orientation of their
dipole moments, in contrast to the twisted arrangement found in <b>3</b>. The dative bonds formed in <b>3</b> and <b>4</b> are commonly stable in the solid state and in less coordinative
solvents such as dichloromethane, while dissociation behavior of platinum
moieties with Cd(II) was observed in more coordinative THF. UV–vis
and NMR spectroscopy unsealed the characteristic association/dissociation
properties depending on the coordination abilities of solvents. Finally,
the present study revealed that the formation of dative bonds between
the platinum moieties with Cd(II) plays important roles not only in
stabilizing the ground states, which leads to blue shifts in both
absorption and emission energies, but also in electronic interactions
between the moieties, which are revealed by electrochemical studies