C O M M U N I C A T I O N S
Scheme 1
triethylamine. The two [Pt(L-)] moieties are not parallel to each
other anymore, and the Pt-Pt separation has increased to 5.555(2)
Å. Instead of intramolecular d8-d8 interaction, the deprotonated 1
possesses a pair of intramolecular π-π interactions between the
two deprotonated pyrazolyl rings on the cyclometalating ligands
and two phenyl rings of the µ-dppm. Interplanar distances between
the interacting aromatic rings are 3.54-3.75 Å. It seems that, upon
deprotonation of the 1-pyrazolyl-NH on C,N,Npyrazolyl, Coulombic
repulsion between the negatively charged cyclometalating ligands,
together with the compensation from the establishment of the two
intramolecular π-π interactions between the pyrazolyl rings and
the phosphino phenyl rings, cleaves the Pt-Pt interaction between
the two [Pt(L-)] moieties. Such a cleavage diminishes the 3MMLCT
emission and enhances the 3MLCT emissions from the two
noninteracting [Pt(L-)] units.
Figure 4. Crystal structures showing the opening and closing of the
molecular pivot-hinge by the protonation and deprotonation of the 1-pyra-
zolyl-NH of the C,N,Npyrazolyl ligands of the binuclear cycloplatinated
complex 1. One phosphino phenyl ring on each side of the µ-dppm bridge
is omitted for clarity.
π-π interactions in both organic and aqueous organic media using
the binuclear cycloplatinated complex 1 with the new C,N,Npyrazolyl
ligand. The dynamic actions involved resemble mechanical motions
of a pivot-hinge and are unambiguously captured by X-ray
crystallography.
The switching from the lower energy 3MMLCT emission to the
higher energy 3MLCT emission via the cleavage of the Pt-Pt
interaction can be reversed by the addition of acid (Figure 3). Such
Acknowledgment. The work described in this paper was funded
by the Research Grants Council of Hong Kong SAR, China (CityU
1108/02P).
Supporting Information Available: Experimental details and
characterizations of 1‚(ClO4)2, X-ray crystallographic data of 1 (pro-
tonated and deprotonated forms), and spectroscopic/spectrofluorometric
titrations of 1. This material is available free of charge via Internet at
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