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and absorption intensity was observed for the square
36
(
∆
e
=
−
15
−
1
−
1
at 336 nm). This change of intensity upon coordination of
silver with the square
M
cm
qualitatively correlates to large binding
constant as expected for the
36
π
-complex
36•Ag
[87].
O
4+
6TfO
-
O
4+
4TfO
-
O
O
PPh
2
PPh
2
Pt
N
ML
2
Pt
N
ML
2
P
Ph
2
Ph
2
Ag
+
N
N
2 AgOTf
36
Ag
+
N
N
Ph
2
P
Ph
2
P
ML
2
N
Pt
ML
2
N
Pt
Ph
2
P
Ph
2
P
O
O
O
O
N
M = Pd, L = PEt
3
(
35
);
M = Pt, L = R-BINAP (
37
); S-BINAP (
38
)
Guests
N
Guests:
O
4+
4TfO
-
N
O
M = Pd (
39a
)
PPh
2
N
Pt
N
ML
2
P
Ph
2
a
Ag
+
N
N
N
M = Pd (
39b
)
N
Ag
+
N
N
Ph
2
P
b
N
ML
2
Pt
Ph
2
P
O
39
O
Scheme 10.4
The subsequent coordination of guest molecules such as
tetramethylpyrazine (a) or phenazine (b) to form the corresponding
inclusion complexes,
, resulted in further decrease
of absorption intensity and Cotton effect (
39a
and
39b
−
∆
e
=
−
7 and
−
6 M
1
−
1
at 336 nm, respectively). Small blue shifts in absorption
spectra (11 and 1 nm, respectively) were also observed indicating
further delocalization of electron density afforded by neutral
guests and silver complexation [88]. Moreover, the introduction of
another chiral ligand in molecular squares such as BINAP showed
more prominent decrease in Cotton effect and intensity because
BINAP is conformationally more rigid, thus having a Cotton effect
approximately double than that of diphosphene. For example, Pt
cm
−
Pt
squares
37
and
38
showed maxima shift of about 15 and 12 nm on
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