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Scheme 10.1 Structure and abbreviation of alkyldiammonium ions
n ¼
2 and 4). A
+
, which is coordinated by eight oxygen atoms, links both intra- and
inter-chain [Pt
2
(pop)
4
] units by A
þ
O coordination bond. B
2+
links inter-chain
[Pt
2
(pop)
4
] units by N
þ
O hydrogen bond.
Other alkali metal ions, Li
+
,Na
+
, and Cs
+
, were not able to be introduced
because of the size mismatch [
31
]. In the case of alkyldiammonium ions, only the
B
2+
which has three to five atoms in main backbone between terminated -NH
3
+
substituents was able to be introduced. The selectivity of the B
2+
can be explained
as follows.
The B
2+
exist in the space surrounded by the four [Pt
2
(pop)
4
] units connected by
A
þ
H
4H
2
O in Fig.
10.2
).
Because the length of coordination bonds is limited, the size of the space is less
variable. This is the reason why longer alkyldiammonium ions such as
H
3
NC
6
H
12
NH
3
2+
cannot be introduced as one of the binary countercations. Simi-
larly, the shorter alkyldiammonium ions such as H
3
NC
2
H
4
NH
3
2+
cannot form the
hydrogen bonding network among the pop ligands, inducing the destabilization of
the MMX chains with binary countercations.
O coordination bonds (e.g., K
2
(NC
3
N)[Pt
2
(pop)
4
I]
10.2.2 Determination of Electronic State by the Crystal Structure
and Polarized Raman Spectra
As mentioned above, it has been known that the oxidation state are concerned with
the distance between bridging iodide ion and platinum ion (Pt-I distance). As the
oxidation number becomes higher, Pt-I distance becomes shorter. Therefore, the
electronic state can be determined from the chain structure.
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