Chemistry Reference
In-Depth Information
Table 2
Intermolecular halogen bond distances (in A) in the iodotetrathiafulvalene salts
with Cl
-
or Br
-
anions, measured at 293 K
Cl
-
Br
-
C-I
···
C-I
···
Refs.
(
D
anis
= 3.54A)
(
D
anis
= 3.60A)
(IET)
2
X
-
3.213
[36]
(DIET)
2
X
·
(H
2
O)
2
3.313(1)
3.211(2)
[62]
(DIETSe)
2
X
·
CH
2
Cl
2
3.074(5)
3.136(1)
[62]
(DIEDO)
2
X
3.252(2)
3.3569(9)
[62]
3.213(2)
3.362(1)
3.521(2)
3.5872(8)
3.113(2)
3.2720(8)
(DIEDO - STF)
2
X
3.316(11)
3.382(12)
[62]
3.235(8)
3.372(9)
3.603(10)
3.611(11)
3.213(12)
3.268(14)
because of the structural requirements of the strong halogen bonding inter-
actions.
3.3.1.2
Polyhalide Anions as Halogen Bond Acceptors
After the description of halogen bonded systems with the simplest Cl
-
or
Br
-
anions, we now describe those salts involving complex polyhalide an-
ions such as I
3
-
or IBr
2
-
as halogen bond acceptors. Several salts have
been obtained upon electrocrystallization with EDT-TTF-Br
2
[66], BTM-TTF-
Br
2
[61, 64], EDO-TTF-I
2
[67] or EDT-TTF-I
2
[66], which all exhibit type II
C - Br(I)
Br(I) interactions. A good example is offered by the 2 : 1 salt
(EDT-TTF-I
2
)(I
3
) where halogen bonding interactions are identified, not only
between the iodo TTF and I
3
-
but also between iodo TTFs (Fig. 8). As shown
in Table 3, the intermolecular distances, albeit shorter than the correspond-
ing
D
anis
, are not as short as observed above in Sect. 3.3.1.1, the signature of
a weaker halogen bonding interaction with anions where the negative charge
is now delocalized on three rather than on one atom.
Moreover, it was shown that the presence of Hal
···
Hal interactions be-
tween the partially oxidized molecules also contribute to the electronic delo-
calization. Indeed, the presence of non-zero atomic coefficients on the halo-
gen atoms in the HOMO of EDT-TTF-Br
2
or EDT-TTF-I
2
[66], together with
the short Hal
···
···
Hal contacts, leads to a sizeable increase of the band disper-
sion and stabilizes a rare
β
structure through the side-by-side arrangement
of the inversion-centred dyads connected by Hal
···
Hal interactions. Both
I
3
-
salts are semiconductors with room temperature conductivities around
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