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R
R
R
N
N
N
N
O
N
N
N
N
O
N
N
N
H
R
R
R
4
5
6
R
N
N
N
N
N
N
N
N
R
7
8
R
R
N
N
N
N
N
R
R
9
N
N
N
NN
N
N
NN
N
N
N
N
N
10
11
R
R
R
R
OCnH
2n+1
OCnH
2n+1
H
2n+1
CnO
R = F ; OCH
3
;
O
O
Figure 7.3 Schematic representation of imino-py ligands bearing various functionalities,
including flexible appendages.
employing the condensation of aldehydes with the aniline derivatives in the presence of
catalytic amounts of acid.
With Cu(I), ligands
6
and
7
afforded deep-green dinuclear complexes in near-quantita-
tive yields. Here, the Cu(I) cations bind preferentially at the N
py
,N
im
part of the ligand
rather than at the central N
py
,N
py
fragment, a coordination mode deduced from NMR
and FT-IR spectroscopy and confirmed by an X-ray structure determination for each (Fig-
ure 7.4).
Indeed, the solid-state structures are best described as double-stranded helicates with
the two copper(I) cations having center to center separations of 2.885 and 2.748 A
, respec-
tively, for [Cu
2
(
7
)
2
](ClO
4
)
2
and [Cu
2
(
6
)
2
](ClO
4
)
2
with R
F [33]. These separations are
among the shortest metal-metal distances yet found in inorganic helicates [40], being of
the same order as found in many copper-containing enzymes [41], but there is no indica-
tion of a copper-copper bond. Each ligand wraps around the two copper(I) cations with
ΒΌ
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