Mixed-Valent Compounds
FULL PAPER
Conclusions
Experimental Section
The availability of binaphthyridylamide (bna) as a penta-
dentate ligand has led to the synthesis and characterization
of a series of novel linear chain complexes of nickel contain-
ing five metal atoms. These complexes are closely related to
the already large family of nickel polypyridylamides with
which they share the helical shape of the ligand coating and
a marked propensity to attach axial ligands at both ends of
the metal chain. As far as the electronic structure is con-
Materials: All reagents and solvents were purchased from commercial
sources and were used as received unless otherwise noted. The precur-
sors, 2-amino-1,8-naphthyridine and 2-chloro-1,8-naphthyridine were pre-
[
31]
pared according to the literature procedures.
Binaphthyridylamine (Hbna): 2-Amino-1,8-naphthyridine
0 mmol), 2-chloro-1,8-naphthyridine (1.64 g, 10 mmol), tBuOK (1.12 g
10 mmol), [Pd2(dba) ] (0.91 mg 0.1 mmol) and dppp (82 mg, 0.2 mmol)
(1.45 g,
1
AHCTREUNG
3
were placed in a flame-dried flask under argon. The mixture was stirred
and refluxed in THF (100 mL) for 72 h. The solvent was removed under
reduced pressure. The mixture was washed by water and the precipitate
1
0+
cerned, complex 2 exhibits the [Ni5]
metal core typical of
2 2
was extracted by CH Cl to obtain light yellow product. Yield: 1.97 g,
[
Ni5
A
C
H
T
R
E
U
N
G
(tpda) Cl ] (5) and related pentanickel chain complexes.
1
4
2
72%; H NMR (400 MHz; [D]DMSO): d=11.00 (s, 1H), 8.91 (dd, J=
As in other nickel chains, the new complex exhibits an anti-
ferromagnetic interaction connecting the Ni atoms located
at both ends of the chain, which are promoted to high spin
because of their square-pyramidal coordination environ-
ment. At variance with the polypyridylamide complexes,
which are usually neutral, complex 2 supports a charge of
5.97, 2.28 Hz, 2H), 8.34 (m, 6H), 7.43 ppm (dd, J=12.23, 3.56 Hz, 2H);
II
+
MS
[Ni
thalene (50 g), and NiCl
A
T
E
N
(FAB): m/z: 274 [M+H] .
A
T
E
N
5
A
H
R
U
G
4
(Cl)
2
]
A
T
E
N
[PF
6
]
2
(1): A mixture of Hbna (273 mg, 1 mmol), naph-
(161 mg, 1.25 mmol) was placed in an Erlen-
2
meyer flask. The mixture was heated (about 2008C) for 15 h. A solution
of tBuOK (112 mg, 1 mmol) in n-butanol (10 mL) was added dropwise.
The solution then turned to dark green. The mixture was heated for an-
other 10 h, cooled to about 708C, and treated with hexane to precipitate
the metal complexes. The precipitate was washed with hexane to remove
4
+ in relation with the monoanionic character of the bna
ligand. The magnetic coupling in 2 is found significantly
weaker than in 5. An important characteristic of this family
of complexes is the accessibility of a stable, reduced form
the residual naphthalene. The metal complex was extracted with CH
2 2
Cl
(
500 mL), and treated with KPF (92 mg, 0.5 mmol) in CH Cl (50 mL).
6
2
2
The resulting solution was stirred for a week and dried under vacuum.
The solid was extracted with CH Cl and layered with hexane. After one
8
+
corresponding to a [Ni5]
metal core, still unprecedented in
2
2
1
the collection of pentametallic chain complexes. In the re-
week, deep green crystals were obtained. Yield: 261 mg, 60%; H NMR
400 MHz; CD CN): d=23.69 (4H), 28.92 (4H), 32.54 (4H), 61.96 (4H),
ca. 110 ppm (very broad peak); MS(MALDI): m/z: 1454 [Ni
max(e)=316 (4.72), 395 (9.01),
8
+
(
3
duced complex 1, as in the other [Ni5] complex 3 charac-
A
H
R
U
G
5
-
terized in the present work, the extra pair is shared between
+
A
H
R
U
G
4
(Cl)
2
+H] ; UV/Vis (CH
3
CN):
[PF
l
the {Ni
A
C
H
T
R
E
U
N
G
(napy) } moieties, but the unsymmetrical environ-
4
ꢀ1
ꢀ1
2
4
6
ment of these fragments in the complex prevents a full de-
A
H
R
U
G
5
A
H
E
N
4
2
]
A
H
R
U
G
6
]
4
2
]
A
H
R
N
6
] (130 mg, 0.396 mmol) was added
Cl (500 mL)
+
localization of the mobile electron, as in [Ni (napy) X ] .
A
T
E
N
2 4 2
2
2
Near-IR spectroscopy and DFT calculations agree to suggest
that both {Ni2(napy) } fragments in 1 could be considered as
under argon atmosphere. The red powder came out after the solution
was stirred overnight. The mixture then was filtered. The remaining solid
ACHTREUNG
4
was dissolved in CH
diethyl ether into this solution. Yield: 125 mg 63%; H NMR (400 MHz;
CD CN): d=7.60 (4H), 9.08 (4H), 23.5 (4H), 26.2 (4H), ca. 90 (very
broad peak); MS
(CH CN): lmax(e)=265 (7.76), 384 (17.34), 526 nm (1.19 10 m cm ).
[Ni (bna) (NCS) [NCS] (3): NaNCS (32 mg, 0.396 mmol) was added to
a solution of compound 1 (174 mg, 0.099 mmol) in CH Cl (500 mL)
under argon atmosphere. The resulting solution was stirred for a week
and dried at vacuum. The solid was extracted with CH Cl (500 mL) and
3
CN. Red crystals were obtained by slow diffusion of
mixed-valent bimetallics and assigned to Robin–Day class II
materials. Electrochemical measurements and the N-IR
spectra can be interpreted in favour of a strong magnetic
coupling between these fragments. A fit of the magnetic sus-
ceptibility curve by means of the usual Heisenberg Hamilto-
nian assuming a coupling between two fully delocalized
magnetic centres yields a relatively strong exchange con-
1
3
+
A
H
R
U
G
5 4 2
(MALDI): m/z: 1454 [Ni (bna) (Cl) +H] ; UV/Vis
A
T
E
N
4
ꢀ1
ꢀ1
3
A
H
R
U
G
5
A
H
R
U
G
4
A
T
E
N
2
]
A
H
R
U
2
2
2
ꢀ
1
2
2
stant J=ꢀ34 cm . However, DFT calculations based upon
similar assumptions failed to confirm such a large order of
magnitude, and the lack of an appropriate model describing
the coupling between two fragments subject to double-ex-
change leaves the question open to further investigation. Fi-
nally, one of the ultimate goals of the current interest to-
wards nanowires, namely nanoelectronics, has been ap-
proached in a practical way by means of measurements of
layered with hexane. After one week, deep green crystals were obtained.
1
Yield: 134 mg, 84%; H NMR (400 MHz, CD CN): d=23.23 (4H), 29.19
3
(4H), 32.95 (4H), 62.12 (4H), ca. 110 (very broad peak); MS
A
C
H
T
R
E
U
N
G
(MALDI):
+
m/z: 1499 [Ni
94 (9.66), 674 nm (0.96 10 m cm ).
[Ni (tpda) (SCN) ] (4): Compound 4 was synthesized according to our
5
A
H
R
U
G
4
A
T
E
N
2
3
4
ꢀ1
ꢀ1
3
A
H
R
U
G
5
A
H
R
U
4
A
H
R
U
G
2
[
16]
previous report and used in STM studies.
Physical measurements: Magnetic susceptibility data were collected on a
Quantum external magnetic field 3000G instrument. FAB mass spectra
were taken on a JEOL HX-110 HF double-focusing spectrometer operat-
ing in the positive ion detection mode. The MALDI spectra were per-
the single-molecular conductance of [Ni
A
H
R
U
G
A
H
R
U
G
5
A
C
H
T
R
E
U
N
G
[NCS] (3) and [Ni
A
H
R
N
A
H
R
U
G
2
5
8
formed on
a
MALDI-TOF mass spectrometer Voyager DE-STR.
H NMR spectra for organic and inorganic complexes were recorded in
DMSO and CD CN with a Bruker AMX 400 MHz spectrometer. Elec-
tronic spectra of 1, 2, and 3 in CH CN were measured in a range of 250–
junction method. The reduced, [Ni5] complex 3 was found
1
1
0+
more conductive by about 40% than the standard [Ni5]
3
compound 4, which provides the first evidence that nickel-
chain complexes could possibly approach the high conduc-
tance values previously reported for cobalt or chromium
3
2500 nm on a Perkin–Elmer Lambda 900 UV-Vis-NIR Spectrometer.
Electrochemistry was carried out on a CH instrument (Model 750 A),
using CH Cl solvent with 0.1m TBAP and 1 mm analytes. Cyclic voltam-
[3]
2
2
wires.
metry was recorded with a home-made three-electrode cell equipped
2
with a BAS glassy carbon (0.07 cm ) disk as the working electrode, a plat-
inum wire as the auxiliary electrode, and a home-made Ag/AgCl (satu-
rated) reference electrode. The reference electrode was separated from
Chem. Eur. J. 2007, 13, 8667 – 8677
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8675