Manipulation of electronic structure via supporting ligands: A charge disproportionate model within the linear metal framework of asymmetric nickel string [Ni7(phdptrany)4Cl](PF6)

Article abstract of DOI:10.1039/b926315b

This paper describes the synthesis and physical properties of an uniquely asymmetric heptanickel string complex exhibiting a charge disproportionate model along the linear nickel framework.

Full text of DOI:10.1039/b926315b

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Manipulation of electronic structure via supporting ligands: a charge
disproportionate model within the linear metal framework of asymmetric
nickel string [Ni7(phdptrany)4Cl](PF6)w
ab
Shao-An Hua,a Gin-Chen Huang,a Isiah Po-Chun Liu,z Jau-Huei Kuo,a Ching-Hong Jiang,a
Chien-Lan Chiu,c Chen-Yu Yeh,c Gene-Hsiang Leea and Shie-Ming Peng*ab
Received 14th December 2009, Accepted 13th May 2010
First published as an Advance Article on the web 4th June 2010
DOI: 10.1039/b926315b
This paper describes the synthesis and physical properties of an
uniquely asymmetric heptanickel string complex exhibiting a charge
disproportionate model along the linear nickel framework.
1D transition-metal complexes are of considerable significance
Scheme 1
for their potential applications as molecular wires, since these
complexes may be envisaged as the macroscopic wires in
miniature at the atomic scale.1 In order to design new
molecular wires, we have reported that novel metal string
complexes can be synthesized by using naphthyridyl-modulated
ligands.2 The modulation of the supporting ligands results in a
remarkable influence on the physical properties of the oligo-
nickel string complexes because of the formation of mixed-
an intriguing charge disproportionate model controlled by the
supporting ligand phdptrany3ꢀ
.
The overall synthetic routes to the H3phdptrany ligand, and
then to complex 1, are summarized in Scheme S1 (see ESIw).
The H3phdptrany ligand was prepared by the reaction of
aniline and 2-(bromodipyridyl-diamino)-1,8-naphthyridine
with a palladium catalyst. Treatment of H3phdptrany with
valence (MV) dinickel units [Ni2(napy)4]3+ (napy
=
t
NiCl2 in the presence of BuOK, followed by excess of KPF6,
naphthyridyl group) within the linear metal framework. It is
known that the mixed-valency plays an important role in
the development of novel electronic materials.3 This MV
[Ni2(napy)4]3+ unit has been shown to exhibit a great electron
mobility and can significantly enhance the conductance of
metal string complexes.2a
generated compound 1.
The crystal structure of 1 is depicted in Fig. 1.y The linear
heptanickel framework is helically wrapped by four
phdptrany3ꢀ ligands, which exhibits approximate C4 symmetry.
The Ni(1)–Ni(2), Ni(1)–N and Ni(2)–N distances are 2.327(1)
A, 2.145(6) A and 2.024(6) A, respectively, in accordance with
the typical structural characteristics for the one-electron
reduced S = 3/2 MV [Ni2(napy)4]3+ unit.2 Interestingly, the
Ni(5)–Ni(6) and N(6)–Ni(7) bond lengths of 1 are 2.253(1) and
In addition to above advances, another breakthrough in this
field is the development of asymmetric ligands. By utilizing
these ligands, the asymmetric electronic structures of metal
frameworks, or the arrangement of hetero-metal ions of metal
string complexes can be controlled.2b,c Promoted by these
recent studies, we designed
a new asymmetric ligand
H3phdptrany (2-(phenyldipyridyltriamino)-1,8-naphthyridine,
Scheme 1). The deprotonated counterpart phdptrany3ꢀ shows
two different coordinated abilities at both ends, since the
naphthyridyl terminal is neutral and the phenylamido part is
anionic. This new ligand can then be used to generate the
related novel metal string complex. Herein, we report the
synthesis and physical properties of the asymmetric heptanickel
string complex, [Ni7(phdptrany)4Cl](PF6) (1), which displays
a Department of Chemistry, National Taiwan University, Taipei, 106,
Taiwan, ROC. E-mail: smpeng@ntu.edu.tw;
Fax: (+886)2-8369-3765
b Institute of Chemistry, Academia Sinica, Taipei, 115, Taiwan, ROC
c Department of Chemistry, National Chung Hsing University,
Taichung, Taiwan
w Electronic supplementary information (ESI) available: Synthesis of
H3phdptrany and 1; Scheme S1, Table S1, computational details,
X-ray structure determinations. CCDC 705297. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/
b926315b
Fig. 1 ORTEP view of the molecular structure of the [Ni7(phdptrany)4-
Cl](PF6) (1, 30% probability). Selected bond distances (averaged):
Ni(1)–Cl 2.405(2), Ni(1)–Ni(2) 2.327(1), Ni(2)–Ni(3) 2.314(1),
Ni(3)–Ni(4) 2.287(1), Ni(4)–Ni(5) 2.255(1), Ni(5)–Ni(6) 2.253(1),
Ni(6)–Ni(7) 2.305(1), Ni(1)–N 2.145(6), Ni(2)–N 2.024(6), Ni(3)–N
1.902(6), Ni(4)–N 1.909(6), Ni(5)–N 1.889(6), Ni(6)–N 1.912(6),
Ni(7)–N 1.923(6) A.
z Current address: Institut fur Anorganische Chemie, Universitat
¨
¨
Bonn, Bonn, Germany.
ꢁc
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Moreover, the wmT value decreases as the temperature lowers
and reaches the minimum (1.10 cm3 Kmolꢀ1) below 50 K,
which indicates that the S = 3/2 and S = 1/2 centers are
antiferromagnetically coupled and the ground state of 1 is S = 1.
The magnetic susceptibility data were tentatively fitted by a
simple isotropic Heisenberg model (H = ꢀ2JABSASB)5a with
the development of the van Vleck equation appropriate to
SA = 3/2 and SB = 1/2.5b The best fit parameters are g3/2 = 2.17,
g1/2 = 2.21 and J = ꢀ53.3 cmꢀ1, which shows antiferro-
magnetic interaction between S = 3/2 and S = 1/2 centers.
To gain more insight into the electronic structure of 1,
DFT/B3LYP calculations were carried out on 1. For the sake
of simplicity, the phenyl rings of phdptrany3ꢀ were replaced
by hydrogen atoms.6 The geometry of 1 was optimized in two
spin states 5A (S = 2) and 3B (S = 1) for comparison
(Scheme 2). The 5A state represents the charge disproportionate
model, while the 3B state represents the charge localized
Fig. 2 Near-IR spectrum of 1 CH2Cl2. Concentration: 2 ꢂ 10ꢀ5 M.
2.305(1) A, respectively, shorter by B0.05 A in comparison
with those of the reported asymmetrical hexanickel analogue
(Ni(4)–Ni(5) and N(5)–Ni(6) bond distances in (4,0)-[Ni6-
(napany)4Cl](BF4)2, napany2ꢀ = (2-naphthyridylamido-7-
phenylamido-1,8-naphthyridine).2b
5
3
model. The optimized bond distances of A and B states are
3
displayed in Fig. 4. The computed geometry of the B state
shows an elongated Ni(1)–Ni(2) bond length, which significantly
deviates from the observed bond distance. On the contrary, the
5
geometry optimized for the A state is in agreement with the
The shortening of these Ni–Ni bonds close to the phenylamido
groups of 1 suggests that the formation of the delocalized
metal–metal bonding within the Ni(5)–Ni(6)–Ni(7) fragment
due to the incomplete population of the s* orbital. This
observation is reminiscent of the one-electron oxidized penta-
nickel complex.4 The structural features of 1, therefore,
suggest an unprecedented internal charge disproportionate
mechanism along the metal framework: the nickel ion
coordinated to the neutral naphthyridyl groups undergoes
one-electron reduction, while those coordinated close to the
anionic phenylamido groups undergo one-electron oxidation.
The near-IR spectrum of 1 reveals two broad absorptions at
1200 (e = 6890) and 1700 nm (e = 2890, Fig. 2). These two
peaks can be tentatively assigned to intervalence charge transfer
(IVCT) bands, which suggest the existance of mixed-valence
units within the metal framework.2a
observed structure, especially the trends of Ni(1)–Ni(2) and
Ni(2)–N bond lengths.2a Furthermore, the calculated
Ni(5)–Ni(6) and Ni(6)–Ni(7) distances of the 5A state are
3
shorter than those of B, correspondence with the experimental
results. The calculated energy for the 5A state is lower by
The temperature-dependent magnetic susceptibility of 1 was
measured in the range 4–300 K (Fig. 3). The wmT value at
300 K is 2.10 cm3 Kmolꢀ1, which is in agreement with the
theoretical value for two independent S = 3/2 and S = 1/2
magnetic centers (2.25 cm3 Kmolꢀ1). This value supports the
existance of the S = 3/2 [Ni2(napy)4]3+ unit and suggests that
the spin state of the one-electron oxidized fragment is 1/2.
Scheme 2 Two electronic configurations calculated for 1.
Fig. 4 Two electronic configurations calculated for 1; selected inter-
atomic distances observed (bottom, plain), computed 5A (middle,
3
bold) and B (top, italics) for 1.
Fig. 3 Plot of wmT versus T for 1. The solid line represents the
theoretical fit.
ꢁc
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Table
1
Details of the gross atomic spin orbital populations
asymmetry results from charge disproportionation, complex 1
might also have a potential application as a molecular
rectifier.2c,8
(a spin ꢀ b spin, electrons; Mulliken analysis) calculated for the
5
high-spin A state of complex 1
The authors thank the National Science Council of the
Republic of China for financial support.
Ni1
Ni2
Ni3
Ni4
Ni5
Ni6
Ni7
sa
db
pc
0.58
0.83
0.03
0.40
0.81
0.03
0.06
0.01
0.00
0.09
0.00
0.00
0.26
0.00
0.01
0.35
0.03
0.01
0.18
0.02
0.00
Notes and references
a
b
c
y Crystal data for 1: Ni7C106H86N28Cl9PF6, Mw = 2627.02, mono-
clinic, space group P21/c, a = 41.262(2) A, b = 13.7958(7) A, c =
18.5806(9) A, a = 901, b = 99.7034(1)1, g = 901, V = 10425.5(9) A3,
Z = 4, d(calcd) = 1.674 Mg mꢀ3, T = 150(2) K, 49140 reflection
dz
2
spin population. dx ꢀy + dxy spin population. dxz + dyz spin
2
2
population.
0.63 eV than that for the 3B state. This substantial energy
difference and the ideal optimized structure of 5A suggests that
the charge disproportionate model of 1 is indeed more stable,
which results in self-redox reactions of nickel ions in the period
of synthesis. It is noteworthy that the approximation of the
antiferromagnetic state (S = 1) of 1 by performing the broken
symmetry (BS) approach7 is unsuccessful, which might be
attributed to the fact that compound 1 contains two different
MV systems, (Ni2)3+ and (Ni3)7+. Since the BS approach is
typically based on a pure Heisenberg system, a comprehensive
treatment of the BS state of 1 is far beyond the possibilities of
the BS approach.2a The spin distribution of the 5A state shows
1.44 e on the terminal Ni(1) and 1.24 e on Ni(2), which exhibits
the partial delocalized behaviour.2a It appears from a more
detailed analysis (Table 1) that this partial delocalization
occurs along the metal axis through a transfer of a b-spin
electron density from Ni(2) to Ni(1) in 1, and leads to the
formation of a three-electron-two-centre s bond.2a Furthermore,
the spin distribution on the terminal Ni(5)–Ni(6)–Ni(7) unit
mainly concentrates on the dz2 orbitals, which indicates that
the delocalization of b-spin electrons through the s pathway
within the (Ni3)7+ unit (Scheme 2, top). This delocalization
results from the formation of a nickel–nickel s bond, since the
s* spin density was depopulated upon one-electron oxidation.4
The related Ni–Ni distances of 1, therefore, are shorter than
those of its analogue.2b It is interesting to note that the spin
densities on closed-shell Ni(3) and Ni(4) are slightly positive,
which indicates the electronic communication between (Ni2)3+
and the (Ni3)7+ terminus. This electronic communication
provides a pathway for AF interaction and enhances the
electron mobility within whole heptanickel framework.
collected, 18168 independent, Rint = 0.1020, R1 = 0.0664, wR2
0.1570 for all data.
=
1 (a) Extended Linear Chain Compounds, ed. J. S. Miller, Plenum,
New York, 1982, vol. 1–3; (b) S. Roth, One-Dimensional Metals,
VCH, New York, 1995; (c) M. H. Chisholm and N. J. Patmore,
Acc. Chem. Res., 2007, 40, 19; (d) L. A. Barrios, D. Aguila,
O. Roubeau, P. Gamez, J. R. -Arino, S. J. Teat and Guillem Aromı
Chem.–Eur. J., 2009, 15, 11235; (e) J. K. Bera and K. R. Dunbar,
´
,
Angew. Chem., Int. Ed., 2002, 41, 4453; (f) T. Ruffer, M. Ohashi,
¨
A. Shima, H. Mizomoto, Y. Kaneda and K. Mashima, J. Am.
Chem. Soc., 2004, 126, 12244; (g) Y. Tatsumi, T. Murahashi,
M. Okada, S. Ogoshi and H. Kurosawa, Chem. Commun., 2008,
477; (h) Y. Takemura, H. Takenaka, T. Nakajima and T. Tanase,
Angew. Chem., Int. Ed., 2009, 48, 2157.
2 (a) I. P.-C. Liu, M. Benard, H. Hasanov, I.-W. P. Chen,
´
W.-H. Tseng, M.-D. Fu, M.-M. Rohmer, C.-h. Chen, G.-H. Lee
and S.-M. Peng, Chem.–Eur. J., 2007, 13, 8667; (b) I. P.-C. Liu,
C.-F. Chen, S.-A. Hua, C.-H. Chen, H.-T. Wang, G.-H. Lee and
S.-M. Peng, Dalton Trans., 2009, 3571; (c) I. P.-C. Liu, C.-H. Chen,
C.-F. Chen, G.-H. Lee and S.-M. Peng, Chem. Commun., 2009, 577;
(d) I. P.-C. Liu, W.-Z. Wang and S.-M. Peng, Chem. Commun.,
2009, 4323.
3 (a) K. Otsubo, A. Kobayashi, H. Kitagawa, M. Hedo, Y. Uwatoko,
H. Sagayama, Y. Wakabayashi and H. Sawa, J. Am. Chem. Soc.,
2006, 128, 8140; (b) M. Yamashita, S. Takaishi, A. Kobayashi,
H. Kitagawa, H. Matsuzaki and Hiroshi Okamoto, Coord. Chem.
Rev., 2006, 250, 2335; (c) K. Uemura, K. Fukui, Hi. Nishikawa,
S. Arai, K. Matsumoto and H. Oshio, Angew. Chem., Int. Ed., 2005,
44, 5459; (d) M. Mitsumi, H. Ueda, K. Furukawa, Y. Ozawa,
K. Toriumi and M. Kurmoo, J. Am. Chem. Soc., 2008, 130, 14102.
4 (a) J. F. Berry, F. A. Cotton, P. Lei, T. Lu and C. A. Murillo,
Inorg. Chem., 2003, 42, 3534; (b) P. Kiehl, M.-M. Rohmer and
M. Benard, Inorg. Chem., 2004, 43, 3151.
´
¯
5 (a) M. Yonemura, Y. Matsumura, H. Furutachi, H. Okawa and
D. E. Fenton, Inorg. Chem., 1997, 36, 2711; (b) For two magnetic
centres with SA = 3/2 , SB = 1/2, the van Vleck equation can be
developed as:
Nb2 10g22 expðꢀ4J=kTÞ þ 2g21 expðꢀ4J=kTÞ
wM
¼
kT
5 þ 3 expðꢀ4J=kTÞ
In summary, we have synthesized and characterized the
longest asymmetric heptanickel string complex. The metal
framework of 1 contains two different MV units, (Ni2)3+
and (Ni3)7+, due to its one-electron reduction and oxidation.
It is the first example of metal string complexes that possesses
this unusual charge disproportionate metal chain. Moreover,
the spin distribution of 1 shows that the (Ni2)3+ and (Ni3)7+
terminus are electronically coupled. This behaviour suggests
that compound 1 not only contains two MV (Ni2)3+ and
(Ni3)7+ units, but also possesses a third extended MV
[(Ni2)3+–(Ni3)7+] system. Since mixed-valent units had been
in which N is Avogadro’s constant, g is the Lande factor, b is the
Bohr magneton, k is the Boltzmann constant, T is temperature
and g1 and g2 are g factors associated with the total spin states
ST = 1 and 2, respectively. The g factors were expressed using
the local g3/2 and g1/2 values as follows: g1 = (5g3/2 ꢀ g1/2)/4 and
g2 = (3g3/2 + g1/2)/4.
6 The calculations were preformed using Gaussian 03w (Revision B.05):
M. J. Frisch et al., see ESI.
7 (a) A. P. Ginsberg, J. Am. Chem. Soc., 1980, 102, 111;
(b) L. Noodleman, J. Chem. Phys., 1981, 74, 5737;
(c) L. Noodleman and E. J. Baerends, J. Am. Chem. Soc., 1984,
106, 2316.
8 See for example and references therein (a) R. M. Metzger,
Chem. Rev., 2003, 103, 3803; (b) G. Ho, J. R. Heath,
´
M. Kondratenko, D. F. Perepichka, K. Arseneault, M. Pezolet and
M. R. Bryce, Chem.–Eur. J., 2005, 11, 2914; (c) J.-W. Ying, A. Cordova,
T. Y. Ren, G.-L. Xu and T. Ren, Chem.–Eur. J., 2007, 13, 6874.
proved to be
a
conductance-enhanced material,2a this
extended MV [(Ni2)3+–(Ni3)7+] system of 1 is expected to
exhibit higher electronic conductance than traditional MV
nickel strings do. It is noteworthy that because of the electronic
ꢁc
This journal is The Royal Society of Chemistry 2010
5020 | Chem. Commun., 2010, 46, 5018–5020