Download HAT(CN)6: a new building block for molecule

Synthetic Metals 122 (2001) 535±542
HAT(CN)6: a new building block for molecule-based magnetic materials
P.S. Szalay, J.R. GalaÂn-MascaroÂs, R. CleÂrac, K.R. Dunbar*
Department of Chemistry, Texas A&M University, PO Box 30012, College Station, TX 77842-3012, USA
Abstract
The ability of reduced forms of HAT(CN)6 to be used as ligands to construct novel magnetic materials is reported and discussed herein.
Binary compounds of ®rst row transition metals with discrete or extended polymeric structures are presented. All compounds exhibit
characteristic paramagnetic behaviour except for a polymeric {Cu-HAT(CN)6} phase that behaves as a canted antiferromagnet below 6 K.
# 2001 Elsevier Science B.V. All rights reserved.
Keywords: Organic radicals; Magnetic properties; N heterocyclic ligand; Coordination chemistry
1. Introduction
Recent activity in molecule-based materials has led to
important achievements in a number of technologically
important areas. Novel molecular and extended networks
constructed from organic and inorganic building blocks have
been found to behave as molecule-based conductors and
superconductors [1], optically active compounds [2] and
magnets [3]. Furthermore, the versatility of molecule-based
materials allows for the design of ``hybrid'' materials with
the possibility of the co-existence of properties, or even
synergy between them [4,5]. In particular, magnetism has
been one of the ®elds that has undergone signi®cant development, with molecule-based magnetic materials that mimic
and even improve on the properties of classic inorganic
magnets (e.g. critical temperatures [6,7], coercive ®elds
[8,9]) having been reported.
A common feature of molecule-based magnets is the
presence of polymeric networks of paramagnetic metals
bridged by ligands capable of promoting magnetic interactions between the localized d-electrons. In addition to the
different pathways for magnetic exchange through the
ligand (s versus p), it is important to consider the size of
the linker which is typically inversely related to the strength
of the interaction. Consequently, most examples of molecular-based magnets are based on ligands consisting of only
a few atoms such as CN [7,10±15], N(CN)2 [8,16±19],
and C2O42 [9,20±23]. One strategy for inducing stronger
magnetic interactions with longer linkers is to use organic
*
Corresponding author. Tel.: ‡1-979-845-5235; fax: ‡1-979-845-7177.
E-mail address: [email protected] (K.R. Dunbar).
radicals as ligands, due to the ability of unpaired electrons on
the ligand to interact with those of the metals. Novel
magnets have been obtained in this way with organic
acceptors such as TCNE [6,24±28], and TCNQ [29,30].
In the vein of organoradical linkers, the hexanitrile derivative of 1,4,5,8,9,11-hexazatriphenylene, namely hexaazatriphenylenehexacarbonitrile (HAT(CN)6) (Scheme 1),
offers interesting possibilities for preparing new magnetic
materials with ®rst row transition metals. The cyclic voltammogram of HAT(CN)6 in acetonitrile, versus Ag/Ag‡,
reveals two reversible one-electron reductions located at
E1=2 ˆ 0:064 and 0.450 V. Reduction by a third electron
leads to decomposition as evidenced by an irreversible
cathodic feature at 1.160 V (Fig. 1) [31].1 The accessibility of the ®rst two redox processes renders [HAT(CN)6]1
and [HAT(CN)6]2 2 viable candidates for isolation as paramagnetic ligands. In considering the two possible coordination modes of this ligand, the chelating bipyridine moieties
in the central rings are expected to be favored over monodentate coordination at the terminal nitrile functionalities.
With this situation, the coordination of up to three metals is
possible, which would result in a triangular arrangement.
Depending upon the metal/ligand ratio, one may anticipate
different solid state architectures and molecular species to
ensue. During the course of our studies, we noted the report
of the compound {[Cu(dppe)]3[HAT(CN)6]} in which the
[HAT(CN)6]1 ligand is chelated to three metal ions (see
1
Although four reversible reductions have been reported for HAT(CN)6
this result could not been reproduced with our purified samples.
2
Preliminary molecular orbital calculations indicate that the LUMO and
LUMO ‡ 1 states are degenerate suggesting that the [HAT(CN)6]2
radical could be paramagnetic.
0379-6779/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 9 - 6 7 7 9 ( 0 1 ) 0 0 3 4 2 - 3
536
P.S. Szalay et al. / Synthetic Metals 122 (2001) 535±542
Scheme 1.
footnote 2). This is the only compound of the [HAT(CN)6]1
radical that has been reported to date. In this case, however,
the magnetic interaction of metal spins through the
[HAT(CN)6]1 core could not be probed, since the Cu(I)
centers are diamagnetic. In this paper, we report our initial
studies on the deliberate reduction of HAT(CN)6 to
[HAT(CN)6]1 and [HAT(CN)6]2 and the reactivity of
these reduced species with transition metals.
2. Experimental
2.1. General procedures
All solvents and chemicals were reagent grade and used
without further puri®cation. All manipulations were carried
out under an inert atmosphere using standard Schlenk-line
techniques. The molecule HAT(CN)6 (1) was prepared
according to the literature method and recrystallized from
a methanol/acetonitrile solution [32]. Cyclic voltammetry
(CV) experiments were carried out on a CH Instruments
Electrochemical Work Station with a Ag/AgCl reference
Fig. 1. Cyclic voltammogram of HAT(CN)6 in acetonitrile.
electrode, a Pt disk as working electrode, and a Pt wire as an
auxiliary electrode. Infrared spectra were recorded on solids
suspended in Nujol on CsI plates using a Nicolet IR/42 FTIR spectrometer. Single crystal X-ray structural determination was performed on a Bruker SMART 1 K CCD platform
diffractometer [33] with graphite monochromated Mo Ka
Ê ). The frames were integrated in
radiation (la ˆ 0:71069 A
the Bruker SAINT software package [34], and the data were
corrected for absorption using the SADABS program [35].
The structures were solved using the SHELXTL V.5.10
package [36]. Pertinent crystallographic data and re®nement
parameters are provided in Table 1, and the corresponding
CIF ®les are included as supplementary material. Electron
spin resonance (ESR) spectra were recorded on a Bruker
Electron Spin Resonance ESP300 E instrument equipped
with an Oxford instrument Cryostat ESR900 in the range
4.2±300 K. Variable temperature magnetic susceptibility
data were obtained in the range 2±300 K on polycrystalline
samples using a Quantum Design, Model MPMS-XL.
2.2. Synthesis
Co(HAT(CN)4O2)(H2O)44H2O (2), precipitates as an
orange crystalline product from aerial evaporation of a solution containing Co(ClO4)26(H2O) (0.013 g, 0.034 mmol)
dissolved in 2 ml of deionized water and HAT(CN)6
(0.008 g, 0.021 mmol) dissolved in 2 ml of acetonitrile.
Ni(HAT(CN)4O2)(H2O)44H2O (3) is prepared under the
same conditions by the reaction of Ni(ClO4)26(H2O) (0.013 g,
0.034 mmol) with HAT(CN)6 (0.008 g, 0.021 mmol).
{(Cp2Fe)3[HAT(CN)6]}CH3CN (4), is prepared by mixing acetonitrile solutions of ferrocene (0.100 g, 0.528 mmol)
and HAT(CN)6 (0.068 g, 0.176 mmol). Concentration of this
solution either in vacuo or by evaporation in air results in the
precipitation of dark green crystals. The compound displays
a characteristic n(CBN) stretching mode at 2243 cm 1.
[(Cp)2Co][HAT(CN)6] (5), is prepared by mixing acetonitrile solutions of HAT(CN)6 (0.304 g, 0.793 mmol) with
cobaltocene (0.050 g, 0.264 mmol). The solution was concentrated and tetrahydrofuran was added to precipitate the
green product which was collected by ®ltration, washed with
tetrahydrofuran followed by diethyl ether, and dried in
vacuo. The yield after drying is 75%. [(Cp)2Co][HAT(CN)6]
displays a characteristic n(CBN) stretch at 2214 cm 1. The
ESR spectrum of a solid sample at 4 K shows an isotropic
signal with g ˆ 2:0084 and a line width of 7 G. Elemental
analysis: Anal. Calcd. for C28N12H10Co1: C, 58.65; H, 1.76;
N, 29.31. Found: C, 58.78; H, 1.92; N, 28.88.
[(Cp)2Co]2[HAT(CN)6] (6) is prepared by combining
acetonitrile solutions of HAT(CN)6 (0.075 g, 0.195 mmol)
and cobaltocene (0.111 g, 0.585 mmol). The blue-green
product, which precipitates from solution with concentration
is collected by ®ltration, washed with tetrahydrofuran followed by diethyl ether, and dried in vacuo. The yield after
drying is 85%. [(Cp)2Co]2[HAT(CN)6] displays a characteristic n(CBN) stretch at 2195 cm 1. Elemental analysis: Anal.
P.S. Szalay et al. / Synthetic Metals 122 (2001) 535±542
537
Table 1
Crystallographic data and structural refinement parameters for HAT(CN)6 (1), {Co(HAT(CN)4O2)(H2O)4}4H2O (2), {Ni(HAT(CN)4O2)(H2O)4}4H2O (3)
and {(Cp2Fe)3[HAT(CN)2]}CH3CN (4)
C16H20N10O10Co
Formula
C18N12
Molecular weight
384.30
571.32
T (K)
110(2)
173(2)
Ê)
l (A
0.71069
0.71069
Space group
42/n n m
P1
Ê)
a (A
23.537(3)
8.571(2)
Ê)
b (A
23.537(3)
10.065(2)
Ê)
c (A
14.834(3)
13.571(3)
a (8)
90.00
81.78(3)
b (8)
90.00
77.43(3)
g (8)
120.00
85.70(3)
Ê 3)
V (A
7178(2)
1129.8(4)
Z
18
2
rcalc (g cm 3)
1.600
1.692
m (Mo Ka, cm 1)
1.11
8.43
F (0 0 0)
3456
586
Y Range
1.72±28.25
1.56±28.38
Reflections
1973
5236
I > ns(I)
2
2
Reflections/parameters
749/137
3199/398
Goodness-of-fit
0.834
1.023
R1a
0.0589
0.0541
R2
0.1449b
0.1252c
P
P
a
R1 ˆ h …Fo Fc †= Fo .
i1=2
P
P
b
R2 ˆ
o…Fo2 Fc2 †2 = o…Fo2 †2
; o ˆ 1=…s2 Fo2 ‡ …0:0916P†2 † where P ˆ …Fo2 ‡ 2Fc2 †=3.
C16H20N10O10Ni
571.09
173(2)
0.71069
P1
8.546(2)
10.072(2)
13.493(3)
82.07(3)
77.53(3)
85.49(3)
1121.7(4)
2
1.691
9.43
588
1.56±28.30
5253
2
2884/398
0.913
0.0556
0.1126d
C50H33N13Fe3
983.44
173(2)
0.71069
P3
16.673(2)
16.673(2)
9.878(2)
90.00
90.00
120.00
2378.0(7)
2
1.373
9.52
1004
1.41±28.24
7587
2
6109/378
1.420
0.089
0.2335e
o ˆ 1=…s2 Fo2 ‡ …0:077P†2 †.
o ˆ 1=…s2 Fo2 ‡ …0:0642P†2 †.
e
o ˆ 1=…s2 Fo2 ‡ …0:100P†2 †.
c
d
Calcd. for C38N12H20Co2: C, 59.86; H, 2.64; N, 22.04.
Found: C, 58.95; H, 2.81; N, 22.49.
M[HAT(CN)6]2 (M: Co (7) or Zn (8)) complexes are
prepared by the reaction of an excess of the metal powder
or chips with a vigorously stirred acetonitrile solution of
HAT(CN)6 (0.200 g, 0.520 mmol). The resulting dark bluegreen solutions are ®ltered through Celite and reduced to
dryness. The solid is washed with dichloromethane followed
by diethyl ether and dried in vacuo. The yields after drying
are 85% for both the Co and Zn compounds. The Co and Zn
compounds display characteristic n(CBN) stretches at 2210
and 2212 cm 1, respectively. The results of ESR studies are
presented in the results and discussion section of this manuscript. Elemental analysis: Anal. Calcd. for C36N24Co: C,
52.25; N, 40.62. Found: C, 51.32; N, 39.95. Anal. Calcd. for
C36N24Zn: C, 51.84; N, 40.31. Found: C, 51.06; N, 39.73.
3. Results and discussion
3.1. Chemistry of neutral HAT(CN)6
The HAT(CN)6 molecule is a strongly electron-de®cient
heterocycle. One consequence of this is that it avoids self-pcomplexation in its neutral form. Crystals obtained from a
methanol/acetonitrile mixture reveal that neutral HAT(CN)6
molecules do not stack and, in fact, they are signi®cantly
offset with respect to one another, forming staircase-like
Ê , which
chains (Fig. 2). The intermolecular spacing is 3.75 A
Ê
is larger than the expected van der Waals radii sum of 3.54 A
[37]. The overall crystal packing is mainly dominated by
perpendicular CN-p interactions which leads to a complicated, but highly symmetric, 3D hexagonal arrangement as
nicely illustrated in Fig. 3.
Although neutral HAT(CN)6 is expected to be a very weak
ligand, reactions with aqueous ®rst row transition metal ions
were nevertheless carried out. When a mixture of water/
acetonitrile was used for the reaction medium, the novel
complex M(HAT(CN)4O2)(H2O)4 (M: Co, Ni) was isolated
(Fig. 4). This result demonstrates the fact that HAT(CN)6 is
hydrolytically unstable and undergoes cleavage of the two
activated nitrile groups adjacent to the coordinated metal
center. The result is a dianionic oxigen ligand. The coordination sphere of the metal center in these compounds is
completed by water molecules.
Ferrocene was initially employed as a reducing agent for
HAT(CN)6, but proved to be an insuf®ciently strong reductant
for this purpose. Thegreen crystalline product that was isolated
from this reaction was shown by single-crystal X-ray crystallography to be the 3:1 phase {(Cp2Fe)3[HAT(CN)6]}CH3CN
(Fig. 5). In support of the neutral assignment for the molecules
in this compound is the n(CBN) stretch at 2243 cm 1 in the
infrared spectrum. It appears that the ferrocene molecules act
as templates in the formation of a layered structure. Within a
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P.S. Szalay et al. / Synthetic Metals 122 (2001) 535±542
Fig. 2. Two different views of the HAT(CN)6 chain in 1.
given layer, the ferrocene resides in the space adjacent to the
chelating bipyridine moieties of HAT(CN)6. Adjacent layers
are staggered such that the ferrocene in one layer lies underneath the cyano groups of the HAT(CN)6 in the layer above it.
3.2. Chemical reduction of HAT(CN)6
A more convenient and successful approach to chemically
reducing HAT(CN)6 is to use cobaltocene. It is a suf®ciently
Fig. 3. View of the 3D structure of HAT(CN)6 (1).
P.S. Szalay et al. / Synthetic Metals 122 (2001) 535±542
539
dimerized in the solid state, perhaps due to the formation of
integrated stacks with interactions between anions and
cations.
The reaction of neutral HAT(CN)6 with an excess of
colbaltocene yields the salt [Cp2Co]2[HAT(CN)6]. The dianion is extremely sensitive to the presence of air or water,
which renders its characterization dif®cult. The IR spectrum
contains a characteristic n(CBN) mode at 2195 cm 1, which
is lower in energy by 19 cm 1 relative to the monoradical
[HAT(CN)6]1 and 48 cm 1 lower relative to neutral
HAT(CN)6.
3.3. Reactions of HAT(CN)6 with metals
Fig. 4. View of the M(HAT(CN)4O2)(H2O)4 complex present in
compounds {Co(HAT(CN)4O2)(H2O)4}4H2O (2) and {Ni(HAT(CN)4O2)(H2O)4}4H2O (3).
strong reducing agent to reduce HAT(CN)6 to both the
monoradical [HAT(CN)6]1 and the doubly reduced
[HAT(CN)6]2
forms. The compound [(Cp)2Co][HAT(CN)6] is isolated as a green powder from the reaction
of cobaltocene with an excess of HAT(CN)6. Although
single crystals have not yet been obtained, some characteristic features of the [HAT(CN)6]1 radical have been identi®ed. The IR spectrum contains a n(CBN) stretch at
2214 cm 1, which is shifted to lower energies from that
of neutral HAT(CN)6. This is analogous to the shifts
observed for other organic radicals with CBN groups
[30,38±43]. The ESR spectrum of a solid sample of
[(Cp)2Co][HAT(CN)6] at 4 K shows a typical isotropic
resonance for an organic radical (S ˆ 1/2), with a g value
of 2.0084(5) and with a narrow line width of 7 G. These data
indicate that the [HAT(CN)6]1 radicals are not strongly
Reactions of [(Cp)2Co][HAT(CN)6] with divalent ®rst
row transition metal ions such as Mn, Fe, Co, and Ni in
acetonitrile at room temperature yield dark green precipitates. The high degree of insolubility of these products in
common solvents suggests the presence of extended structures. Assuming that the preferred [HAT(CN)6]1 binding
mode is through the chelating N-sites and that the nitrile
groups are suf®ciently bulky to force the tetrahedral versus
octahedral geometry (Fig. 6), the expected stoichiometry for
the binary metal-[HAT(CN)6] coordination polymers would
be 3:2. The presence of the [HAT(CN)6]1 radical and the
absence of [(Cp)2Co]2 was veri®ed by IR spectroscopy, but
the low crystallinity of these samples precluded a structural
study. Thus, it remains unknown if the compounds are
discrete or polymeric, or if the solid state structure is
controlled solely by metal±ligand interactions or also by
ligand±ligand interactions. The magnetic measurements for
these compounds revealed only paramagnetic behavior characteristic of the metal ions with no contributions from the
ligand. This fact, taken together with the absence of signi®cant magnetic exchange between localized moments in
the metal ions in all cases, hints at p±p dimerization of the
ligand in the solid state. Such a situation would yield
Fig. 5. View of the crystal structure of {(Cp2Fe)3[HAT(CN)6]}CH3CN (4) down the a (left) and c axis (right).
540
P.S. Szalay et al. / Synthetic Metals 122 (2001) 535±542
Fig. 6. Model for the M[HAT(CN)6]2 complex that emphasizes the steric role of the cyano substituents.
diamagnetic dimers (S ˆ 0) similar to many other salts of
organic radicals [44].
An alternative method for preparing binary transition
metal compounds of [HAT(CN)6]1 is to directly react
HAT(CN)6 with ®rst row transition metals such as Co and
Zn. The resulting dark blue-green powders are soluble in
polar organic solvents such as acetonitrile, which is a good
indication that discrete molecules are being formed.
Although X-ray quality single crystals have not been
obtained, several spectroscopic characterization techniques
have been employed that support their formulation as
M[HAT(CN)6]2 (M: Co, Zn). The n(CBN) stretches of
2210 and 2212 cm 1 are consistent with the presence of
[HAT(CN)6]1 . Both compounds are ESR silent in the solid
state, but spectra obtained form acetonitrile/toluene frozen
solutions at 4 K exhibit signals. The spectrum of the Zn
compound consists of a single isotropic feature at
g ˆ 2:0031(5) with DH ˆ 15 G. Hyper®ne coupling would
not be expected due to the low natural abundance of 67 Zn
(4%). The compound, Co[HAT(CN)6]2 however, with 59 Co
(I ˆ 7/2, 100% abundant), exhibits an ESR signal with
hyper®ne coupling to the Co nucleus at g ˆ 2:0051(5) with
DH ˆ 480 G. Additionally, a broad signal was observed for
the S ˆ 3/2 Co(II) at g ˆ 2:180. This g value is in good
agreement with the one obtained from magnetic susceptibility studies of the compound, which revealed a high
temperature moment of meff ˆ 4:2 B.M. and a g value of
2.17. These data indicate that tetrahedral Co(II) centers are
magnetically isolated from each other. As con®rmed by ESR
studies of the compound in the solid state, there is no
contribution to the magnetization from [HAT(CN)6]1 presumably due to the intermolecular interactions in the solid
state. The Zn compound is rendered diamagnetic in the solid
state due to these stacking interactions.
The reaction of anhydrous CuCl with HAT(CN)6 (3:2
ratio) in an acetonitrile/methanol mixture yields a shiny
brown precipitate that is insoluble in all common solvents.
This compound differs from the others in that the most
intense n(CBN) stretch appears at 2132 cm 1, which is lower
than the corresponding stretches for either the mono- or the
dianion species. Also the elemental analysis indicates a high
Cu content (Cu/HAT(CN)6 ratio >2:1), but no satisfactory
stoichiometry could be calculated. The most interesting
aspect of this product is the magnetic behavior. As Fig. 7
shows, wT continously decreases from room temperature, in
accord with antiferromagnetic interactions between spin
carriers. Since the stoichiometry for this compound is not
known, the data are plotted per mol of Cu metal. The high
temperature regime can be conveniently ®t to a Curie±Weiss
law with C ˆ 0:37 emu/mol of Cu, which indicates that one
unpaired electron is present per Cu atom. If we assume the
Fig. 7. Temperature dependence of wT for the {Cu-[HAT(CN)6]} polymer
(1000 G). Inset: temperature dependence of the magnetic susceptibility in
the field-cooled and zero-field-cooled experiments (with an applied field
of 15 G).
P.S. Szalay et al. / Synthetic Metals 122 (2001) 535±542
541
transition metals with the pre-reduced [HAT(CN)6]1 anion.
The structures of these salts are not known, but they show
magnetic behavior indicative of a dimerization of the
[HAT(CN)6]1 radicals in the solid state. Finally, and most
interestingly, the reaction of HAT(CN)6 with CuCl yields a
new molecule-based magnet. Although no structural information is currently available on this system, the fact that this
compound shows spontaneous magnetization below 6 K
with a coercive ®eld of 184 G at 2 K is an appealing result
that con®rms our prediction that this ligand will produce
interesting materials in the realm of molecule-based and
molecular magnetism.
Acknowledgements
Fig. 8. Field dependence of the first magnetization of the {Cu[HAT(CN)6]} polymer measured at 2 K. Inset: hysteresis loop between
2000 and 2000 G.
presence of Cu(II) centers (S ˆ 1/2) then this translates to no
contribution from HAT(CN)6 radicals, most likely due to
dimerization of these units in the solid state. Another
possibility that cannot be discounted is the presence of
diamagnetic Cu(I) centers with the [HAT(CN)6]1 radicals
as spin carriers. The Weiss constant is large and negative
(y ˆ 93:1 K), indicating that antiferromagnetic interactions are dominant between nearest neighbors. The most
striking feature of the magnetic data appears at very low
temperatures when wT reaches a minimum and then
increases very rapidly, which is a signature of spontaneous
magnetization. This hypothesis was con®rmed by performing ®eld-cooled and zero ®eld-cooled measurements (inset
in Fig. 7), which reveal an obvious difference at 6 K. The
®eld dependence of the magnetization at 2 K (Fig. 8) does
not saturate even at 7 T, which is indicative of some degree
of canting between the individual spins. A hysteresis loop is
observed for this compound (inset Fig. 8) with a coercive
®eld of 184 G at 2 K.
4. Conclusions
Convenient outer-sphere chemical reduction routes of
HAT(CN)6 to the radical [HAT(CN)6]1 species and the
dianion [HAT(CN)6]2 have been described. Transition
metals can also be used as reducing agents, but in these
cases complexation of the metal with the reduced HAT(CN)6
species occurs. Discrete, soluble paramagnetic complexes
are obtained by direct reaction of HAT(CN)6 with Co and
Zn. We plan to use these molecules and related analogues as
building blocks for extended structures. Insoluble polymeric
binary salts have been obtained from reactions of divalent
KRD gratefully acknowledges the National Science
Foundation for support of this work (NSF CHE-9906583)
and for funding the CCD X-ray instrument (NSF-9807975)
and the SQUID magnetometer (NSF-9974899). JRGM
thanks the Ministerio de Educacion y Cultura for a postdoctoral fellowship.
References
[1] J.M. Williams, J.R. Ferraro, R.J. Thorn, K.D. Carlson, U. Geiser,
H.H. Wang, A.M. Kini, M.H. Whangbo, in: R.N. Grimes (Ed.),
Organic Superconductors (Including Fullerenes). Synthesis, Structure, Properties and Theory, Prentice Hall, Englewood Cliffs, NJ,
1992.
[2] J. Zyss (Ed.), Molecular Nonlinear Optics, Academic Press, New
York, 1994.
[3] C.P. Landee, D. Melville, J.S. Miller, in: D. Gatteschi, O. Kahn, J.S.
Miller, F. Palacio (Eds.), Magnetic Molecular Materials, NATO-ASI
Series E198, Kluwer Academic Publishers, Dordrecht, 1996, p. 395.
[4] O. Sato, T. Iyoda, A. Fujishima, K. Hashimoto, Science 272 (1996)
704.
[5] M. Kurmoo, A.W. Graham, P. Day, S.J. Coles, M.B. Hursthouse, J.L.
Caulfield, J. Singleton, F.L. Pratt, W. Hayes, L. Ducasse, P.
Guioneau, J. Am. Chem. Soc. 117 (1995) 12209.
[6] J.M. Manriquez, G.T. Yee, R.S. McLean, A.J. Epstein, J.S. Miller,
Science 252 (1991) 1415.
[7] T. Mallah, S. ThieÁbault, M. Verdaguer, P. Veillet, Science 262 (1993)
1554.
[8] M. Kurmoo, C.J. Kepert, New J. Chem. 22 (1998) 1515.
[9] E. Coronado, J.R. GalaÂn-MascaroÂs, C.J. GoÂmez-GarcõÂa, Adv. Mater.
11 (1999) 558.
[10] K.R. Dunbar, R.A. Heintz, Prog. Inorg. Chem. 35 (1996) 4449.
[11] M. Verdaguer, A. Bleuzen, V. Marvaud, J. Vaissermann, M.
Seuleiman, C. Desplanches, A. Scullier, C. Train, R. Garde, G.
Gelly, C. Lomenech, I. Rosenman, P. Veillet, C. Cartier, F. Villain,
Coord. Chem. Rev. 190±192 (1999) 1285.
[12] M. Ohba, H. Okawa, Coord. Chem. Rev. 198 (2000) 313.
[13] W.R. Entley, G.S. Girolami, Inorg. Chem. 33 (1994) 5156.
[14] O. Sato, Y. Einaga, A. Fujishima, K. Hashimoto, Inorg. Chem. 38
(1999) 4405.
[15] J. Larionova, R. CleÂrac, J. Sanchiz, O. Kahn, S. Golhen, L. Ouahab,
J. Am. Chem. Soc. 120 (1998) 13088.
[16] J.L. Manson, C.R. Kmety, Q.-Z. Huang, J.W. Lynn, G.M. Bendele, S.
Pagola, P.W. Stephens, L.M. Liable-Sands, A.L. Rheningold, A.J.
Epstein, J.S. Miller, Chem. Mater. 10 (1998) 2552.
542
P.S. Szalay et al. / Synthetic Metals 122 (2001) 535±542
[17] J.L. Manson, C.R. Kmety, A.J. Epstein, J.S. Miller, Inorg. Chem. 38
(1999) 2552.
[18] S.R. Batten, P. Jensen, B. Moubaraki, K.S. Murray, R. Robson,
Chem. Commun. (1998) 439
[19] S.R. Batten, P. Jensen, C.J. Kepert, M. Kurmoo, B. Moubaraki, K.S.
Murray, D.J. Price, J. Chem. Soc., Dalton Trans. (1999) 2987.
[20] H. Tamaki, Z.J. Zhong, N. Matsumoto, S. Kida, M. Koikawa, N.
Achiwa, Y. Hashimoto, H. Okawa, J. Am. Chem. Soc. 114 (1992)
6974.
[21] R. Pellaux, H.W. Schmalle, R. Huber, P. Fisher, T. Hauss, B.
Ouladdiaf, S. Decurtins, Inorg. Chem. 36 (1997) 2301.
[22] M. HernaÂndez-Molina, F. Lloret, C. Ruiz-PeÂrez, M. Julve, Inorg.
Chem. 37 (1998) 4131.
[23] E. Coronado, J.R. GalaÂn-MascaroÂs, C.J. GoÂmez-GarcõÂa, J. Ensling, P.
GuÈtlich, Chem. Eur. J. 6 (2000) 552.
[24] J. S Miller, A.J. Epstein, Angew. Chem. Int. Ed. Engl. 33 (1994) 385.
[25] J. S Miller, A.J. Epstein, Chem. Industry 2 (1996) 49.
[26] J. Zhang, J. Ensling, V. Ksenofontov, P. GuÈtlich, A.J. Epstein, J.S.
Miller, Angew. Chem. Int. Ed. Engl. 37 (1998) 657.
[27] G.T. Yee, J.M. Manriquez, D.A. Dixon, R.S. McLean, D.M. Groski,
R.B. Flippen, K.S. Narayan, A.J. Epstein, J.S. Miller, Adv. Mater. 3
(1991) 309.
[28] J.S. Miller, D.T. Glatzhofer, D.M. O'Hare, W.M. Reiff, A.
Chakraborty, A.J. Epstein, Inorg. Chem. 28 (1989) 2930.
[29] K.R. Dunbar, J. Cowen, H. Zhao, R.A. Heintz, X. Ouyang,
G. Grandinetti, in: J. Veciana (Ed.), NATO ASI: Supramolecular
Engineering of Synthetic Metallic Materials: Conductors and
Magnets, Vol. 518, Kluwer Academic Publishers, Dordrecht, 1999,
p. 353.
[30] J. Cowen, R. CleÂrac, R.A. Heintz, S. O'Kane, X. Ouyang, H. Zhao,
K.R. Dunbar, Mol. Cryst. Liq. Cryst. 335 (1999) 113.
[31] J.C. Beeson, L.J. Fitzgerald, J.C. Gallucci, R.E. Gerkin, J.T.
Rademacher, A.W. Czarnik, J. Am. Chem. Soc. 116 (1994) 4621
[32] J.T. Rademacher, K. Kanakarajan, A.W. Czarnik, Synthesis (1994)
378.
[33] SMART 1000, Bruker Analytical X-Ray Instruments, Madison, WI
53719 (1999).
[34] SAINT 1000, Bruker Analytical X-Ray Instruments, Madison, WI
53719 (1999).
[35] G.M. Sheldrick, SADABS: Siemens Area Detector Absorption (and
Other) Correction, University of GoÈttingen, GoÈttingen, Germany, 1998.
[36] SHELXTL ver. 5.10, Reference Manual, Bruker Industrial Automation, Analytical Instrument, Madison, WI 53719 (1999).
[37] A. Bondi, J. Phys. Chem. 68 (1964) 441.
[38] J.P. Cornelissen, J.H. van diemen, L.R. Groeneveld, J.G. Haasnoot,
A.L. Spek, J. Reedijk, Inorg. Chem. 31 (1992) 198.
[39] W. Pukacki, M. Pawlak, A. Graja, M. Lequan, R.M. Lequan, R.M.
Inorg. Chem. 26 (1987) 1328.
[40] L. Ballester, M.C. Barral, A. GutieÂrrez, R. JimeÂnez-Aparicio, J.M.
Martinez-Muyo, M.F. PerpinÄan, M.A. Monge, C.J. Ruiz-Valero,
Chem. Soc., Chem. Commun. (1991) 1396.
[41] W. Kaim, M. Moscherosh, Coord. Chem. Rev. 129 (1994) 157.
[42] R.A. Heintz, H. Zhao, X. Ouyang, G. Grandinetti, J. Cowen, K.R.
Dunbar, Inorg. Chem. 38 (1999) 144.
[43] H. Zhao, R.A. Heintz, X. Ouyang, K.R. Dunbar, C.F. Campana, R.D.
Rogers, Chem. Mater. 11 (1999) 736.
[44] S.A. O'Kane, R. CleÂrac, H. Zhao, X. Ouyang, J.R. GalaÂn-MascaroÂs,
R. Heintz, K.R. Dunbar, J. Solid State Chem. 152 (2000) 159.