Organization of spin- and redox-labile metal centers into Langmuir and Langmuir-Blodgett films

Article abstract of DOI:10.1039/b926023d

New sal₂(trien) ligands that contain alkoxy substituents of various length in meta position of the phenolate entities were coordinated to electronically and magnetically active iron(III) and cobalt(iii) centers. The electrochemical and spectroscopic properties of these amphiphilic complexes are virtually unaffected upon alteration of the alkoxy substituents, thus providing a system in which the physical behavior and the metal-centered chemical activity can be tailored independently. The amphiphilic character has been exploited for preparing Langmuir monolayers at the air-water interface and for constructing Langmuir-Blodgett films, hence allowing for hierarchical assembling of electronically and magnetically active systems. While Langmuir films were stable, transfer onto solid supports was limited, which restricted the magnetic analysis of the Langmuir-Blodgett assemblies.

Full text of DOI:10.1039/b926023d

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Organization of spin- and redox-labile metal centers into Langmuir and
Langmuir–Blodgett films†
Claudio Gandolfi,a Naoko Miyashita,‡b Dirk G. Kurth,b Paulo N. Martinho,c Grace G. Morganc and
Martin Albrecht*a,c
Received 10th December 2009, Accepted 17th March 2010
First published as an Advance Article on the web 6th April 2010
DOI: 10.1039/b926023d
New sal2(trien) ligands that contain alkoxy substituents of various length in meta position of the
phenolate entities were coordinated to electronically and magnetically active iron(III) and cobalt(III)
centers. The electrochemical and spectroscopic properties of these amphiphilic complexes are virtually
unaffected upon alteration of the alkoxy substituents, thus providing a system in which the physical
behavior and the metal-centered chemical activity can be tailored independently. The amphiphilic
character has been exploited for preparing Langmuir monolayers at the air–water interface and for
constructing Langmuir–Blodgett films, hence allowing for hierarchical assembling of electronically and
magnetically active systems. While Langmuir films were stable, transfer onto solid supports was limited,
which restricted the magnetic analysis of the Langmuir–Blodgett assemblies.
Introduction
Many metal-centered processes are amplified if the active sites are
operating in a cooperative fashion.1 A classic example for such
enhanced activity due to cooperation is the spin transition in spin-
labile complexes.2,3 Synchronized spin crossover typically results in
abrupt transitions, often accompanied by a hysteresis, while non-
Fig. 1 Sal2(trien) complexes for remote functionalization via substitution
of the phenoxide fragment.
cooperative transitions are gradual and hence much less attractive.
Hierarchical self-assembly,4 that is, supramolecular organization
that is controlled in at least one dimension by stepwise growth,
constitutes a useful concept for achieving cooperativity.5 In
order to effectively allow for tailoring structure and function
independently, this concept requires a proper separation of struc-
turally directing elements from active sites such as spin crossover
centers.6 A major advantage of this concept then consists in the
possibility to extrapolate structural trends to other functional
entities. For example, layer-by-layer deposition7 has become a
widely applicable method for the arrangement of functional units
of great variety on a surface.8
the redox activity of the metal center only marginally.9c This
position hence offers a suitable anchor for covalently installing
entities for supramolecular engineering without affecting the
bonding situation around the metal center. Similar to amine
functionalization,10 aryl substitution addresses two mutually cis-
oriented donor sites of the sal2(trien) ligand. Introduction of
lipophilic substituents therefore provides a methodology for
evoking amphiphilic behavior of the molecule, especially when
bound to a MIII metal center that induces an ionic coordination
environment. Systems with pronounced amphiphilic character
tend to self-assemble, for example into Langmuir films at the air–
water interface.11 This methodology is often more predictable than
crystal engineering12 for organizing the redox- and spin-crossover
active metal centers in a distinct arrangement.13 In addition to
this two-dimensional self-assembly at the air–water interface,
stepwise organization of the material into the third dimension
can be achieved through repetitive immobilization of layers onto
a support. Such Langmuir–Blodgett (LB) film fabrication ideally
affords multilayered systems with a hierarchical structure. While
films of spin crossover-active iron(II) complexes have been known,
the use of iron(III) complexes for film fabrication is rare.13,14
This is surprising when considering the pronounced stability of
FeIII towards oxidation at the air–water interface. Moreover, we
have recently evidenced the improved activity of such assembled
systems in solution.15 By expanding these efforts, we here report
on the synthesis of different redox-active and potentially spin-
labile CoIII and FeIII complexes comprising variably long alkyl
We have applied this concept by using potentially spin- and
redox-labile metal complexes of the dianionic sal2(trien) ligand
(Fig. 1), a system that has been well-studied for spin crossover.9
Ligand functionalization with a methoxy group at the aryl ring
(R = OMe) was reported to affect the spin crossover and
aDepartment of Chemistry, University of Fribourg, Chemin du Musee 9,
CH-1700, Fribourg, Switzerland
bMax Planck Institute of Colloids and Interfaces, D-14424, Potsdam,
Germany
cSchool of Chemistry and Chemical Biology, University College Dublin
Belfield, Dublin 4, Ireland. E-mail: martin.albrecht@ucd.ie; Fax: +353
17162501; Tel: +353 17162504
† Electronic supplementary information (ESI) available: Synthetic proce-
dures for the synthesis of the ligands, pressure-area isotherms of complexes
6, stability plots of films comprising the cobalt(III) complexes and the
iron(III) complexes 7e-g, and Brewster angle microscopy images for 7d.
See DOI: 10.1039/b926023d
‡ Present address: Chemische Technologie der Materialsynthese, Univer-
sita¨t Wu¨rzburg, Am Ro¨ntgenring 11, 97070 Wu¨rzburg, Germany
4508 | Dalton Trans., 2010, 39, 4508–4516
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Scheme 1 Synthesis of amphiphilic iron(III) and cobalt(III) complexes.
chains in the sal2(trien) aryl backbone and on the parameters
that are relevant for assembling these systems into Langmuir
and Langmuir–Blodgett films. Preliminary analysis of mono and
bilayer structures suggests that in contrast to solid material, the
self-assembled films do undergo spin-crossover.
new iron(III) complexes 7e-g were synthesized analogously to the
previously reported alkyl functionalized complexes 7a-d.15
While the paramagnetic nature of the iron complexes 7 pre-
cluded NMR investigations, the corresponding cobalt complexes
were diamagnetic. The NMR spectra of complexes 5 consistently
indicate a symmetrical arrangement of ligand, as only half of the
expected number of signals are apparent. All methylene protons
are diastereotopic, thus pointing to a rigid chelation of the
hexadentate ligand. While different isomers were proposed for
unfunctionalized complexes,18b our results suggest that long alkyl
chains restrict fluxional processes. A symmetrical arrangement is
consistent with the trans imine configuration as shown in Scheme 1
(cf crystallographic analyses below). Complexation is indicated by
small but diagnostic low-field shifts of the aromatic and the imine
Results and discussion
Cobalt(III) and iron(III) complexes
Functionalization of 4-hydroxy salicylaldehyde 1 according to
published methods16 facilitated the introduction of alkyl chains
of variable length in the phenolic part of the ligand precursor,
thus affording the aldehydes 3a-d (Scheme 1). The regioselectivity
of alkylation was confirmed by nOe effects between the a-protons
of the alkyl chain and the two aryl protons meta to the aldehyde. In
a similar manner, two lipophilic side chains per phenolic unit were
incorporated by using the benzylbromides 2e-g containing two
alkoxy-residues in the 3,5-positions,17 thus yielding the bulkier
aldehydes 3e-g in good yields, even when performing the reaction
on a multigram scale.
Subsequent condensation with triethylenetetramine (trien) gave
the potentially hexadentate ligand precursors 4, which were
metallated either after isolation or preferably in situ due to the
sensitivity of 4 towards hydrolysis.18 Reaction with CoCl2 and
subsequent standing in air gave the corresponding cobalt(III)
complexes 5. Acceleration of metal oxidation by saturating the
reaction mixture with O2 lowered the yields of 5 substantially,
suggesting that initial metal coordination requires a cobalt(II)
center. The non-coordinating counter anion in 5 was readily
displaceable because of the high solubility of 5 in organic solvents.
Thus, stirring a solution of 5 in THF in the presence of AgNO3
gave the corresponding nitrate salts 6 in excellent yields. The
1
protons (Dd 0.1) in the pertinent H NMR spectra. The largest
displacements were noted for the CH2 protons attached to the
imine donor site, which shifted approximately 0.5 ppm downfield
upon cobalt coordination.
Structural analyses of the iron(III) complexes 7 are more
limited. Single crystals of 7a were obtained, though the refinement
did not converge due to strong disorder and weak diffraction.
Nevertheless, a connectivity pattern around the iron center was
established that was in agreement with the arrangement deduced
from solution NMR-analysis of the cobalt complexes 5. Together
with the crystal structure previously determined for 7b,15 these
results suggest that the complexes generally adopt a conformation
as shown in Scheme 1, including a mutual cis arrangement of both
the phenolate units and the amine donors, and a trans orientation
of the imine ligands.
All complexes were analyzed by electrochemistry. The cobalt(III)
complexes undergo an irreversible reduction at around -0.8 V,
irrespective of the nature of the counter anion.19 In contrast, cyclic
voltammetry on the iron(III) complexes 7 revealed a reversible
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 4508–4516 | 4509
©

View Article Online
Table 1 Electrochemical and spectroscopic data of iron(III) complexes
E1/2/V DE/mV lmax/nm e/M-1cm-1 nC–N
(Fig. 3) indicate that simple spin coating induces ◦only a little
organization of complex 7d. Upon annealing at 90 C, however,
nanosize domains form that reflect the affinity of the complexes
to aggregate and self-assemble.
complex R
sal2(trien)
-0.45 134
-0.51 176
-0.50 161
-0.45 121
-0.50 131
497
497
497
497
497
496
497
494
3290
4350
4610
4760
4070
4180
3460
3900
1622
1604
1604
1604
1604
1602
1603
1602
7a
7b
7c
7d
7e
7f
C6H13
C8H17
C12H25
C18H37
C6H3-(C8H17)2 -0.51 255
C6H3-(C12H25)2 -0.48 338
C6H3-(C18H37)2 -0.53 224
7g
aAll measurements in CH2Cl2 solution; E1/2 vs. SCE, Pt working electrode,
scan rate 100 mV s-1 and 0.1 M nBu4PF6 as supporting electrolyte. Fc+/Fc
as internal standard (E1/2 = +0.46 V).
reduction of the metal center at -0.50 V (vs. SCE; Table 1).20
The reduction potentials for all iron(III) complexes are essentially
identical and indicate that functionalization of the phenolate unit
does not alter the electronic properties of the metal center.
Obviously, the electronic activity of the metal center is not affected
by variation of the structurally directing hydrophobic tails. Further
support for an effective separation of structural and functional
elements in complexes 7 was obtained from spectroscopic analyses
using UV-vis and IR techniques. Modification of the alkyl tail
length (7a-d) or the number of alkyl chains (7e-g) had virtually
no impact on the low-energy absorption wavelength in the visible
region (lmax), attributed to a ligand-to-metal charge transfer. This
band is expected to be highly sensitive to modifications in the
ligand donor properties and to changes in the ligand coordination
geometry.
Spectroelectrochemical measurements using an optically trans-
parent thin layer electrode (OTTLE) cell21 allowed the electro-
chemically generated iron(II) complexes to be characterized in situ.
For example in complex 7a, a bathochromic shift of the absorption
maximum to 536 nm was noted upon reduction (Fig. 2). In
addition a new maximum at 346 nm is observed, perhaps due
to a ligand centered process.22
Fig. 3 Complex 7d spin-coated on highly ordered pyrolytic graphite
(HOPG), (a) before and (b) after annealing (90 ◦C).
Langmuir films
Langmuir films at the air–water interface were investigated for
all complexes 7 and for selected cobalt complexes. Representative
pressure-area isotherms and stability plots of the films are shown
in Fig. 4. These measurements allow for a number of conclusions.
First, it appears that a critical number of apolar sites is required
in order to achieve high-density films. Complex 7a does not form
films, perhaps due to partial water solubility, while 7b with short C8
alkyl chain functionalities does not pack well, which is reflected by
the low accessible surface pressure and the steady decrease of the
pressure upon keeping the surface constant (Fig. 4a, 4b). This low
tendency of film formation may be a consequence of the limited
number of apolar molecular recognition sites, inducing only small
attractive forces. In addition, the hydrophobic–hydrophilic bias
within the molecule may be too small to induce a high tensor
difference and hence a preferred orientation of the molecules at the
air–water interface. In contrast, films of complexes 7c and 7d were
stable over extended periods of time (> 90 min) and formed a dense
two-dimensional network. Film formation with these complexes
was fully reversible and expansion upon pressure release occurred
with virtually no hysteresis even after repetitive compression–
expansion cycles. The suitability of these complexes for Langmuir
films was further supported by monitoring the film forming
process by Brewster angle microscopy (BAM), which revealed a
homogeneous process without the appearance of specific domains
(Fig. 5).
When using complexes with twice the number of alkyl chains per
head group, viz. complexes 7e-g (Fig. 4c), assembly started earlier,
perhaps induced by the larger fractional volume of apolar groups
when compared to 7b-d. The isotherm of films from 7g provides a
rare case where a distinct transition from the liquid condensed to
the solid phase is apparent.23 No significant differences in terms
of stability were observed upon doubling the number of alkyl
Fig. 2 Spectrophotochemical comparison of 7a (black) and [7a]- (grey),
generated electrochemically by applying a potential of -0.55 V. The inset
shows the cyclic voltammogram of 7a.
chains. Irrespective of the number of alkyl chains, the specific
2
˚
molecular area is consistently around 80–85 A per molecule,
which may seemingly be dictated by the polar iron sal2(trien)
head group rather than the alkyl tails. However, models based
on crystal structure analyses suggest a surface area of the polar
Self-assembly
2
9
˚
The potential of the functionalized complexes to form organized
structures was probed at the air–water interface and on highly
ordered pyrolytic graphite (HOPG). Representative AFM imaging
iron sal2(trien) unit of ca. 65 A , thus requiring three alkyl
2
˚
chains of 20 A each for reaching similar projection planes of
the polar and apolar fragments.24 Possibly, back folding25 of
4510 | Dalton Trans., 2010, 39, 4508–4516
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Fig. 4 (a) Pressure–area isotherms for 7a-d comprising two alkyl chains per iron sal2(trien) unit; (b) stability plots at constant surface area for 7b-d;
(c) pressure–area isotherms for 7e-g comprising four alkyl chains per iron sal2(trien) unit; (d) pressure–area isotherms for the cobalt complexes 5c-g.
and providing an explanation for the similar surface area of the
dialkylated complexes with the tetralkylated (and presumably not
back folding) species 7e-g. Such a model is also consistent with the
low film stability of complex 7b, as back folding is inefficient and
less probable with shorter C8 alkyl chains. Upon increasing the
number of C8 chains to four as in 7e, back folding is not required
anymore and the complexes pack densely.
The general features deduced for films comprised of iron(III)
complexes are also valid for assembling the analogous cobalt(III)
complexes at the air–water interface. High surface pressures up
to 60 mN m-1 were accessible with these components. The anion
exerted only little influence and films comprising either chloride (5)
or nitrate (6) showed only small differences.19 Characteristically,
however, the surface area per molecule is markedly influenced by
the number of alkyl chains. Films of complexes comprising four
alkyl chains (5f, 5g) can be compressed to a minimum area of
2
˚
approximately 80 A per molecule (Fig. 4d), which corroborates
the results obtained with iron complexes. In contrast when using
complexes 5c or 5d, functionalized with two alkyl chains only,
2
˚
the minimum area shrinks to ca. 55 A per molecule, a value
only slightly smaller than the calculated surface of the metal
sal2(trien) unit. Hence, these results are consistent with a model in
which the polar group is limiting the specific surface area if two
alkyl groups are used, whereas with complexes containing four
alkyl groups, the apolar fraction determines the specific molecular
area. While our results do not allow for deducing of a rationale
for this distinctly different behavior of iron(III) and cobalt(III)
complexes, it is interesting to note that the driving forces for
Fig. 5 Brewster Angle Microscopy on film formation using complex 7d.
the alkyl chains in the complexes 7c and 7d may occur, thus
2
˚
accounting for the observed surface per molecule (~ 4 ¥ 20 A )
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 4508–4516 | 4511
©

View Article Online
Table 2 Multilayer deposition of 7d onto a glass supporta
stroke the transfer ratios were initially close to zero, indicating that
immersion did not result in film transfer. Multilayer fabrication
was limited to a maximum of four layers, as subsequent layer
deposition occurred only partially (transfer ratio ~ 0.7) and, most
significantly, these layers were released again upon immersion.
Attempts to increase the number of layers by changing the
solid support from glass to silicon wafers or to gold showed
no improvement. Modification of the surface pressure during
film transfer from 4 to 8 mN m-1 enhanced the initial transfer
ratio (0.97 for first emersion, 0.89 for second emersion), however,
only oligolayers were obtained again. Based on the absence of
film transfer upon immersion, formation of a Z-type layer may
be surmised (Fig. 6b),26 with the polar headgroups oriented
towards the support. While we do not have any model so far that
may rationalize this unusual Z-type layering,27 clearly, potential
applications are attractive due to the anisotropy generated by such
a hierarchical organization.
Due to the low transfer ratio, analysis of the physical properties
of the film were hampered and spin crossover behavior could
not be reliably established. The UV-vis spectrum of the film at
297 K revealed the characteristic high spin absorption around
500 nm (Fig. 7),19 which is considerably sharper than in solution
measurements. Cooling the film to lower temperatures does,
however, not indicate a clear transition, as the diagnostic low spin
absorption bands around 380 nm and 650 nm are barely detectable.
Better film properties and in particular improved transfer ratios
may be required, perhaps upon modification of the molecular
recognition sites. Work along these lines is currently in progress.
2
˚
layer number
transferred area (A /molecule)
transfer ratio
1
2
3
4
5
6
7
8
9
4.8
-1.0
3.6
-1.4
3.8
-2.9
3.9
0.87
-0.18
0.65
-0.25
0.69
-0.53
0.74
-3.9
3.9
-0.74
0.74
a glass area approximately 7 cm2, transfer at P = 4 mN m-1, at least 10 min
drying allowed before immersion (even layer numbers).
assembly might be swapped by changing the central metal atom.
Irrespectively, both types of complexes display a low tendency for
hydrolysis in contact with water, as illustrated with the prolonged
stability of the Langmuir films.
Transfer of Langmuir films onto supports
Multilayers rather than monolayers, which intrinsically display
low signal-to-noise ratios, are often desirable for the fabrication
of devices that are potentially useful for electronic or magnetic
applications. Multilayer deposition on a solid support and the
formation of Langmuir–Blodgett films provides a versatile tool
to achieve a hierarchical arrangement of the active units with
controlled intermolecular interactions. To this end, the transfer of
the iron-containing films from 7d onto glass was investigated in
detail. The transfer ratio was generally high (~ 0.9), though only
upon emersion of the support (Table 2, Fig. 6a). During down-
Fig. 7 UV-vis spectroscopic characterization of Langmuir–Blodgett films
at 297 K (red), 170 K (orange) and 91 K (blue); difference spectrum of
measurements at 297 K and 91 K (black).
Conclusions
An approach has been developed that allows for functionalization
of electronically and magnetically active iron(III) and cobalt(III)
complexes with molecular recognition sites at remote positions
that do not affect the function of the metal. As a consequence,
independent optimization of the structurally directing elements
for self-assembly and in parallel of the functional activity is
possible in these entities. Using this methodology, stable films were
successfully prepared, thus entailing the controlled assembly of
potentially redox and spin labile systems. When transferred on a
suitable support, such hierarchical assemblies may provide access
to magnetically switchable devices with improved metal–metal
cooperativity, potentially applicable for example in data storage
technology. Independent of the spin transition properties, the
redox activity of the film components may constitute an attractive
feature for molecular electronics.
Fig. 6 (a) Langmuir film transfer of 7d onto glass at 4 mN m-1; emersion
starts are indicated by a solid line, immersions with a dashed line (10-15 min
drying after each emersion). (b) Schematic representation of the Z-type LB
film deduced from the transfer ratios, blue circles represent the polar head
groups and orange lines the alkyl tails.
4512 | Dalton Trans., 2010, 39, 4508–4516
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
6.01 (d, 2H, J = 8.1 Hz, C5H), 5.04 (s br, 2H, NH), 4.37–4.21
(m, 2H, CH2N=), 4.09–3.96 (m, 2H, CH2N=), 3.75–3.62 (m,
4H, CH2O), 3.17–2.95 (m, 4H, CH2CH2N= and NCH2CH2N),
2.55–2.41 (m, 2H, NCH2CH2N), 2.41–2.23 (m, 2H, CH2CH2N=),
1.63–1.48 (m, 4H, CH2CH2O), 1.37–1.01 (m, 36H, all CH2),
Experimental section
General Comments
The synthesis of the bromides 2e-g,28 the 4-alkoxy-functionalized
salicylaldehydes 3a-d,29 the aldehydes 3e-g,19 and the complexes
7a, 7b, and 7d were reported elsewhere.15 THF was dried by
passage through a solvent purification column. All other reagents
were commercially available and were used as received. Flash
chromatography was performed using silica gel 60 (63-200 mesh)
0.86 (t, 6H, J = 6.6 Hz, CH3). 13C NMR (CDCl3, 90 MHz): d
6
=
166.7, 164.7 (COBn and COCo), 165.6 (N CH), 135.5 (C H),
113.2 (CCHN), 105.7 (C5H), 104.9 (C3H), 67.9 (OCH2), 58.6
(CH2N=), 54.2 (CH2CH2N=), 51.9 (NCH2CH2N), 32.0, 30.0–
29.1, 22.8 (all CH2), 29.5 (CH2CH2O), 26.1 (CH2CH2CH2O), 14.3
(CH3). MS (ESI): m/z = 779.5 [M–Cl]+. Anal. found (calcd) for
C44H72N4O4ClCo (815.47) ¥ 0.5 CHCl3: C 60.91 (61.07); H 8.68
(8.35); N 5.98 (6.40).
or basic alox (0.05–0.15 mm, pH 9.5). All 1H and 13C{ H} NMR
1
spectra were recorded at 25 ◦C on Bruker or Varian spectrometers
and referenced to residual solvent 1H or 13C resonances (d in
ppm, J in Hz). Assignments are based either on distortion-
less enhancement of polarization transfer (DEPT) experiments
or on homo- and heteronuclear shift correlation spectroscopy.
Melting points were determined using an OptiMelt apparatus
(Stanford Research Systems) or a Mettler Toledo TGA/SDTA
851 analyzer and are uncorrected. UV-vis measurements were
performed on a Perkin Elmer Lambda 40 instrument in CH2Cl2
solution (0.2 mM). IR spectra were recorded on a Mattson
5000 FTIR instrument in CHCl3 solution. High resolution mass
spectra and mass spectra were measured by electrospray ionization
(ESI-MS) in CHCl3–MeOH on a Bruker 4.7 T BioAPEX II
and a Bruker Daltonics esquire HCT instruments, respectively.
Elemental analyses were performed by the Microanalytical Lab-
oratory of Ilse Beetz (Kronach, Germany) and at the ETH
Zurich (Switzerland). Electrochemical studies were carried out
using an EG&G Princeton Applied Research Potentiostat Model
273A employing a gastight three-electrode cell under an argon
atmosphere. A saturated calomel electrode (SCE) was used as
reference; a Pt disk (3.14 mm2) and a Pt wire were used as the
working and counter electrode, respectively. The redox potentials
were measured in dry CH2Cl2 (~1 mM) with n-Bu4NPF6 (0.1 M)
as electrolyte and ferrocene (E1/2 = 0.46 V vs. SCE)30 as internal
standard. Spectroelectrochemical studies were carried out in the
same electrolytic solution as in the case of cyclic voltammetry
using a SPECAC Ottle cell with CaF2 windows, platinum mesh
working, counter electrode and a silver wire reference electrode.
The corresponding UV-vis spectra were recorded on a Perkin
Elmer Lambda 900 instrument in transmission mode.
Synthesis of 5d. According to the preparation of 5c, starting
from CoCl2 ¥ 6H2O (286 mg, 1.2 mmol) in EtOH (12 mL) and 4d
(1.07 g, 1.2 mmol) in THF (42 mL), the title compound was ob-
tained as a brown waxy solid (0.88 g, 78%). M.p. 245 ◦C (decomp.).
-1
=
=
IR (CHCl3): 1634 (C N), 1606 cm (C C). UV-vis (CH2Cl2): lmax
(e) = 377 nm (7460 M-1cm-1). 1H NMR (CDCl3, 360 MHz): d 7.93
6
3
=
(s, 2H, N CH), 7.05 (d, 2H, J = 8.7 Hz, C H), 6.20 (s, 2H, C H),
6.08 (d, 2H, J = 8.5 Hz, C5H), 5.24 (s br, 2H, NH), 4.38–4.18
(m, 2H, CH2N=), 4.10–3.95 (m, 2H, CH2N=), 3.74 (t, 4H, J =
6.1 Hz, CH2O), 3.20–2.96 (m, 4H, CH2CH2N= and NCH2CH2N),
2.48–2.31 (m, 2H, NCH2CH2N), 2.31–2.16 (m, 2H, CH2CH2N=),
1.70–1.57 (m, 4H, CH2CH2O), 1.37–1.01 (m, 60H, all CH2), 0.86
(t, 6H, J = 6.6 Hz, CH3). 13C NMR (CDCl3, 50 MHz): d 166.8,
6
=
164.8 (COBn and COCo), 165.7 (N CH), 135.6 (C H), 113.2
(CCHN), 105.9 (C5H), 104.9 (C3H), 68.0 (OCH2), 58.5 (CH2N=),
54.0 (CH2CH2N=), 51.8 (NCH2CH2N), 32.0, 29.8–29.2, 22.8 (all
CH2), 26.1 (CH2CH2CH2O), 14.2 (CH3). MS (ESI): m/z = 747.7
[M–Cl]+. Anal. found (calcd) for C56H96ClCoN4O4 (983.79) ¥ 0.5
CHCl3: C 64.91 (65.03); H 9.49 (9.32); N 5.28 (5.37); Co 5.53
(5.65).
Synthesis of 5f. Triethylenetetramine (70 mg, 0.48 mmol) was
dissolved in EtOH (6 mL) and treated with a solution of 3f
(573 mg, 0.96 mmol) in THF (6 mL). After 15 min stirring at
RT, a solution of CoCl2 ¥ 6H2O (114 mg, 0.48 mmol) in EtOH
(4 mL) was added dropwise under an Ar atmosphere. The mixture
became immediately brown and was stirred at RT for 20 min and
exposed to air for 7 h. The suspension was filtered over a bed of
silica, eluted with EtOH–THF 2 : 1 (40 mL). After evaporation
the residue was purified on a short pad of Al2O3 by first washing
with CHCl3 (30 mL) and subsequent eluting with EtOH–THF 2 : 1
(50 mL). After evaporation of the EtOH–THF fraction the residue
was redissolved in pentane (15 mL), filtered through celite and
evaporated in vacuo to give 5f as a brown waxy solid (287 mg, 43%).
Analytically pure complex aggregated from a solution in Et2O–
MeOH 5 : 1 by slow evaporation of Et2O within some days. M.p.
Syntheses
Synthesis of 5c. A solution of CoCl2 ¥ 6H2O (125 mg,
0.52 mmol) in EtOH (10 mL) was added dropwise to 4c (378 mg,
0.52 mmol) in warm THF (18 mL) under an Ar atmosphere. The
mixture became immediately brown, and was stirred at RT for
20 min and exposed to air for 7 h. The suspension was filtered
over a bed of silica and eluted with EtOH–THF 2 : 1 (80 mL).
After evaporation the residue was purified on a short pad of
Al2O3 by first washing with CHCl3 (60 mL) and subsequent
eluting with EtOH–THF 2 : 1 (80 mL). After evaporation of
the EtOH–THF fraction, the product was redissolved in CHCl3
(5 mL) and centrifuged. The supernatant was evaporated and
dried under reduced pressure to give 5c as a brown waxy solid
◦
-1
=
=
218 C (decomp.). IR (CHCl3): 1635 (C N), 1604 cm (C C).
UV-vis (CH2Cl2): lmax (e) = 377 nm (8130 M-1cm-1). H NMR
1
=
(CDCl3, 500 MHz): d 8.03 (s, 2H, N CH), 7.14 (d, 2H, J =
8.8 Hz, C6H), 6.46 (d, 4H, J = 2.2 Hz, C8H), 6.38–6.35 (m, 4H,
C3H and C10H), 6.23 (dd, 2H, J = 8.7, 2.3 Hz, C5H), 5.10 (s br,
2H, NH), 4.82 (s, 2H, CarCH2O), 4.45–4.33 (m, 2H, CH2N=),
4.21–4.10 (m, 2H, CH2N=), 3.88 (t, 4H, J = 6.6 Hz, CH2O),
3.32–3.13 (m, 4H, CH2CH2N= and NCH2CH2N), 2.57–2.47 (m,
2H, NCH2CH2N), 2.45–2.35 (m, 2H, CH2CH2N=), 1.79–1.67
(m, 4H, CH2CH2O), 1.45–1.19 (m, 72H, all CH2), 0.87 (t, 6H,
(0.43 g, quant.). M.p. 217 ◦C (decomp.). IR (CHCl3): 1632
-1
=
=
(C N), 1606 cm (C C). UV-vis (CH2Cl2): lmax (e) = 377 nm
(7460 M-1cm-1). 1H NMR (CDCl3, 360 MHz): d 7.95 (s, 2H,
N CH), 7.03 (d, 2H, J = 8.5 Hz, C H), 6.14 (s, 2H, C H),
6
3
=
This journal is The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 4508–4516 | 4513
©

View Article Online
J = 7.0 Hz, CH3). 13C NMR (CDCl3, 125 MHz): d 166.7, 164.7
and NCH2CH2N), 1.73–1.59 (m, 4H, CH2CH2O), 1.41–1.00 (m,
60H, all CH2), 0.87 (t, 6H, J = 6.6 Hz, CH3).
9
7
=
(COBn and COCo), 165.7 (N CH), 160.6 (C ), 138.8 (C ), 135.7
(C6H), 113.5 (CCHN), 106.4 (C5H), 105.9 (C8H), 105.5 (C3H),
100.9 (C10H), 69.9 (OCH2Car), 68.2 (OCH2), 58.5 (CH2N=),
53.9 (CH2CH2N=), 51.7 (NCH2CH2N), 32.1, 30.0–29.2, 22.8 (all
CH2), 26.2 (CH2CH2CH2O), 14.3 (CH3). MS (ESI): m/z = 1359.9
[M–Cl]+. Anal. found (calcd) for C82H132N4O8ClCo (1396.36) ¥
MeOH: C 69.65 (69.79); H 9.40 (9.60); N 3.70 (3.92).
◦
Complex 6f. Yield: 89 mg (98%). M.p. 187 C (decomp.). IR
-1
=
=
(CHCl3): 1634 (C N), 1606 cm (C C). UV-vis (CH2Cl2): lmax
1
(e) = 377 nm (7990 M-1cm-1). H NMR (CDCl3, 360 MHz): d
6
=
7.94 (s, 2H, N CH), 7.07 (d, 2H, J = 7.67 Hz, C H), 6.43 (s,
4H, C8H), 6.39–6.27 (m, 4H, C3H and C10H), 6.23 (d, 2H, J =
7.9 Hz, C5H), 5.02 (s br, 2H, NH), 4.74 (s, 2H, CarCH2O), 4.30–
4.14 (m, 2H, CH2N=), 4.14–4.00 (m, 2H, CH2N=), 3.96–3.76 (m,
4H, CH2O), 3.18–2.96 (m, 4H, CH2CH2N= and NCH2CH2N),
2.50–2.21 (m, 4H, CH2CH2N= and NCH2CH2N), 1.83–1.57 (m,
4H, CH2CH2O), 1.51–0.98 (m, 72H, all CH2), 0.87 (t, 6H, J =
6.4 Hz, CH3).
Synthesis of 5g. According to the preparation of 5f, starting
from triethylenetetramine (51 mg, 0.35 mmol) in EtOH (2 mL), 3g
(536 mg, 0.70 mmol) in THF (25 mL) and CoCl2 ¥ 6H2O (83 mg,
0.35 mmol) in EtOH (3 mL) gave a brown waxy solid (230 mg,
38%). Analytically pure complex was obtained by precipitation
with MeOH (30 mL) from an Et2O (6 mL) solution, followed by
precipitation with acetone (30 mL) from pentane (4 mL). M.p.
Synthesis of 7c. Solid NaOMe (83 mg, 1.54 mmol) was added
to 4c (444 mg, 0.61 mmol) in warm THF (20 mL). After 10 min
stirring, a solution of Fe(NO3)3 ¥ 9H2O (248 mg, 0.61 mmol) in
EtOH (7 mL) was added dropwise. The dark purple suspension
was stirred for 30 min at RT and filtered over a bed of silica. The
product was eluted with EtOH–THF 2 : 1 (50 mL) and dried under
reduced pressure. The residue was taken into CHCl3 (5 mL) and
purified on a short pad of Al2O3 by consecutive elution with CHCl3
(100 mL), THF (100 mL), and finally EtOH (120 mL). After
evaporation of the EtOH fraction, the product was redissolved in
CHCl3 (10 mL) and centrifuged. The supernatant was evaporated
under reduced ◦pressure to give a purple waxy solid (266 mg,
◦
-1
=
=
229 C (decomp.). IR (CHCl3): 1635 (C N), 1603 cm (C C).
UV-vis (CH2Cl2): lmax (e) = 497 nm (8380 M-1cm-1). H NMR
1
=
(CDCl3, 360 MHz): d 7.97 (s, 2H, N CH), 7.09 (d, 2H, J =
8.6 Hz, C6H), 6.43 (s br, 4H, C8H), 6.38–6.29 (m, 4H, C3H and
C10H), 6.18 (d, 2H, J = 8.5 Hz, C5H), 5.14 (s br, 2H, NH), 4.75
(s, 2H, CarCH2O), 4.40–4.22 (m, 2H, CH2N=), 4.15–3.98 (m, 2H,
CH2N=), 3.84 (t, 4H, J = 6.3 Hz, CH2O), 3.24–2.98 (m, 4H,
CH2CH2N= and NCH2CH2N), 2.55–2.19 (m, 4H, NCH2CH2N
and CH2CH2N=), 1.76–1.74 (m, 4H, CH2CH2O), 1.45–1.09 (m,
120H, all CH2), 0.87 (t, 6H, J = 6.7 Hz, CH3). 13C NMR (CDCl3,
=
52%). M.p. 227 C (decomp.). IR (CHCl3): 1604 cm-1 (C N). UV-
90 MHz): d 166.7, 164.4 (COBn and COCo), 165.8 (N CH),
=
160.5 (C9), 138.7 (C7), 135.8 (C6H), 113.5 (CCHN), 106.5 (C5H),
105.9 (C8H), 105.4 (C3H), 100.8 (C10H), 69.8 (OCH2Car), 68.2
(OCH2), 58.8 (CH2N=), 54.1 (CH2CH2N=), 52.0 (NCH2CH2N),
32.1, 30.0–29.2, 22.8 (all CH2), 26.2 (CH2CH2CH2O), 14.3 (CH3).
MS (ESI): m/z = 1696.9 [M–Cl]+. Anal. found (calcd) for
C106H180N4O8ClCo (1733.01) ¥ 3 MeOH: C 71.48 (71.57); H 10.55
(10.58); N 3.24 (3.06).
vis (CH2Cl2): lmax (e) = 497 nm (4760 M-1cm-1). HR–MS (ESI,
MeOH): Calcd. for C44H72FeN4O4 [M–NO3]+ m/z = 776.4903,
found m/z = 776.4885. Anal. found (calcd) for C44H72N5O7Fe
(838.93): C 63.10 (62.99), H 8.73 (8.65), N 8.36 (8.35).
Synthesis of 7e. Triethylenetetramine (175 mg, 1.2 mmol) was
dissolved in EtOH (6 mL) and treated with a solution of 3e
(1.17 g, 2.4 mmol) in THF (18 mL). After 10 min, solid NaOMe
(178 mg, 3.3 mmol) was added and the yellowish suspension was
stirred for 10 min. An ethanolic solution of Fe(NO3)3 ¥ 9H2O
(481 mg, 1.2 mmol in 9 mL) was then added dropwise. The dark
purple suspension was stirred at RT for 30 min and filtered over
a bed of silica. The product was eluted with EtOH–THF 2 : 1
(90 mL) and evaporated at reduced pressure. The residue was
dissolved in CHCl3 and purified on a short pad of Al2O3 (5 cm)
using as eluents first CHCl3 (70 mL) and subsequently EtOH–
THF 2 : 1 (250 mL). Evaporation of the EtOH–THF fraction, the
product was redissolved in CHCl3 (20 mL) and centrifuged. The
supernatant was evaporated at reduced pressure to give 7e as a
dark purple wax (1.30 g, 48%). Analytically pure material was
obtained from a hexane (120 mL) solution upon extraction with
MeOH (3 ¥ 15 mL). M.p. 191 ◦C (decomp.). IR (CHCl3): 1602 cm-1
General procedure for the synthesis of 6. Chloride complex
5 (0.37 mmol) was dissolved in THF (10 mL) and treated with
AgNO3 (0.37 mol) dissolved in H2O (5 mL). The mixture was
stirred for 2 h in the dark. The mixture was centrifugated and the
supernatant evaporated to dryness. The residue was redissolved in
CHCl3 (30 ml) and centrifuged. The supernatant was filtered over
Celite, evaporated and dried in vacuo.
Complex 6c. Yield: 302 mg (97%). M.p. 232 ◦C (decomp.). IR
-1
=
=
(CHCl3): 1634 (C N), 1606 cm (C C). UV-vis (CH2Cl2): lmax
(e) = 377 nm (8230 M-1cm-1). 1H NMR (CDCl3, 360 MHz): d 7.98
6
3
=
(s, 2H, N CH), 7.08 (d, 2H, J = 8.4 Hz, C H), 6.25 (s, 2H, C H),
6.11 (d, 2H, J = 8.1 Hz, C5H), 4.89 (s br, 2H, NH), 4.33–4.03
(m, 4H, CH2N=), 3.84–3.70 (m, 4H, CH2O), 3.23–3.00 (m, 4H,
CH2CH2N= and NCH2CH2N), 2.53–2.26 (m, 4H, NCH2CH2N
and CH2CH2N=), 1.73–1.59 (m, 4H, CH2CH2O), 1.44–1.10 (m,
36H, all CH2), 0.87 (t, 6H, J = 6.6 Hz, CH3).
(C N). UV-vis (CH2Cl2): lmax (e) = 496 nm (4180 M-1cm-1). HR–
=
MS (ESI): calcd for C66H100FeN4O8 [M–NO3]+ m/z = 1132.6885,
found m/z = 1132.6885. Anal. found (calcd) for C66 H100FeN5O11
(1195.4) ¥ MeOH: C 65.13 (65.56); H 8.13 (8.54); N 5.40 (5.71).
Complex 6d. Yield: 336 mg (92%). M.p. 239 ◦C (decomp.). IR
-1
=
=
(CHCl3): 1634 (C N), 1606 cm (C C). UV-vis (CH2Cl2): lmax
Synthesis of 7f. According to procedure for 7e, reaction of
triethylenetetramine (57 mg, 0.39 mmol) in EtOH (2 mL), 3f
(463 mg, 0.78 mmol) in THF (6 mL), NaOMe (58 mg, 1.07 mmol)
with ethanolic Fe(NO3)3 ¥ 9H2O (157 mg, 0.39 mmol in 3 mL) gave
7f as a dark purple wax (289 mg, 52%). Analytically pure complex
was obtained from a hexane (120 mL) solution by extraction with
(e) = 377 nm (8000 M-1cm-1). 1H NMR (CDCl3, 360 MHz): d 7.99
6
3
=
(s, 2H, N CH), 7.09 (d, 2H, J = 8.7 Hz, C H), 6.26 (s, 2H, C H),
6.13 (d, 2H, J = 8.5 Hz, C5H), 4.93 (s br, 2H, NH), 4.36–4.07 (m,
4H, CH2N=), 3.79 (t, 4H, J = 6.3 Hz, CH2O), 3.26–3.05 (m, 4H,
CH2CH2N= and NCH2CH2N), 2.55–2.30 (m, 4H, CH2CH2N=
4514 | Dalton Trans., 2010, 39, 4508–4516
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
MeOH (2 ¥ 25 mL). M.p. 181 ◦C (decomp.). IR (CHCl3): 1603 cm-1
2008, 130, 9019; (m) S. Brooker and J. A. Kitchen, Dalton Trans., 2009,
7331.
(C N). UV-vis (CH2Cl2): lmax (e) = 497 nm (3460 M-1cm-1). HR–
=
3 Similarly, redox activity may be engineered to obtain conducting and
semiconducting materials:(a) C. Joachim, J. K. Gimzewski and A.
Aviram, Nature, 2000, 408, 541; (b) Z. Bao, Adv. Mater., 2000, 12,
227; (c) R. Naaman and Z. Vager, Acc. Chem. Res., 2003, 36, 291;
(d) A. Schenning and E. W. Meijer, Chem. Commun., 2005, 3245; (e) for
recent examples, see: M. Lemieux, M. Roberts, S. Y. W. Barman Jin,
J. M. Kim and Z. Bao, Science, 2008, 321, 101.
4 (a) J.-M. Lehn, Supramolecular Chemistry (Wiley-VCH), Weinheim,
1995; (b) J. M. Lehn, Science, 2002, 295, 2400; (c) J. C. Love, L. A.
Estroff, J. K. Kriebel, R. G. Nuzzo and G. M. Whitesides, Chem. Rev.,
2005, 105, 1103.
5 (a) M. Ruben, U. Ziener, J.-M. Lehn, V. Ksenofontov, P. Gu¨tlich and
G. B. M. Vaughan, Chem.–Eur. J., 2005, 11, 94; (b) Y. Bodenthin, U.
Pietsch, H. Mo¨hwald and D. G. Kurth, J. Am. Chem. Soc., 2005, 127,
3110; (c) S. Cobo, G. Molnar, J. A. Real and A. Bousseksou, Angew.
Chem., Int. Ed., 2006, 45, 5786; (d) A. B. Gaspar, M. Seredyuk and
P. Gu¨tlich, Coord. Chem. Rev., 2009, 253, 2399; (e) Y. Bodenthin, G.
Schwarz, Z. Tomkowicz, M. Lommel, T. Geue, W. Haase, H. Mo¨hwald,
U. Pietsch and D. G. Kurth, Coord. Chem. Rev., 2009, 253, 2414.
6 For an example from catalysis:M. Albrecht, N. J. Hovestad, J. Boursma
and G. van Koten, Chem.–Eur. J., 2001, 7, 1289.
MS (ESI): calcd for C82H132FeN4O8 [M–NO3]+ m/z = 1356.9389,
found m/z = 1356.94025. Anal. found (calcd) for C82H132N5O11Fe
(1419.83): C 69.47 (69.37); H 9.35 (9.37); N 4.82 (4.93).
Synthesis of 7g. According to procedure for 7e, the reaction
of triethylenetetramine (80 mg, 0.55 mmol) in EtOH (3 mL), 3g
(842 mg, 1.10 mmol) in THF (8 mL), NaOMe (58 mg, 1.07 mmol)
with ethanolic Fe(NO3)3 ¥ 9H2O (222 mg, 0.55 mmol in 4 mL)
gave 7g as a dark purple wax (317 mg, 33%). An analytically
pure sample was obtained by extraction of a hexane solution
(120 mL) of 7g with MeOH (3 ¥ 30 mL). M.p. 188 ◦C (decomp.).
IR (CHCl3): 1602 cm-1 (C N). UV-vis (CH2Cl2): lmax (e) = 496 nm
=
(3900 M-1cm-1). HR–MS (ESI, MeOH): calcd for C106H180FeN4O8
[M–NO3]+ m/z = 1693.3145, found m/z = 1693.3148. Anal. found
(calcd) for C106H180N5O11Fe (1756.47) ¥ MeOH: C 71.81 (71.86);
H 10.33 (10.37); N 3.70 (3.92).
7 (a) G. Decher, Science, 1997, 277, 1232; (b) N. Miyashita and D. G.
Kurth, J. Mater. Chem., 2008, 18, 2636.
8 (a) J. F. Quinn, A. P. R. Jonhnston, G. K. Such, A. N. Zelikin and F.
Caruso, Chem. Soc. Rev., 2007, 36, 707; (b) S. Srivastava and N. A.
Kotov, Acc. Chem. Res., 2008, 41, 1831; (c) Q. He, Y. Cui and J. Li,
Chem. Soc. Rev., 2009, 38, 2292.
9 (a) M. F. Tweedle and L. J. Wilson, J. Am. Chem. Soc., 1976, 98, 4824;
(b) E. Sinn, G. Sim, E. V. Dose, M. F. Tweedle and L. J. Wilson, J. Am.
Chem. Soc., 1978, 100, 3375; (c) R. Pritchard, S. A. Barrett, C. A. Kilner
and M. A. Halcrow, Dalton Trans., 2008, 3159.
10 P. N. Martinho, C. J. Harding, H. Mu¨ller-Bunz, M. Albrecht and G. G.
Morgan, Eur. J. Inorg. Chem., 2010, 675.
11 (a) K. B. Blodgett, J. Am. Chem. Soc., 1934, 56, 495; (b) K. B. Blodgett
and I. Langmuir, Phys. Rev., 1937, 51, 964; (c) D. R. Talham, Chem.
Rev., 2004, 104, 5479.
12 (a) M. D. Hollingsworth, Science, 2002, 295, 2410; (b) M. Hostettler,
K. W. To¨rnroos, D. Chernyshov, B. Vangdal and H.-B. Bu¨rgi, Angew.
Chem., Int. Ed., 2004, 43, 4589; (c) C. Felser, G. H. Fecher and B. Balke,
Angew. Chem., Int. Ed., 2007, 46, 668.
Langmuir Measurements
Pressure–area isotherms and time stability were measured at
25 ◦C on a KSV MiniMicro Langmuir–Blodgett trough (KSV,
Finland) with a surface area between 1700 and 8700 mm2.
Water was purified with a Barnstead Nanopure system (Thermo
Scientific), and its resistivity was measured to be higher than
18 MX cm. Chloroform (puriss. p.a. ≥ 99.8%, Fluka) was used
as spreading solvent. Typically drops of the surfactant solution
(20 mL, 0.50 mM) were deposited using a microsyringe on the
water subphase. After letting the solvent evaporate for 30 min, the
barriers were compressed at 6 mm min-1 (3 cm2 min-1) and the
surface pressure was monitored using a platinum Willhelmy plate.
13 (a) C. Mingotaud, P. Delhaes, M. W. Meisel, and D. R. Talham,
in Magnetism: Molecules to Materials II: Molecule-Based Materials,
J. S. Miller, M. Drillon, ed. Wiley-VCH, Weinheim, Germany, 2002,
p. 457; (b) P. Coronel, A. Barraud, R. Cluade, O. Kahn, A. Ruaudel-
Teixier and J. Zarembowitch, J. Chem. Soc., Chem. Commun., 1989,
193; (c) D. G. Kurth, P. Lehmann and M. Schu¨tte, Proc. Natl. Acad.
Sci. U. S. A., 2000, 97, 5704; (d) O. Roubeau, B. Agricole, R. Clerac
and S. Ravaine, J. Phys. Chem. B, 2004, 108, 15110.
Acknowledgements
We thank Prof. H. Mo¨hwald for valuable discussions. This work
was financially supported by ERA-net Chemistry. M.A. is very
grateful for an Alfred Werner Assistant Professorship.
14 (a) H. Soyer, C. Mingotaud, M.-L. Boillot and P. Delhaes, Langmuir,
1998, 14, 5890; (b) H. Soyer, E. Dupart, C. J. Gomez-Garcia, C.
Mingotaud and P. Delhaes, Adv. Mater., 1999, 11, 382.
15 C. Gandolfi, C. Moitzi, P. Schurtenberger, G. G. Morgan and M.
Albrecht, J. Am. Chem. Soc., 2008, 130, 14434.
16 P. Zell, F. Mo¨gele, U. Ziener and B. Rieger, Chem.–Eur. J., 2006, 12,
3847.
Notes and references
1 (a) E. Breuning, M. Ruben, J. M. Lehn, F. Renz, Y. Garcia, V.
Ksenofontov and P. Gu¨tlich, Angew. Chem., Int. Ed., 2000, 39, 2504;
(b) M. Ruben, J. Rojo, F. J. Romero-Salguero, L. H. Uppadine and
J.-M. Lehn, Angew. Chem., Int. Ed., 2004, 43, 3644; (c) M. L. Tang,
A. D. Reichardt, N. Miyaki, R. M. Stoltenberg and Z. Bao, J. Am.
Chem. Soc., 2008, 130, 6064.
17 C. J. Hawker and J. M. J. Frechet, J. Am. Chem. Soc., 1990, 112,
2 (a) O. Kahn, Molecular Magnetism (VCH), New York, 1993; (b) P.
Gu¨tlich, Y. Garcia, and H. Spiering, in Magnetism: Molecules to
Materials IV, J. S. Miller, M. Drillon, ed. Wiley-VCH, Weinheim,
Germany, 2002, p 271; (c) P. Gu¨tlich, A. Hauser and H. Spiering,
Angew. Chem., Int. Ed. Engl., 1994, 33, 2024; (d) J. A. Real, A. B.
Gaspar, V. Niel and M. C. Munoz, Coord. Chem. Rev., 2003, 236, 121;
(e) O. Sato, Acc. Chem. Res., 2003, 36, 692; (f) P. Gu¨tlich and H. A.
Goodwin, Top. Curr. Chem., 2004, 233, 1; (g) J.-F. Letard, P. Guionneau
and L. Goux-Capes, Top. Curr. Chem., 2004, 235, 221. For key examples
relevant to this work, see:; (h) J. A. Real, E. Andres, M. C. Munoz, M.
Julve, T. Granier, A. Bousseksou and F. Varret, Science, 1995, 268,
265; (i) O. Kahn and C. J. Martinez, Science, 1998, 279, 44; (j) S.
Hayami, Z. Gu, H. Yoshiki, A. Fujishima and O. Sato, J. Am. Chem.
Soc., 2001, 123, 11644; (k) M. Seredyuk, A. B. Gaspar, V. Ksenofontov,
Y. Galyametdinov, J. Kusz and P. Gu¨tlich, J. Am. Chem. Soc., 2008,
130, 1431; (l) S. Cobo, D. Ostrovskii, S. Bonhommeau, L. Vendier, G.
Molnar, L. Salmon, K. Tanaka and A. Bousseksou, J. Am. Chem. Soc.,
7638.
18 (a) B. D. Sarma and J. C. Bailar, J. Am. Chem. Soc., 1955, 77, 5476;
(b) Y. Yamamoto and S. Tsukuda, Bull. Chem. Soc. Jpn., 1985, 58, 1509;
(c) A. S. Rothin, H. J. Banbery, F. J. Berry, T. A. Hamor, C. J. Jones and
J. A. McCleverty, Polyhedron, 1989, 8, 491.
19 See the supporting material for further details.
20 K. M. Kadish, K. Das, D. Schaeper, C. L. Merrill, B. R. Welch and
L. J. Wilson, Inorg. Chem., 1980, 19, 2816.
21 M. Krejcik, M. Danek and F. Hartl, J. Electroanal. Chem., 1991, 317,
179.
22 Attempts to reduce complexes 7 chemically by using an excess of CrCl2
induced the substitution of the hexadentate coordinated metal center
from Fe3+ to Cr3+ only, as indicated by the pertinent mass spectrometric
data.
23 (a) B. Lin, M. C. Shih, T. M. Bohanon, G. E. Ice and P. Dutta, Phys.
Rev. Lett., 1990, 65, 191; (b) S. Ramos and R. Castillo, J. Chem. Phys.,
1999, 110, 7021; (c) R. Johann and D. Vollhardt, Mater. Sci. Eng., C,
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 4508–4516 | 4515
©

View Article Online
1999, 8–9, 35; (d) R. Johann, D. Vollhardt and H. Mo¨hwald, Langmuir,
2001, 17, 4569.
24 D. K. Chattoraj, E. Halder, K. P. Das and A. Mitra, Adv. Colloid
Interface Sci., 2006, 123–126, 151.
28 (a) K. Sivanandan, S. V. Aathimanikandan, C. G. Arges, C. J. Bardeen
and S. Thayumanavan, J. Am. Chem. Soc., 2005, 127, 2020; (b) Z. Bo,
X. Zhang, X. Yi, M. Yang, J. Shen, Y. Ren and S. Xi, Polym. Bull.,
1997, 38, 257; (c) Y. Azefu, H. Tamiaki, R. Sato and K. Toma, Bioorg.
Med. Chem., 2002, 10, 4013.
29 (a) S. Inoue, T. Yanai, S. Ando, A. Nakazawa, K. Honda, Y. Hoshino
and T. Asai, J. Mater. Chem., 2005, 15, 4746; (b) I. Aiello, M. Ghedini,
M. La Deda, D. Pucci and O. Francescangeli, Eur. J. Inorg. Chem.,
1999, 1367.
25 T. Hasegawa, Y. Iiduka, H. Kakuda and T. Okada, Anal. Chem., 2006,
78, 6121.
26 M. C. Petty, Langmuir–Blodgett Film: An Introduction, Cambridge
University Press, Cambridge, 1996.
27 R. Popovitz-Biro, K. Hill, E. M. Landau, M. Lahav, L. Leiserowitz, J.
Sagiv, H. Hsiung, G. R. Meredith and H. Vanherzeele, J. Am. Chem.
Soc., 1988, 110, 2672.
30 N. G. Connelly and W. E. Geiger, Chem. Rev., 1996, 96,
877.
4516 | Dalton Trans., 2010, 39, 4508–4516
This journal is
The Royal Society of Chemistry 2010
©