Spin-dimer networks: Engineering tools to adjust the magnetic interactions in biradicals

Article abstract of DOI:10.1039/c7tc03357e

Magneto-structural correlations in stable organic biradicals have been studied on the example of weakly exchange coupled models with nitronyl nitroxide and imino nitroxide spin-carrying entities. Here, heteroatom substituted 2,2′-diaza- and 3,3′-diaza-tolane bridged biradicals were compared with the hydrocarbon analogue, while a biphenyl model with its 2,2′-bipyridine counterpart. For a 3,3′-diazatolane bridge the torsional angle between the nitronyl nitroxides and the pyridyl rings increased heavily (～52-54°) leading to a smaller theoretical intra-dimer exchange coupling value. However, a very large antiferromagnetic coupling was obtained experimentally. This could be appropriately explained by the presence of dominating inter-dimer exchange between the molecules. For the bis(imino nitroxide) with tolane bridge a field induced ordered state between 1.8 to 4.3 T in AC-susceptibility measurements was observed. In terms of a Bose Einstein condensate (BEC) of triplons this phenomenon could be described as a magnetic field induced ordered phase with 3D character.

Full text of DOI:10.1039/c7tc03357e

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10.1039/C7TC03357E.
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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
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Spin-Dimer Networks: Engineering Tools to Adjust the Magnetic
Interactions in Biradicals
Yulia B. Borozdina,a,b Evgeny A. Mostovich,a,c Pham Thanh Cong,d Lars Postulka,d Bernd Wolf,d
Michael Langd and Martin Baumgartena,*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Magneto-structural correlations in stable organic biradicals have been studied on example of weakly exchange coupled
models with nitronyl nitroxide and imino nitroxide spin-carrying entities. Here, heteroatom substituted 2,2′-diaza- and
3,3′-diaza-tolane bridged biradicals were compared with the hydrocarbon analogue, while a biphenyl model - with its 2,2′-
bipyridine counterpart. For a 3,3′-diazatolane bridge the torsional angle between the nitronyl nitroxides and the pyridyl
rings increased heavily (~52-54°) leading to a smaller theoretical intra-dimer exchange coupling value. However, a very
large antiferromagnetic coupling was obtained experimentally. This could be appropriately explained by the presence of
dominating inter-dimer exchange between the molecules. For the bis(imino nitroxide) with tolane bridge a field induced
ordered state between 1.8 to 4.3 T in AC-susceptibility measurements was observed. In terms of a Bose Einstein
condensate (BEC) of triplons this phenomenon could be described as magnetic field induced ordered phase with 3D
character.
www.rsc.org/
ease of various devices fabrication. Advanced chemistry
techniques permit small structural modifications in already
achieved model systems in order to fine-tune their physical
Introduction
Magnetic
dimers
formed
by
weakly
interacting
properties. In addition, organic-based magnetic materials offer
a number of convenient tools extremely helpful in controlling
the intra- and interdimer exchange coupling, such as πꢀπ
interactions, hydrogen bonding, etc. Nitronyl nitroxide (NN)
radicals are well-known for their stability and bidentate
character.9,10 NN are among the most popular spin carriers
used to construct molecular-based magnets.10
antiferromagnetically coupled spin S=1/2 centres are
recognized as suitable candidates for exploring the critical
phenomena under well-controlled conditions.1 When these
systems are placed in a magnetic field strong enough to close
the dimer gap, a gas of triplet excitations (triplons) is formed.1
Depending on the topology of the dimer-dimer couplings,
various scenarios can be observed. Prominent examples
include the Bose-Einstein condensation (BEC) of triplons in
three-dimensionally-coupled dimer systems, as described by
Tchernyshyov et al.2, and the Luttinger-liquid behavior
revealed in a one-dimensional spin-ladder system by Krämer
1
2
3
4
5
n = 1, X = N, Y = C
n = 1, X = C, Y = N
n = 0, X, Y = C
n = 0, X = N, Y = C
n = 1, X, Y = C
(
)
n
and co-workers.3 More recently,
a Berezinskii-Kosterlitz-
Thouless scenario was observed by Tutsch et al. in a two-
dimensional coordinated copper polymer with large interlayer
spacing.4
(a) R = -CHO (b) R =
(c) R =
(d) R =
In general, organic magnetic materials possess properties
not shown by traditional inorganic compounds.5-8 Plasticity,
flexibility and solubility in common organic solvents define the
Fig. 1 Structure of the biradical model systems 1-5.
Importantly, in these radicals the spin density of the
unpaired electron is delocalized over two semi-equivalent sites
of coordination. This in turn allows to arrange the NN-
molecules into
a supramolecular network of interacting
spins.11 Theoretical studies emphasized the importance of the
mutual orientation and the relative distances in the crystal
packing for promoting an efficient magnetic coupling.11,12 As
was mentioned by Lahti,13 minor changes in the crystal packing
of biradicals could result in significant alterations of the
magnetic behavior in the bulk material. In this regard the
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influence of the
π-bridges on the intra- and intermolecular in the presence of dilute HCl (3%) resulted in precipitation of
exchange interactions in conjugated biradical networks was the acid by the triple bond. Thus, the final step towards 1a was
studied on example of the diazotolane dinitroxide models (Fig. performed under milder conditions. To a solution of the
1). It was anticipated, that heteroatom substitution could offer dioxolane precursor in acetone-water mixture (7:1) a catalytic
a particularly effective pathway for transmitting the magnetic amount of p-TsOH acid (2 mol%) was added.24 Stirring the
interactions.14
Typically, imino nitroxides (IN) reveal a reduced
reaction for 3 days at room temperature provided the target
J
dimer value 2,2’-diazatolane 4,4’-dialdehyde 1a in nearly quantitative yield
when compared to the corresponding NN biradicals. Taking (81%).
this fact into consideration, already known bridges could be
used, where otherwise a strong intramolecular exchange
coupling was observed.11 Following this strategy, three
(iv)
(v)
(vi)
bisimino nitroxides 3d, 4d,
5d were prepared (Fig. 1).15
1a
9
10
(iii)
In the current work we report the synthesis of a series of
new nitroxide biradicals (Fig. 1), their characterization,
including X-ray structural analysis and their magnetic
properties, which are discussed with respect to the quantum
chemical calculations based on the DFT approach.
(ii)
(i)
(vii)
11
6
7
8
(viii)
(x)
(ix)
Results and discussion
2a
12
13
Synthesis of nitroxide biradicals.
Reagents and conditions: (i) (a) n-BuLi, Et2O, -78ºC, under Ar, 45 min, (b) DMF, -78ºC,
under Ar, 105 min, (c) HCl (3%), 20 min; (ii) ethyleneglycol, p-TsOH, benzene, reflux, 20
h; (iii) TMSA, Pd(PPh3)2Cl2, CuI, PPh3, DMF, Et3N, heating at 80ºC under Ar, 14 h; (iv) 1M
NaOH, H2O-THF, 5ºC, 35 min; (v) 8, Pd(PPh3)2Cl2, CuI, PPh3, CH3CN, Et3N, at rt under Ar,
18 h; (vi) p-TsOH, H2O-acetone, 84 h; (vii) (a) n-BuLi, toluene, -78ºC, under Ar 2 h, (b)
DMF, -78ºC, under Ar, 2 h, (c) NH4Cl, 30 min; (viii) TMSA, Pd(PPh3)2Cl2, CuI, PPh3, DMF,
Et3N, heating at 80ºC under Ar, 16 h; (ix) K2CO3, MeOH, under Ar 90 min; (x) 11,
Pd(PPh3)2Cl2, CuI, PPh3, DMF, Et3N, heating at 80ºC under Ar, 12 h.
Access to the family of diazatolane biradicals 1c
, 2c required
synthesis of the key precursors 1a 2a, which were prepared
,
following Sonogashira-Hagihara methodology.16 Interestingly,
both structural isomers 1a and 2a could be achieved starting
from the same precursor, i.e. commercially available 2,5-
dibromopyridine
6
(Scheme 1). Depending on the reaction
could be
conditions (such as solvent, base) compound
6
selectively monolithiated.17-21 More precisely, reaction times
and solvents played a crucial role on the course of the
electrophilic substitution, leading to predominant formation of
the organolithium intermediate at the 2 or 5 position.22,23 In
order to drive the reaction in the course of kinetically more
Scheme 1. Synthesis of dialdehyde 1a and 2a.
The isomeric 3,3’-diazatolane dialdehyde 2a was obtained
in a similar way (Scheme 1). Here, 2,5-dibromo-pyridine
selectively monolithiated in position 2 in toluene media. Time
of the exchange reaction with -BuLi was increased to 90 min
6 was
favorable 2-bromo-5-carbaldehyde-pyridine
7, it was carried
n
out in dry diethyl ether at -78ºC, and DMF was added to the
to ensure the desired organolithium intermediate formation,
and precursor 11 was obtained in 49% yield.21 Next, standard
Sonogashira-Hagihara methodology16 was employed. Final
separation on a silica gel column with hexane/EtOAc eluent
mixture (3:2) yielded 5,5’-ethyne-1,2-diylbis(pyridine-2-
carbaldehyde) 2a in decent yield (69%).
mixture already 20 min after the addition of
completed (Scheme 1).
n-BuLi was
According to the preliminary results obtained in our group,
2-ethynyl-5-formyl-pyridine was unstable. Therefore, at first
aldehyde
7
was transformed into the 2-bromo-5-[1,3]dioxolan-
following the standard protocol.24 Compound
2-yl-pyridine
8
8
(i)
was involved into Pd-catalyzed Sonogashira-Hagihara coupling
with trimethylsilyl acetylene (TMSA) giving rise to the
3a
14
derivative 9. Hydrolysis of the trimethylsilyl group using 1N
NaOH solution in deaerated THF - water mixture (1:1) granted
NMR-pure ethynyl derivative 10, which was used further
without additional purification.
(ii)
(iii)
4a
15
16
Sonogashira-Hagihara coupling reactions can be
successfully carried out under various conditions.16 For our
systems it was found that by decreasing the reaction
Reagents and conditions: (i) (a) n-BuLi, THF, TMEDA, under Ar, -78ºC 30 min, -50ºC 30
min; (b) DMF, -78ºC, under Ar, 1h, (c) NH4Cl, 20 min; (ii) NBS, CCl4, benzoyl peroxide,
reflux under Ar, 14 h; (iii) hexamethylenetetramine, EtOH-H2O, reflux, 60 h.
temperature from 80
°C
(DMF/Et3N, 1:1) to
~22°C
(CH3CN/Et3N, 1:1) formation of several side-products was Scheme 2. Synthesis of dialdehyde 3a and 4a.
prevented. Therefore, the attachment of the bromo derivative
8
to the pre-organized ethynyl-pyridine 10 was carried out at
Several synthetic procedures towards compound 3a were
reported in the literature.15 Inspired by the efficiency and
simplicity of the approach sketched in Scheme 2, commercially
room temperature in CH3CN/Et3N solvent mixture, and led to
the corresponding product in a reasonable yield (72%).
Notably, our attempts to remove dioxolane protective groups
available 4,4’-dibromobiphenyl 14 was treated with n-BuLi in
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the presence of catalytic amount of TMEDA. After addition of nitrogens of the imidazoline ring (as presented in the Toc and
dry DMF, typical work-up and purification, biphenyl dialdehyde Table S2).
3a was isolated in 58% yield.
Crystal structure analysis.
Bipyridine-4,4'-dicarbaldehyde 4a was achieved upon
formation of 5,5’-bis-(bromo-methyl)-2,2’-bipyridine 16 from
the corresponding dimethyl-bipyridine precursor 15 following
the procedure described by Vögtle.25 Then nucleophilic
Crystals were obtained by a slow diffusion of hexane in
dichloromethane solutions of the nitroxide biradicals at room
temperature. Deep-blue needle crystals of the nitronyl
substitution under Sommelet conditions led to 4a 26
. Synthesis
nitroxides 1c
, 2c and red blocks of the imino nitroxides 1d, 3d,
of the tolane dialdehyde 5a was described elsewhere.11
4d, 5d were then characterized by X-ray diffraction analysis.
Selected torsion angles are reported in Table 1 (with some
additional structural data given in SI).
(i)
All the nitroxide biradicals 1c, 2c, 1d, 3d, 4d, 5d under
1b
1a
(ii)
(iii)
study possess a planar backbone – the necessary prerequisite
for the propagation of weak intramolecular magnetic
interactions. Importantly, in such biradical models the torsion
angles θ (see Table 1) play a central role in modulation of the
magnetic exchange interactions.
1c
1d
Reagents and conditions: (i) BSA, toluene, reflux under Ar, 4-6 h; (ii) NaIO4, CH2Cl2-H2O,
Table 1. Selected bond lengths and dihedral angles for the synthesized biradicals.
0-5ºC, 30-40 min; (iii) MnO2, CH3NO2, 35 min.
Biradical
d, Å
θ, deg
Scheme 3. Synthesis of nitroxide biradicals 1c and 1d.
1.4513(15) on C18
1.4564(15) on C5
21.62(9)
1c
2c
1d
24.84(10)
Final steps in the synthesis of nitroxides included
condensation
between
2,3-bis(hydroxyamino)-2,3-
O
O
1.472(18)
53.72(11)
dimethylbutane (BSA) with an aldehyde, followed by the
oxidation of the condensation products (i.e. imizadolidine
derivatives 1-5b).11,15 Typically, the first reaction was
performed under strictly anaerobic conditions in refluxing
toluene (Scheme 3). Here, the corresponding N,N′-
N
N
1.4743(12) on C25
1.4717(12) on C5
23.16(12)
24.85(9)
d
20.2(2) O1
3d
1.471(2)
15.35(18) at O2
4d
5d
1.473(2)
13.57(19)
5.97(12)
dihydroxyimidazolidines 1b, 3b, 4b, 5b were obtained in
1.4754(17)
quantitative yields. As an exception synthesis of diazotolane
imidazolidine 2b was realized in absolute degassed methanol
at room temperature.
Not surprisingly, similar torsions
θ of about ~24°, result in
nearly identical degree of conjugation.11,15 Consequently, a
comparable spin polarization and close values of the exchange
integrals were expected for most of the obtained biradical
models (see for comparison Table 1). In contrast to the
described situation, the radical units in the nitronyl nitroxide
In order to avoid further oxidation, and, therefore, to
diminish the loss of the radical units, oxidation of the N,N′-
dihydroxyimidazolidine intermediate 1b with sodium
periodate was carried out at ~0-5º
C using an ice bath.27 The
progress of the reaction could be conveniently monitored by
TLC analysis of the reaction mixture aliquots. Synthesis of the
derivative 2c was achieved using the excess of MnO2 in
2c were far more twisted (> 50°). From this crystal structure
analysis it was assumed that the nitronyl biradical 2c would
exhibit a unique behavior among the compounds investigated
here.
methanol. Imino biradicals 1d, 3d, 4d were obtained following
the procedure described by Tretyakov et al.28,29 This method
helped to avoid the harmful usage of acids and to synthesize
the target molecules in better yields. As an illustration,
transformation of the imidazolidine 1b into the corresponding
imino biradical 1d with excess of MnO2 in CH3NO2 media is
depicted in Scheme 3. To aid the interpretation of magnetic
properties of the isomeric NN 1c and 2c related IN biradical 1d
was also prepared.
The UV-Vis absorption spectra of 1c and 2c with maxima
around 600 nm were typical for the nitronyl nitroxides , while
the red bisiminonitroxides absorbed around 460 nm (Table
S2). The EPR spectra of bisnitronylnitroxides exhibited nine
lines with An/2 spacing for four equivalent nitrogens with two
strongly coupled radicals. The bisiminonitroxides (1d, 3b, 4b,
5d) featured 13 lines, corresponding to the inequivalent
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Figure 3. Molecular structure (top) and crystal packing (bottom) of biradical 2c (view
along the a axes).
Biradical 2c crystallizes in the P21/c space group and the
molecular structure is shown in Fig. 3. Compound 2c features a
transoid arrangement with an inversion center of symmetry
located in the C1-C1′ bond, which is typical for the derivatives
containing acetylene bridges (Fig. 3). In general, the structural
data of 2c are rather similar to those described for the other
nitronyl nitroxide biradicals in the literature (Table 1, Table
S1).11,14 A remarkable difference is found in the largely
increased torsion between the pyridyl ring and the
imidazolidine fragment O1-N2-C7 (O2-N3-C7) with a dihedral
angle of 53.72(11) (Fig. 3).
Figure 2. Molecular structure (top) of biradical 1c with ORTEP drawn at the 50% of the
probability level and crystal packing (bottom) with emphasized short contacts.
Biradical 1c adopts a triclinic space group with an inversion
centre residing in the middle of the acetylene bridge (Fig. 2).
Remarkably, in the asymmetric unit there are two
crystallographically independent molecules with a nearly equal
geometry. The dihedral angles of the mean plane of the
imidazolidine ring and the two coplanar pyridine rings was
The crystal packing of 2c presents a beautiful example
where the bidentate character of the nitronyl nitroxide
fragment plays the major role in spatial arrangement of the
biradical chains. Here, the molecules of 2c form infinite zig-zag
ribbons along the
b axes (Fig. 3, Fig. S3) Notably, the
neighboring molecules are organized in an alternate fashion,
placing NN groups next to the pyridine plane and, thereby,
stabilizing the crystal packing (Fig. S3).
found to be ≈25° for O1-N2-C7 (O2N3-C7) towards C5 and 22°
with O3N5-C20 (O4-N6--C20) towards C18 (see table 1). Here,
the N(2)-O(1) 1.280(1), N(3)-O(2) 1.278(2), N(5)-O(3) 1.279(1),
N(6)-O(4) 1.272(2) Å bond lengths occur in the typical range
for the nitroxides;11,14,15 The N(2)-C(7) 1.355(2), N(2)-C(11)
1.503(1), N(3)-C(7) 1.351(1), N(3)-C(8) 1.503(2); N(5)-C(20)
1.358(2), N(5)-C(24) 1.502(1); N(6)-C(20) 1.354(2), N(6)-C(21)
1.497(1) Å bond distances are elongated due to the short
intermolecular contacts that stabilize the crystal packing (for
instance, the ones formed by N(6)O(4)).
Imino biradical 1d crystalizes in the triclinic space group P-
1 . There are two independent centrosymmetric half molecules
in the asymmetric unit cell. (Fig. 4). The main structural
characteristics are similar to those described for the
corresponding nitronyl nitroxide derivative 1c. Thus, the
pyridine rings form anglesof
≈23° and ≈25º with the
imidazolidine plane (Table 1). The N(2)-O(1) 1.269(1), N(221)-
O(211) 1.277(2), and N(222)-O(212) 1.257(5) Å bond distances
featured minor differences.
The intermolecular contacts between NO groups of the
first molecule with the pyridine rings (O4···C1′3.036, O4···C2
3.135 Å) of the neighboring biradical leads to V-shaped
′
alignment of dimers (Fig. 2, Fig. S1).
Figure 4. Molecular structure (top) with two biradical molecules per asymmetric unit of
biradical 1d and short contacts and π-stacking specified in fragments of molecule from
crystal packing.
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The packing arrangement of the radical dimers 1d is shown 3.177 Å between the neighboring oxygen atoms and phenyl
in Fig. 4, and can be described as a ladder-like structure with rings in 3d define the formation of ribbon-like structures which
biradicals of the first kind forming a stair, and nitroxides of the are further organized in a zig-zag pattern. Likewise, multiple
second type extending from both sides of each step (Fig. S4). oxygen contacts (i.e. O1···H91′ 2.302, O2···H51′ 2.473,
The structure is supported by numerous hydrogen bonds O2···H93′ 2.600, O1···C9′ 3.199 and O2···C5′ 3.085 Å)
arising from the pyridine π-bridges and the imino nitroxide accompany the molecular ordering in the case of imino
chelating units. Most important seems the short contacts of derivative 4d (Fig. S4). Notably, the neighboring chains in 4d
the NO groups and the hydrogen atoms of the pyridine core are connected with close O2···O2′ 2.801 Å contacts.
O211···H261′=2.456, O212···H261′=2.538
Å (Fig. 4). The
shortest interchain distances of 3.352 Å (C6···C25′) are found
between the two neighboring diazatolane bridges (Fig. 4). The
closest intermolecular contacts between NO groups and a
pyridine ring are slightly larger, and are within the range:
∼2.4-
2.7 (O1··· H41′, O1··· H31′, respectively) and ~3.1 Å (O1···C4′).
Imino biradicals 3d and 4d feature isomorphic crystal
structures. Thus, they possess P21/n space group with a center
of symmetry located in the middle of the aromatic C-C′ bond
(Fig. 5, Fig. S4). The biphenyl bridge in 3d is surprisingly planar,
and the dihedral angle between the mean plane of the
benzene ring and the imidazolidine moiety is only 20.2
slightly disordered, since the the five membered ring can flip
around 180 such that the two NO groups could be oriented ‘E’
º. 3d is
º
or ‘Z’ with 50% probability.. The N(1)-O(1) 1.226(3) and N(2)-
O(2) 1.213(3) Å bond lengths are in the standard range.15
Figure 6. Molecular structure (top) and crystal packing (bottom) of biradical 5d.
Imino nitroxide biradical 5d crystallizes in a monoclinic
space group with P21/n symmetry. The structure of compound
5d is shown in Fig. 6. In contrast to the previously described
biradicals compound 5d has surprisingly small torsion angles
between the radical unit and the adjacent phenyl ring of only
30
about 6
°
.
The overall tolane backbone is fairly planar. The
N(2)-O(1) 1.271(1) Å bond distances are similar for this type of
compounds.
The oxo atoms in 5d act as bridging ligands (O1···H141′
2.622, O1···H131′ 2.654 Å) connecting the neighboring
biradical molecules into 1D zig-zag shaped chain structures in
the crystal cell. These radical ribbons are then piled up along
the b crystallographic axis (Fig. S5), using C7···C10′ 3.381 Å
close contacts to stabilize the packing (Fig. 6, S7).
Figure 5. Molecular structure (top) and crystal packing (bottom) of biradical 3d.
Magnetic characterization.
Naturally, for the isomorphic imino nitroxide derivatives 3d
and 4d the main structural characteristics are very similar.14,27
Thus, in 4d the O-N-C-N-O moiety is planar, with the N(3)-O(2)
bond slightly shorter than N(2)-O(1) 1.167(4) and 1.215(3) Å,
respectively (Fig. S4). Furthermore, in the asymmetric unit of
4d there are two crystallographically independent forms with
To gain a more complete picture of the influence of a given π-
spacer on the electronic properties, and especially on the
intra- and inter-dimer exchange couplings, DFT calculations
were performed. To get a first idea on the sizeable changes of
the exchange interaction in the studied biradical models,
geometry optimization with the B3LYP hybrid function and 6-
31G* basis set was carried out.31 Then the broken symmetry
approach (BS) for the singlet and triplet states with the BLYP
functional (to avoid Hartree-Fock contamination) and the same
basis set were applied.12 Therefore, the direct exchange
interaction for a weakly coupled spin dimer can be described
the ratio ∼2:3 belonging to different biradical chains (Fig. S4).
An important feature already mentioned for the other
biradicals of the current series is the abundance of close
intermolecular contacts between the N-O entities and the
aromatic moieties in asymmetric unit. In particular, the
hydrogen bonding O1 ··H31′ 2.580, O1···H123′ 2.696, O1 ··C3′
as
J
/
kB
=
E(BS)–E(T), since the spin expectation values < S2(BS)>
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and <S2 (T)> for the broken symmetry configuration are close
Journal Name
~
120 K followed by a more pronounced drop below ~50 K. This
to 1 and for the triplet configuration are close to 2 such that overall behavior reflects the dominant antiferromagnetic intra-
their difference is close to unity.32 Notably, in the case of dimer coupling
intra. The inset of Fig. 7 shows the molar
antiferromagnetic interactions takes negative values. The magnetic susceptibility as a function of temperature. The
calculations were then redone in accordance with the X-ray Bleany-Bowers equation34 for a model of an isolated dimer χiso
geometries, as listed in Table 2. with mean-field correction was applied to fit the
J
J
a
Applying a Quantum Design SQUID magnetometer the experimental data (solid line in the inset of Fig. 7). Using this
temperature dependence of the molar magnetic fitting the size of the intra-dimer Jintra and the inter-dimer
susceptibilities χmol(T) of microcrystalline samples 1c
3d 4d 5d was determined in the range 2 K ≤ ≤ 270 K in coupling constants were extracted:
magnetic fields = 1T. The obtained data were corrected for
,
2c
,
1d,
zJ’inter (where z is the number of the nearest neighbors)
,
,
T
B
χmol
= χiso /[1 – (z J'.
χiso /Ng2ꢀB2)] (eq. 1)
the temperature-independent diamagnetic core contribution
of the constituents.33 Magnetic contribution of the sample
holder was determined in an independent experiment without
a sample. The results are graphically displayed in the form of
Thus, for 1c an experimental intra-dimer coupling constant
Jintra kB = -5.4 0.2 K was obtained. This value is in tangible
/
±
agreement with the coupling constant acquired from the
broken-symmetry approach (Table 2). It should be mentioned,
that the experimental and theoretical Jintra values of 1c are
χmol
Figs. 7 and 8 and in the SI (Fig. S8). AC-susceptibility
measurements ( ac) were performed only on 5d as a function
of magnetic field at = 0.028 K using an ultra-high resolution
T vs. T in the main panel, and as χmol vs. T in the insets of
χ
very similar to the ones reported for tolane NN (Jintra/kB = -4.8
K).11 In this light it is reasonable to assume, that a mere
substitution of N for C in the position X (as indicated in Fig.1), if
it does not severely affect the geometry of a given crystal
structure, has practically no influence on the magnetic
interactions.
T
AC-susceptometer adapted to a 3He-4He top-loading dilution
refrigerator. The compensated-coil susceptometer was
optimized for measuring small single crystals in the mg range.
ꢈꢉꢊ
ꢁꢂꢃꢄꢅ
ꢆꢅꢇꢆ
Table 2. Calculated ꢀ
and experimentally obtained ꢀ
intra-dimer exchange
ꢁꢂꢃꢄꢅ
ꢈꢉꢊ
ꢁꢂꢃꢈꢄ
coupling constants. zꢀ′
describes the inter-dimer coupling, where z is the number
of the nearest neighbors. Tmax corresponds to the maximum in the χmol(T) plot.
ꢒꢓꢔ
ꢒꢓꢔ
ꢋꢌꢍꢎꢏ
[K]a
ꢀ
[K]b
ꢐꢏꢑꢐ
ꢋꢌꢍꢎꢏ
ꢐꢏꢑꢐ
ꢋꢌꢍꢎꢏ
ꢀ
[K]
zꢀ′
[K]
ꢋꢌꢍꢒꢎ
Biradical
T
max [K]
ꢀ
1c
2c
6.8
53
-
-19.6
-9.8
-5.4 ± 0.2
-12.0 ± 3.0c
< -1.5
-1.4 ± 0.4
-42.4 ± 1.7c
-
-2.4
-2.4
-4.7
-3.2
-2.6
-3.1
-1.1
-5.0
-3.6
-1.6
1d
3d
4d
5d
[a]
4.2
3.2
2.8
-3.3 ± 0.1
-2.5 ± 0.1
-2.2 ± 0.1
-2.0 ± 0.5
-5.8 ± 1.4
-0.5 ± 0.1
1c
Optimized geometries were obtained from DFT calculations (B3LYP, 6-31 G*),
then single point calculations for the energy of the broken symmetry and the
triplet state were applied (UBLYP, 6-31 G* for the evaluation of J);31
Figure 7. χmolT as a function of temperature (solid orange circles) of 1c. The black
broken line indicates the theoretical value of 0.75 cm3 K/mol, expected for the two
[b] The exchange interactions were evaluated for X-ray crystal structures applying
the broken symmetry approach with BLYP functionals and 6-31G* basis set.
uncoupled spin
S = ½ entities. Inset: molar susceptibility χmol as a function of
temperature (solid green circles) in a semilog representation, and a theoretical fit with
a mean-field correction (red solid line).33
[c]
Note, that dominant magnetic exchange in 2c is between two adjacent NN-
units belonging to different biradicals (for details see text and fig.3).
An unexpected result was acquired for the NN derivative 2c
where N was substituted with C in the Y position (Fig. 1). For
this system the DFT calculations predict Jintra values of a few
Kelvin, i.e. similar to those found for the other materials under
investigation. The magnetic properties of 2c determined
Generally, all the biradicals under investigation (1c
4d 5d) featured a similar magnetic behavior in the studied
temperature range. The observed χmol values at 300 K of the
, 2c, 1d,
3d
,
,
T
nitroxides are around 0.7 cm3 K/mol. Importantly,
experimental data are rather close to the theoretical value of
0.75 cm3 K/mol, which is expected for the two uncoupled spin
S = 1/2 units (indicated by the broken line in Fig. 7). This
indicates the high quality of the studied single crystals.
experimentally are shown in Fig. 8. The χmolT data decreased
gradually and leveled off around 20 K at a small value of
approximately 0.02 cm3 K/mol. In the inset of Fig. 8 a broad
maximum in χmol at 53 K is clearly visible. From a theoretical
fit33 corrected with a Curie term for uncoupled S = ½ entities
(solid red line in the inset of Fig. 8), inter-dimer coupling
As a typical example, χmol
T (T) of the NN-biradical 1c is
shown in Fig. 7. Upon decreasing the temperature χmol
features an approximately linear moderate decrease down to
T
6 | J. Name., 2012, 00, 1-3
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constant of Jinter
/
k
intra of 1c and tolane NN in ref. 11.
B = -42.4 K was obtained. This is significantly single peak in susceptibility
χ
, the field derivative of the
larger than
J
magnetization. Fig. 9 shows the AC-susceptibility of the IN
biradical 5d as a function of magnetic field at 0.028 K (right
scale) together with the magnetization of the material at the
same temperature (left scale).
2c
Figure 8. χmolT as a function of temperature (solid orange circles) of 2c. The black
broken line indicates the theoretical value of 0.75 cm3 K/mol, expected for the two
uncoupled spin
S = ½ entities. Inset: molar susceptibility χmol as a function of
Figure 9. Magnetization M(B) of 5d (solid red line, left scale) at 28 mK normalized to
the saturation magnetization together with the magnetic AC-susceptibility χac(B)
(orange full circles, right scale).
temperature (solid green circles), and a theoretical fit with a mean-field correction (red
solid line),33 including a Curie term corresponding to S = ½ entities.
This observation is conceivable in terms of the crystal
structure peculiarities. As described above, the radical units in
The AC susceptibility was measured only for IN biradical 5d
since only for this sample a large single crystal was available.
Polycrystalline samples have been shown to be critical for their
inter crystalline contacts and depend on their powder to
crystallinity content and several mg are still needed. The data
the nitronyl nitroxide 2c are far more twisted (∼53°) in
comparison to other biradical models described here. The
further analysis of the X-ray data revealed exceptionally short
contacts of ∼3.51 Å between two neighboring NO fragments in
highlight a well-pronounced double-peak feature in χac, an
3,3’-diazatolane nitronyl nitroxide 2c (Fig. S7). Apparently,
these short contacts are responsible for the unpredicted
strong antiferromagnetic exchange interactions found in the
solid. Taking only these intermolecular interactions into
account and replacing the second radical unit by hydrogen, the
evidence of a field-induced ordered state between Bc1 = 1.8 T
and Bc2 = 4.3 T at 0.028 K. Such field-induced phases are
expected for a coupled-dimer system where the lower edge of
a band of magnetic excitations crosses the ground state at Bc1.
Here, Bc2 corresponds to the saturation field Bs where the full
magnetization of the system is obtained. The magnetization
exhibits no hysteretic behaviour. This feature is attributed to
small magnetic intermolecular interactions between the
neighboring biradical molecules mediated via hydrogen bonds.
The strength of these interactions depends on the distance
and the relative orientation of the radicals.35,36 The anomalies
at the critical fields Bc1 and Bc2 are much sharper than the one
found in a quasi-2D system.11 More likely, the inter-dimer
coupling in 5d has a 3D character, and therefore, this field-
induced ordered phase can be described in terms of a BEC of
triplons.
value Jinter
/
k
the experimentally obtained one of -42.4
B = -45.6 K was calculated, which was very close to
1.7 K (Table 2).
±
Such short inter-dimer distances between spin centers could
not be found in the other biradicals.
In accordance with the theoretical predictions and crystal
structure analysis the IN biradicals 1d, 3d, 4d and 5d featured
week antiferromagnetic intramolecular coupling. Their intra-
dimer exchange constants are listed in Table 2 (see also Fig.
S8). Interestingly, in case of IN-biradicals 3d and 4d the N-
heteroatomic substitution has barely affected their magnetic
properties in accordance to the previous statement. From the
experimental data recorded for the imino biradical 1d no clear
maximum could be resolved, indicating an extremely weak
intra-dimer coupling constant < -1.5 K.
Experimental section
Remarkably, a closer examination of the low-temperature
(T < Jintra/kB) susceptibility data for the IN-biradical 5d revealed
Materials and methods
All chemicals and reagents were used as received from
commercial sources (Acros Organics, Aldrich, Fluka, Lancaster,
Merck and Strem) without additional purification. Solvents for
synthesis were used as received, unless otherwise mentioned.
ESR spectra were recorded in dilute, oxygen-free solutions in
a
significant deviation from the isolated-dimer model.
Typically, magnetization of the isolated-dimer systems changes
in step-wise manner at the saturation field Bs and
a
temperatures T < Jintra/kB. Such field-temperature induced
transitions correspond to the alteration in the spin-state
population of the dimers, namely, the occupation of the low-
lying triplet state. The phenomenon is reflected in form of a
toluene, concentration
~ ×L, using a Bruker X-band
10-4 mol
spectrometer ESP300 E, equipped with an NMR gaussmeter
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DOI: 10.1039/C7TC03357E
ARTICLE
Journal Name
(Bruker ER035), a frequency counter (Bruker ER041XK) and a deep red. The temperature (-78°C) was maintained for further
variable temperature control continuous flow N2 cryostat 90 min, and then slowly raised. After that 3% HCl (100 mL) was
(Bruker B-VT 2000). The g-factor corrections were obtained added. The resulted mixture was stirred for 20 min.
using the DPPH (g = 2.0037) as standard. UV-Vis spectra were Diethylether was concentrated in vacuo. To the oily residue 60
recorded in toluene solutions with
a
Perkin-Elmer mL of dichloromethane was added, and the mixture was
spectrometer (UV/Vis/NIR Lambda 900) using a 1-cm optical neutralized with solid NaHCO3. Organic phase was separated
path quartz cell at room temperature, unless otherwise and the water layer was extracted with dichloromethane
specified. H and 13C NMR spectra were recorded on a Bruker (3
1
×
60 mL). Combined organic extracts were dried over MgSO4,
DPX 250, Bruker DMX 300 spectrometer. Solid powders were and the solvent was evaporated. Crystals were filtrated and
pressed and IR spectra of the samples were recorded as they washed carefully with hexane (3 20 mL). The filtrate was
were (Nicolet 730 FT-IR spectrometer). Mass spectra were reduced to a small volume (ca. 2 mL), and purified on a flash
obtained on FDMS, VG Instruments ZAB-2 mass spectrometer. column (SiO2, dichloromethane). The aldehyde was obtained
Elemental analyses were performed at the University of Mainz, in 72% total yield. 1H-NMR (CDCl3, 250 MHz, 298K, 16 scan), δ
×
7
3
3
Faculty of Chemistry and Pharmacy on a Foss Heraeus Varieo ppm: 7.66 (d, 1H, J = 8 Hz, H-3), 8.01 (dd, 1H, J = 8 Hz, H-4),
EL. The melting points were measured on a Büchi B-545 8.82 (s, 1H, H-6), 10.08 (s, 1H, -CHO). 13C-NMR (CDCl3, 63 MHz,
apparatus (uncorrected) by using open-ended capillaries. 298K, 256 scan) δ ppm: 129.4 (C-3), 131 (C-5), 137.9 (C-4),
Crystallographic data for the reported structures of the 148.7 (C-2), 152.9 (C-6), 189.9 (-CHO). MS-FD (70 eV, CH2Cl2)
biradicals have been deposited with the Cambridge m/z: 187.3 (M+), MW calculated C6H4BrNO (MW+) 186.01.
Crystallographic Data Centre.‡ 2,3-Bis(hydroxyamino)-2,3-
dimethylbutane (BHA) synthesis was described elsewhere.11,15
2-Bromo-5-[1,3]-dioxolan-2-yl-pyridine
(8).
Starting
compound 7 (5g, 26.85 mmol) was charged into a flask
A1. General procedure for Sonogashira-Hagihara coupling together with benzene (100 mL), ethyleneglycol (2.7 mL, 48.5
reaction. An aryl bromide (21.7 mmol, 1 eq.) was transferred mmol) and catalytic amount of para-toluene-sulfonic acid (0.4
into a flame-dried flask in argon stream. A mixture of dry g, 2.1 mmol). The solution was heated to reflux with Deane-
DMF/NEt3 (50 mL, 1:1) solvents was added through the rubber Stark for 20 h. Then reaction mixture was cooled down to rt,
septum. Solution was carefully deaerated by purging with and neutralized with NaHCO3 aqueous solution, and the
argon for 20-25 min, and the catalytic mixture of Pd(PPh3)2Cl2 phases were separated. The aqueous layer was extracted with
(1.1 mmol, 0.05 eq.), PPh3 (2.2 mmol, 0.1 eq.), CuI (1.1 mmol, small portions of benzene (3
0.05 eq.) was added at once. The resulting mixture was slightly collected, dried over MgSO4 and filtrated. The solvent was
heated (to 45oC) and ethynyl-trimethyl-silan (32.6 mmol, 1.5 evaporated under the reduced pressure. Compound
was
eq.) was added through the septum. After that the heating was obtained as yellowish oil in 85% yield (5.4 g), and was used
increased to 80oC. A white precipitate began to form after 15 further without additional purification. 1H-NMR (CDCl3, 250
×15 mL). Benzene extracts were
8
~
min of heating. After the reported time (4 to 16 h), the mixture MHz, 298K, 16 scan), δ ppm: 3.92 (m, 4H, -CH2), 5.71 (s, 1H, H-
was cooled to ambient temperature, and the crystalline white 7), 7.34 (d, 1H, 3J = 8 Hz, H-3), 7.62 (dd, 1H, 3J = 8 Hz, H-4), 8.47
solid of triethylamine hydrobromide was isolated by filtration. (s, 1H, H-6). 13C-NMR (CDCl3, 63 MHz, 298K, 256 scan), δ ppm:
The orange-brown filtrate was concentrated, mixed with NH4Cl 64.4 (-CH2), 100.2 (C-7), 126.9 (C-3), 132.4 (C-5), 135.9 (C-4),
saturated aqueous solution (50 mL), and extracted with 142 (C-2), 147.9 (C-6). MS-FD (70 eV, CH2Cl2) m/z: 231.2 (M+),
dichloromethane or diethyl ether (3
fractions were combined, dried over magnesium sulfate, and
concentrated with silica gel in vacuo. The residue was purified The derivative
using column chromatography. procedure A1
A2. Using the same set-up and the catalyst/reagents ratio a dichloromethane/hexane eluent (3:2) afforded the precursor
mixture of dry NEt3/CH3CN (1:1) as the solvent media was in 89% yield. 1H-NMR (CDCl3, 250 MHz, 298K, 16 scan), δ ppm:
preferred. Here, after minutes of stirring at room 0.28 (s, 9H, -CH3), 4.09 (m, 4H, -CH2), 5.85 (s, 1H, H-7), 7.47 (d,
×
40 mL). The organic MW calculated C8H8BrNO2 (MW+) 230.06.
2-Ethynyl-trimethyl-silyl-5-[1,3]-dioxolan-2-yl-pyridine (9).
was synthesized according to the synthetic
Purification on silica gel column with
9
.
a
9
5
temperature formation of triethylamine hydrobromide salt 1H, 3J = 8 Hz, H-3), 7.74 (dd, 1H, J = 8 Hz, H-4), 8.65 (s, 1H, H-
was observed. Light yellow reaction mixture was stirred at 6). 13C-NMR (CDCl3, 63 MHz, 298K, 256 scan), δ ppm: 0 (-CH3),
room temperature for 17-19 h. The work-up was done in 67.1 (-CH2), 94.8 (C-9), 102.2 (C-7), 104.1 (C-8), 126.7 (C-3),
3
accordance with the protocol A1.
132.6 (C-5), 134.9 (C-4), 143.4 (C-2), 148.6 (C-6). MS-FD (70 eV,
2-Bromo-5-pyridinecarbaldehyde (7). 2,5-Dibromopyridine CH2Cl2) m/z: 247.1 (M+), MW calculated C13H17NO2Si (MW+)
6
(10 g, 42.2 mmol) was charged into a flame-dried flask, 247.37.
evacuated and kept under argon. Dry diethylether (250 mL)
2-Ethynyl-5-[1,3]-dioxolan-2-yl-pyridine (10). Solution of
was added, and the resulting solution was cooled to -78°C in 2-ethynyl-trimethyl-silyl-5-[1,3]-dioxolan-2-yl-pyridine 10 (0.33
dry ice/acetone bath. Then n-BuLi (34 mL, 1.6 M in hexane, g, 1.3 mmol) in THF (25 mL) was treated with 1N NaOH (50 mL)
53.8 mmol) was added dropwise within 20-25 min. Upon under argon at 5°C (ice/water bath). After 35 min the reaction
addition of n-BuLi the resulting solution turned red. The was complete (according to the TLC analysis of the reaction
temperature (-78
then dry dimethylformamide (4.7 mL, d = 0.94 g ml-1, 60.3 reduced pressure, and brine (50 mL) was added to the residue.
mmol) was added dropwise within 15 min. The mixture turned The aqueous layer was extracted with dichloromethane (3 60
°C) was kept constant for further 45 min, and mixture aliquots). The solvent was evaporated under the
×
8 | J. Name., 2012, 00, 1-3
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Journal of Materials Chemistry C
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ARTICLE
mL). The combined organic fractions were dried over MgSO4 in vacuo. The oily residue was purified through a flash column
and concentrated in vacuo. The so-obtained compound 10 (SiO2, petroleum ether/ethyl acetate, 100:3). 5-Bromo-2-
(89% yield) was used for the next step without additional pyridinecarbaldehyde 11 was synthesized in 49% yield. 1H-
purification. 1H-NMR (CDCl3, 250 MHz, 298K, 16 scan), δ ppm: NMR (CDCl3, 250 MHz, 298K, 16 scan), δ (ppm): 7.8 (d, 1H, H-
3
3.2 (s, 1H, H-9), 4.11 (m, 4H, -CH2), 5.88 (s, 1H, H-7), 7.51 (d, 6), 7.9 (dd, 1H, J = 8 Hz, H-4), 8.78 (d, 1H, H-3), 9.97 (s, 1H, -
3
1H, J = 8 Hz, H-3), 7.78 (dd, 1H, 3J = 8 Hz, H-4), 8.69 (s, 1H, H- C=O). 13C-NMR (CDCl3, 63 MHz, 298K, 256 scan), δ ppm: 122.7
6). 13C-NMR (CDCl3, 63 MHz, 298K, 256 scan), δ ppm: 65.4 (- (C-5), 126.2 (C-3), 139.9 (C-4), 151.1 (C-2), 151.5 (C-6), 192.3 (-
CH2), 72.8 (C-9), 81.4 (C-8), 101.8 (C-7), 127.4 (C-3), 134.2 (C- CHO). MS-FD (70 eV, CH2Cl2) m/z: 187.3 (M+), MW calculated
5), 134.7 (C-4), 142.5 (C-2), 149.4 (C-6). MS-FD (70 eV, CH2Cl2) C6H4BrNO (MW+) 186.01.
m/z: 175.3 (M+), MW calculated C10H9NO2 (MW+) 175.18.
5-Ethynyl-trimethyl-silyl-2-formylyl-pyridine (12). The
2,2′-Ethyne-1,2-diylbis(pyridine-5-carbaldehyde)
(1a). trimethyl-silyl derivative 12 was obtained in 87% yield (2.37 g)
Sonogashira cross-coupling between precursors
8 and 10 was following the general procedure A1 after the purification on a
realized following the methodology A2. As the major product silica gel chromatographic column (ethyl acetate/hexane, 3:
1,2-bis(5-(1,3-dioxolan-2-yl)pyridine-2-yl)ethyne was isolated 100). 1H-NMR (CDCl3, 250 MHz, 298K, 16 scan), δ ppm: 0.26 (s,
3
in 72% yield using flash chromatography (SiO2, 9H, -CH3), 7.86 (d, 2H, J = 2 Hz, H-3, H-4), 8.77 (s, 1H, H-4),
dichloromethane). 1H-NMR (CDCl3, 250 MHz, 298K, 16 scan), δ 8.65 (s, 1H, H-6), 10.02 (s, 1H, -C=O). 13C-NMR (CDCl3, 63 MHz,
ppm: 4.01 (m, 8H, -CH2), 5.8 (s, 2H, H-7), 7.56 (d, 2H, 3J = 8 Hz, 298K, 256 scan), δ ppm: 0 (-CH3), 98.8 (C-8), 101.9 (C-7), 121.1
3
H-3), 7.72 (dd, 2H, J = 8 Hz, H-4), 8.65 (s, 2H, H-6). 13C-NMR (C-3), 122.4 (C-5), 140.4 (C-4), 150.8 (C-2), 151.7 (C-6), 192.7
(CDCl3, 63 MHz, 298K, 256 scan), δ ppm: 65.8 (-CH2), 88.5 (C-8), (C=O). MS-FD (70 eV, CH2Cl2) m/z: 202.7 (M+), MW calculated
101.9 (C-7), 127.8 (C-3), 133.9 (C-5), 134.9 (C-4), 143.5 (C-2), C11H13NOSi (MW+) 203.31.
149.1 (C-6). MS-FD (70 eV, CH2Cl2) m/z: 324.5 (M+), MW
calculated C18H16N2O4 (MW+) 324.33.
5-Ethynyl-2-formyl-pyridine (13). Solution of 12 (1.43 g, 7
mmol) and K2CO3 (0.46 g, 3.33 mmol) in deaerated THF/water
Next, to the solution of the corresponding dioxolane mixture (80 mL, 1:1 v/v) was stirred at rt for 1.5 h. Brine was
precursor (0.38 g, 1.35 mmol) in acetone-water mixture (7:1, added to the mixture, organic layer was separated, and the
40 mL) para-toluene-sulfonic acid (52 mg, 0.027 mmol, 2 water phase was extracted with Et2O (4×30 mL). Combined
mol%) was added. The progress of the reaction was monitored organic extracts were dried over Na2SO4, and the solvents
by TLC (SiO2, hexane/ethyl acetate, 3:1). After 84 h of stirring were evaporated under the reduced pressure. Light-brown
at room temperature the reaction was complete. Acetone was solid was washed with hot hexane/acetone mixture (~20:1) to
evaporated, and the residue was diluted with dichloromethane give pale yellow precipitate in 51% yield (0.47 g). 1H-NMR
(30 mL). The organic layer was separated, and the water phase (CDCl3, 250 MHz, 298K, 16 scan), δ ppm: 3.36 (s, 1H, H-8), 4
was extracted with dichloromethane (3×
30 mL). The combined 7.87 (d, 2H, 3J = 8 Hz, H-3, H-4), 8.79 (t, 1H, 3J = 8 Hz, H-6), 10.0
organic extracts were dried over MgSO4. The solvent was (s, 1H, -C=O). 13C-NMR (CDCl3, 63 MHz, 298K, 256 scan), δ
removed in vacuo giving 0.26 g (81%) of the dialdehyde 1a as ppm: 78.7 (C-7), 83.6 (C-8), 119.9 (C-3), 122.7 (C-5), 139.2 (C-
yellow solid. 1H-NMR ((CD3)2SO, 250 MHz, 298K, 16 scan), δ 4), 150.4 (C-2), 152.0 (C-6), 191.4 (-CHO). MS-FD (70 eV,
3
3
ppm: 8.01 (d, 2H, J = 8 Hz, H-2), 8.37 (dd, 2H, J = 8 Hz, H-3), CH2Cl2) m/z: 130.3 (M+), MW calculated C8H5NO (MW+) 131.13.
9.19 (s, 2H, H-6), 10.20 (s, 2H, -CHO). 13C-NMR ((CD3)2SO, 63
5,5′-Ethyne-1,2-diylbis(pyridine-2-carbaldehyde) (2a).
MHz, 298K, 256 scan), δ ppm: 90.1 (C-8), 128.8 (C-3), 131.1 (C- Compound 2a was synthesized applying Sonogashira-Hagihara
5), 137.3 (C-4), 145.7 (C-2), 152.2 (C-6), 192.2 (-CHO). MS-FD coupling methodology A1 towards the precursors 11 and 13
(70 eV, CH2Cl2) m/z: 236.3 (M+), MW calculated C14H8N2O2 After evaporation of the solvent, the residue was diluted with
(MW+) 236.23.
chloroform (40 mL), and washed with NH4Cl saturated
.
5-Bromo-2-pyridinecarbaldehyde (11). n-BuLi (48 mL, 1.6 aqueous solution. The solvent was evaporated in vacuo. The
M solution in hexane, 76.8 mmol) and 50 mL of dry toluene product was isolated from the reaction mixture using flash
were transferred into a flame-dried flask filled with argon chromatography (SiO2, hexane/chloroform/ethyl acetate,
through the rubber septum. Solution was cooled to -78
dry ice/acetone bath, and solution of 2,5-dibromopyridine
(15 g, 63 mmol) in dry toluene (300 mL) was added dropwise yellow solid in 62% yield. 1H-NMR (CDCl3, 250 MHz, 298K, 64
within 1.5 h. Upon addition of the starting compound
to the scan), δ ppm: 8.04 (d, 2H, 3J = 8 Hz, H-4), 8.33 (d, 2H, 3J = 8 Hz,
mixture the color changed from colorless to yellow. The H-3), 9.09 (s, 2H, H-6), 10.03 (s, 2H, -CHO). 13C-NMR (CDCl3, 63
mixture was stirred at -78 C for 30 min, and the temperature MHz, 298K, 256 scan), δ ppm: 59.3 (C-7), 121.6 (C-4), 125.1 (C-
was allowed slowly to rise till -65 C. Then the solution was 5), 138.8 (C-3), 150.2 (C-2), 150.5 (C-6), 191.2 (-CHO). MS-FD
cooled again to -78
C, and dry dimethylformamide (5.89 mL, d (70 eV, CH2Cl2) m/z: 236.0 (M+), MW calculated C14H8N2O2
= 0.94 g/mL, 75.8 mmol) was added slowly dropwisewithin 20 (MW+) 236.23.
ºC in 2:4:1), and recrystallized from hexane/acetone/THF mixture
6
(2:1:1) to give 1,2-bis(2-formyl-5-yl)pyridinel)ethyne 2a as
6
º
°
°
min. The mixture was left stirring for overnight, and then
Biphenyl-4,4'-dicarbaldehyde (3a). n-BuLi (10 mL, 1.6 M
decomposed with 3% HCl (100 mL). The organic layer was solution in hexane, 16 mmol) was charged into a flame-dried
separated, and the water was extracted with dichloromethane flask filled with argon through a septum. Dry TMEDA (2 mL,
(4
×
50 mL). The combined organic extracts were washed with 0.013 mmol) was added. After stirring at room temperature
C (dry ice/i-
NaHCO3, dried over MgSO4 and the solvents were evaporated for 15 minutes the mixture was cooled to -78
º
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PrOH), and solution of 4,4'-dibromo-biphenyl 14 (2 g, 6.4 dried on air. The so-obtained derivatives were used further
mmol) in dry THF (20 mL) was added slowly dropwise within 30 without additional purification.
min. The temperature was slightly increased (to -50
ºC), due to
B2. The solution containing BHA (1.3 eq. for each aldehyde
a dramatic decrease of the solubility of the starting substrate group) and an aldehyde (1.0 eq.) in absolute deaerated
at a lower temperature, and kept at this level for 25 minutes. methanol (10 mL/1 mmol) was stirred at room temperature
After that the temperature was lowered again to -78
dry dimethylformamide (1.25 mL, d = 0.94 g/mL, 16.1 mmol) cold (
was added. The temperature was kept constant for 1 h, and for the next step without additional purification.
then it was allowed to rise slowly. The obtained dense mixture 2,2'-(2,2'-(Ethyne-1,2-diyl)bis(pyridine-2,5-
was decomposed with NH4Cl saturated aqueous solution and diyl))bis(4,4,5,5-tetramethylimidazolidine-1,3-diol)
extracted with diethyl ether (3 50 mL). The combined organic Following the protocol B1 starting from dipyridinedialdehyde
ºC, and for 12-72 h. Formed precipitate was filtered off, washed with
~5ºC) methanol and dried on air. The product was used
(1b).
×
extracts were dried over MgSO4, and the solvents were 1a (0.25g, 1.1 mmol) was converted into the corresponding
evaporated under the reduced pressure. The orange residue imidazolidine derivative 1b in 4 h. The product 1b was
was recrystallized from dimethylformamide/water (1:2), obtained as pale-yellow powder in 80% yield (0.42 g). 1H-NMR
yielding 0.78g (58%) of light-yellow dialdehyde 3a.
1H NMR ((CD3)2SO, 250 MHz, 298K, 128 scan), δ ppm: 1.08 (d, 24H,
3
(CDCl3, 250.13 MHz), δ ppm: 7.71-7.75 (d, 4H, J=8.0 Hz, H-2), CH3), 4.62 (s, H-7), 7.72 (d, 2H, 3J = 8 Hz, H-3), 7.92 (dd, 2H, 3J =
3
7.92-7.95 (d, 4H, J=8.0 Hz, H-3), 10.02 (s, 2H, -CHO). 13C-NMR 8 Hz, H-4), 8.69 (s, 2H, H-6). 13C-NMR ((CD3)2SO, 75 MHz, 298K,
(CDCl3, 63 MHz, 298K, 206 scan), δ ppm: 128.1 (C-1), 130.4 (C- 18904 scan), δ ppm: 17.6, 24.5 (CH3), 66.7 (C-CH3), 88.1 (C-7),
2), 136 (C-3), 145.6 (C-4), 191.7 (-CHO). MS-FD (70 eV, CH2Cl2) 127.2 (C-3), 136.8 (C-4), 137.9 (C-5), 140.9 (C-2), 150.7 (C-6).
m/z: 210.1 (M+), MW calculated C14H10O2 (MW+) 210.1.
MS-FD (70 eV, CH2Cl2) m/z: 496.4 (M+), MW calculated
Bipyridine-2,2'-dicarbaldehyde (4a). A solution of dimethyl C26H36N6O4 (MW+) 496.60.
bipyridine 15 (1 g, 5.38 mmol, 1 eq.), NBS (2.49 g, 14 mmol, 2.6
2,2'-(5,5'-(Ethyne-1,2-diyl)bis(pyridine-2,5-
eq.), and benzoyl peroxide (0.29 g, 1.2 mmol, 0.22 eq.) in CCl4 diyl))bis(4,4,5,5-tetramethylimidazolidine-1,3-diol)
(2b).
(50 mL) was refluxed under argon for 14 h. The precipitated Bisimidazolidine-diol 2b was synthesized in 67% yield from the
succinimide was removed from the hot mixture by filtration. dialdehyde 2a (0.1 g, 0.4 mmol) and BHA (0.14 g 0.96 mmol)
The precipitate was washed with CCl4 (2×10 mL), and the following the general protocol B2.
1H-NMR§ ((CD3)2SO, 250
combined CCl4 extracts were evaporated in vacuo. The MHz, 298K, 16 scan), δ ppm: 1.09 (s, 24H, CH3), 4.69 (s, H-7),
resulting yellowish solid containing 5,5’-bis(bromomethyl)- 7.68 (d, 2H, 3J = 8 Hz, H-3), 8.02 (dd, 2H, 3J = 8 Hz, H-4), 8.71 (d,
2,2’-bipyridine 16 (1 g, 2.95 mmol, 1 eq.) was refluxed with 2H, H-6). MS-FD (70 eV, CH2Cl2) m/z: 496.1 (M+), MW
hexamethylenetetramine (1.65 g, 11.8 mmol, 4 eq.) in 100 mL calculated C26H36N6O4 (MW+) 496.60.
of ethanol/water (1:1) for 60 h. The mixture was extracted
2,2'-(Biphenyl-4,4'-diyl)bis(4,4,5,5-
with ethyl acetate/toluene (1:1) (4×50 mL) to afford effective tetramethylimidazolidine-1,3-diol) (3b). Compound 3b was
phase separation. The organic extracts were collected and synthesized in accordance with the general procedure B1 from
dried over MgSO4. The filtrate was concentrated in vacuo to a biphenyl-4,4'-dicarbaldehyde 3a (0.305 g, 1.5 mmol) and BHA
volume of ca. 2 mL, placed on a column with silica, and eluted (0.64 g, 4.3 mmol) in quantitative yield (0.65 g, 95%). 1H NMR
with ethyl acetate/hexane gradient solvent mixture (1:4, 1:3). ((CD3)2SO, 250.13 MHz), δ ppm: 1.11 (s, 12H, CH3), 1.13 (s,
The colorless fractions were collected and evaporated leading 12H, CH3), 4.59 (s, 2H, N-CH-N), 7.42-7.76 (m, 8H, ArH), 7.83 (s,
to the product 4a in 57% overall yield. 1H NMR (CDCl3, 63 MHz, 4H, -OH). 13C NMR ((CD3)2SO, 63 MHz, 298K, 256 scan), δ ppm:
298K, 256 scan), δ ppm: 7.60-7.64 (d, 2H, 3J=8.02 Hz, H-4), 17.6, 24.8 (CH3), 66.5 (C-CH3), 90.4 (N-CH-N), 126.3, 129.5
7.94-7.98 (dd, 2H, 3J=8.02 Hz, H-6), 8.76 (d, 2H, 3J=1.6 Hz, H-3), (CHAr), 139.8, 141.4 (CAr). MS-FD (70 eV, CH2Cl2) m/z: 470.1
10.02 (s, 2H, -CHO). 13C-NMR (THF-d8, 63 MHz, 298K, 338 (M+), MW calculated C26H30N6O4 (MW+) 470.60.
scan), δ ppm: 121.3 (C-3), 127.6 (C-5), 129.4 (C-4), 131.9 (C-6),
136.4 (C-2), 189.7 (-CHO). MS-FD (70 eV, CH2Cl2) m/z: 211.6 tetramethylimidazolidine-1,3-diol) (4b). The bipyridine
(M+), MW calculated C14H10O2 (MW+) 212.1.
imidazolidine 4b was synthesized following methodology B1
B1. General synthesis of 4,4,5,5- Thus, 4b was obtained from the reaction between bipyridine-
tetramethylimidazolidine-1,3-diol precursors 2,2'-dicarbaldehyde 4a (0.15 g, 0.71 mmol) with BHA (0.28 g,
2,2'-(Bipyridine-1,1'-diyl)bis(4,4,5,5-
.
the
1-5b.
A
suspension of BHA (1.1 eq. for each aldehyde group) and an 1.85 mmol) in 88% yield (0.30 g). 1H NMR ((CD3)2SO, 250.13
aldehyde (1.0 eq.) in toluene (5 mL/1 mmol) was carefully MHz), δ ppm: 0.84-0.87 (d, 24H, CH3), 4.40 (s, 2H, N-CH-N),
deaerated by purging with argon for ~20-25 minutes. The flask 7.68 (s, 4H, -OH), 7.73-7.77 (d, 2H, ArH), 8.12-8.15 (d, 2H, ArH),
was provided with a condenser equipped with an argon 8.48 (s, 2H, ArH). 13C NMR ((CD3)2SO, 63 MHz, 298K, 256 scan),
balloon, and moved into an oil bath. The mixture was heated δ ppm: 17.3, 20.8 (CH3), 66.3 (C-CH3), 87.9 (N-CH-N), 125.8,
under argon near reflux for 2-18 h. The progress of the 127.9, 131.9 (CHAr), 137.4, 146.5 (CAr). MS-FD (70 eV, CH2Cl2)
reaction was monitored by TLC (SiO2, hexane/ethyl acetate or m/z: 471.8 (M+), MW calculated C26H30N6O4 (MW+) 472.28.
dichloromethane with 5% of methanol). After the process was
2-(4-{2-[4-(1,3-Dihydroxy4,4,5,5-tetramethyl-
completed and the flask was cooled down to room imidazolidine-2-yl)phenyl]ethynyl}phenyl)-4,4,5,5-
temperature, the precipitate (white or yellowish) was filtered tetramethyl-imidazolidine-1,3-diol (5b). Following the general
off, washed with toluene (2
×
10 mL), heptane (1
×
10 mL) and method B1 from 0.45 g (1.94 mmol) of the tolane dialdehyde
10 | J. Name., 2012, 00, 1-3
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5a11 0.94 g of pale-yellow bisimidazolidine 5b was synthesized temperature the oxidant was filtered off and washed carefully
(98% yield). 1H-NMR ((CD3)2SO, 250 MHz, 298K, 105 scan), δ with small portions of ethyl acetate on filter. The filtrate was
ppm: 1.05, 1.09 (both s 12 Н, -СН3), 4.54 (s, 2Н, Cimid-2), 7.53 (w. diluted with toluene (12 mL) and concentrated to a volume of
s, 8Н, Ar-H), 7.84 (w. s, 4Н, -N-OH). 13C-NMR ((CD3)2SO, 63 ca. 2 mL in vacuo. The residue was placed on a column wetted
MHz, 298K, 256 scan), δ ppm: 17.4, 24.5 (-СН3), 66.4 (Cimid-4, with toluene, and eluted with ethyl acetate/hexane mixture.
Cimid-5), 88.2 (-C≡С-), 90.1 (Cimid-2), 121.6 (Ar-C), 128.2, 131.0
(ArC-H), 143.5 (Ar-C). MS-FD (70 eV, (CD3)2SO) m/z: 494.293 diyl))bis(4,4,5,5-tetramethyl-4H,5H-imidazoline-1-oxyl) (1d).
(M+), MW calculated C28H38N4О4 (MW+) 494.291.
Compound 1d was synthesized as described in the protocol
2,2'-(2,2'-(Ethyne-1,2-diyl)bis(pyridine-2,5-
D
C. General procedure for the oxidation of 4,4,5,5- from the imidazolidine 1b (0.47g, 0.95 mmol) using MnO2 (1.23
tetramethylimidazolidine-1,3-diol derivatives to nitronyl g, 14.1 mmol) in 61% yield (250 mg). M.p.: compound
nitroxides. A suspension of 4,4,5,5-tetramethylimidazolidine- decomposed at 195°C. UV-Vis (toluene)
λ
ν
/nm (
ε
, mol-1×cm-1):
1,3-diol (1 mmol) in Н2О/CH2Cl2 (1:2) mixture ( 50 mL) was 467 (944), 326 (35207). FT-IR (powder,
~
/cm-1): 3067, 2969,
cooled down to 0-5оС using an ice bath. To that mixture NaIO4 2924 (s, Py-C-H stretching), 2136 (w, C≡C), 1591 (s, PyC=C
5% aqueous solution (0.8 eq.) was added dropwise. The stretching), 1555 (s, C=Nimid), 1368 (m, N-O). Elemental
progress of the reaction was monitored by TLC (SiO2, analysis: C 67.6; H 6.43; N 18.07; calculated for C26H30N6O2: C
hexane/ethyl acetate or dichloromethane with 5% of 68.10; H 6.59; N 18.30.
methanol). After the reaction was complete (0.5-3 h), dark-
blue organic layer was separated. The aqueous layer was tetramethylimidazolidine-1-oxyl) (3d). Oxidation of the
extracted with dichloromethane (3 25 mL). The combined precursor 3b (0.3 g, 0.64 mmol) with excess of MnO2 (0.83 g,
organic extracts were additionally washed with water (2 30 9.5 mmol) according to the methodology was completed in
mL), brine (1 50 mL), and dried over MgSO4 (in some cases - 20 minutes. The radical 3d was purified on a chromatographic
2,2'-(Biphenyl-4,4'-diyl)bis(4,4,5,5-
×
×
D
×
Na2SO4). The residue after filtration was reduced to a 2 mL column with hexane/ethyl acetate gradient solvent mixture
volume, and purified on a chromatographic column (SiO2, (5:1, 3:1). Yield of the orange crystalline 3d was 0.14 g (47%).
hexane/ethyl acetate or CH2Cl2/MeOH).
M.p.: 248.5-250°C. UV-Vis (CHCl3)
(1090), 486 (1016). FT-IR (powder,
λ
ν
/nm (
ε
, mol-1×cm-1): 461
2,2'-(2,2'-(Ethyne-1,2-diyl)bis(pyridine-2,5-
/cm-1): 3069, 2973, 2926,
diyl))bis(4,4,5,5-tetramethyl-4H,5H-imidazoline-1-oxyl-3-oxo) 2862 (s, Ph-C-H stretching), 1611 (s, Ph C=C stretching), 1567
(1c). Procedure and subsequent purification through a short (w, C=N), 1364 (s, N-O). Elemental analysis: C 71.86; H 7.32; N
flesh-column (SiO2, hexane/ethyl acetate, 1:3) afforded 54 mg 12.66; calculated for C26H32N4O2: C 72.19; H 7.46; N 12.95.
of the bluish crystals of 1c (13%). M.p.: 219-220 C. UV-Vis 2,2'-(Bipyridine-1,1'-diyl)bis(4,4,5,5-
(CHCl3) /nm (
, mol-1×cm-1): 612 (808), 344 (55554); (toluene) tetramethylimidazolidine-1-oxyl) (4d). The titled biradical 4d
/nm (
, mol-1× cm-1) 623 (483), 345 (50402). FT-IR (solid; was achieved using a similar to the one described above
ν/cm-1): 3108, 3072, 2986, 2939 (s, Py-C-H stretching), 2144 (w, procedure in 44% yield. M.p.: compound began to decompose
C≡C), 1734 (m, C=O), 1583 (s, PyC=C stretching), 1549 (s, at 253 C. UV-Vis (CHCl3) /nm (
, mol-1×cm-1): 448 (625), 476
C=Nimid), 1347 (s, N-O). Elemental analysis: C 62.7; H 5.96; N (548). FT-IR (powder,
/cm-1): 3087, 3043, 2981 (s, Py-C-H
C
°
λ
ε
λ
ε
°
λ
ε
ν
17.02; calculated for C26H30N6O4: C 63.66; H 6.16; N 17.13.
stretching), 1603 (s, PyC=C stretching), 1562 (s, C=Nimid), 1366 (s,
2,2'-(5,5'-(Ethyne-1,2-diyl)bis(pyridine-2,5-
N-O). Elemental analysis: C 65.36; H 7.02; N 19.11; calculated
diyl))bis(4,4,5,5-tetramethyl-4H,5H-imidazoline-1-oxyl-3-oxo) for C24H30N6O2: C 66.34; H 6.96; N 19.34.
(2c). To a magnetically stirred solution of imidazolidine 2b
2-(4-{2-[4-(1-Oxyl-4,4,5,5-tetramethyl-4H,5H-imidazolin-2-
(0.133g, 0.27 mmol) in absolute methanol (3 mL) excess of yl)phenyl]-ethynyl}phenyl)-4,4,5,5-tetramethyl-imidazoline-
MnO2 (0.35g, 4 mmol, 15 eqivalents with respect to 2b) was 1-oxyl-3-oxo (5d). Compound 5d was synthesized from the
added. The process was monitored by TLC to avoid precursor 5b (0.27g, 0.55 mmol) employing excess of MnO2
overoxidation, and formation of imino nitroxide radical. After (0.7 g, 8.05 mmol) as described in more details in the general
reaction was completed MnO2 was filtered off and methanol procedure
C
.
Isolation of the product 5d using
a
was evaporated. The radical was purified using thin-plate chromatographic column with silica gel and hexane/ethyl
chromatography (SiO2, chloroform/ethyl acetate, 2:1). After acetate (3:2) eluent mixture afforded the red crystalline 5d in
evaporation of the solvent blue crystals were obtained in 34% 58% total yield. M.p.: compound began decomposing above
total yield. M.p.: 236-239
°
C. UV-Vis (CHCl3)
λ
/nm (
ε
, mol-1×cm- 195
°
C. UV-Vis (toluene)
λ
ν
/nm (
ε
, mol-1×cm-1): 467 (944), 326
1): 591 (503), 341 (38929). FT-IR (powder,
ν
/cm-1): 3048, 2985, (35207). FT-IR (powder,
/cm-1): 3067, 2969, 2924 (s, Py-C-H
2933, 2868 (s, Py-C-H stretching), 2141 (w, C≡C), 1733 (m, C=O), stretching), 2136 (w, C≡C), 1591 (s, PyC=C stretching), 1555 (s,
1588 (m, PyC=C stretching), 1560 (s, C=Nimid), 1360 (s, N-O). C=Nimid), 1368 (m, N-O). Elemental analysis: C 73.15; H 6.76; N
Elemental analysis: C 63.1; H 6.22; N 16.62; calculated for 12.11; calculated for C28H32N4O2: C 73.66; H 7.06; N 12.27.
C26H30N6O4: C 63.66; H 6.16; N 17.13.
D. General procedure for the oxidation of 4,4,5,5-
Conclusion
tetramethylimidazolidine-1,3-diol derivatives to imino
nitroxides. To
imidazolidine (1 mmol) in nitromethane (12 mL) MnO2 (14
mmol) was added. After 35 minutes stirring at room
a magnetically stirred solution of the
We have demonstrated that the synthesis and study of structurally
similar compounds exhibiting different magnetic behaviors provides
a reasonable approach for understanding the relationship between
~
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ARTICLE
Journal Name
4
U. Tutsch, B. Wolf, S. Wessel, L. Postulka, Y. Tsui, H. O.
Jeschke, I. Opahle, T. Saha-Dasgupta, R. Valenti, A. Brühl, K.
Removic-Langer, T. Kretz, H.-W. Lerner, M. Wagner and M.
the substituents in the aromatic ring and the intramolecular
exchange constant Jintra. Unfortunately, the magnetic interactions
based on structural peculiarities are difficult to predict as their
strength strongly depends on the relative orientation between the
interacting magnetic orbitals. Here, the torsion angles θ have crucial
impacts on the overall π-conjugation in the nitroxide biradicals
systems. The latter in turn is responsible for the efficient
communication between the nitroxide fragments. The crystal
structure analysis shows that the synthesized biradicals are planar
with relatively small torsions between the radical fragments and the
aromatic bridges (with an exception in the case of derivative 2c).
Lang, Nat. Commun., 2014,
J. Veciana, J. Cirujeda, C. Rovira, E. Molins and J. J. Novoa, J.
Phys. I France, 1996, , 1967.
5, 5169.
5
6
7
6
H. Sasaki, L.-R. Lin, T. Yokoyama, M. D. Sevilla, V. N. Reddy
and F. J. Giblin, IOVS, 1998, 39, 544.
W. Bi, J. Cai, Y. Zhang, S. Liu, S. A. Green and L. Bi, Bioorg.
Med. Chem. Lett., 2008, 18, 1788.
M. C. Krishna and W. DeGraff, J. Med. Chem., 1998, 41, 3477.
8
9
J. H. Osiecki and E. F. Ullman, J. Am. Chem. Soc., 1968, 90
1078.
,
These are the essential prerequisites for obtaining
a weak
10 A. Caneschi, D. Gatteschi, P. Rey and R. Sessoli, Inorg. Chem.,
1988, 27, 1756; A. Caneschi, D. Gatteschi, R. Sessoli and P.
Rey, Acc. Chem. Res., 1989, 22, 392.
11 Y. B. Borozdina, E. A. Mostovich, V. Enkelmann, B. Wolf, P. T.
Cong, U. Tutsch, M. Lang and M. Baumgarten, J. Mat. Chem.
C, 2014, 2, 6618.
12 K. Yamaguchi, M. Okumura, J. Maki, T. Noro, H. Namimoto,
M. Nakano, T. Fueno and K. Nakasuji, Chem. Phys. Lett.,
1992, 190, 353.
intramolecular coupling. A rapid increase of the torsion hinders the
conjugation within the biradical system 2c, decreasing the
intramolecular exchange interactions within the molecule. This
structural feature causes enhancement of the intermolecular
coupling within 2c. As a result, an unprecedentedly high value of
the coupling constant is observed in the NN biradical 2c. This work
illustrates the difficulties in the design and prediction of a target
structure, and the need for an experimental proof.
13 G. Seber, R. S. Fretas, J. T. Mague, A. Paduan-Filho, X.
Gratens, V. Bindilatti, N. F. Oliveira Jr., N. Yoshioka and P. M.
Lahti, J. Am. Chem. Soc., 2012, 134, 3825.
14 G. Zoppellaro, A. Geies and M. Baumgarten, Eur. J. Org.
Chem. 2004, 11, 2367.
15 E. Mostovich, Y. Borozdina, V. Enkelmann, K. Remović-
Langer, B. Wolf, M. Lang, and M. Baumgarten, Crystal
Growth Des., 2012, 12, 54.
Magnetic measurements, carried out on single-crystalline
samples, confirmed that for the biradicals 1c, 1d, 3d, 4d and 5d,
weak
antiferromagnetic
intramolecular
interactions
are
predominant. According to the magnetic characterization studied π-
bridged nitroxides possess a moderate intra-dimer coupling in the
range -2 to -6 K as derived from the fits based on an isolated dimer
model. Furthermore, magnetic measurements and their
interpretation revealed that NN biradical 2c exhibits surprisingly 16 S. Takahashi, Y. Kuroyama, K. Sonogashira and N. Hagihara,
Communications, 1980, 627.
17 C. Bolm, M. Ewald, M. Felder and G. Schlinglo, Chem. Ber.,
1992, 125, 1169.
18 F. C. Alderweireldt, I. Vrijens, E. L. Esmans and E. D. Clercq,
Nucleosides Nucleotides, 1989, 8, 891.
strong antiferromagnetic interactions, owing to the short (∼3.5 Å)
interdimer interaction. The IN biradical 5d features a field-induced
ordered phase assigned to 3D inter-dimer couplings, which accounts
for a description in terms of a BEC of triplons.
In summary, we have found promising candidates for the
quest to synthesize purely organic molecular magnets and
crystalline networks with higher ordering.
19 J. Wicha and M. Masnyl, Heterocycles, 1981, 16, 521.
20 F. J. Romero-Salguero and J.-M. Lehn, Tetrahedron Lett.,
1999, 40, 859.
21 X. Wang, P. Rabbat and P. O'Shea, Tetrahedron Lett., 2000,
41, 4335.
22 A. Landa, A. Minkkila and G. Blay, Chem. Eur. J., 2006, 12
3472.
,
Acknowledgements
23 M. A. Peterson and J. Mitchell, J. Org. Chem., 1997, 62, 8237.
24 T. W. Greene and P. G. Wuts, Protective groups in organic
synthesis, 1991.
25 F. Ebmeyer and F. Vögtle, Chem. Ber., 1989, 122, 1725.
26 I. Karamé, M. Jahjah and M. Lemaire, Tetrahedron Asymm.,
2004, 15, 1569.
We wish to thank Dr. Dieter Schollmeyer (Johannes
Gutenberg-University Mainz) and Dr. Volker Enkelmann for
crystallographic data analysis. The authors are pleased to
acknowledge continued support from the Max Planck Society
and the DFG- SFB TR49.
27 R. Ziessel and G. Ulrich, J. Mater. Chem., 1999, 9, 1435.
28 E. V. Tretyakov, S. Tolstikov, A. Mareev, Eur. J.Org. Chem.,
2009, 78, 2548.
29 E. V. Tretyakov, V. I. Ovcharenko, Russian Chemical Reviews,
2009, 78, 971.
Notes and references
‡
Crystallographic data for the reported structures of biradicals 1c, 2c, 1d, 3d, 4d
30 E. Önal, Y. Yerli, B. Cosut, G. Pilet, V. Ahsen, D. Luneau and C.
Hirel, New J. Chem., 2014, 38, 4440.
and 5d have been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC-823716, 816632, 816630, 823717, 858078,
810139, respectively. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via ww.ccdc.cam.ac.uk/data_request/cif.
31 DFT calculations were carried out with gaussian 09, B3LYP
hybrid functionals for geometry optimization and BLYP
functional for energy calculation of broken symmetry vs.
triplet states together with 6-31g(d) basis sets. See M. J.
Frisch,et al. Gaussian 09, Revision D.01,Gaussian, Inc.,
Wallingford CT, 2013.
32 Md. E. Ali and S. N. Datta, J. Phys. Chem. A, 2006, 110, 2776.
33 O. Kahn, Molecular Magnetism, VCH, Weinheim-New York,
1993.
§
unstable in DMSO and began to oxidize in the NMR tube upon the measurement.
The 13C-NMR spectrum of 2b was not obtained, as the sample appeared to be
1
2
S. Sachdev, Nat. Phys., 2008,
T. Giamarchi, Ch. Rüeggv and O. Tchernyshyov, Nat. Phys.,
2008, , 198-204.
4, 173.
4
3
Ch. Rüegg, K. Kiefer, B. Thielemann, D. F. McMorrow, V. Zapf,
B. Normand, M. B. Zvonarev, P. Bouillot, C. Kollath, T.
Giamarchi, S. Capponi, C. Poilblanc, D. Biner and K. W.
Krämer, Phys. Rev. Lett., 2008, 101, 247202.
34 B. Bleaney and D. K. Bowers, Proc. R. Soc. London, Ser. A.,
1952, 214, 451.
12 | J. Name., 2012, 00, 1-3
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35 T. Mitsumori, K. Inoue, N. Koga and H. Iwamura, J. Am.
Chem. Soc., 1995, 117, 2467.
36 R. Akabane, M. Tanaka, K. Matsuo, N. Koga, K. Matsuda and
H. Iwamura, J. Org. Chem., 1997, 62, 8854.
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