Mixed Phenyl and Thiophene Oligomers for Bridging Nitronyl Nitroxides

Article abstract of DOI:10.1021/acs.joc.7b00435

The synthesis of four nitronyl nitroxide (NN) biradicals is described which are conjugatively linked through p-ter-phenyl (PPP), ter-thiophene (TTT) and alternating phenylene (P) and thiophene (T) units as PTP and TPT. We first utilized Suzuki and Stille

Full text of DOI:10.1021/acs.joc.7b00435

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Article
Mixed Phenyl and Thiophene Oligomers for Bridging Nitronyl Nitroxides
Kubandiran Kolanji, Prince Ravat, Artem S. Bogomyakov, Victor
I. Ovcharenko, Dieter Schollmeyer, and Martin Baumgarten
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b00435 • Publication Date (Web): 30 Jun 2017
Downloaded from http://pubs.acs.org on July 1, 2017
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Mixed Phenyl and Thiophene Oligomers for Bridging
Nitronyl Nitroxides
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Kubandiran Kolanji,† Prince Ravat ,†,# Artem S. Bogomyakov,§ Victor I. Ovcharenko,§ Dieter
Schollmeyer,‡ and Martin Baumgarten†*
†Max Planck Institute for Polymer Research Ackermannweg 10, 55128 Mainz (Germany)
#Present Addresses Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel
(Switzerland).
§International Tomography Center, Siberian Branch, Russian Academy of Sciences, Institutskaya Str.
3a, 630090 Novosibirsk, Russian Federation.
‡Institut fuer Organische Chemie, Universitaet Mainz, Duesbergweg 10-14, 55099, Mainz (Germany).
KEYWORDS. Organic radical, Spin-spin interaction, Broken symmetry DFT calculation,
Intramolecular exchange interactions, Magnetic susceptibility.
SYNOPSIS (TOC).
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ABSTRACT. The synthesis of four nitronyl nitroxide (NN) biradicals is described which are
conjugatively linked through p-ter-phenyl (PPP), ter-thiophene (TTT) and alternating phenylene (P) and
thiophene (T) units as PTP and TPT. We first utilized Suzuki and Stille coupling reactions through
protection and deprotection protocols to synthesize these (NN) biradicals. Single crystals were
efficiently grown for radical precursors of 3, 5, 6, PPP-NNSi, PTP-NNSi and final biradicals of TTT-
NN, TPT-NN, and PPP-NN, of which structures and their molecular packing were examined by X-ray
diffraction studies. Thereby much smaller torsions between the NN and thiophene units (~10°) in TTT-
NN and TPT-NN than for NN and phenyl units (~29°) in PPP-NN were observed due to smaller
hindrance for a five vs. a six membered ring. All four biradicals TTT-NN, TPT-NN, PTP-NN and
PPP-NN were investigated by EPR and optical spectroscopy combined with DFT calculations. The
magnetic susceptibility was studied by SQUID measurements for TTT-NN and TPT-NN. The
intramolecular exchange interactions for TPT-NN and TTT-NN were found in well agreements with
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the
ones
calculated
by
broken
symmetry
DFT calculations.
INTRODUCTION
Organic molecules are currently of high impact in the field of materials science owing to fabrication
of low cost, simple and flexible device1-2. Stable radical moieties connected with aromatic oligomers
have concerned great attention3-5 due to their potential applications in spintronics6-8, quantum molecular
magnets9-10, spin-labeling11, spin-trapping12, magneto conducting materials13-15, magnetic resonance
imaging16, biomedicine17, organic photo excited spin systems18-19, field effect transistors20-22, solar
cell23-26, sensors27, and batteries28-29. All these properties are dependent on the type of radical entities
and their connection to a conjugated core.
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The spin-spin interaction between the stable free radicals such as nitronylnitroxides (NN), tert-
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butylnitroxides, iminonitroxides (IN), and verdazyl (VZ) can be fine tuned through their combination
with conjugated oligomers30-41. Previously reported NN biradicals where built upon biphenyl42,
terpyridine43, pyrene44, and tolane45 as a π-bridge and their optical, electrochemical, EPR, and magnetic
properties were studied.
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Weakly antiferromagnetically (AFM) coupled spin-dimers with singlet ground state which can be
tuned by a magnetic field in to the triplet state are of peculiar interest46. The self-assembly of the spin-
dimer molecules is used for the development of solid state Bose-Einstein Condensation (BEC)
materials47-49, where two guiding principles should hold: 1) The intra molecular exchange coupling
should dominate and exceed the intermolecular coupling and 2) The intramolecular coupling should be
small enough for laboratory-scaled magnets to switch the spin state (ground state singlet into the triplet
state).
Recently we found that tolane bridged NN biradicals undergo quasi two dimensional magnetic field
induced quantum phase transition at very low temperatures in the routine laboratory magnetic field up to
11 T41. While thiophene extension with NN biradical entities were explored50-51, mixed thiophene and
phenylene oligomers with NN radicals are not reported to the best of our knowledge to tune the
magnetic and electronic properties of biradical systems. From previous observations the intra molecular
magnetic interactions depend on the conjugation between the aromatic cores, the distance between the
radicals and the torsional angles among NN and the aromatic bridge.
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Figure 1. Optimized structure of PPP, PTP, TPT and TTT by using the B3LYP functional and 6-31G(d)
basis set and HOMO, LUMO and energy gap (Eg) of the bridging oligomers.
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Therefore, it is a necessary to better-understand the effect of the aromatic bridge on the spin-spin
interaction between the radical units. Hence we designed four molecular bridges, p-ter-phenyl, (PPP),
ter-thiophene, (TTT) and two mixed thiophene and phenylene oligomers (TPT and PTP) (Figure 1) and
investigated the molecular length and torsion angles (Figure S1), as well as their HOMO, LUMO,
electron density distribution and the energy gap (Eg) by density functional theory (DFT). The Eg of TTT
is 3.64 eV which is much lower than for PPP (4.75 eV), TPT (4.10 eV) and PTP (4.04 eV). Based on
these π-units (PPP, TTT, TPT and PTP), four (NN) biradicals (TPT-NN, PPP-NN, TTT-NN, and PTP-
NN) were designed (Figure 2). The NN radical units are attached to para-substitution of the phenyl unit
for PPP-NN, and PTP-NN. And the NN are attached to the 5th-position of the thiophene ring for TTT-
NN, and for TPT-NN. In the molecular design, we predicted by spin polarization rule that the spins on
the NN groups are AFM coupled to each other (Figure S2).
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O
O
O
N
O
N
N
N
S
S
S
S
N
O
S
N
O
N
N
O
O
TPT-NN; 13.51 Å
TTT-NN; 13.10 Å
O
N
O
N
O
N
O
N
S
N
O
N
O
N
O
N
O
PTP-NN; 13.84 Å
PPP-NN; 14.44 Å
Figure 2. Structures of TTT-NN, TPT-NN, PTP-NN and PPP-NN; distance between C2-C2 of NN.
Hence, as a model system for Bose-Einstein condensation (BEC) in the solid state, our aim is to
synthesize weakly AFM coupled biradicals, where the intramolecular exchange interaction can be
controlled or adjusted in the range of J/kB = 2–10 K. These biradicals were characterized by EPR, UV-
Vis spectrometry, single crystal X-ray structural analysis and their magnetic properties were
investigated by SQUID magnetometry and supported with the quantum chemical DFT calculations.
RESULTS AND DISCUSSION
Synthesis of biradicals
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The tert-butyldimethylsilyl (TBDMS) protected bromothiophene mono radical moiety 3 was
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introduced by Suzuki coupling reaction with 1,4-benzenediboronic acid bis(pinacol) ester and
deprotection to obtain TPT-NN (Scheme 1). This was necessary since the first attempt to synthesize the
target compound TPT-NN by condensation of di-aldehydes with 2,3-bis(hydroxyamino)-2,3-
dimethylbutane (BHA) failed Scheme S1 although often announced in the literature as suitable step.
And the PPP-NN was synthesised from di-aldehydes with low (5.2%) yield.52 This was mainly because
of the poor solubility of the corresponding di-aldehyde precursor in common organic solvents. Later a
similar synthetic protocol was applied to synthesize the other three biradicals. Reaction of the 5-bromo-
2-thiophenecarboxaldehyde or 4-bromobenzaldehyde with BHA at room temperature in methanol
yielded compounds 2 and 4 with good yields (>80 %). Then the N-OH groups were protected with
TBDMS by tert-butyldimethylsilyl chloride (t-BuMe2SiCl) in the presence of imidazole in DMF as
solvent to afford 3 and 5 with excellent yields (>90 %). The highly stable biradical precursors TPT-
NNSi and PPP-NNSi were obtained by Suzuki coupling reactions between 3 or 5 with 1,4-
benzenediboronic acid bis(pinacol) ester in moderate to good (>60 %) yield.
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HO
N
TBDMSO
TBDMSO
OSTBDM
N
(a)
(a)
(b)
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N
N
S
S
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3
S
N
HO
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N
Br
Br
OSTBDM TBDMSO
TBDMSO
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3
TPT-NNSi
HO
TBDMSO
OSTBDM
N
TBDMSO
(b)
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N
N
N
Br
Br
N
HO
N
N
N
TBDMSO
OSTBDM
TBDMSO
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Br
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TBDMSO
TBDMSO
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TBDMSO
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OSTBDM
N
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O
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O
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B
Sn
B
S
S
S
S
Sn
O
O
N
N
3
3
OSTBDM
TBDMSO
7
8
TTT-NNSi
Reaction conditions: (a) t-BuMe2SiCl, imidazole, DMF, 50 °C, (b) 1,4-benzenediboronic acid bis(pinacol) ester,
K2CO3, Pd(PPh3)4, THF: H2O, 60 °C (c) THF, -78 °C, n-BuLi, 2-isopropylboronic acid, pinacol ester,
(d) Pd(PPh3)4, toluene:DMF, 60 °C.
OSTBDM
N
OSTBDM
N
O
N
O
N
TBAF
N
N
N
N
O
THF, rt
OSTBDM
O
OSTBDM
TPT-NNSi, PPP-NNSi, PTP-NNSi and TTT-NNSi
TPT-NN, PPP-NN, PTP-NN and TTT-NN
Scheme 1 Synthetic route of biradicals.
The preparation of PTP-NNSi from 5 either by Suzuki coupling between 5 and thiophene-2,5-
diboronic- bis(pinacol) ester,(7) or Stille coupling between 5 with 2,5-bis(trimethylstannyl)thiophene,(8)
was unsuccessful. Therefore boronic-bis(pinacol)ester,(6) was prepared from 5 by its treatment with n-
BuLi, followed by 2-isopropylboronic acid, pinacol ester. The Suzuki coupling of 2,5-dibromothiophene
and 6 successfully yielded PTP-NNSi in 66 % yield. An attempt to synthesize TTT-NNSi by Suzuki
coupling with 3 and thiophene-2,5-diboronic-bis(pinacol)ester provided only 18 % along with 51 %
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mono substituted side product obtained. The yield of TTT-NNSi could be highly improved by Stille
coupling reaction between 3 and 2,5-bis(trimethylstannyl)thiophene, (74%). All the precursors were
characterized by NMR and mass spectra, and the precursors 3, 5, 6, PPP-NNSi and PTP-NNSi were
also verified by single crystal X-ray structure analysis (Figures S3-S7).
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All biradicals TTT-NN, TPT-NN, PTP-NN, and PPP-NN were obtained by subsequent cleavages of
the (TBDMS) protecting groups in one step with tetrabutylammonium fluoride (TBAF) in THF
(Scheme 1 bottom). The reaction was carefully monitored by TLC to get best yield of NN biradicals,
which were purified by column chromatography. These biradicals were characterized by EPR and UV-
vis spectroscopy and ESI mass spectrometry. The structures of TTT-NN, TPT-NN, and PPP-NN were
further verified by single crystal X-ray analysis (Figures S8-S10).
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Optical properties
The UV-vis absorption spectra of the biradicals (TTT-NN, TPT-NN, PTP-NN, and PPP-NN) were
measured in toluene (c∼10-5 M) at room temperature and are depicted in Figure 3. The absorption data
of biradicals (λmax, ε and optical gap Eg) are given in Table 1. The absorption spectra of the biradicals
are compared with their precursors (Figure S12) together with their data summarized in Table S2. Only
one absorption band was observed for all precursors (TPT-NNSi, PPP-NNSi, PTP-NNSi and TTT-
NNSi) due to the π–π* transition of the π-bridge. All the four biradicals exhibited two absorption bands,
around 280-500 nm due to the π–π* transition of the conjugated backbone, and the characteristic n–π*
transition of the NN radical moieties around 510-840 nm. The UV–vis spectra clearly indicate the
presence of pure NN biradicals, without contamination by imino-nitroxide.
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Figure 3. UV−vis absorption spectra of PPP-NN PTP-NN, TPT-NN, and TTT-NN (~10−5 M in
toluene).
The effect of the π-bridge on the absorption spectra for NN biradicals were investigated previously53.
The π–π* transitions of the radicals are red shifted compared to their protected precursors by 40-50 nm
demonstrating the conjugation enhancement upon radical formation (Figure S12). Differences between
the n–π* transitions can be traced back to better conjugation between a thiophene unit with NN than a
phenylene with NN unit (larger torsion).
Table 1. Optical, and EPR, properties of TTT-NN, TPT-NN, PPP-NN, and PTP-NN
OP
aEg
λmax(nm),
baN/2/mT
bg
Radicals
(ε cm–1M–1)
TTT-NN 427 (47315),
709 (956)
1.46
1.45
0.375
2.0067
2.0065
TPT-NN 390 (64795),
695 (1267)
0.370
PTP-NN
384 (37885),
669 (468)
1.63
1.64
0.381
0.371
2.0065
2.0066
PPP-NN
331 (50757),
651 (680)
a,Optical energy gap calculated according to the absorption edge; bcalculated from EPR spectra.
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The optical gaps Eg derived from the onset of the absorption edge of the n–π* transition for TPT-NN
and TTT-NN are 1.45 and 1.46 eV which are smaller than for PPP-NN (1.64 eV) and PTP-NN (1.63
eV), respectively. The optical properties are thus tuned by enhancing the number and position of
thiophenes in the molecular bridge.
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EPR studies
EPR spectra of the all four biradicals were recorded in argon saturated toluene solutions. The room
temperature, simulated and variable temperature, EPR spectra of TPT-NN are displayed in Figure 4.
The EPR spectra for TTT-NN, PPP-NN and PTP-NN are provided in the supporting information
(Figure S13). At room temperature, all the four biradicals exhibited nine line spectra due to effective
through-bond coupling via spin-polarization effects of the nitronyl nitroxides, indicating that exchange
interactions J are much larger than the hyperfine coupling constants (J >> aN). The calculated g factors
and hyperfine coupling constants (aN/2) for all biradicals are summarized in Table 1. These values are in
agreement with those typically observed in the NN biradicals found in the literature.
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Figure 4. EPR spectra of the biradical TPT-NN in toluene (∼10−4 M in toluene), (a) room temperature,
experimental (black), and simulated (red) (b) variable temperature (290-210 K), (c) ꢀMS = 1 transition
of TPT-NN (black) at 130 K, (d) half field ꢀMS = 2 transition at 130 K.
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Upon decreasing temperature the EPR signal intensity of TPT-NN is reduced but the spectral widths
are slightly broadened. The other biradicals followed the same characteristics (Figure S14). The frozen
solution spectra of TPT-NN recorded at 130 K (Figure 4c) are asymmetric and an anisotropic
component of the monoradical overlaps with the ꢀMS = 1 region giving the different number of the
shoulders in the outermost region. We verified the anisotropic nature by comparison with thiophene
mono radical (T-NN) frozen solution spectra at 130 K demonstrated in Figure S15 (a). The frozen
solution spectra of TTT-NN recorded at 130 K and displayed in Figure S15 (b). The half field ꢀMS = 2
transition although weak due to small zero field splitting, however, is clear evidence for the biradical
nature of TPT-NN.
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Crystal structure analysis
The magnetic interactions highly depend on the geometry and packing of the molecules in the crystal
lattice. Therefore crystal structure analysis is a vital requirement to understand magnetic interactions
operating in synthesized biradical systems. While the crystals suitable for single crystal X-ray analysis
were obtained by slow evaporation of DCM solution of biradicals for the TPT-NN and TTT-NN, the
same for the PPP-NN were grown by slow diffusion of hexane to its solution in DCM.
The green needle of TPT-NN crystallized in monoclinic, P21/c space group, which has an inversion
center of C2 symmetry and thus is symmetric to the central phenyl ring (Figure 5a). There is an
intramolecular contact between thiophene sulfur (S) and the radical oxygen atom 2.85 Å (S9…O15) and
the torsions between the radical moiety and thiophene unit are very small, only 9.5° (S9-C7-C10-N11)
and 11.1° (C6-C7-C10-N14). The torsions between the central phenyl ring and the thiophene units,
however, are larger with 25.7° for (C1-C2-C4-C5) and 24.2° for (C3-C2-C4-S9).
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Figure 5. X-ray crystal structure of TPT-NN (a) molecule, (b) edge-to-edge packing mode, (c) face-to-
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face mode of crystal packing, hydrogen atoms are omitted for clarity.
The molecular packing of the TPT-NN is displayed in Figure 5b and the molecules are arranged in two
different directions. The TPT-NN molecules are networking over radical (N-O) unit through adjacent
molecules of thiophene carbon as 3.2 Å for (O15-C5) and at the same time the nearest molecule of N-O
units also interact with first molecule of thiophene 3.2 Å (C5-O15). The other side radical (N-O) units
interact with methyl group of nearest molecules 3.3 Å (N-O20…C17) and methyl groups also interact
with next to the nearest molecule of N-O units. The π-π distance between two TPT-NN as edge-to-edge
(between thiophene and thiophene) approach of the molecules is 3.5 Å. The slipped π-stacked structures
are shown in Figure 5c. The further examination of the crystal packing of the molecules is that the
molecules are stacked along the crystallographic a axis as a face-to-face manner and the π-π distance is
3.63 Å for (C3…C10) shown in Figure S11.
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Table 2 Crystal data and structure refinement details of TPT-NN, TTT-NN, and PPP-NN.
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TPTNN
TTTNN
C26H30N4O4S3
558.74
PPP-NN
C32H36N4O4
540.65
Formula
C28H32N4O4S2
Formula weight[g/mol] 552.20
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Crystal system
monoclinic
monoclinic
P 21/n
Monoclinic
P 21/n
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Space group
a /Å
P 21/c
10.9341(19)
11.8693(18)
11.054(2)
104.497(7)
2
12.5445(12)
11.1792(7)
20.4146(21)
107.466(8)
4
11.5064(9)
9.9143(10)
12.9226(12)
112.061(7)
2
b/Å
c/Å
β°
Z
wR2
R1
0.1100
0.0776
1.322
0.2159
0.2959
0.0709
0.0963
Density
ꢀ/mm-1
1.359
1.314
0.23
0.31
0.70
no. independent
reflections
3331
6703
2446
no. of refined
parameter
176
342
186
Goodness of fit
CCDC
1.140
1.013
0.961
1501331
1501330
1501332
The green plate of TTT-NN crystallized in monoclinic, P21/n space group and the X-ray single crystal
structure is displayed in Figure 6a. The crystal data and refinement details are listed in the Table 2.
From the single crystal X-ray structure analysis, intramolecular contacts between radical N-O and sulfur
atom of the thiophene are 2.9 Å for (O11-S13) and 2.8 Å for (S23-O32), respectively. Slightly different
bond lengths are observed as well among thiophene and radical (NN) units which are 1.434 Å for (C1-
C12) and 1.426 Å for (C24-C27) due to different mode of molecular packing.
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Figure 6. X-ray crystal structure of TTT-NN (a) molecule, (b) crystal packing 2D mode (c) crystal
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packing 3D mode, hydrogen atoms are omitted for clarity.
The deep investigation of crystal packing of the TTT-NN shows that both terminal thiophene and
radical moiety (NN) are linked with different torsions which are 9.7° (N2-C1-C12-C16), 12.0° (N5-C1-
C12-S13) and 3.3° (S23-C24-C27-N28) and 3.2° (C25-C24-C27-N31). Also all the three thiophenes are
connected with different torsions 10.6° (S13-C14-C17-C21), 11.1° (C15-C14-C17-S18), 7.3° (C20-
C19-C22-S23), 9.1° (S18-C19-C22-C26). The molecular packing of the TTT-NN is given in the Figure
6a. Further analysis of molecular packing revealed that the molecules interact through N-O unit with
neighboring molecules of thiophene as 3.19 Å (O11-C26) at the same time second molecule N-O
interact with first molecule 3.12 Å (C21-O37). The molecules are further stacked along the
crystallographic b axis (Figure S11). The π-π distance between molecules is 3.58 Å for (N2-O6…C25).
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Figure 7. X-ray crystal structure of PPP-NN (a) molecule, (b) crystal packing.
The single crystal structure of PPP-NN is provided in Figure 7a and crystallographic parameters are
listed in Table 2. The dark blue plate of PPP-NN crystallized in monoclinic, P21/n space group and Ci
symmetry. The radical NN units are connected with phenyl ring with torsion of 29.7° for (C6-C7-C10-
N11) and 29.4° for C8-C7-C10-N14. The phenyl rings are linked with the torsion of 27.1° for (C1-C2-
C4-C5) and 30.3° for (C3-C2-C4-C9). The molecular packing of the PPP-NN is shown in Figure 7b.
The molecules are extended through hydrogen bonding with adjacent molecules. There is no direct
intermolecular π electron contact between molecules but the intermolecular distance between molecules
(edge to edge) is 3.42 Å for (N-O15…C1) and (face to face) molecular distance is 4.66 Å for (C10-
C10).
DFT Calculations
The DFT calculations (Gaussian 09 program package)54 were carried out to find the influence of the
π-bridge on the electronic properties and especially the intra-molecular exchange interactions of the
biradicals. The geometries were optimized by UB3LYP/6-31G(d) level. The optimized structures of
PPP-NN, PTP-NN, TTT-NN and TPT-NN are shown in Figure S16.
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The simplest Hamiltonian for the molecule with two exchange coupled unpaired electrons is given by
H = –2J12S1S2. The calculations were carried out by the broken-symmetry (BS) approach where the
exchange interaction J becomes, J/kB = (E(BS) – E(T)) / (S2(T) – S2(BS)), with E(BS) energy of broken
symmetry and E(T) the triplet energy. S2 are the eigenvalues of the spin operator and for S2(BS) close to
1 and S2(T) close to 2 the direct exchange becomes J/kB = E(BS) – E(T). Thus we applied Heisenberg-
Dirac-Van Vleck (HDVV) Hamiltonian.55-59
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The UBLYP functional and 6-31G(d) basis set was used to elucidate Jcalc from optimised structure
and compared with those from X-ray structure of TPT-NN, TTT-NN and PPP-NN (first two columns
Table 3). The large deviation here is mainly due to different geometries from optimization versus X-ray
structures differing mainly in the torsional angles between the radical unit NN and the π-bridge. Very
interestingly Jcalc from X-ray structure provided very close values to the ones obtained experimentally
from magnetization measurements Jexp (Table 3) as found also in other cases before.41,45
Table 3 The intra-dimer magnetic exchange coupling calculated Jcalc, and experimental Jexp values. The
Tmax denotes the position of the maximum in χmol(T), (cm3/mol) as a function of temperature and Φ/K
represents the Weiss temperature.
Radicals
TTT-NN
TPT-NN
PTP-NN
PPP-NN
Jcalc/Kc Jcalc/Kd
Φ/Ke
Tmax/Kf Jexp/Kg
–23.9
–11.1
–2.7
–14.7
–25.7
10.0
–11.9
–5.3
–32.4
3.8
–6.2
h
h
h
h
h
h
h
–2.1
–2.5
cCalculated from optimized structure using UBLYP/6-31G(d), dCalculated from X-ray structure using
UBLYP/6-31G(d), eEstimated from Curie–Weiss model, f,gCalculated from molar magnetic
susceptibility, χmol (cm-1mol-1) as function of temperature, hnot determined.
The UBLYP functional and 6-31G(d) basis set is necessary since when calculating J values with
UB3LYP functional and 6-31G(d) basis set, it is well known, that over estimation of Jintra(calc) occurs,
due to the spin contamination from Hartree-Fock contributions.60 This was also found here (Table S3).
The theoretical exchange interaction of the TTT-NN was studied previously with UB3LYP functional,61
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leading to stronger exchange than with BLYP functional. From the triplet state the spin density
distributions were derived for TPT-NN and TTT-NN. The spin density is delocalized most on the O-N-
C-N-O fragment of NN with small spin density distribution into the connected thiophenes and very
minor spin found at the central phenyl ring in TPT-NN and the central thiophene unit in TTT-NN
(Figure S17).
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Magnetic properties
The molar magnetic susceptibility, (χmol) of polycrystalline sample for TTT-NN and TPT-NN were
recorded using a SQUID magnetometer in the temperature range 2 K ≤ T ≤ 300 K to elucidate
magnetizations and magnetic exchange interaction as shown in Figure 8.
Figure 8. Molar magnetic susceptibility χmol (cm3mol–1) of TPT-NN and TTT-NN and Inset: Effective
magnetic moment, ꢀeff, as function of temperature.
The data reveal that both the samples behave almost temperature independent in the range from about
100 K to 300 K. The molar magnetic susceptibility (χmol) initially increased by decreasing the
temperature with the Curie-Weiss behaviour at higher temperature region (~150-10 K for TTT-NN and
150-3.8 K for TPT-NN) and decreased by decreasing the temperature at lower temperature (< 10 0.5
K for TTT-NN and < 3.8 0.5 K for TPT-NN) mainly caused by intramolecular antiferromagnetic
(AF) interactions, which means that the biradicals switch from a thermally populated magnetic spin
triplet state to a non magnetic spin singlet ground state.
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The mean value for the magnetic exchange coupling at high-temperature regime can be obtained by
fitting the curve with inverse magnetic susceptibility 1/χmol by a Curie–Weiss model straight line (Figure
S18). The fitting gave negative Weiss temperatures are ΦW = –32.4 0.5 K and –25.7 0.5 K for
TTT-NN and TPT-NN respectively. These negative Weiss constants are indicating that there is
intramolecular antiferromagnetic coupling interaction between NN radical units through the π-bridge.
For a more precise determination of the intradimer coupling constant Jintra of TTT-NN and TPT-NN
was estimated by the temperature dependence of the molar magnetic susceptibility over the temperature
range 2 K ≥ T ≤ 300 K using the Bleaney–Bowers equation for isolated dimer models.62 The intra-dimer
magnetic exchange coupling constant Jintra between two S = 1/2 spins used in this expression refers to a
Hamiltonian of the form H = -2J12S1S2, which was taken also for the DFT calculations. These coupling
constants are J/kB = –6.2 K for TPT-NN and J/kB = –11.9 K for TTT-NN, respectively. The observed
effective magnetic moment (ꢁeff) values for TTT-NN and TPT-NN are calculated from temperature
dependence of magnetic susceptibility as a function of temperature (inset of Figure 8).
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At room temperature the magnetic moments are close to the theoretical value 2.45 ꢁB for magnetically
uncorrelated spins of biradicals. The theoretical exchange coupling constants, as J/kB calculated from
optimized structure using UBLYP/6-31G(d) which are listed in the Table 3. We did not further inspect
the susceptibility experiment for PPP-NN and PTP-NN because the calculated coupling constant from
DFT are very low as J/kB = –2.1 K for PPP-NN and J/kB = –2.7 K for PTP-NN which are less
interesting for the molecular quantum magnets.
CONCLUSIONS
In summary, we have designed and synthesized four nitronyl nitroxide biradicals with different
numbers of phenyl and thiophene units as molecular bridge. The intramolecular magnetic interaction
were predicted by spin polarization rule, the NN groups are AFM coupled to each other. All the
precursors were characterised by NMR spectroscopy, mass spectrometry and 3, 5, 6, PPP-NNSi and
PTP-NNSi were confirmed by single crystal X-ray studies. The structure of biradicals (TPT-NN, TTT-
NN, and PPP-NN) were confirmed by single crystal X-ray studies and their intra and inter molecular
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packing were investigated. All the biradicals were characterised by EPR spectroscopy and compared
with computer simulation. A variable temperature and low temperature EPR studies as ∆MS = 1 and
ꢀMS = 2 were carried out. The biradicals were examined by UV–Vis spectroscopy. The thiophene
containing biradicals demonstrated more red shifted absorption than the p-ter-phenyl based biradicals.
The strength of intra molecular magnetic interactions depends on the distance of the π-bridges and
torsion between the aromatic rings in the π-bridge and among π-bridge and NN unit. The distance
between the radical centers follows the trend PPP-NN > PTP-NN > TPT-NN > TTT-NN and the order
of the planarity of the π-bridges were PPP < PTP < TPT < TTT. The torsion of the thiophene and NN
are smaller than for the neighboring phenyl and NN units due to smaller steric hindrance of five vs six
membered rings. The calculated magnetic interactions for the optimized structures deviated more than
those estimated from single crystal X-ray structure with experimental values. These deviation may be,
due to optimized structures are more planar than single crystal X-ray structures. The calculated
magnetic interactions from single crystal X-ray structure are quite similar with experimental values for
TTT-NN and TPT-NN. The biradicals (TPT-NN and TTT-NN) are promising molecules for further
assessment because the magnetic coupling constants are –6.2 K for TPT-NN and –11.9 K for TPT-NN
respectively.
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EXPERIMENTAL SECTION
Materials and Methods
Oven dried glassware were used. All manipulations were performed under a dry argon atmosphere
using standard technique. NMR spectra were recorded using 250, 300, 500 or 700 MHz Bruker
1
spectrometers. Chemical shifts are reported for H NMR and 13C NMR relative to residual proton or
carbon resonances in CD2Cl2, DMSO-d6 or THF-d8. Molecular mass was recorded using ESI HRMS or
MALDI-TOF mass spectrometric analyses. All reagents and chemicals were purchased from
commercial sources and used as received, unless otherwise specified. The compounds 2,3-
bis(hydroxyamino)-2,3-dimethylbutane (BHA), 263 and 411 were synthesized by modified reported
procedures.
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DFT calculations
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Geometry optimizations of the all the structures were performed with full relaxation of all atoms in
gas phase and without solvent effects carried out by Gaussian 09 program using the B3LYP functional
and 6-31G(d) basis set.54
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UV-vis and EPR Spectroscopy
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UV–vis absorption spectra were recorded at room temperature using Perkin Elmer Lambda 900
spectrophotometer. The spectroscopic experiments were carried out in toluene as a solvent at room
temperature. The EPR spectra were recorded in an argon-purged toluene as solvent (∼10–4 M) on a
Bruker EMX-plus spectrometer equipped with an NMR gauss meter and a variable-temperature control
continuous-flow-N2 cryostat (Bruker B-VT 2000).
X-ray Crystallography
The X-ray crystallographic data were collected on a Smart CCD diffractometer using a graphite
monochromator Mo-Kα as a radiation source for TPT-NN at 23 °C and STOE IPDS 2T diffractometer
using a graphite monochromator Mo-Kα as a radiation source for TTT-NN at -100 °C and Cu-Kα IµS
mirror system as a radiation source for PPP-NN at -153 °C. The structures were solved by direct
methods (SIR-2004) and refined by SHELXL-2014 (full matrix), 176 refined parameters for TPT-NN,
342 refined parameters for TTT-NN and 186 refined parameters for PPP-NN were used. The X-ray
crystallographic data and structure refinement information of 3, 5, 6, PPP-NNSi and PTP-NNSi are
given in the supporting information (Table S1).
2-(5-Bromothiophen-2-yl)-4,4,5,5-tetramethylimidazolidine-1,3-diol (2). A mixture of 2,3-
bis(hydroxylamino)-2,3-dimethylbutane,
(1.02
g,
6.75
mmol)
and
of
5-bromo-2-
thiophenecarboxaldehyde (1.31 g, 6.75 mmol) in 10 mL of methanol was taken in the 50 mL round
bottom flask and the reaction mixture was stirred for 24 h at room temperature under argon atmosphere.
The solution was filtered to obtain 2 as white powder (1.73 g, 80%). 1H NMR (300 MHz, DMSO-d6) δ:
1.02 (s, 6H), 1.04 (s, 6 H) 4.69 (s, 1 H), 6.9 (d, J = 3.9 Hz, 1H), 7.04 (d, J = 3.91 Hz, 1 H), 8.02 (s, 2 H).
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13C NMR (75 MHz, CDCl3), δ: 17.2, 24.1, 66.4, 86.6, 110.6, 126.4, 129.5, 149.4. ESI HRMS calculated
for C11H17BrN2O2SNa: 343.0092; found 343.0090, [M+Na]+.
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2-(5-Bromothiophen-2-yl)-1,3-bis((tert-butyldimethylsilyl)oxy)-4,4,5,5-tetramethylimidazolidine
(3). A DMF solution (10 ml) of 2 (1.01 g, 3.11 mmol), t-butyldimethylsilyl chloride (2.34 g, 5.56
mmol), and imidazole (2.14 g, 31.44 mmol) in 50 mL Schlenk flask and the reaction mixture was stirred
for 24 h at 50 °C under argon atmosphere. Solvent was removed under reduced pressure then the crude
product was extracted with ether, and washed with water. The ether layer was dried over magnesium
sulfate, and concentrated under reduced pressure. The residue was chromatographed on silica gel with
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hexane as the eluant to give 3 (1.60 g, 93%). mp 69−70 °C, H (300 MHz, CD2Cl2) δ: -0.52 (s, 6 H,
SiCH3), -0.04 (s, 6 H, SiCH3), 0.83 (s, 18 H, Si-t-Bu), 1.13 (s, 12 H, CCH3), 4.87 (s, 1 H, CH), 6.75 (d,
2 H, J = 4.0 Hz, Ar), 6.84 (d, 2 H, J = 4 Hz). 13C NMR (75 MHz, CDCl3) δ: -4.6, -3.7, 17.5, 18.5, 24.6,
26.6, 68.7, 90.6, 113.9, 128.7, 129.9, 149.2. ESI HRMS calculated for C23H46BrN2O2SSi2: 549.2002;
found: 549.2000, [M+H]+.
(TPT-NNSi). 1,4-Benzenediboronic acid bis(pinacol) ester, (0.15 g, 0.45 mmol), 3 (0.59 g, 1.08
mmol), K2CO3 (0.38 g, 2.71 mmol) and Pd(PPh3)4 (0.105 g, 0.09 mmol) were taken in 50 mL Schlenk
tube and argon purged THF (15 mL) and water (3 mL) were added then the mixture was stirred for 24 h
at 60 °C under argon atmosphere. The mixture was poured into water and extracted with ether. The
ether layer was dried over magnesium sulfate, and the solution was concentrated under reduced
pressure. The residue was chromatographed on silica gel with hexane as eluant to obtain TPT-NNSi
(0.37 g, 81%). mp 236−237 °C, 1H NMR (300 MHz, CD2Cl2) δ: -0.51 (s, 12 H, SiCH3), -0.05 (s, 12 H,
SiCH3), 0.83 (s, 36 H, Si-t-Bu), 1.16 (s, 24 H, CCH3), 4.92 (s, 2 H, CH), 6.96 (d, 2 H, J = 4 Hz, Ar),
7.15 (d, 2 H, J = 4 Hz), 7.62 (s, 4 H). 13C NMR (175 MHz; CDCl3) δ: –4.8, -3.7, 17.6, 18.5, 25.2, 26.6,
30.3, 68.7, 91.0, 121.9, 126.3, 130.6, 134.4, 145.4, 147.4. ESI HRMS calculated for C52H95N4O4S2Si4:
1015.5872; found: 1015.5897, [M+H]+.
(TPT-NN). A precursor TPT-NNSi (0.20 g, 0.21 mmol) was dissolved in dry THF (15 mL) in the
round bottom flask and (4.7 mL) Bu4NF, 1 M solution in THF was added then the mixture was stirred
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for 16 h at room temperature and while the reaction was monitored by TLC. The product was
concentrated under reduced pressure and the mixture was purified by column chromatography, DCM
and MeOH (0-2 %) as eluant to provide TPT-NN as green solid (90 mg, 83%). mp, decompd. 245−246
°C, ESI HRMS calculated for C28H32N4O4NaS2: 575.1763; found: 575.1759 [M+Na]+.
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2-(4-Bromophenyl)-4,4,5,5-tetramethylimidazolidine-1,3-diol, (4).
A
mixture of 2,3-
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bis(hydroxylamino)-2,3-dimethylbutane (2.9 g, 19.6 mmol) and of 4-bromobenzaldehyde (3.6 g, 19.6
mmol) in 30 mL of methanol in 50 mL round bottom flask was stirred for 24 h at room temperature
under argon atmosphere. The solution was filtered to obtain 4 as a white powder (5.3 g, 86%). 1H NMR
(300 MHz, DMSO-d6) δ: 1.03 (s, 6 H, CH3), 1.06 (s, 6 H, CH3), 4.47 (s, 1 H, CH), 7.41 (d, 2 H, J = 9.0
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Hz, Ar), 7.50 (d, 2 H, J = 8.0 Hz, Ar), 7.81 (s, 2 H, OH). C NMR (75 MHz, DMSO-d6) δ: 17.2, 24.4,
66.2, 89.6, 120.4, 130.5, 130.6,141.4. ESI HRMS calculated for C13H20BrN2O2 315.0703 found
315.10694 [M+H]+.
2-(4-Bromophenyl)-1,3-bis((tert-butyldimethylsilyl)oxy)-4,4,5,5-tetramethylimidazolidine, (5).
The 2-(4-Bromophenyl)-4,4,5,5-tetramethylimidazolidine-1,3-diol,
4
(3.0 g, 9.5 mmol), t-
butyldimethylsilyl chloride (7.2 g, 47.6 mmol), and imidazole (6.5 g, 95.2 mmol) were dissolved in dry
DMF (45 mL) in 100 mL Schlenk flask and the mixture was stirred for 24 h at 50 °C under argon
atmosphere. DMF was removed under reduced pressure and extracted with diethyl ether and washed
with water. The organic layer was dried over magnesium sulfate, and concentrated under reduced
pressure. The residue was purified by column chromatography on silica gel with hexane as the eluant to
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give 5 as white powder (4.8 g, 92%). H NMR (300 MHz, CD2Cl2) δ: -0.84 (s, 6 H, SiCH3), -0.04 (s, 6
H, SiCH3), 0.79 (s, 18 H, Si-t-Bu), 1.16 (s, 12 H, CCH3), 4.59 (s, 1 H, CH), 7.26 (d, 2 H, J = 10 Hz, Ar),
7.40 (d, 2 H, J = 10 Hz). δ: 13C NMR (125 MHz, CD2Cl2) δ: -19.1, -17.6, –3.2, -3.9, 10.52, 12.1, 54.2,
79.5, 107.8, 116.7, 118.8. ESI HRMS calculated for C25H48BrN2O2Si2: 543.2438; found 543.2419,
[M+H]+.
(PPP-NNSi). A mixture of 1,4-benzenediboronic acid bis(pinacol) ester, (0.15 g, 0.45 mmol), 2-(4-
Bromophenyl)-1,3-bis((tert-butyldimethylsilyl)oxy)-4,4,5,5-tetramethylimidazolidine, 5, (0.50 g, 0.91
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mmol), K2CO3 (0.19 g, 1.38 mmol), and Pd(PPh3)4 (0.05 g, 0.09 mmol), was taken in a 50 mL Schlenk
tube and argon purged THF (20 mL) and water (5 mL) were added. Then the mixture was stirred for 24
h at 60 °C under argon atmosphere. The mixture was poured into water and filtered to give PPP-NNSi
as white solid (0.34 g, 74%). mp 248−249 °C, 1H NMR (300 MHz, CD2Cl2) δ: -0.77 (s, 12 H, SiCH3), -
0.02 (s, 12 H, SiCH3), 0.82 (s, 36 H, Si-t-Bu), 1.22 (s, 24 H, CCH3), 4.71 (s, 1 H, CH), 7.49 (d, 2 H, J =
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10 Hz, Ar), 7.65 (d, 2 H, J = 10 Hz), 7.71 (s, 4 H). C NMR (125 MHz, CD2Cl3) δ: -4.5, -3.3, 17.8,
18.8, 25.9, 26.9, 30.7, 69.3, 95.0, 126.9, 128.0, 132.2, 140.7, 141.6. ESI HRMS calculated for
C56H99N4O4Si4: 1003.6743; found 1003.6768, [M+H]+.
(PPP-NN). PPP-NNSi (0.10 g, 0.10 mmol) was dissolved in dry THF (10 mL) and (2.4 mL,) and 1 M
solution of Bu4NF in THF was added then the mixture was stirred for 3 h at room temperature, while
the reaction was monitored by TLC. The reaction mixture was concentrated under reduced pressure, and
then the crude product was purified by column chromatography, DCM and MeOH (0-2 %) as eluant to
obtain PPP-NN as a blue solid (0.037 g, 68%). mp, decompd. 260−261 °C, ESI HRMS calculated for
C32H36N4O4Na: 563.2634; found 563.2650, [M+Na]+.
1,3-Bis((tert-butyldimethylsilyl)oxy)-4,4,5,5-tetramethyl-2-(4-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)phenyl)imidazolidine, (6). The compound 5 (4.80 g, 8.83 mmol), was dissolved in
dry THF (50 mL) in the 100 mL Schlenk tube and cooled to -78 °C then n- butyllithium (1.6 M
solution) in hexane (6.7 mL, 10.56 mmol) was added and the mixture was stirred at same temperature
for 1 h, then 2-isopropylboronic acid, pinacol ester (1.97 g, 2.16 mL, 10.59 mmol), was added and the
reaction mixture was stirred at same temperature for further 1 h then quenched with water (10 mL), and
extracted with ether. The ether layer was dried over magnesium sulfate, and concentrated under reduced
pressure. The residue was chromatographed on silica gel with hexane as eluant to obtain 6 (4.9 g, 94%).
mp 132-133 °C, 1H NMR (300 MHz, CD2Cl2) δ: -0.90 (s, 6 H, SiCH3), -0.04 (s, 6 H, SiCH3), 0.79 (s, 18
H, t-Bu), 1.17 (s, 12 H, CCH3), 4.62 (s, 1 H, CH), 7.39 (d, 2 H, J = 6 Hz), 7.65 (d, 2 H, J = 9 Hz). 13C
NMR (125 MHz; CD2Cl2) δ; -4.7, -3.5, 17.7, 18.4, 25.1, 25.4, 26.6, 68.7, 84.3, 94.9, 129.2, 130.9,
134.5, 145.2. ESI HRMS calculated for C31H60BN2O4Si2: 590.4215; found: 590.4205 [M+H]+.
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(PTP-NNSi). 2,5-Dibromothiophene, (0.10 g, 0.42 mmol), 6 (0.50 g, 0.85 mmol), K2CO3 (0.35 g,
2.53 mmol), and Pd(PPh3)4 (0.11 g, 0.09 mmol) were taken in 50 mL Schlenk tube. And then argon
purged THF (15 mL), and water (5 mL) was added then the mixture was stirred for 24 h at 60 °C under
argon atmosphere. Then the mixture was poured into water and extracted with ether. The ether layer was
dried over magnesium sulfate, and concentrated under reduced pressure. The residue was
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chromatographed on silica gel with hexane to obtain PTP-NNSi (0.28 g, 66%). mp 210−211 °C, H
NMR (250 MHz, CD2Cl2) δ: -0.78 (s, 12 H, SiCH3), -0.01 (s, 12 H, SiCH3), 0.81 (s, 36 H, Si-t-Bu), 1.19
(s, 24 H, CCH3), 4.65 (s, 1 H, CH), 7.35 (s, 2 H), 7.42 (d, 2 H, J = 7.5 Hz), 7.60 (d, 4 H, J = 7.5 Hz). 13C
NMR (125 MHz; CD2Cl3) δ: -4.6, -3.5, 17.6, 18.4, 25.1, 26.6, 68.6, 94.1, 124.3, 125.1, 132.1, 134.3,
141.7, 143.9. ESI HRMS calculated for C54H97N4O4Si4S: 1009.6308; found 1009.6298 [M+H]+.
(PTP-NN). PTP-NNSi (0.05 g, 0.05 mmol) was dissolved in dry THF and (1.19 mL) and Bu4NF, 1 M
solution in THF was added then the mixture was stirred for 16 h at room temperature, while the reaction
was monitored by TLC. The reaction mixture was concentrated under reduced pressure and the mixture
was purified by column chromatography, DCM and MeOH (0-2 %) as eluant to obtain PTP-NN (18
mg, 70%). mp, decompd. mp 206−207 °C, MALDI-TOF calculated for C30H34N4O4S; 546.6900; found:
546.2100 [M]+.
(TTT-NNSi). Thiophene-2,5-diboronic acid bis(pinacol) ester (0.20 g, 0.59 mmol), 3 (0.72 g, 1.31
mmol), K2CO3 (0.49 g, 3.57 mmol) and Pd(PPh3)4 (0.07 g, 0.06 mmol) were taken in a Schlenk tube and
argon purged THF (30 mL) and water (10 mL) were added then the mixture was stirred for 24 h at 60
°C under argon atmosphere. Then the mixture was poured into water and extracted with diethyl ether.
The ether layer was dried over magnesium sulfate, concentrated under reduced pressure. The residues
were chromatographed on silica gel with hexane as an eluent, and to TTT-NNSi obtain (0.11 g, 18 %).
1H NMR (300 MHz, CD2Cl2) δ: -0.51 (s, 12 H, SiCH3), -0.05 (s, 12 H, SiCH3), 0.83 (s, 36 H, Si-t-Bu),
1.16 (s, 24 H, CCH3), 4.92 (s, 1 H, CH), 6.96 (d, 2 H, J = 4 Hz, Ar), 7.15 (d, 2 H, J = 4 Hz), 7.62 (s, 4
13
H). C NMR (125 MHz, CDCl3) δ: -4.7, -3.7, 17.5, 18.5, 25.1, 26.5, 30.3, 68.7, 122.4, 124.3, 130.1,
137.1, 138.7, 146.9. ESI HRMS calculated for C50H93N4O4S3Si4: 1021.5436; found 1021.5461, [M+H].+
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Mono coupled product. 0.171 g, 51 %; H NMR (300 MHz, CD2Cl2) δ: -0.51 (s, 12 H, SiCH3), -0.05
(s, 12 H, SiCH3), 0.83 (s, 36 H, Si-t-Bu), 1.16 (s, 24 H, CCH3), 4.92 (s, 1 H, CH), 6.96 (d, 2 H, J = 4 Hz,
Ar), 7.15 (d, 2 H, J = 4 Hz), 7.62 (s, 4 H).
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(TTT-NNSi) By Stile coupling: 2,5-bis(trimethylstannyl)thiophene (0.10 g, 0.23 mmol), 3 (0.33 g,
0.61 mmol), and Pd(PPh3)4 (0.06 g, 0.05 mmol), were taken in 50 mL Schleck tube and argon purged
dry DMF (10 mL), was added then the mixture was stirred for 30 h at 60 °C. Then DMF was removed
under reduced pressure. The residue was extracted with diethyl ether (2 X 50 mL). The ether layer was
dried over magnesium sulfate, and concentrated under reduced pressure. The residue was
chromatographed on silica gel with hexane to obtain TTT-NNSi (0.18 g, 79 %).
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(TTT-NN). TTT-NNSi (0.10 mg, 0.10 mmol) was dissolved in dry THF (7 mL) and (2.4 mL)
Bu4NF, 1 M solution in THF was added then the mixture was stirred for 16 h at room temperature,
while the reaction was monitored by TLC. The solution was concentrated under reduced pressure and
the mixture was purified by column chromatography, DCM and MeOH (0-2 %) as eluant to obtain
TTT-NN as green solid (36 mg, 66%). mp, decompd. 219−220 °C, ESI calculated for C26H30N4O4S3:
558.14, found: 558.16 [M]+.
ASSOCIATED CONTENT
Supporting Information
The supporting information and crystallographic data are available free of charge on the
website at DOI:
Optimized structure of π bridges (PPP, PTP, TPT and TTT), prediction of magnetic
interaction, crystallographic data for compounds 3, 5, 6, PPP-NNSi, and PTP-NNSi, TPT-NN,
TTT-NN, and PPP-NN, (CIF), and structures and refinement details of 3, 5, 6, PPP-NNSi, and
PTP-NNSi, and structures of the TPT-NN, TTT-NN, and PPP-NN, optical spectra and optical
data of PPP-NNSi, PPP-NN, TPT-NNSi, TPT-NN, TTT-NNSi, TTT-NN, and PTP-NNSi,
PPP-NN in dilute toluene, EPR spectra of (experimental and simulated) the biradicals (TTT-
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NN, PPP-NN and PTP-NN) in toluene, EPR spectra of T-NN, monoradical and TTT-NN in
toluene, optimized structures of PPP-NN, TTT-NN, TPT-NN, and PTP-NN, the magnetic
exchange coupling calculated Jcalc by optimized structure using U3BLYP/6-31G(d), and X-ray
structure using U3BLYP/6-31G, calculated spin density distribution of the triplet state of TPT-
NN and TTT-NN, curie–Weiss model straight line of TPP-NN and TTT-NN, characterization
of new compounds, NMR spectra, and DFT calculations data and reference.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: martin.baumgarten@mpip-mainz.mpg.de
ACKNOWLEDGMENT
We acknowledge the SFB-TR49 for financial support.
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