Effects of solvation on charge distribution of 1,2-semiquinonato/ catecholatocobalt complexes containing bis(3-pyridyl) phenylvinylsilane

Article abstract of DOI:10.1007/s11243-012-9622-3

Recrystallization of [Co(3,5-dbbq)₂(L)] (3,5- dbbq = 3,5-di-tert-butyl-1,2-benzoquinone; L = bis(3-pyridyl)- phenylvinylsilane) from diethyl ether at -20 °C produces trans-[Co(3,5-dbbq)₂(L) ₂] while the recrystallization f

Full text of DOI:10.1007/s11243-012-9622-3

Transition Met Chem (2012) 37:563–567
DOI 10.1007/s11243-012-9622-3
Effects of solvation on charge distribution
of 1,2-semiquinonato/catecholatocobalt complexes
containing bis(3-pyridyl) phenylvinylsilane
•
Woosik Hong Sojung Lee Haeri Lee
•
•
•
Tae Hwan Noh Young-A Lee Ok-Sang Jung
•
Received: 19 April 2012 / Accepted: 29 May 2012 / Published online: 30 June 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Recrystallization of [Co(3,5-dbbq)2(L)2] (3,5-
dbbq = 3,5-di-tert-butyl-1,2-benzoquinone; L = bis(3-pyridyl)-
phenylvinylsilane) from diethyl ether at -20 °C produces
trans-[Co(3,5-dbbq)2(L)2] while the recrystallization from
toluene at -20 °C gives trans-[Co(3,5-dbbq)2(L)2]Á2PhMe.
The complex exists as trans-[CoIII(3,5-dbsq)(3,5-dbcat)(L)2]
(3,5-dbsq = 3,5-di-tert-butyl-1,2-semiquinonato; 3,5-dbcat = 3,
5-di-tert-butylcatecholato) in the solid state at 173 K. Differ-
ences in charge distribution between trans-[Co(3,5-dbbq)2(L)2]
and trans-[Co(3,5-dbbq)2(L)2]Á2PhMe have been observed
based on the effective magnetic moments and IR spectra of the
complexes along with their X-ray crystal structures.
catecholato (cat2-, S = 0) ligands have shown a specific
bistability involving the intramolecular electron transfer
between the metal and the ligand, even in the solid state
around room temperature [5].Their different valence states
have significantly different charges and spin distributions
and thus show characteristic optical, electrical, and mag-
netic properties [12, 21]. This phenomenon has been
clearly revealed for the cobalt complexes, where equilibria
between the [CoIII] and [CoII] valence tautomeric species
have been observed, both in the solution and in the solid
state [2, 6]. Such electronic-labile complexes are known to
be very sensitive to environmental factors such as tem-
perature, solvent, state, and photo-energy [5]. Although
solvent effects on cobalt valence tautomeric systems have
been reported [5, 22], direct comparison of solvation
effects on the same parent molecules remains unexplored.
In this paper, solvation effects based on the charge distri-
bution of solvated versus non-solvated 1,2-semiquinonato/
catecholatocobalt complexes containing bis(3-pyridyl)
phenylvinylsilane (L, Scheme 1) are reported.
Introduction
Valence tautomers that exhibit different charge distribu-
tions via intramolecular electron transfer including spin-
crossover processes are a class of bistable molecules that
can be switched by temperature, light, or pressure [1–3].
Much research has been directed toward controlling the
cooperativity of the tautomerism [4, 5], studying photos-
witching effects [6–13], and constructing new valence
tautomeric systems [14–18] as potential building blocks for
molecular electronic devices [19, 20]. Some metal com-
plexes containing 1,2-semiquinonato (sq-, S = 1/2) and
Experimental
Materials and measurements
Co2(CO)8, 3,5-di-tert-butyl-1,2-benzoquinone (3,5-dbbq),
and dichlorophenylvinylsilane were purchased from
Aldrich and Gelest and used without further purification.
Elemental microanalyses (C, H, N) were performed on
crystalline samples by the Pusan Center, KBSI, using a
Vario-EL III instrument. Infrared spectra were obtained on
a Nicolet 380 FTIR spectrophotometer with samples pre-
pared as KBr pellets. Electronic spectra were obtained
on a UV–vis spectrophotometer S-3105. Temperature-
W. Hong Á S. Lee Á H. Lee Á T. H. Noh Á O.-S. Jung (&)
Department of Chemistry and Research Institute of Functional
Materials Chemistry, Pusan National University,
Pusan 609-735, Korea
e-mail: oksjung@pusan.ac.kr
Y.-A. Lee
Department of Chemistry, Chonbuk National University,
Jeonju 561-756, Korea
123

564
Transition Met Chem (2012) 37:563–567
Scheme 1 Ligand L
C64H72N4O4Si2Co: C, 71.4; H, 6.7; N, 5.2. Found: C, 71.4;
H, 6.6; N, 5.2. IR (KBr, cm-1): 3650(br, s), 2956(s),
1571(s), 1473(s), 1394(s), 1355(s), 1194(m), 1118(s), 985(s),
897(m), 714(s), 559(w), 487(w).
Synthesis of trans-[Co(3,5-dbbq)2(L)2]Á2PhMe
Co2(CO)8 (43 mg, 0.12 mmol) and L (144 mg, 0.50 mmol)
were combined in 30 mL of toluene. The mixture was
stirred for 5 min, and a solution of 3,5-dbbq (110 mg,
0.50 mmol) in toluene (30 mL) was added. The solution
was stirred for 1 h at room temperature. Dark blue crystals
suitable for crystallographic characterization were grown
from toluene solution at -20 °C in 55 % yield. Anal.
Calcd. for C78H88N4O4Si2Co: C, 74.3; H, 7.0; N, 4.4.
Found: C, 74.3; H, 7.0; N, 4.3. IR (KBr, cm-1): 3660(br, s),
2954(s), 1571(s), 1473(s), 1396(s), 1355(s), 1193(m),
1106(s), 987(s), 896(m), 713(s), 559(w), 487(w).
dependent magnetic measurements were obtained using a
Quantum Design PPMS-9T SQUID magnetometer at a
1
field of strength 10 kG. H and 13C NMR spectra were
recorded on a Varian Mercury Plus 300 spectrometer, and
the chemical shifts are given relative to internal Me4Si.
Synthesis of bis(3-pyridyl)phenylvinylsilane
n-Butyllithium (35.0 mmol, 2.5 M solution in n-hexane)
was added to a solution of 3-bromopyridine (33.0 mmol) in
dry diethyl ether (60 mL) under nitrogen gas at -78 °C,
and the resulting mixture was stirred for 1.5 h. Dichlor-
ophenylvinylsilane (16.0 mmol) was slowly added to the
yellow suspension, and the mixture was stirred overnight at
0 °C. Distilled water (50 mL) was added into the reaction
solution, and the organic layer was separated, washed with
water, and then dried over MgSO4. The crude product was
purified by column chromatography on silica gel with ethyl
acetate as eluent. The solvent was evaporated to obtain the
product L as a solid in a 63 % yield. Anal. Calcd. for
C18H16N2Si: C, 75.0; H, 5.6; N, 9.7. Found: C, 74.9; H, 5.5;
N, 9.5. IR (KBr, cm-1): 3068(w), 1571(s), 1468(m),
1394(s), 1331(m), 1192(m), 1120(s), 1030(s), 968(s),
805(s), 714(s), 557(s), 474(m). 1H NMR (CDCl3, SiMe4): d
8.70 (s, 2H, Py), 8.67 (dd, J = 4.8 Hz, J = 1.5 Hz, 2H,
Py), 7.78 (dt, J = 7.2 Hz, J = 1.8 Hz, 2H), 7.51 (dd,
J = 7.8 Hz, J = 1.5 Hz, 2H, Py), 7.60 (d, J = 6.9 Hz,
1H), 7.42 (d, J = 6.9 Hz, 2H), 7.31 (dd, J = 7.8 Hz,
J = 4.8 Hz, 2H, Py), 6.68 (dd, J = 20.1 Hz, J = 14.4 Hz,
1H), 6.42 (dd, J = 14.4 Hz, J = 3.3 Hz, 1H), 5.82 (dd,
J = 20.1 Hz, J = 3.3 Hz, 1H). 13C NMR (CDCl3, SiMe4):
d 156.1, 151.1, 143.5, 138.7, 135.8, 131.7, 130.5, 128.4,
123.5, 77.6, 76.7.
Crystal structure determination
X-ray data were collected on a Bruker SMART automatic
diffractometer with graphite-monochromated Mo Ka radi-
˚
ation (k = 0.71073 A) and a CCD detector at 170 K.
Thirty-six frames of two dimensional diffraction images
were collected and processed to obtain the cell parameters
and orientation matrix. The data were corrected for Lorentz
and polarization effects. The absorption effects were cor-
rected using the multi-scan method (SADABS) [23]. The
structures were solved using direct methods (SHELXS 97)
and refined by full-matrix least square techniques (SHEL-
XL 97) [24, 25]. The non-hydrogen atoms were refined
anisotropically, and the hydrogen atoms were placed in
calculated positions and refined only for the isotropic
thermal factors. The crystal parameters and procedural
information corresponding to the data collection and
structure refinement are listed in Table 1.
Results and discussion
Synthesis
Synthesis of trans-[Co(3,5-dbbq)2(L)2]
The synthetic method described in earlier studies was used
to prepare the present complex trans-[Co(3,5-dbbq)2(L)2]
[22]. Thus, the reaction between Co2(CO)8 and 3,5-dbbq in
the presence of L as coligand afforded the present complex
in toluene at room temperature. trans-[Co(3,5-dbbq)2(L)2]
containing two monodentate L coligands was formed
instead of the species containing a bidentate L, presumably
owing to the steric hindrance resulting from chelation
of L. An important feature is that recrystallization from
diethyl ether at -20 °C produces trans-[Co(3,5-dbbq)2(L)2],
Co2(CO)8 (43 mg, 0.12 mmol) and L (144 mg, 0.50 mmol)
were combined in 30 mL of toluene. The mixture was
stirred for 5 min, and a solution of 3,5-dbbq (110 mg,
0.50 mmol) in toluene (30 mL) was added into the solution,
which was then stirred for 1 h at room temperature. Slow
evaporation of the solvent gave a dark green microcrystal-
line product. Dark blue crystals suitable for crystallographic
characterization were obtained by recrystallization from
diethyl ether at -20 °C in 60 % yield. Anal. Calcd. for
123

Transition Met Chem (2012) 37:563–567
565
common organic solvents such as toluene, benzene, tetra-
hydrofuran, acetone, dimethyl sulfoxide, and N,N-dimeth-
ylformamide. However, the products were easily dissociated
in dimethyl sulfoxide, alcohols, and N,N-dimethylformam-
ide. The solubility characteristicsindicate that thecomplexes
are discrete molecules instead of polymeric species. The
complexes were characterized by spectral, thermal, and
magnetic properties along with the crystal structures. The
same products were formed upon varying the mole ratio of
reactants, indicating that the discrete trans- products are
favorable species. Formation of the discrete molecular spe-
cies instead of polymers may be attributed to the small and
rigid L coligand.
Table 1 Crystal data and structure refinement for trans-[Co(3,
5-dbbq)2(L)2] and trans-[Co(3,5-dbbq)2(L)2]Á2PhMe
trans-[Co(3,
5-dbbq)2(L)2]
trans-[Co(3,
5-dbbq)2(L)2]Á
2PhMe
Empirical formula
Weight
C64H72N4O4Si2Co C78H88N4O4Si2Co
1076.37
Triclinic
P¯ı
1260.63
Triclinic
P¯ı
Crystal system
Space group
˚
a (A)
10.2316(2)
11.2622(2)
13.4227(3)
100.301(1)
91.233(1)
105.349(1)
1463.62(5)
1.221
10.3115(5)
12.6999(6)
13.3212(6)
81.848(3)
85.502(3)
81.660(3)
1705.6(1)
1.227
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
Volume (A )
Density (mg/m3)
Crystal structures
3
˚
The crystal structures of trans-[Co(3,5-dbbq)2(L)2] and
trans-[Co(3,5-dbbq)2(L)2]Á2PhMe are depicted in Fig. 1,
and selected bond lengths and angles are listed in Table 2.
The L coligand is monodentate, resulting in discrete
centrosymmetric mononuclear complexes with two free
pyridyl groups. The molecule approximates to the charge
distribution of trans-[CoIII(3,5-dbsq)(3,5-dbcat)(L)2] (3,5-
Z
1
1
Absorption coefficient
(mm-1
0.384
0.339
)
F(000)
Rint
571
671
0.0572
99.7
0.1303
96.9
Completeness (%)
GoF on F2
R1 [I [ 2r(I)]a
wR2 (all data)b
dbsq- = 3,5-di-tert-butyl-1,2-semiquinonate; 3,5-dbcat2-
=
1.032
0.0609
0.1693
1.043
0.0800
0.2286
3,5-di-tert-butylcatecholate) rather than trans-[CoII(3,5-
dbsq)2(L)2] in the solid state at 173 K; this assignment is
consistent with the IR data and effective magnetic moments
as well as the Co-O bond lengths. The Co–O bond lengths
P
P
a
R1 = ||Fo| - |Fc||/ |Fo|
P
P
b
wR2 = ( w(F2o - Fc2)2/ wFo2)1/2
˚
(1.877(2) and 1.887(2) A for trans-[Co(3,5-dbbq)2(L)2];
˚
1.878(3) and 1.874(3) A for trans-[Co(3,5-dbbq)2(L)2]Á
2PhMe) are also shorter than generally observed for CoII-O
whereas crystallization from toluene at -20 °C gives
trans-[Co(3,5-dbbq)2(L)2]Á2PhMe. The crystalline products
gave satisfactory chemical analyses and were soluble in
bonds (C2.00 A). The radius of low-spin CoIII is roughly 0.2
˚
II
A smaller than that of high-spin Co [5]. The low-spin Co
III
˚
Fig. 1 ORTEP drawings of
trans-[Co(3,5-dbbq)2(L)2] (left)
and trans-[Co(3,5-
N2
dbbq)2(L)2]Á2PhMe (right)
showing thermal ellipsoids at
Si1
Si1
20 % probability. Hydrogen
atoms are omitted for clarity
N2
N1
Co1
N1
O1
O1
Co1
O2
O2
123

566
Transition Met Chem (2012) 37:563–567
Table 2 Selected bond lengths
˚
trans-[Co(3,5-dbbq)2(L)2]
trans-[Co(3,5-dbbq)2(L)2]Á2PhMe
(A) and angles (°) for trans-
[Co(3,5-dbbq)2(L)2] and trans-
[Co(3,5-dbbq)2(L)2]Á2PhMe
Co(1)–O(1)
1.877(2)
1.887(2)
1.953(2)
1.327(3)
1.334(3)
93.20(8)
90.1(1)
Co(1)–O(1)
1.878(3)
1.874(3)
1.946(4)
1.321(6)
1.340(6)
87.0(1)
Co(1)–O(2)
Co(1)–O(2)
Co(1)–N(1)
Co(1)–N(1)
C(1)–O(1)
C(1)–O(1)
C(2)–O(2)
C(2)–O(2)
O(1)–Co(1)–O(2)
O(1)–Co(1)–N(1)
O(2)–Co(1)–N(1)
O(1)–Co(1)–O(1)#1
O(1)–Co(1)–O(2)#1
O(1)–Co(1)–O(2)
O(1)–Co(1)–N(1)
O(2)–Co(1)–N(1)
O(1)–Co(1)–O(1)#2
O(1)–Co(1)–O(2)#2
90.7(2)
90.80(9)
180.0
90.0(2)
Symmetry transformations
used to generate equivalent
atoms: #1 -x, -y?1, -z;
#2 -x?1, -y?2, -z?1
180.00(1)
93.00(1)
86.80(8)
would be expected to be in a strictly octahedral geometry, in
contrast to a few known examples of the high-spin CoII tri-
gonal prismatic geometry [27]. The centrosymmetric mole-
cules result in similar C – O bonds: C(1)-O(1) = 1.327(3)
should converge to 1.7 lB at the lowest temperature,
resulting from the 1,2-semiquinonato (sq-, S = 1/2) moiety
of low-spin trans-[CoIII(3,5-dbsq)(3,5-dbcat)(L)2]. Electron
transfer from the 3,5-dbcat ligand to the CoIII center controls
the ratio of [CoIII]/[CoII] species. Thus, the ratio of [CoIII]/
[CoII] can be controlled by the donor effects of the coligand
L, with great sensitivity.
The characteristic IR band around 4,000 cm-1 (Fig. 4)
indicates the presence of [CoIII] species in the solid state at
room temperature [22], which is consistent with the X-ray
crystal structures and effective magnetic moments dis-
cussed above. A more important result is that the IR band
of the solvated crystal, trans-[Co(3,5-dbbq)2(L)2]Á2PhMe,
is stronger than that of trans-[Co(3,5-dbbq)2(L)2], indicat-
ing that the [CoIII]/[CoII] ratio of the solvated crystal is
larger than that of the non-solvated crystal, which is
coincident with the above magnetic susceptibility
measurements.
˚
A, C(2)-O(2) = 1.334(3) A for trans-[Co(3,5-dbbq)2(L)2];
˚
˚
˚
C(1)-O(1) = 1.321(6) A, C(2)-O(2) = 1.340(6) A for
trans-[Co(3,5-dbbq)2(L)2]Á2PhMe. For trans-[Co(3,5-dbbq)2
(L)2]Á2PhMe, the two solvate toluene molecules are located in
the vacancies within the unit cell (Fig. 2).
Spectroscopic data
The temperature-dependent magnetic moments [26] recor-
ded on solid samples of the two complexes are depicted in
Fig. 3. For trans-[Co(3,5-dbbq)2(L)2], the effective mag-
netic moment remains at approximately 2.3 lB at 5 K and,
finally, approaches 5.0 lB at 360 K, indicating that trans-
[CoIII(3,5-dbsq)(3,5-dbcat)(L)2] shifts to the tautomeric
species trans-[CoII(3,5-dbsq)2(L)2] with increasing temper-
ature in the solid state. At high temperatures, the value of 5.0
lB is indicative of weak antiferromagnetic exchange
between the S = 3/2 metal center and the two S = 1/2
semiquinonato (3,5-dbsq) ligands. For trans-[Co(3,5-
dbbq)2(L)2]Á2PhMe, leff is 1.7 lB at 5 K, rising to 3.6 lB at
360 K, indicating that valence tautomerism occurs in the
solid state in this case also. The magnetic moment value
The electronic spectrum (*10-4 M) of trans-[Co(3,5-
dbbq)2(L)2] in the range of 400–900 nm was measured in
tetrahydrofuran (Fig. 5). The two bands observed at 640
and 740 nm are the characteristic of the [CoIII] and [CoII]
tautomers, respectively [22]. Hence, the electronic
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
0
50
100
150
200
250
300
350
Temperature (K)
Fig. 2 Packing diagrams of trans-[Co(3,5-dbbq)2(L)2] (left) and
trans-[Co(3,5-dbbq)2(L)2]Á2PhMe in a-axis view. All hydrogen atoms
are omitted for clarity
Fig. 3 Temperature-dependent effective magnetic moments for
trans-[Co(3,5-dbbq)2(L)2] (solid line) and trans-[Co(3,5-dbbq)2(L)2]Á
2PhMe (dashed line) in the solid state
123

Transition Met Chem (2012) 37:563–567
567
Supplementary material
Crystallographic data have been deposited with the Cam-
bridge Crystallographic Data Center, under deposition
number CCDC 871339 and 871340 for the complex trans-
[Co(3,5-dbbq)2(L)2] and trans-[Co(3,5-dbbq)2(L)2]Á2C6
H5CH3, respectively. Copy of the data can be obtained free
of charge on application to The Director, CCDC, 12 Union
Road, Cambridge CB2, 1EZ, UK (fax: ?44-1223-336033);
E-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk).
5000
4500
4000
3500
3000
2500
Wavenumber (cm−1
)
Fig. 4 IR spectra of trans-[Co(3,5-dbbq)2(L)2] (solid line) and trans-
[Co(3,5-dbbq)2(L)2]Á2PhMe (dashed line)
Acknowledgments This work was supported by the National
Research Foundation of Korea Grant funded by the Korean Govern-
ment (MEST) (NRF-2010-0026167).
0.6
0.4
0.2
0.0
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Conclusion
Mononuclear cobalt complexes with two free nitrogen
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direct evidence for differences in charge distribution
between solvated and non-solvated crystals has been
observed in this work. Further experiments on such bistable
molecular systems will provide more detailed information
on the notable solvation effects.
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