- Email: [email protected]
Crystal structure and electrical conductivity of (TTF)5Hg6(SCN)16
Synthetic Metals. 27 (1988) B15 B21
BI5 "The submitted manuscript has been authored by a contractor of the U . S . Government under contact No, W-31-109-ENG-38. Accordingly, the U.S Government retains a nonexclusive, royaltyfree license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes."
CRYSTAL STRUCTURE AND ELECTRICAL
N. THORUP,
CONDUCTIVITY
M. A. BENO, C. S. CARISS,
OF (TTF)5Hg6(SCN)I6
K. D. CARLSON, U. GEISER,
S. KLEINJAN,
L. C. PORTER, H. H. WANG and J. M. WILLIAMS Chemistry and Materials Argonne National
Science Divisions
Laboratory,
Argonne,
Illinois 61)439 (U.S.A.)
ABSTRACT The crystal structure been determined. cell dimensions
and electrical
properties
The crystals are monoclinic, a = 15.032(3),
= 108.92(i) ° .
b = 16.846(5),
of (TTF)5Hg6(SCN)16
space group P21/a , with unit c = 17.364(3)
The TTF units are stacked along the c axis.
stacks, dimers and trimers alternate. well as non-bridging
SUN- ligands.
behavior with a room temperature
have
A and Within the
The complex anion contains bridging as
The crystals exhibit semicondncting
conductivity
of 8.7 x 10 -4 S'cm -1.
INTRODUCTION Tetrathiafulvalene anions.
(TTF) forms cation-radical
The structures
salts with many inorganic
of a number of such salts are already known,
(TTF)CIO 4 [I], (TTF)3(BF4) 2 [2] and (TTF)HgCI 3 [3]. form stacks,
but the electrical
irregularities
within
non-stoichiometric
BEDT-TTF,
of TTF, however,
rather unusual
Some
the anion Cu(SCN) 2- with
phase
[5-8], we have studied
crystal structure and conductivity composition
0379-6779/88/$3.50
localization.
eclipsed stacking of TTF [4].
Hg(SCN) 3- salts of TTF and BEDT-TTF.
the preparation,
often
are highly conducting which may be
by the recent success of combining
leading to a i0 K superconducting
corresponding
The TTF molecules
is usually rather low due to
the stacks which lead to electron
halides
related to the regular, Encouraged
conductivity
e.g.,
The present paper reports of a compound with the
(TTF)5Hg6(SCN)16.
© Elsevier Sequoia/Printed in The Netherlands
BI6
EXPERIMENTAL The title compound was prepared by slow diffusion of a 20 mL CH2CI 2 solution containing 600 mg of NBu4Hg(SCN) 3 (0.97 mmol), solution containing 24 mg of TTF (0.12 mmol).
into a I0 mL CH2CI 2
48.1 mg of good quality tiny
black needles mixed with small amounts of Hg were obtained.
Mp.
gingle crystal X-ray diffraction and conductivity measurements out on the as-grown needles.
127-129°C.
were carried
The crude product can be recrystallized
from
CH3CN. X-ray data were collected on a Syntex diffractometer Mo-radiation.
the full-matrix least squares refinement. tropically,
N and C atoms isotropically.
corrected for Lorentz, residuals:
using monochromated
3168 unique refle×ions with I>3o(I) and 4°<20<45 ° were used in Hg and S atoms were refined anisoNo H atoms were included.
polarization and absorption effects.
Data
Resultant
R = 0.055, wR = 0.058.
Resistivity measurements the temperature interval
as a function of temperature were carried out over
160-300 K using the standard four-probe
technique.
Lead contacts consisted of a silver paste securing gold wires to the surface of the crystal,
and temperature control and variation were obtained using a
closed-cycle helium refrigerator.
RESULTS The unit cell (see abstract) (TTF)5Hg6(SCN)I6. included on Figs.
contains
Atomic coordinates are given in Table i.
Bond lengths are
1 and 2, which also show the atomic numbering.
a packing diagram of the structure. the c axis (spaced by c/3). to four SCN- ions if Hg-(S,N) SCN
two formula units of
Figure 3 is
The Hg atoms are nearly lined up along
Each of the three unique Hg atoms is coordinated distances up to 2.80 % are considered.
Some
ions are bonded to one Hg only (via S) whereas others form bridges
between Hg atoms bonding via S as well as N (Figs. anion, Hg6(SCN)164-,
contains
1 and 3).
The complex
three Hg atoms on one line connected to three Hg
atoms on another llne with a center of symmetry between the two halves. The TTF units form one-dimensional
stacks along the c axis.
These stacks
fit into channels formed by the anions, and no stack has any S..-S contacts shorter than 3.6 % to surrounding anions.
Within a stack the planar TTF units
are almost parallel with interstack distances 3.46, 3.47 and 3.49 %, i.e., nearly equidistant
spacing.
However,
differences
in molecular overlap between
BI7 neighbur[qg TTF units
indicate a separation
are three un[que TTF units
into d[mers aud tr[~ ~ ,o
(actL~ally 2 1/2) which are d e s i g n a t e d 4, 5 and & in
accordance with the atomic numbering scheme. units
Ynec,
related by a center of symmetry.
The dimer
The trimer
is formed by two TT!-~
[s formed by one TTF-6 unit
lc)cated at a center of symmetry and sandwiched between two symmetry related TTF-4 units.
The molecular overlaps within a dimer
(4-6) are similar and close to eclipsed, mode or overlap
(5-5') and within a tr[mer
which is supposed
to be a preferred
for TTF units carrying a rather h~gh formal
charge
[9].
The
t]l[rd type of overlap
(5'-4) involves a 38 ° nwist and implies an ~nteractio,
of molecular orbitals
which
is not favorable
for metal-like band formation.
The resistivity as a function of reciprocal radical salt is presented
in Fig. 4.
displayed a room temperature
temperature
for this cation-
The sample used for the measurements
conductivity of ~.7 x 10 -4 S.cm -I and was
s e m i c o n d u c t i n g with a calculated activation energy of 0.173 eV. irregularity as described probably responsible Unfortunately,
above and the associated charge
neutral
and charged TTF ,mits.
five TTF units carry a net charge or 4+.
I.
By
The central TTF of a
and the others singly charged, but a more even charge
is also possible.
.,
Fig.
are
the low precision associated with the bond lengths within TTF
trimer may be neutral d~stribution
locallzations
for the rather low conductivity of the crystals.
units does not allow distinction between charge balance
The stacking
Unique half of Hg6(SCN)I6
anion with bond distances.
r-t
o
o
n,
c~
t~
I
b~
L~ U3
LYI
h-i CO
BI9
Fig. 3.
Packing viewed along a axis.
6
OJ
5
4
~ a
--
'
I
I
I
4 5 6 Temperature (1/K x 1000)
Fig. 4.
Variation
of resistivity
with temperature.
B20 TABLE 1 Fractional atomic coordinates and thermal parameters.
Atom Hgl Hg2 Hg3 $11 S12 $21 $22 $23 $31 $32 $33 NIl NI2 N21 N22 N23 N31 N32 N33 CII C12 C21 C22 C23 C31 C32 C33 $41 $42 $43 $44 C41 C42 C43 C44 C45 C46 $51 $52 $53 $54 C51 C52 C53 C54 C55 C56 $61 $62 C61 C62 C63
x 0.48575(6) 0.99799(6) 0.99679(7) 0.3329(4) 0.6474(4) 1.1128(4) 0.8425(4) 0.9973(5) 1.1350(4) 0.8596(4) 0.4900(4) 0.353(2) 0.6262(13) 1.122(2) 0.8849(13) 1.0694(13) 0.5822(13) 0.9199(13) 0.4353(12) 0.3485(14) 0.6329(13) 1.113(2) 0.8721(14) 1.0369(13) 1.1020(14) 0.8984(14) 0.4591(14) 0.9349(4) 0.8613(4) 1.1483(4) 1.0753(4) 0.9584(14) 1.0490(13) 0.811(2) 0.779(2) 1.2306(15) 1.198(2) 0.4156(4) 0.3523(4) 0.6~06(4) 0.5723(4) 0.4431(13) 0.5374(13) 0.295(2) 0.267(2) 0.7188(15) 0.692(2) 0.1338(5) 0.0871(4) 0.0470(13) 0.228(2) 0.207(2)
y 0.16426(6) 0.34207(6) 0.32889(6) 0.1781(5) 0.1721(4) 0.2543(4) 0.3216(4) 0.5319(4) 0.2703(4) 0.2596(4) 0.0300(3) 0.190(2) 0.2068(12) 0.332(2) 0.3239(11) 0.4267(11) 0.2617(12) 0.2301(11) 0.0775(10) 0.1823(13) 0.1898(12) 0.298(2) 0.3244(13) 0.4693(12) 0.2533(13) 0.2434(12) 0.0576(13) 0.1129(4) -0.0499(4) 0.0450(4) -0.1179(4) 0.0138(12) -0.0185(11) 0.1007(14) 0.0282(14) -0.0341(13) -0.1062(13) 0.6016(4) 0.4375(4) 0.5441(4) 0.3796(4) 0.5021(12) 0.4785(11) 0.588(2) 0.512(2) 0.4728(13) 0.3991(14) 0.0624(4) -0.1058(4) -0.0093(13) -0.004(2) -0.081(2)
z 0.39233(6) 0.05587(6) 0.71717(6) 0.2978(4) 0.4745(3) 0.1495(4) -0.0480(4) -0.1501(4) 0.8139(4) 0.6163(4) 0.6602(4) 0.146(2) 0.6264(12) 0.294(2) -0.1952(12) -0.0216(11) 0.9521(12) 0.4816(12) 0.4956(11) 0.2086(13) 0.5644(12) 0.233(2) -0.1325(13) -0.0762(12) 0.8950(13) 0.5361(13) 0.5651(13) 0.7850(4) 0.7606(4) 0.8456(4) 0.8199(4) 0.7872(12) 0.8153(12) 0.7438(14) 0.7361(14) 0.8659(13) 0.8538(13) 0.3719(4) 0.3652(4) 0.4351(4) 0.4266(4) 0.3866(11) 0.4124(11) 0.337(2) 0.3325(15) 0.4579(13) 0.4526(14) 0.0387(4) 0.0211(4) 0.0137(13) 0.064(2) 0.053(2)
Ueq/Uis o 104 451(4) 420(4) 502(4) 712(32) 453(22) 425(23) 484(24) 555(27) 513(26) 452(23) 508(25) 947(82) 546(55) 944(81) 512(52) 464(51) 556(55) 515(53) 389(46) 364(54) 279(49) 650(77) 363(53) 275(48) 372(55) 337(53) 353(54) 477(24) 440(23) 435(23) 494(25) 326(52) 264(48) 506(65) 472(61) 410(57) 419(58) 468(24) 504(25) 448(23) 445(23) 272(48) 260(48) 612(73) 542(67) 410(57) 468(61) 558(26) 536(26) 354(53) 568(68) 603(72)
B21 ACKNOWLEDGEMENTS Work at Argonne National Laboratory
is sponsored
Energy (DOE), Office of Basic Energy Sciences, under contract W-31-109-ENG-38. from the Technical Danish Natural student Programs Dakota,
University
participants
from Humboldt Grand Forks,
Division of Materials
N.T. is a Scientist of Denmark,
Science Research Council.
research
by the U.S. Department
sponsored
Lyngby, C.S.C.
in Residence
Sciences,
on leave
Denmark and supported
by the
and S.K. are undergraduate
by the Argonne Division
State University,
of
Arcata,
of Educational
CA, and University
of North
ND, respectively.
REFERENCES 1
K. Yakushi,
S. Nishimura,
T. Sugano and H. Kuroda,
Acta Crystallogr.,
B36
(1980) 358. 2
J.-P. Legros, M. Bousseau, Cr~st.,
3
100 (1983)
T. J. Kistenmacher, A. R. Siedle,
M. Rossi,
Inorg.
4
B. A. Scott,
5
H. Urayama,
6
K. D. Carlson,
L. Valade and P. Cassoux,
C. C. Chiang,
S. J. La Placa, J. B. Torrance,
B. D. Silverman and B. Welber,
(1977) 6631.
H. Yamochi,
S. Sato, K. Oshima,
G. Saito, K. Nozawa, T. Sugano, M. Kinoshita,
A. Kawamoto and J.
Tanaka,
Chem. Lett.,
(1988)
55.
U. Geiser, A. M. Kini, H. Wang, L. K. Montgomery,
W. K. Kwok, M. A. Beno, C. S. Cariss,
7
R. P. Van Duyne and
Chem., 1 9 (1980) 3604.
J° Am. Chem. Soc., 9 9
M. Evain,
Mol° Cryst. Liq.
181.
G. W. Crabtree,
M.-H. Whangbo and
Inorg. Chem., 27 (1988) 965.
S. Ggrtner,
E. Gogu,
Solid State Commun., 8
J. E. Schirber,
9
B. D. Silverman
and D. Schweltzer,
A. M. Kini, N. H. Wang, J. R. Whitworth,
Physica C, 152 (1988)
in Crystal Cohesion Springer-Verlag
T. Klutz,
1531.
E. L. Venturini,
and J. M. Williams,
R. M. Metzger,
I. Heinen, N. J. Keller, 65 (1988)
1981.
157.
and Conformational
Energies
ed.
BI5 "The submitted manuscript has been authored by a contractor of the U . S . Government under contact No, W-31-109-ENG-38. Accordingly, the U.S Government retains a nonexclusive, royaltyfree license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes."
CRYSTAL STRUCTURE AND ELECTRICAL
N. THORUP,
CONDUCTIVITY
M. A. BENO, C. S. CARISS,
OF (TTF)5Hg6(SCN)I6
K. D. CARLSON, U. GEISER,
S. KLEINJAN,
L. C. PORTER, H. H. WANG and J. M. WILLIAMS Chemistry and Materials Argonne National
Science Divisions
Laboratory,
Argonne,
Illinois 61)439 (U.S.A.)
ABSTRACT The crystal structure been determined. cell dimensions
and electrical
properties
The crystals are monoclinic, a = 15.032(3),
= 108.92(i) ° .
b = 16.846(5),
of (TTF)5Hg6(SCN)16
space group P21/a , with unit c = 17.364(3)
The TTF units are stacked along the c axis.
stacks, dimers and trimers alternate. well as non-bridging
SUN- ligands.
behavior with a room temperature
have
A and Within the
The complex anion contains bridging as
The crystals exhibit semicondncting
conductivity
of 8.7 x 10 -4 S'cm -1.
INTRODUCTION Tetrathiafulvalene anions.
(TTF) forms cation-radical
The structures
salts with many inorganic
of a number of such salts are already known,
(TTF)CIO 4 [I], (TTF)3(BF4) 2 [2] and (TTF)HgCI 3 [3]. form stacks,
but the electrical
irregularities
within
non-stoichiometric
BEDT-TTF,
of TTF, however,
rather unusual
Some
the anion Cu(SCN) 2- with
phase
[5-8], we have studied
crystal structure and conductivity composition
0379-6779/88/$3.50
localization.
eclipsed stacking of TTF [4].
Hg(SCN) 3- salts of TTF and BEDT-TTF.
the preparation,
often
are highly conducting which may be
by the recent success of combining
leading to a i0 K superconducting
corresponding
The TTF molecules
is usually rather low due to
the stacks which lead to electron
halides
related to the regular, Encouraged
conductivity
e.g.,
The present paper reports of a compound with the
(TTF)5Hg6(SCN)16.
© Elsevier Sequoia/Printed in The Netherlands
BI6
EXPERIMENTAL The title compound was prepared by slow diffusion of a 20 mL CH2CI 2 solution containing 600 mg of NBu4Hg(SCN) 3 (0.97 mmol), solution containing 24 mg of TTF (0.12 mmol).
into a I0 mL CH2CI 2
48.1 mg of good quality tiny
black needles mixed with small amounts of Hg were obtained.
Mp.
gingle crystal X-ray diffraction and conductivity measurements out on the as-grown needles.
127-129°C.
were carried
The crude product can be recrystallized
from
CH3CN. X-ray data were collected on a Syntex diffractometer Mo-radiation.
the full-matrix least squares refinement. tropically,
N and C atoms isotropically.
corrected for Lorentz, residuals:
using monochromated
3168 unique refle×ions with I>3o(I) and 4°<20<45 ° were used in Hg and S atoms were refined anisoNo H atoms were included.
polarization and absorption effects.
Data
Resultant
R = 0.055, wR = 0.058.
Resistivity measurements the temperature interval
as a function of temperature were carried out over
160-300 K using the standard four-probe
technique.
Lead contacts consisted of a silver paste securing gold wires to the surface of the crystal,
and temperature control and variation were obtained using a
closed-cycle helium refrigerator.
RESULTS The unit cell (see abstract) (TTF)5Hg6(SCN)I6. included on Figs.
contains
Atomic coordinates are given in Table i.
Bond lengths are
1 and 2, which also show the atomic numbering.
a packing diagram of the structure. the c axis (spaced by c/3). to four SCN- ions if Hg-(S,N) SCN
two formula units of
Figure 3 is
The Hg atoms are nearly lined up along
Each of the three unique Hg atoms is coordinated distances up to 2.80 % are considered.
Some
ions are bonded to one Hg only (via S) whereas others form bridges
between Hg atoms bonding via S as well as N (Figs. anion, Hg6(SCN)164-,
contains
1 and 3).
The complex
three Hg atoms on one line connected to three Hg
atoms on another llne with a center of symmetry between the two halves. The TTF units form one-dimensional
stacks along the c axis.
These stacks
fit into channels formed by the anions, and no stack has any S..-S contacts shorter than 3.6 % to surrounding anions.
Within a stack the planar TTF units
are almost parallel with interstack distances 3.46, 3.47 and 3.49 %, i.e., nearly equidistant
spacing.
However,
differences
in molecular overlap between
BI7 neighbur[qg TTF units
indicate a separation
are three un[que TTF units
into d[mers aud tr[~ ~ ,o
(actL~ally 2 1/2) which are d e s i g n a t e d 4, 5 and & in
accordance with the atomic numbering scheme. units
Ynec,
related by a center of symmetry.
The dimer
The trimer
is formed by two TT!-~
[s formed by one TTF-6 unit
lc)cated at a center of symmetry and sandwiched between two symmetry related TTF-4 units.
The molecular overlaps within a dimer
(4-6) are similar and close to eclipsed, mode or overlap
(5-5') and within a tr[mer
which is supposed
to be a preferred
for TTF units carrying a rather h~gh formal
charge
[9].
The
t]l[rd type of overlap
(5'-4) involves a 38 ° nwist and implies an ~nteractio,
of molecular orbitals
which
is not favorable
for metal-like band formation.
The resistivity as a function of reciprocal radical salt is presented
in Fig. 4.
displayed a room temperature
temperature
for this cation-
The sample used for the measurements
conductivity of ~.7 x 10 -4 S.cm -I and was
s e m i c o n d u c t i n g with a calculated activation energy of 0.173 eV. irregularity as described probably responsible Unfortunately,
above and the associated charge
neutral
and charged TTF ,mits.
five TTF units carry a net charge or 4+.
I.
By
The central TTF of a
and the others singly charged, but a more even charge
is also possible.
.,
Fig.
are
the low precision associated with the bond lengths within TTF
trimer may be neutral d~stribution
locallzations
for the rather low conductivity of the crystals.
units does not allow distinction between charge balance
The stacking
Unique half of Hg6(SCN)I6
anion with bond distances.
r-t
o
o
n,
c~
t~
I
b~
L~ U3
LYI
h-i CO
BI9
Fig. 3.
Packing viewed along a axis.
6
OJ
5
4
~ a
--
'
I
I
I
4 5 6 Temperature (1/K x 1000)
Fig. 4.
Variation
of resistivity
with temperature.
B20 TABLE 1 Fractional atomic coordinates and thermal parameters.
Atom Hgl Hg2 Hg3 $11 S12 $21 $22 $23 $31 $32 $33 NIl NI2 N21 N22 N23 N31 N32 N33 CII C12 C21 C22 C23 C31 C32 C33 $41 $42 $43 $44 C41 C42 C43 C44 C45 C46 $51 $52 $53 $54 C51 C52 C53 C54 C55 C56 $61 $62 C61 C62 C63
x 0.48575(6) 0.99799(6) 0.99679(7) 0.3329(4) 0.6474(4) 1.1128(4) 0.8425(4) 0.9973(5) 1.1350(4) 0.8596(4) 0.4900(4) 0.353(2) 0.6262(13) 1.122(2) 0.8849(13) 1.0694(13) 0.5822(13) 0.9199(13) 0.4353(12) 0.3485(14) 0.6329(13) 1.113(2) 0.8721(14) 1.0369(13) 1.1020(14) 0.8984(14) 0.4591(14) 0.9349(4) 0.8613(4) 1.1483(4) 1.0753(4) 0.9584(14) 1.0490(13) 0.811(2) 0.779(2) 1.2306(15) 1.198(2) 0.4156(4) 0.3523(4) 0.6~06(4) 0.5723(4) 0.4431(13) 0.5374(13) 0.295(2) 0.267(2) 0.7188(15) 0.692(2) 0.1338(5) 0.0871(4) 0.0470(13) 0.228(2) 0.207(2)
y 0.16426(6) 0.34207(6) 0.32889(6) 0.1781(5) 0.1721(4) 0.2543(4) 0.3216(4) 0.5319(4) 0.2703(4) 0.2596(4) 0.0300(3) 0.190(2) 0.2068(12) 0.332(2) 0.3239(11) 0.4267(11) 0.2617(12) 0.2301(11) 0.0775(10) 0.1823(13) 0.1898(12) 0.298(2) 0.3244(13) 0.4693(12) 0.2533(13) 0.2434(12) 0.0576(13) 0.1129(4) -0.0499(4) 0.0450(4) -0.1179(4) 0.0138(12) -0.0185(11) 0.1007(14) 0.0282(14) -0.0341(13) -0.1062(13) 0.6016(4) 0.4375(4) 0.5441(4) 0.3796(4) 0.5021(12) 0.4785(11) 0.588(2) 0.512(2) 0.4728(13) 0.3991(14) 0.0624(4) -0.1058(4) -0.0093(13) -0.004(2) -0.081(2)
z 0.39233(6) 0.05587(6) 0.71717(6) 0.2978(4) 0.4745(3) 0.1495(4) -0.0480(4) -0.1501(4) 0.8139(4) 0.6163(4) 0.6602(4) 0.146(2) 0.6264(12) 0.294(2) -0.1952(12) -0.0216(11) 0.9521(12) 0.4816(12) 0.4956(11) 0.2086(13) 0.5644(12) 0.233(2) -0.1325(13) -0.0762(12) 0.8950(13) 0.5361(13) 0.5651(13) 0.7850(4) 0.7606(4) 0.8456(4) 0.8199(4) 0.7872(12) 0.8153(12) 0.7438(14) 0.7361(14) 0.8659(13) 0.8538(13) 0.3719(4) 0.3652(4) 0.4351(4) 0.4266(4) 0.3866(11) 0.4124(11) 0.337(2) 0.3325(15) 0.4579(13) 0.4526(14) 0.0387(4) 0.0211(4) 0.0137(13) 0.064(2) 0.053(2)
Ueq/Uis o 104 451(4) 420(4) 502(4) 712(32) 453(22) 425(23) 484(24) 555(27) 513(26) 452(23) 508(25) 947(82) 546(55) 944(81) 512(52) 464(51) 556(55) 515(53) 389(46) 364(54) 279(49) 650(77) 363(53) 275(48) 372(55) 337(53) 353(54) 477(24) 440(23) 435(23) 494(25) 326(52) 264(48) 506(65) 472(61) 410(57) 419(58) 468(24) 504(25) 448(23) 445(23) 272(48) 260(48) 612(73) 542(67) 410(57) 468(61) 558(26) 536(26) 354(53) 568(68) 603(72)
B21 ACKNOWLEDGEMENTS Work at Argonne National Laboratory
is sponsored
Energy (DOE), Office of Basic Energy Sciences, under contract W-31-109-ENG-38. from the Technical Danish Natural student Programs Dakota,
University
participants
from Humboldt Grand Forks,
Division of Materials
N.T. is a Scientist of Denmark,
Science Research Council.
research
by the U.S. Department
sponsored
Lyngby, C.S.C.
in Residence
Sciences,
on leave
Denmark and supported
by the
and S.K. are undergraduate
by the Argonne Division
State University,
of
Arcata,
of Educational
CA, and University
of North
ND, respectively.
REFERENCES 1
K. Yakushi,
S. Nishimura,
T. Sugano and H. Kuroda,
Acta Crystallogr.,
B36
(1980) 358. 2
J.-P. Legros, M. Bousseau, Cr~st.,
3
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