Preparation of η2-complexes of fullerenes by reduction. Crystal structure and optical properties of {Ni(dppp)·(η2- C70)}·(C6H4Cl2)0.5

Article abstract of DOI:10.1039/c1dt10839e

The new reduction method for preparation of η²-complexes of fullerenes with nickel-1,3-bis(diphenylphosphino)propane has been developed in which Ni(dppp)Cl₂ and C₆₀(C₇₀) mixtures are reduced with sodium tetraphenylborate. Single crystals of the first η²-complex of nickel with fullerene C₇₀: {Ni(dppp)·(η²-C₇₀)}·(C₆H ₄Cl₂)_0.5 (1) (C₆H₄Cl ₂ = o-dichlorobenzene) have been obtained as well as the previously described complex with fullerene C₆₀: {Ni(dppp) ·(η²-C₆₀)}·(Solvent) (2). The crystal structure of 1 has been solved to show the coordination of nickel to the C-C bond of C₇₀ at the 6-6 ring junction of η²-type to form Ni-C(C₇₀) bonds of 1.929-1.941(2) A length, the shortest M-C bonds among those known for η²-complexes of fullerenes C ₆₀ and C₇₀. The length of the C-C bond to which Ni atom is coordinated (1.494(3) A) is noticeably longer than the average length of these bonds in C₇₀ (1.381(2) A). Optical spectra of 1 in the IR- and UV-visible ranges have been analyzed to show the splitting of some C₇₀ bands due to C₇₀ symmetry lowering. The complex has a red-brown color in solution and manifests three bands in the visible range at 379, 467 and 680 nm. The solution of 1 is air sensitive since air exposure restores the color and absorption bands of the starting C₇₀ at 383 and 474 nm.

Full text of DOI:10.1039/c1dt10839e

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PAPER
Preparation of g2-complexes of fullerenes by reduction. Crystal structure and
optical properties of {Ni(dppp)·(g2-C70)}·(C6H4Cl2)0.5†
Dmitri V. Konarev,*a Sergey V. Simonov,b Salavat S. Khasanovb and Rimma N. Lyubovskayaa
Received 4th May 2011, Accepted 23rd June 2011
DOI: 10.1039/c1dt10839e
2
The new reduction method for preparation of h -complexes of fullerenes
with nickel–1,3-bis(diphenylphosphino)propane has been developed in which Ni(dppp)Cl2 and
2
C60(C70) mixtures are reduced with sodium tetraphenylborate. Single crystals of the first h -complex of
2
nickel with fullerene C70: {Ni(dppp)·(h -C70)}·(C6H4Cl2)0.5 (1) (C6H4Cl2 = o-dichlorobenzene) have been
2
obtained as well as the previously described complex with fullerene C60: {Ni(dppp)·(h -C60)}·(Solvent)
(2). The crystal structure of 1 has been solved to show the coordination of nickel to the C–C bond of
2
˚
C70 at the 6–6 ring junction of h -type to form Ni–C(C70) bonds of 1.929–1.941(2) A length, the shortest
2
M–C bonds among those known for h -complexes of fullerenes C60 and C70. The length of the C–C
bond to which Ni atom is coordinated (1.494(3) A) is noticeably longer than the average length of these
˚
˚
bonds in C70 (1.381(2) A). Optical spectra of 1 in the IR- and UV-visible ranges have been analyzed to
show the splitting of some C70 bands due to C70 symmetry lowering. The complex has a red–brown color
in solution and manifests three bands in the visible range at 379, 467 and 680 nm. The solution of 1 is air
sensitive since air exposure restores the color and absorption bands of the starting C70 at 383 and 474 nm.
addition of Vaska-type compounds IrCOCl(R3E)2 (E = P, As, R =
Introduction
alkyl or aryl) to fullerenes.7
Fullerenes C60 and C70 contain several types of C–C bonds.
Shorter C–C bonds at the 6–6 ring junction behave as olefinic
units and transition metal compounds can coordinate to them by
Compounds containing positively charged metals coordinating
phosphine ligands are another wide family of metal complexes.16
They can easily be prepared by the interaction of metal salts of dif-
ferent metals (Ni2+, Co2+, Fe2+ and etc.) with phosphine ligands. We
2
h -bonding. As a result, fullerenes form a variety of transition-
metal complexes bonded by M–C coordination bonds.1–15 Those
were mainly prepared with C60,1–7 whereas relatively fewer such
complexes, among them complexes with platinum, palladium,
molybdenum and iridium, are known for C70.8–13 Several complexes
of C70 were structurally characterized as multiaddition prod-
2
developed a reduction method for preparation of h -coordination
complexes of fullerenes with nickel starting from (Ni(dppp)Cl2)
(dppp = 1,3-bis(diphenylphosphino)propane). Sodium fluorenone
was used as a reductant and the nickel-containing fullerene
2
complex {Ni(dppp)·(h -C60)}·(Solvent) (2) was obtained as single
2
2
14
2
2
2
2
crystals and structurally characterized.17 As sodium fluorenone is
extremely air-sensitive, and all manipulations with this reductant
require strictly anaerobic conditions, we thus searched for a more
convenient reductant to prepare nickel–fullerene coordination
complexes. It was shown18,19 that air-stable sodium tetraphenylb-
orate (NaBPh4) reduces C60 in a tetrahydrofuran–chlorobenzene
mixture producing ionic (M+)x·(THF)y·(C60-) (x = 0.39, y = 2.2;
M = Li, Na, K) complexes. This reagent can also be used to
generate nickel–fullerene coordination complexes for both C70
and C60. The reaction of a stoichiometric mixture of fullerene
(C70 or C60) and Ni(dppp)Cl2 with two equivalents of NaBPh4
(1 : 1 : 2 molar ratio) in o-dichlorobenzene (C6H4Cl2) yielded red–
brown and green solutions, respectively. Single crystals of the
coordination complexes can be obtained from the solutions by
ucts such as (h ,h -C70)·{(Me2PhP)2IrCOCl}2 and (h ,h ,h ,h -
C70)·{(Ph3P)2Pd}4.15 No coordination complexes of nickel with
fullerene C70 are known.
Generally, zerovalent compounds of nickel, platinum, palla-
dium, molybdenum, chromium and some other metals are used for
the preparation of fullerene coordination complexes, for example,
2
(Ph3P)2M(h -C2H4) (M = Pd, Pt), (R3P)4M (R = Et or Ph, M = Ni,
Pd, Pt) and others. Upon reaction the fullerene substitutes one or
two ligands in the coordination sphere of the transition metal.1–6
Another way of preparing fullerene coordination complexes is
aInstitute of Problems of Chemical Physics RAS, Chernogolovka, Moscow
region, 142432, Russia. E-mail: konarev@icp.ac.ru; Fax: +7-49652-21852
bInstitute of Solid State Physics RAS, Chernogolovka, Moscow region,
142432, Russia
2
slow diffusion of hexane. {Ni(dppp)·(h -C70)}·(C6H4Cl2)0.5 (1) is
† Electronic supplementary information (ESI) available: IR-spectra of
complex 1 and starting compounds. CCDC reference number 823121.
For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c1dt10839e
2
the first h -complex of nickel with fullerene C70 and here we
discuss its crystal structure and optical properties. The crystals
2
of {Ni(dppp)·(h -C60)}·(Solvent) (2) were isostructural to those of
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2
in such a way that bonds of this type only are involved in
previously described {Ni(dppp)·(h -C60)}·(C6H14)0.84·(C6H4Cl2)0.16
-
coordination.14,15 Moreover, dimerization of the C70· radical
(C6H14 = hexane) obtained by the reduction of Ni(dppp)Cl2–C60
anions21–23 and polymerization of the C70 dianions24,25 in ionic
2-
mixture with sodium fluorenone.17
compounds are also realized by carbon atoms involved in these
bonds. Thus, the C–C bonds at the 6–6 ring junction in C70 are
most active in coordination, dimerization and polymerization of
fullerene C70. Indeed, the Hu¨ckel molecular orbital calculations
showed26 that these bonds have one of the highest p-bond orders
among different C–C bonds of C70.
Results and discussion
The crystal structure of 1 was determined at 130(2) K and the
2
complex has a triclinic unit cell. The Ni(dppp)·(h -C70) units are
well ordered, whereas solvent C6H4Cl2 molecules are statistically
disordered between two orientations. Ni(dppp) coordinates to the
C–C bond of C70 at the 6–6 ring junction (Fig. 1). The bond
is similar to the 6–6 bonds of C60. Coordination is realized by
Fullerene C70 forms distorted hexagonal layers in 1 with six
neighbors for each C70 (Fig. 2a). Distances between the center of
˚
mass of fullerene C70 are 10.561 A along the [100] direction and
2
h -attachment to form two slightly different Ni–C(C60) bonds of
˚
10.012 A along the [001] direction (with one neighbor). In this case,
˚
lengths 1.927(2) and 1.940(2) A. These bonds are even shorter
multiple short van der Waals C ◊ ◊ ◊ C contacts are formed between
17
˚
than the length of the Ni–C bonds in 2 (1.948–1.951(2) A) and
˚
fullerenes in the 2.956–3.181 A range (Fig. 2a, green dashed
2
other known h -complexes of C60 and C70 fullerenes. According
to CCDC database the following lengths of the M–C bonds were
2
found for h -coordination complexes of fullerene C70: 2.11–2.12
˚
˚
˚
A for Pd, 2.07–2.15 A for Pt, 2.11–2.20 A for Ir and 2.27–
8–15
˚
2.30 A for Mo.
The Ni–P(dppp) distances are noticeably
˚
longer (2.1436(6) and 2.1519(6) A) than the Ni–C(C70) distances,
and the PNiP and CNiC angles are 99.06(2) and 45.41(8)◦,
˚
respectively. The C–C bond length (1.491(3) A) where Ni atom
is coordinated is noticeably longer than the average length of these
˚
bonds in C70 (1.381(2) A) and is probably caused by metal-to-
C70 p-back-donation.1 Similar elongation of the C–C bonds is
2
observed at the formation of various coordination (ML)·(h -C70)
units (1.460–1.522 A).8–15 The Ni coordination geometry is planar
˚
since all five atoms (nickel, two C70 carbon and two phosphorus
atoms bonded to nickel) are nearly coplanar with a maximum
˚
deviation of 0.011 A from the least-square plane. As a whole, the
2
geometry of the Ni(dppp)·(h -C70) units is similar to that of the
Ni(dppp)·(h -C60) units17 and the theoretically predicted geometry
2
2
of the (PH3)2Ni·(h -C60) units (predicted length of the Ni–C(C60)
20
˚
bonds is 1.989 A).
Fullerene C70 coordinates to metals by C–C bonds at the
6–6 ring junction8–13 and even multiaddition to C70 is realized
2
Fig. 2 Packing of the Ni(dppp)·(h -C70) units in 1. View along the [010]
direction on the fullerene layers (a) and along the [100] direction and
fullerene layers (b). Green dashed lines show the shortest van der Waals
C ◊ ◊ ◊ C contacts between fullerenes. Solvent molecules are not depicted for
clarity.
2
Fig. 1 Molecular structure of the Ni(dppp)·(h -C70) unit.
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lines). The center-to-center distances with three other neighbors
C70 under oxidation of Ni(dppp)·(h -C70) indicates that oxygen
˚
in the layer are essentially longer (10.66–12.30 A) and prevent the
can add to the Ni(dppp) fragment. The comparison of the
2
formation of van der Waals C ◊ ◊ ◊ C contacts between fullerenes
(Fig. 2a). The C70 molecules have denser packing in the layers of 1
than that of the C60 molecules in the layers of 2. This may be due to
smaller size of vacancies occupied by solvent molecules. Fullerene
layers are separated by bulky Ni(dppp) fragments (Fig. 2b).
The IR spectrum of 1 shows the absorption bands which can be
attributed to ten C70 modes, Ni(dppp) and solvent molecules (see
ESI†). It is known22 that the absorption band of C70 at 1430 cm-1
is sensitive to the charge state of C70 and shifts up to 1392–
Ni(dppp)·(h -C70) and the C70 spectra allows a conclusion that
the C70 band at 383 nm nearly disappears upon the formation of
the coordination complex, the band at 467 nm strongly increases in
intensity (possibly due to the appearance of a new band at 467 nm
or the increase in intensity and a slight shift of the C70 band at
474 nm), and a new broad band is manifested at 680 nm. Green
2
Ni(dppp)·(h -C60) has two new bands in the visible spectrum at
436 and 672 nm.17 Therefore, the coordination of metals to both
fullerenes C60 and C70 similarly changes their visible spectra. A
new band appears or the absorption increases at 430–470 nm and
weak broad bands are manifested at 670–680 nm.
∑
1394 cm-1 for C70 -. However, this band is not shifted in the
spectrum of 1. Rather, C70 and Ni(dppp) absorption bands
coincide and show one intense band at 1431 cm-1. Thus, no
noticeable increase in electron density on C70 is observed in 1. On
the contrary, two well separated bands at 1416 (C60) and 1434 cm-1
(Ni(dppp) were found in the spectrum of 2. The shift of the F1u(4)
mode of C60 (which is sensitive to the charge state of C60)27,28 from
1429 to 1416 cm-1 indicates the increase in electron density on
C60.17 The coordination of Ni(dppp) to C70 splits the band at 576
cm-1 into two bands at 573 and 579 cm-1 due to C70 symmetry
lowering. Similar splitting of the F1u(2) C60 mode at 576 cm-1 into
three bands at 573, 577 and 584 cm-1 is observed in the spectrum
of coordination complex 2.17
Conclusion
In this work we developed a new reduction method to pre-
pare nickel–fullerene coordination complexes from Ni(dppp)Cl2,
neutral fullerenes and sodium tetraphenylborate as a reductant.
Single crystals of the first coordination complex of nickel with
2
fullerene C70, {Ni(dppp)·(h -C70)}·(C6H4Cl2)0.5 (1), were synthe-
sized allowing its crystal structure determination. It was shown
that nickel forms unusually short Ni–C(C70) bonds of 1.929(2)
˚
and 1.941(2) A length. These bonds are slightly shorter than the
2
17
˚
Ni–C(C60) bonds in Ni(dppp)·(h -C60) of 1.948–1.951(2) A and
Starting C70 has a clear red color in o-dichlorobenzene. Upon
coordination of Ni(dppp) to C70 the color of the solution turns
red–brown. There are three bands in the UV-visible spectrum of
2
are the shortest metal–carbon bonds among known h -complexes
of both fullerenes C60 and C70. The C–C bond to which Ni atom
2
˚
is coordinated elongates to 1.494(3) A compared with the average
Ni(dppp)·(h -C70) in o-dichlorobenzene: a weak band at 379 nm,
˚
length of these bonds in C70 (1.381(2) A) probably due to p-back
an intense band at 467 nm and a broad weak band near 680 nm
(Fig. 3a). Similar visible spectra are observed for coordination
donation. However, the IR band of C70 at 1430 cm-1 which is
sensitive to the charged state of C70 is not shifted in the spectrum
of 1. The coordination of Ni(dppp) to C70 lowers its symmetry
and splits the C70 band at 576 cm-1 into two bands. The formation
2
complexes of C70 with other metals. For example, Pd(dppf)·(h -
2
C70) and Pt(dppf)·(h -C70) complexes (dppf is (diphenylphos-
phino)ferrocene) also manifest three bands in the visible spec-
trum with intense bands nearly at the same position (455 and
2
of Ni(dppp)·(h -C70) is accompanied by an increase in intensity
2
467 nm, respectively).13 We found that Ni(dppp)·(h -C70) is rather
of the band at 467 nm and the appearance of a new broad band
at 680 nm. Similar changes were observed at the formation of
sensitive to oxygen. As a result of oxidation, the bands observed
for the complex disappear and new bands attributed to starting
C70 are manifested at 383 and 474 nm (Fig. 3b). The formation of
Ni(dppp)·(h -C60) (two new bands appear at 436 and 672 nm).17
2
2
Ni(dppp)·(h -C70) is rather air sensitive in solution and is oxidized
by air to starting C70.
Experimental
Materials
Ni(dppp)Cl2 was purchased from Aldrich. C60 of 99.8% and C70 of
99% purity was received from MTR Ltd. Solvents were purified in
an argon atmosphere. o-Dichlorobenzene (C6H4Cl2) was distilled
over CaH2 under reduced pressure, benzene and hexane were
distilled over Na/benzophenone. KBr pellets for IR and solutions
of 1 and 2 for UV-visible spectra were prepared in a glove-box.
Synthesis
For preparation of complexes 1 and 2, a stoichiometric mixture of
Ni(dppp)Cl2 and fullerene was reduced by 2 equivalents of sodium
tetraphenylborate in 10 ml of o-dichlorobenzene. The ratio of
Ni(dppp)Cl2 : C70(C60) : NaBPh4 was 0.031 : 0.031 : 0.062 mmol
for 1 and 0.042 : 0.042: 0.084 mmol for 2. All the components
were dissolved at stirring for 5 h to yield clear red–brown
(1) and deep-green (2) solutions which were filtered. The
2
Fig. 3 UV-visible spectrum of (a) the Ni(dppp)·(h -C70) coordination
complex in o-dichlorobenzene solution measured in anaerobic conditions
and (b) of the solution of the complex exposed in the air (b). For attribution
of the bands see the text.
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2
crystals
of
{Ni(dppp)·(h -C70)}·(C6H4Cl2)0.5
(1)
and
Notes and references
2
{Ni(dppp)·(h -C60)}·(Solvent) (2) were obtained by the diffusion
of hexane layered over the o-dichlorobenzene solution during 1
month. The solvent was decanted from the crystals which were
washed with hexane to yield black pikes (1) and small well-shaped
black prisms (2). The crystals of 1 up to 0.2 ¥ 0.3 ¥ 0.5 mm3 size
were obtained in 50–60% yield.
The composition of 1 was determined from X-ray diffraction on
a single crystal. Several crystals tested from the synthesis had the
same unit cell parameters and were attributed to one crystal phase.
The crystals of 2 were isostructural to those of the previously
1 P. J. Fagan, J. C. Calabrese and B. Malone, Acc. Chem. Res., 1992, 25,
134.
2 A. L. Balch and M. M. Olmstead, Chem. Rev., 1998, 98, 2123.
3 P. J. Fagan, J. C. Calabrese and B. Malone, Science, 1991, 252, 1160.
4 V. V. Bashilov, P. V. Petrovskii, V. I. Sokolov, S. V. Lindeman, I. A.
Guzey and Yu. T. Struchkov, Organometallics, 1993, 12, 991.
5 L.-C. Song, G.-A. Yu, Q.-M. Hu, C.-M. Che, N. Zhu and J.-S. Huang,
J. Organomet. Chem., 2006, 691, 787.
6 Yu. A. Shevelev, G. V. Markin, D. V. Konarev, G. K. Fukin, M. A.
Lopatin, A. S. Shavyrin, E. V. Baranov, R. N. Lyubovskaya and G. A.
Domrachev, Dokl. Chem., 2007, 412, 18.
7 A. L. Balch, V. J. Catalano and J. W. Lee, Inorg. Chem., 1991, 30, 3980.
8 M. M. Olmstead, L. Hao and A. L. Balch, J. Organomet. Chem., 1999,
578, 85.
9 A. L. Balch, V. J. Catalano, J. W. Lee, M. M. Olmstead and S. R. Parkin,
J. Am. Chem. Soc., 1991, 113, 8953.
2
described complex {Ni(dppp)·(h -C60)}·(C6H14)0.84·(C6H4Cl2)0.16
(C6H14: hexane, C6H4Cl2: o-dichlorobenzene).17
General
10 H.-F. Hsu, Y. Du, T. E. Albrecht-Schmitt, S. R. Wilson and J. R.
Shapley, Organometallics, 1998, 17, 1756.
FT-IR spectra were measured in KBr pellets with a Perkin-Elmer
1000 Series spectrometer (400–7800 cm-1). The visible spectrum in
the range 400–900 nm was measured on a Specord M40.
11 P. Cui, L. Li, K. Tang and X. Jin, J. Chem. Res., 2001, 240.
12 A. L. Balch, D. A. Costa and M. M. Olmstead, Chem. Commun., 1996,
2449.
13 L.-C. Song, G.-F. Wang, P.-C. Liu and Q.-M. Hu, Organometallics,
2003, 22, 4593.
X-Ray crystal structure determination
14 A. L. Balch, J. W. Lee and M. M. Olmstead, Angew. Chem., Int. Ed.
Engl., 1992, 31, 1356.
X-Ray diffraction data for 1 (see ESI†) were collected at 130(2)
K on an Oxford diffraction “Gemini-R” CCD diffractometer
with graphite monochromated Mo-Ka radiation using an Oxford
Instrument Cryojet system. Raw data reduction on F2 was carried
out using CrysAlisPro, Oxford Diffraction Ltd. The structures
were solved by the direct method29 and refined by the full-
matrix least-squares method against F2 using SHELX-97.30 Non-
hydrogen atoms were refined in the anisotropic approximation.
Positions of hydrogen atoms were calculated geometrically. Sub-
sequently, the positions of H atoms were refined by the “riding”
model with Uiso = 1.2Ueq of the connected non-hydrogen atom or
as ideal CH3 groups with Uiso = 1.5Ueq.
15 A. L. Balch, L. Hao and M. M. Olmstead, Angew. Chem., Int. Ed.
Engl., 1996, 35, 188.
16 W. Levason, Phosphine Complexes of Transition Metals, in The
Chemistry of Organophosphorus Compounds, ed. F. R. Hartley, Wiley,
New York, 1990, vol. 1, pp. 568–641.
17 D. V. Konarev, S. S. Khasanov, E. I. Yudanova and R. N. Lyubovskaya,
Eur. J. Inorg. Chem., 2011, 816.
18 H. Moriyama, H. Kobayashi, A. Kobayashi and T. Watanabe, Chem.
Phys. Lett., 1995, 238, 116.
19 H. Moriyama, M. Abe, H. Motoki, T. Watanabe, S. Hayashi and H.
Kobayashi, Synth. Met., 1998, 94, 167.
20 F. Nunzi, A. Sgamellotti, N. Re and C. Floriani, Organometallics, 2000,
19, 1628.
21 D. V. Konarev, S. S. Khasanov, I. I. Vorontsov, G. Saito, Yu. A. Antipin,
A. Otsuka and R. N. Lyubovskaya, Chem. Commun., 2002, 2548.
22 D. V. Konarev, S. S. Khasanov, G. Saito, A. Otsuka, Y. Yoshida and R.
N. Lyubovskaya, J. Am. Chem. Soc., 2003, 125, 10074.
23 D. V. Konarev, S. S. Khasanov, S. V. Simonov, E. I. Yudanova and R.
N. Lyubovskaya, CrystEngComm, 2010, 12, 3542.
24 H. Brumm, E. Peter and M. Jansen, Angew. Chem., Int. Ed., 2001, 40,
2069.
25 U. Wedig, H. Brumm and M. Jansen, Chem.–Eur. J., 2002, 8, 2769.
26 R. Taylor, J. Chem. Soc., Perkin Trans. 2, 1993, 813.
27 T. Picher, R. Winkler and H. Kuzmany, Phys. Rev. B: Condens. Matter,
1994, 49, 15879.
Crystallographic data for 1. C100H28ClNiP2, Mr = 1385.32
-1
¯
g mol , black, triclinic, space group P1, a = 10.5609(6), b =
˚
14.0596(7), c = 19.8880(10) A, a = 100.191(4), b = 97.361(4), g =
◦
3
-3
˚
97.999(4) , V = 2842.6(3) A , Z = 2, Dc = 1.619 g cm , F(000) =
1406, m = 0.509 mm-1, T = 130(2) K, max. 2q = 62.52◦, Rint
=
0.0386, Reflections I > 2s(I) = 13129, R1 = 0.0558 [I > 2s(I)],
wR2 = 0.1530, restraints/parameters 0/926, GOF = 1.036.
28 N. V. Semkin, N. G. Spitsina, S. Krol and A. Graja, Chem. Phys. Lett.,
1996, 256, 616.
29 M. C. Burla, M. Camalli, B. Carrozzini, G. L. Cascarano, C. Giacov-
azzo, G. Polidori and R. Spagna, J. Appl. Crystallogr., 2003, 36, 1103.
30 G. M. Sheldrick, SHELX97, University of Go¨ttingen, Germany, 1997.
Acknowledgements
The work was supported by the RFBR grant No. 09-02-01514.
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