Orientational disorder in the one-dimensional coordination polymer catena-poly[[bis­(acetyl­acetonato-κ2O,O′)cobalt(II)]-μ-1,4-di­aza­bicyclo­[2.2.2]octane-κ2N1:N4]

Dumitru, F.; Englert, U.; Braun, B.

doi:10.1107/S205698901600428X

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ISSN: 2056-9890

Volume 72| Part 4| April 2016| Pages 548-551

https://doi.org/10.1107/S205698901600428X

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Orientational disorder in the one-dimensional coordination polymer catena-poly[[bis(acetylacetonato-κ²O,O′)cobalt(II)]-μ-1,4-diazabicyclo[2.2.2]octane-κ²N¹:N⁴]

Florina Dumitru,^a Ulli Englert ^b and Beatrice Braun ^c ^*

^aFaculty of Applied Chemistry and Materials Science, University Politehnica of Bucharest, Polizu 1, RO-011061 Bucharest, Romania, ^bInstitute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany, and ^cInstitute of Chemistry, Humboldt University of Berlin, Brook-Taylor-Strasse 2, D-12489 Berlin, Germany
^*Correspondence e-mail: beatrice.braun@hu-berlin.de

Edited by M. Weil, Vienna University of Technology, Austria (Received 1 March 2016; accepted 13 March 2016; online 31 March 2016)

The title compound, [Co(C₅H₇O₂)₂(C₆H₁₂N₂)]_n, was obtained as a one-dimensional coordination polymer from bis(acetylacetonato)diaquacobalt(II), [Co(acac)₂(OH₂)₂], and 1,4-diazabicyclo[2.2.2]octane (DABCO), a diamine with good bridging ability and rod-like spacer function. In the chain complex that extends along the c axis, the Co^II atom is six-coordinated, the O-donor atoms of the chelating acac ligands occupying the equatorial positions and the bridging DABCO ligands being in trans-axial positions. In the crystal structure, the DABCO ligand is conformationally disordered in a 50:50 manner as a result of its location across a crystallographic mirror plane. The metal–metal distance is very close to that in a related compound exhibiting weak antiferromagnetic exchange between the Co^II ions, and the title compound can thus be useful for obtaining more information about the contribution of different bridges to the magnetic coupling between paramagnetic ions.

Keywords: crystal structure; one-dimensional coordination polymer; orientational disorder; acetylacetonate complexes; cobalt(II); DABCO; magnetic behaviour.

CCDC reference: 1454848

1. Chemical context

Self-assembly of coordination polymers from simple building blocks is of considerable interest due to their diverse architectures and potential applications in catalysis and advanced materials, such as magnetic, optic and electronic materials.

In this paper, two simple building blocks, namely 1,4-diazabicyclo[2.2.2]octane (DABCO), a diamine with good bridging ability and rod-like spacer function, and the unsaturated square-planar metal complex bis(acetylacetonato-κ²O,O′)cobalt(II), [Co(acac)₂], have been chosen to design a one-dimensional coordination polymer in which the paramagnetic Co^II ions are separated by a distance of 7.2328 (7) Å. This metal–metal distance is very close to the distance of 7.267 (3) Å reported by Ma et al. (2001 ) for the structurally related [Co(acac)₂(pyrazine)]_n compound which exhibits weak antiferromagnetic exchange between the Co^II ions.

Within this context, the title compound catena-poly[[bis(acetylacetonato-κ²O,O′)cobalt(II)]-μ-1,4-diazabicyclo[2.2.2]octane-κ²N¹:N⁴], [Co(acac)₂(DABCO)]_n, (I), can serve for a comparative investigation of the magnetic behaviour of analogous compounds and, thus, allow more information about the contribution of different bridges to the magnetic coupling between paramagnetic ions to be obtained.

2. Structural commentary

In the crystalline state, the title compound, (I), represents a one-dimensional coordination polymer self-assembled from bis(acetylacetonato)cobalt(II) units as metal–complex connectors and 1,4-diazabicyclo[2.2.2]octane (DABCO) as linkers.

The acetylacetonate (acac) ligand, which is the deprotonated form of acetylacetone (pentane-2,4-dione, acacH), is a well-known mononegative O,O′-chelating donor agent and its metal coordination chemistry is well documented [for reviews on the coordination chemistry of acac ligands, see: Aromí et al. (2008 ); Bray et al. (2007 ); Vigato et al. (2009 )]. For DABCO, the bridging coordination behaviour is most exploited for the generation of coordination polymers and metal–organic frameworks (MOFs), with Zn²⁺ being the most common metal ion used in these structures [for representative examples, see: Furukawa et al. (2009 ); Uemura et al. (2007 )].

The complex crystallizes in the orthorhombic Pnnm space group with the metal atom on a special position with site symmetry ..2/m. The Co^II atom shows an octahedral environment defined by four equatorial acac O atoms on a mirror plane, with bond lengths ranging from 2.0299 (10) to 2.0411 (10) Å, and with two N atoms of bridging DABCO groups on a twofold rotation axis in the axial positions at distances of 2.3071 (12) Å (Fig. 1).

Figure 1
A section of the coordination polymer of (I)

. Only one of the 50:50 DABCO disorder forms and one orientation of the disordered acac methyl groups are shown. Displacement ellipsoids are drawn at the 50% probability level and H atoms are represented by circles. [Symmetry codes: (a) −x, −y, −z; (c) x, y, −z + 1; (d) −x, −y, −z + 1.]

3. Supramolecular features

The centrosymmetric DABCO ligand is bonded to two [Co(acac)₂] units, which gives rise to the formation of chains extending along the c axis (Fig. 2). The individual chains run parallel in the crystal and do not interact with each other. This polymer is essentially a one-dimensional coordination polymer, the only structural motif that is present being based on the Co^II coordination requirements.

Figure 2
The molecular packing of the coordination polymer chains.

4. Database survey

Although some polymeric complexes of the form [Co(acac)₂(μ-diamine)]_n [diamine = NH₂–R–NH₂, with R = C_yH_2y+1 (y = 6, 11, 12; Fine, 1973 ), piperazine (Pellacani et al., 1973 ), 2,5-dimethylpyrazine (Blake & Hatfield, 1978 ), and 1,2-bis(4-pyridyl)ethane and trans-1,2-bis(4-pyridyl)ethylene (Atienza et al., 2008 )] have been synthesized over the years, their structures were elucidated only on the basis of spectroscopic and magnetic analyses. [Co(acac)₂(μ-diamine)]_n complexes similar in structure to the title compound, with square-planar [Co(acac)₂] units connected by bridging diamine ligands into infinite linear chains, were retrieved from the Cambridge Structural Database (CSD, Version 5.36 of November 2014; Groom & Allen, 2014 ), viz. [Co(acac)₂{μ-1,3-bis(pyridin-4-yl)propane}]_n (Lennartson & Håkansson, 2009 ), [Co(acac)₂(pyrazine)]_n and [Co(acac)₂(4,4′-bipyridine)]_n (Ma et al., 2001).

5. Synthesis and crystallization

[Co(acac)₂(H₂O)₂] was prepared by precipitation of CoCl₂·6H₂O with aqueous ammonia, followed by solubilization and complexation with acetylacetone. Elemental analysis calculated for [Co(C₅H₇O₂)₂(H₂O)₂] (%): C 40.96, H 6.14; found: C 40.94, H 6.19.

[Co(acac)₂(H₂O)₂] (293 mg, 1 mmol) and 1,4-diazabicyclo[2.2.2]octane (DABCO) (112 mg, 1 mmol) were stirred in CH₃OH (15 ml) at 333 K for 1 h. The pink precipitate which formed was collected by filtration and redissolved in dimethyl sulfoxide (DMSO, 5 ml). Elemental analysis calculated for [Co(acac)₂(DABCO)] (%): C 52.04, H 7.05, N 7.59; found: C 51.63, H 7.39, N 7.41. Layering the solution of the complex in DMSO with CH₃OH at 293 K gave pale-pink crystals suitable for X-ray single-crystal analysis.

Elemental analyses were carried out on a Heraeus CHNO Rapid apparatus (Institute of Inorganic Chemistry, RWTH Aachen University).

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. Space filling more symmetric than atom positions leads to pronounced orientational disorder (Herberich et al., 1993 ) for the DABCO ligand over two positions due to mirror symmetry. As a result, the site occupancies of the C atoms are constrained to 0.5. In principle, the same should be true for the associated H atoms, their alternative positions for the different C positions overlap very closely, thus forming the hexagon of local residual electron-density maxima about the C-atom scaffold shown in Fig. 3. These maxima can be freely refined as H atoms with reasonable C—H geometry and displacement parameters.

Table 1
Experimental details

Crystal data
Chemical formula	[Co(C₅H₇O₂)₂(C₆H₁₂N₂)]
M_r	369.32
Crystal system, space group	Orthorhombic, Pnnm
Temperature (K)	100
a, b, c (Å)	7.7468 (3), 15.1573 (4), 7.2328 (7)
V (Å³)	849.28 (9)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	1.03
Crystal size (mm)	0.48 × 0.10 × 0.04

Data collection
Diffractometer	Stoe IPDS 2T
Absorption correction	Multi-scan (MULABS in PLATON; Spek, 2003 )
T_min, T_max	0.637, 0.960
No. of measured, independent and observed [I > 2σ(I)] reflections	11457, 1045, 944
R_int	0.045
(sin θ/λ)_max (Å⁻¹)	0.649

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.020, 0.055, 1.09
No. of reflections	1045
No. of parameters	81
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.25, −0.39
Computer programs: X-AREA (Stoe & Cie, 2002 ), X-RED (Stoe & Cie, 2002), SHELXS2013 (Sheldrick, 2008 ), SHELXL2014 (Sheldrick, 2015 ), DIAMOND (Brandenburg, 1999 ), Mercury (Macrae et al., 2006 ), PLATON (Spek, 2009 ) and publCIF (Westrip, 2010 ).

Figure 3
Difference-density Fourier synthesis in the ab plane through three DABCO C atoms before assignment of the DABCO H-atom positions; contour lines are drawn at 0.2 e A⁻³ intervals.

H atoms attached to C atoms were calculated, introduced in their idealized positions and treated as riding, with C—H = 0.95 Å and U_iso(H) = 1.5U_eq(C) for methyl H atoms and U_iso(H) = 1.2U_eq(C) otherwise. For consistency, we opted to calculate the positions of the DABCO H atoms and fix them in their idealized positions. Due to the fact that the acac ligand lies on a mirror plane, the acac methyl groups are therefore equally disordered over two orientations.

Supporting information

CCDC reference: 1454848

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S205698901600428X/wm5278sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S205698901600428X/wm5278Isup2.hkl

checkCIF report

Computing details top

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA (Stoe & Cie, 2002); data reduction: X-RED (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS2013 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 1999) and Mercury (Macrae et al., 2006); software used to prepare material for publication: PLATON (Spek, 2009) and publCIF (Westrip, 2010).

catena-Poly[[bis(acetylacetonato-κ²O,O')cobalt(II)]-µ-1,4-diazabicyclo[2.2.2]octane-κ²N¹:N⁴] top

Crystal data top

[Co(C₅H₇O₂)₂(C₆H₁₂N₂)]	D_x = 1.444 Mg m⁻³
M_r = 369.32	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pnnm	Cell parameters from 16455 reflections
a = 7.7468 (3) Å	θ = 3.8–29.5°
b = 15.1573 (4) Å	µ = 1.03 mm⁻¹
c = 7.2328 (7) Å	T = 100 K
V = 849.28 (9) Å³	Elongated plate, pale pink
Z = 2	0.48 × 0.10 × 0.04 mm
F(000) = 390

Data collection top

Stoe IPDS 2T diffractometer	1045 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	944 reflections with I > 2σ(I)
Plane graphite monochromator	R_int = 0.045
Detector resolution: 6.67 pixels mm^-1	θ_max = 27.5°, θ_min = 3.8°
rotation method scans	h = −10→10
Absorption correction: multi-scan (MULABS in PLATON; Spek, 2003)	k = −19→19
T_min = 0.637, T_max = 0.960	l = −8→9
11457 measured reflections

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.020	H-atom parameters constrained
wR(F²) = 0.055	w = 1/[σ²(F_o²) + (0.0389P)²] where P = (F_o² + 2F_c²)/3
S = 1.09	(Δ/σ)_max < 0.001
1045 reflections	Δρ_max = 0.25 e Å⁻³
81 parameters	Δρ_min = −0.39 e Å⁻³

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Co1	0.0000	0.0000	0.0000	0.00790 (10)
O1	0.24789 (12)	0.04561 (6)	0.0000	0.0122 (2)
O2	−0.08057 (13)	0.12744 (7)	0.0000	0.0173 (2)
N1	0.0000	0.0000	0.31898 (17)	0.0106 (3)
C1	0.29942 (18)	0.12455 (10)	0.0000	0.0134 (3)
C2	0.19083 (19)	0.19922 (9)	0.0000	0.0148 (3)
H2	0.2442	0.2557	0.0000	0.018*
C3	0.01048 (18)	0.19635 (10)	0.0000	0.0127 (3)
C4	−0.0887 (2)	0.28217 (9)	0.0000	0.0196 (3)
H4A	−0.1733	0.2817	0.1008	0.029*	0.5
H4B	−0.1488	0.2891	−0.1184	0.029*	0.5
H4C	−0.0085	0.3314	0.0176	0.029*	0.5
C5	0.49196 (18)	0.13858 (12)	0.0000	0.0228 (3)
H5A	0.5190	0.1944	−0.0619	0.034*	0.5
H5B	0.5481	0.0899	−0.0659	0.034*	0.5
H5C	0.5340	0.1405	0.1277	0.034*	0.5
C6	0.1745 (3)	−0.02067 (16)	0.3932 (3)	0.0167 (4)	0.5
H6A	0.2582	0.0237	0.3477	0.020*	0.5
H6B	0.2115	−0.0793	0.3477	0.020*	0.5
C7	−0.1237 (3)	−0.06034 (13)	0.3934 (3)	0.0155 (4)	0.5
H7A	−0.0975	−0.1206	0.3484	0.019*	0.5
H7B	−0.2402	−0.0442	0.3484	0.019*	0.5
C8	−0.0438 (3)	0.09127 (13)	0.3934 (3)	0.0142 (4)	0.5
H8A	−0.1589	0.1093	0.3477	0.017*	0.5
H8B	0.0420	0.1345	0.3477	0.017*	0.5

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Co1	0.01008 (15)	0.00601 (15)	0.00760 (15)	−0.00078 (8)	0.000	0.000
O1	0.0133 (5)	0.0109 (5)	0.0122 (5)	−0.0013 (4)	0.000	0.000
O2	0.0147 (5)	0.0089 (5)	0.0282 (6)	−0.0001 (4)	0.000	0.000
N1	0.0122 (6)	0.0114 (6)	0.0081 (5)	0.0000 (4)	0.000	0.000
C1	0.0158 (7)	0.0143 (7)	0.0102 (6)	−0.0041 (5)	0.000	0.000
C2	0.0195 (7)	0.0093 (6)	0.0156 (6)	−0.0036 (5)	0.000	0.000
C3	0.0202 (7)	0.0089 (7)	0.0089 (6)	0.0004 (5)	0.000	0.000
C4	0.0238 (8)	0.0106 (6)	0.0243 (8)	0.0022 (5)	0.000	0.000
C5	0.0151 (7)	0.0177 (8)	0.0355 (9)	−0.0031 (5)	0.000	0.000
C6	0.0143 (9)	0.0269 (10)	0.0090 (9)	0.0046 (8)	0.0003 (8)	0.0007 (8)
C7	0.0219 (10)	0.0169 (9)	0.0079 (9)	−0.0109 (8)	0.0005 (8)	−0.0015 (7)
C8	0.0252 (10)	0.0099 (9)	0.0075 (9)	0.0030 (7)	−0.0007 (8)	0.0006 (7)

Geometric parameters (Å, º) top

Co1—O2ⁱ	2.0299 (10)	C2—H2	0.9500
Co1—O2	2.0299 (10)	C3—C4	1.511 (2)
Co1—O1	2.0410 (10)	C4—H4A	0.9800
Co1—O1ⁱ	2.0411 (10)	C4—H4B	0.9800
Co1—N1	2.3071 (12)	C4—H4C	0.9800
Co1—N1ⁱ	2.3071 (12)	C5—H5A	0.9800
O1—C1	1.2612 (18)	C5—H5B	0.9800
O2—C3	1.2603 (18)	C5—H5C	0.9800
N1—C7ⁱⁱ	1.4299 (19)	C6—C6ⁱⁱⁱ	1.545 (4)
N1—C7	1.4299 (19)	C6—H6A	0.9900
N1—C6	1.488 (2)	C6—H6B	0.9900
N1—C6ⁱⁱ	1.488 (2)	C7—C7ⁱⁱⁱ	1.542 (4)
N1—C8	1.523 (2)	C7—H7A	0.9900
N1—C8ⁱⁱ	1.523 (2)	C7—H7B	0.9900
C1—C2	1.410 (2)	C8—C8ⁱⁱⁱ	1.541 (4)
C1—C5	1.5067 (19)	C8—H8A	0.9900
C2—C3	1.398 (2)	C8—H8B	0.9900

O2ⁱ—Co1—O2	180.0	O1—C1—C5	116.56 (13)
O2ⁱ—Co1—O1	91.89 (4)	C2—C1—C5	118.50 (14)
O2—Co1—O1	88.11 (4)	C3—C2—C1	124.83 (14)
O2ⁱ—Co1—O1ⁱ	88.11 (4)	C3—C2—H2	117.6
O2—Co1—O1ⁱ	91.89 (4)	C1—C2—H2	117.6
O1—Co1—O1ⁱ	180.0	O2—C3—C2	125.82 (14)
O2ⁱ—Co1—N1	90.0	O2—C3—C4	115.39 (13)
O2—Co1—N1	90.0	C2—C3—C4	118.79 (14)
O1—Co1—N1	90.0	C3—C4—H4A	109.5
O1ⁱ—Co1—N1	90.0	C3—C4—H4B	109.5
O2ⁱ—Co1—N1ⁱ	90.0	H4A—C4—H4B	109.5
O2—Co1—N1ⁱ	90.0	C3—C4—H4C	109.5
O1—Co1—N1ⁱ	90.0	H4A—C4—H4C	109.5
O1ⁱ—Co1—N1ⁱ	90.0	H4B—C4—H4C	109.5
N1—Co1—N1ⁱ	180.0	C1—C5—H5A	109.5
C1—O1—Co1	128.25 (9)	C1—C5—H5B	109.5
C3—O2—Co1	128.06 (9)	H5A—C5—H5B	109.5
C7ⁱⁱ—N1—C7	135.78 (17)	C1—C5—H5C	109.5
C7ⁱⁱ—N1—C6	52.41 (12)	H5A—C5—H5C	109.5
C7—N1—C6	109.78 (13)	H5B—C5—H5C	109.5
C7ⁱⁱ—N1—C6ⁱⁱ	109.78 (13)	N1—C6—C6ⁱⁱⁱ	111.15 (9)
C7—N1—C6ⁱⁱ	52.41 (12)	N1—C6—H6A	109.4
C6—N1—C6ⁱⁱ	137.70 (17)	C6ⁱⁱⁱ—C6—H6A	109.4
C7ⁱⁱ—N1—C8	55.60 (12)	N1—C6—H6B	109.4
C7—N1—C8	107.38 (12)	C6ⁱⁱⁱ—C6—H6B	109.4
C6—N1—C8	105.43 (13)	H6A—C6—H6B	108.0
C6ⁱⁱ—N1—C8	58.58 (12)	N1—C7—C7ⁱⁱⁱ	112.11 (9)
C7ⁱⁱ—N1—C8ⁱⁱ	107.38 (12)	N1—C7—H7A	109.2
C7—N1—C8ⁱⁱ	55.60 (12)	C7ⁱⁱⁱ—C7—H7A	109.2
C6—N1—C8ⁱⁱ	58.58 (12)	N1—C7—H7B	109.2
C6ⁱⁱ—N1—C8ⁱⁱ	105.43 (13)	C7ⁱⁱⁱ—C7—H7B	109.2
C8—N1—C8ⁱⁱ	138.58 (17)	H7A—C7—H7B	107.9
C7ⁱⁱ—N1—Co1	112.11 (9)	N1—C8—C8ⁱⁱⁱ	110.71 (8)
C7—N1—Co1	112.11 (9)	N1—C8—H8A	109.5
C6—N1—Co1	111.15 (9)	C8ⁱⁱⁱ—C8—H8A	109.5
C6ⁱⁱ—N1—Co1	111.15 (9)	N1—C8—H8B	109.5
C8—N1—Co1	110.71 (8)	C8ⁱⁱⁱ—C8—H8B	109.5
C8ⁱⁱ—N1—Co1	110.71 (8)	H8A—C8—H8B	108.1
O1—C1—C2	124.93 (13)

Co1—O1—C1—C2	0.0	Co1—N1—C6—C6ⁱⁱⁱ	179.998 (1)
Co1—O1—C1—C5	180.0	C7ⁱⁱ—N1—C7—C7ⁱⁱⁱ	−0.002 (1)
O1—C1—C2—C3	0.0	C6—N1—C7—C7ⁱⁱⁱ	55.94 (12)
C5—C1—C2—C3	180.0	C6ⁱⁱ—N1—C7—C7ⁱⁱⁱ	−79.70 (11)
Co1—O2—C3—C2	0.0	C8—N1—C7—C7ⁱⁱⁱ	−58.19 (11)
Co1—O2—C3—C4	180.0	C8ⁱⁱ—N1—C7—C7ⁱⁱⁱ	79.37 (10)
C1—C2—C3—O2	0.0	Co1—N1—C7—C7ⁱⁱⁱ	179.998 (1)
C1—C2—C3—C4	180.0	C7ⁱⁱ—N1—C8—C8ⁱⁱⁱ	−76.77 (11)
C7ⁱⁱ—N1—C6—C6ⁱⁱⁱ	77.79 (11)	C7—N1—C8—C8ⁱⁱⁱ	57.32 (11)
C7—N1—C6—C6ⁱⁱⁱ	−55.39 (11)	C6—N1—C8—C8ⁱⁱⁱ	−59.70 (11)
C6ⁱⁱ—N1—C6—C6ⁱⁱⁱ	−0.002 (1)	C6ⁱⁱ—N1—C8—C8ⁱⁱⁱ	77.23 (10)
C8—N1—C6—C6ⁱⁱⁱ	59.99 (10)	C8ⁱⁱ—N1—C8—C8ⁱⁱⁱ	0.000 (1)
C8ⁱⁱ—N1—C6—C6ⁱⁱⁱ	−77.99 (10)	Co1—N1—C8—C8ⁱⁱⁱ	180.000 (1)

Symmetry codes: (i) −x, −y, −z; (ii) −x, −y, z; (iii) x, y, −z+1.

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