Crystal structure of di-μ-hydroxido-κ4O:O-bis[bis(acetyl­acetonato-κ2O,O′)cobalt(III)]

Richers, C.P.; Bertke, J.A.; Rauchfuss, T.B.

doi:10.1107/S2056989015013663

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Volume 71| Part 8| August 2015| Pages 983-985

https://doi.org/10.1107/S2056989015013663

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Crystal structure of di-μ-hydroxido-κ⁴O:O-bis[bis(acetylacetonato-κ²O,O′)cobalt(III)]

Casseday P. Richers,^a Jeffery A. Bertke ^a ^* and Thomas B. Rauchfuss ^a

^aSchool of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
^*Correspondence e-mail: jbertke@illinois.edu

Edited by M. Weil, Vienna University of Technology, Austria (Received 9 July 2015; accepted 17 July 2015; online 29 July 2015)

The dinuclear title complex, [Co₂(C₅H₇O₂)₄(μ-OH)₂] or [Co(acac)₂(μ-OH)]₂, where acac is acetylacetonate, is centrosymmetric with half of the molecule per asymmetric unit. The molecular structure is a dimer of octahedrally coordinated Co^III atoms with four O atoms from two chelating acac ligands and two O atoms from bridging hydroxide ligands. The crystal packing features weak C—H⋯O interactions between neighboring molecules, leading to the formation of chains normal to the ac plane. The hydroxide H atoms are not involved in hydrogen bonding because of the bulky acac ligands. This is the first crystal structure reported of a dimeric transition metal bis-acac complex with OH⁻ as the bridging group.

Keywords: crystal structure; cobalt(III); acac ligand; bridging hydroxide ligand.

CCDC reference: 1413567

1. Chemical context

Well-defined cobalt(III) hydroxide complexes are relatively rare, especially in the absence of amine ligands (Bryndza & Tam, 1988 ). One of the earliest examples is [Co(acac)₂(μ-OH)]₂ (acac is acetylacetonate, C₅H₇O₂), (I), which was prepared by oxidation of Co(II)(acac)₂ with hydrogen peroxide. The complex reacts with 2,4-pentanedione to form Co^III(acac)₃ and may serve as a useful model for hydration and oxidation catalysts (Masłowska & Baranovski, 1978 ; Bergquist et al., 2003 ; Zinn et al., 2007 ; Wang et al., 2009 ) Boucher and Herrington characterized the complex according to IR and ¹H NMR spectra (Boucher & Herrington, 1971 ). These data indicated a single diastereoisomer, the identity of which was not clear from the spectra. We now report its crystal structure, confirming that it is centrosymmetric.

2. Structural commentary

The structure of (I) contains one crystallographically independent Co^III atom with an approximately octahedral coordination environment. The coordination sphere of Co1 is filled by the oxygen atoms of two κ²-O,O′ acac ligands [Co1—O2 = 1.8830 (16) Å, Co1—O3 = 1.8770 (16) Å, Co1—O4 = 1.8814 (16) Å, Co1—O5 = 1.8820 (17) Å) and two μ₂-hydroxyl groups [Co1—O1 = 1.9131 (16) Å, Co1—O1ⁱ = 1.9087 (17) Å; symmetry code: (i) −x, −y+2, −z+1]. The angles around Co1 are distorted slightly from the ideal 90° and 180° of a perfect octahedron. The cis angles range from 82.07 (7) to 95.92 (7)° while the trans angles range from 173.53 (7) to 178.37 (6)°.

The molecular structure of (I) contains a [Co₂(μ₂-OH)₂] motif with each metal coordinated by two acac ligands in a κ²-O,O′ mode (Fig. 1). The two halves of the dimer are related via inversion symmetry. The Co1⋯Co1ⁱ distance is 2.8829 (7) Å. This distance falls within the range (2.696–3.355 Å) of all Co⋯Co distances reported in the Cambridge Crystallographic Database (Groom & Allen, 2014 ) for OH⁻-bridged Co complexes in which the metals are coordinated by six oxygen atoms. It is well below the average Co⋯Co distance of 3.108 Å.

Figure 1
The molecular structure of (I)

, showing displacement ellipsoids at the 35% probability for non-H atoms and spheres of arbitrary size for H atoms. The unlabeled atoms are related by the symmetry operator (−x, −y + 2, −z + 1).

3. Supramolecular features

There are no significant supramolecular features to discuss with the extended structure of (I). There are weak C—H⋯O intermolecular interactions (Table 1) between one methyl group of an acac ligand and the hydroxide oxygen atom. These interactions result in the formation of chains normal to the ac plane (Fig. 2). It should be noted that the hydroxyl H atom does not participate in hydrogen bonding. Examination of the packing diagram shows that the bulky acac ligands prevent any hydrogen-bonding interactions with neighboring molecules.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C1—H1B⋯O1ⁱ	0.98	2.42	3.395 (3)	174
Symmetry code: (i) x, y-1, z.

Figure 2
A view along the a axis of the crystal structure of (I)

, showing extended chains normal to the ac plane. The weak C—H⋯O interactions are shown as red dashed lines. All H atoms except the hydroxide H atom (H1) and the interacting H atoms (H1B) have been omitted for clarity. Color code: blue = Co, red = O, gray = C, green = H.

4. Database survey

One closely related crystal structure, [Co(L)₂(μ-OH)]₂; L = 1-(dibenzylamino)-5,5-dimethyl-1,4-dioxohex-2-en-2-olate, has been reported previously (Wang et al., 2009). The ligand in this complex is a modified acac with a tert-butyl group in place of one methyl and a {CON(CH₂Ph)₂} group in place of the other methyl group. The coordination environment of the Co^III atoms is the same as in (I). The average Co—O_L distance of 1.890 Å is similar to the average Co—O_acac distance in (I) of 1.881 Å. The average Co—OH distance of 1.907 Å is also comparable to that of (I) (1.911 Å).

A search of the Cambridge Crystallographic Database (Groom & Allen, 2014) returned 13 dimeric complexes with the general formula [TM(acac)₂(μ-X)]₂; TM = transition metal, and X = O, OR, NO, or S (Bottomley et al., 1982 ; Nakahanada et al., 1992 ; Smith et al., 1972 ; Sokolov et al., 1999 ). Complex (I) is the first crystal structure reported that fits this general formula in which the bridging group is OH⁻.

5. Synthesis and crystallization

The title complex was synthesized according to the procedures reported by Boucher & Herrington (1971). To a mixture of Co(acac)₂·2H₂O (2 g, 7.27×10 ⁻³ mol, 1 equiv) and KOAc (3.2 g, 3.26×10 ⁻² mol, 4.5 equiv) in methanol (125 ml) was added a solution of H₂O₂ in water (30%_wt, 2 ml). The resulting solution changed color from pink to green. The reaction was stirred at room temperature for 1 h under an ambient atmosphere. The reaction was then concentrated to dryness on a rotary evaporator. The residual green solid was washed with water (3 × 20 ml) and then acetone (3 × 20 ml), and then dried in air, leaving the product (0.85 g, 1.55×10 ⁻³ mol, 43% yield). Crystals, suitable for X-ray diffraction, were grown by slow diffusion of pentane into chloroform solutions of the green product.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The hydroxyl H atom was located in a difference map and its position was allowed to refine freely. Methyl H atom positions, R-CH₃, were optimized by rotation about R—C bonds with idealized C—H, R—H and H⋯H distances. Remaining H atoms were included as riding idealized contributors. Methyl and hydroxide H atom U_iso's were assigned as 1.5U_eq of the carrier atom; remaining H atom U_iso's were assigned as 1.2U_eq of the carrier atom.

Table 2
Experimental details

Crystal data
Chemical formula	[Co₂(C₅H₇O₂)₄(OH)₂]
M_r	548.30
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	173
a, b, c (Å)	7.8610 (11), 8.2481 (11), 9.8372 (13)
α, β, γ (°)	100.786 (8), 106.708 (8), 99.492 (9)
V (Å³)	583.67 (14)
Z	1
Radiation type	Mo Kα
μ (mm⁻¹)	1.47
Crystal size (mm)	0.23 × 0.19 × 0.04

Data collection
Diffractometer	Bruker Kappa APEXII CCD
Absorption correction	Integration (SADABS; Bruker, 2012)
T_min, T_max	0.776, 0.945
No. of measured, independent and observed [I > 2σ(I)] reflections	16164, 2617, 2228
R_int	0.083
(sin θ/λ)_max (Å⁻¹)	0.646

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.036, 0.093, 1.05
No. of reflections	2617
No. of parameters	152
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.39, −0.53
Computer programs: APEX2 and SAINT (Bruker, 2013 ), SHELXS and SHELXTL (Sheldrick, 2008 ), SHELXL2013/4 (Sheldrick, 2015 ), CrystalMaker (CrystalMaker, 1994 ), XCIF (Bruker, 2013) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1413567

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989015013663/wm5186sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989015013663/wm5186Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989015013663/wm5186Isup3.cdx

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2013); cell refinement: SAINT (Bruker, 2013); data reduction: SAINT (Bruker, 2013); program(s) used to solve structure: SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013/4 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008), CrystalMaker (CrystalMaker, 1994); software used to prepare material for publication: XCIF (Bruker, 2013) and publCIF (Westrip, 2010).

Di-µ-hydroxido-κ⁴O:O-bis[bis(acetylacetonato-κ²O,O')cobalt(III)] top

Crystal data top

[Co₂(C₅H₇O₂)₄(OH)₂]	Z = 1
M_r = 548.30	F(000) = 284
Triclinic, P1	D_x = 1.560 Mg m⁻³
a = 7.8610 (11) Å	Mo Kα radiation, λ = 0.71073 Å
b = 8.2481 (11) Å	Cell parameters from 3791 reflections
c = 9.8372 (13) Å	θ = 2.6–25.5°
α = 100.786 (8)°	µ = 1.47 mm⁻¹
β = 106.708 (8)°	T = 173 K
γ = 99.492 (9)°	Plate, blue
V = 583.67 (14) Å³	0.23 × 0.19 × 0.04 mm

Data collection top

Bruker Kappa APEXII CCD diffractometer	2617 independent reflections
Radiation source: fine-focus sealed tube	2228 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.083
profile data from φ and ω scans	θ_max = 27.3°, θ_min = 2.2°
Absorption correction: integration (SADABS; Bruker, 2012)	h = −10→10
T_min = 0.776, T_max = 0.945	k = −10→10
16164 measured reflections	l = −12→12

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F² > 2σ(F²)] = 0.036	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.093	w = 1/[σ²(F_o²) + (0.0366P)² + 0.1984P] where P = (F_o² + 2F_c²)/3
S = 1.05	(Δ/σ)_max = 0.001
2617 reflections	Δρ_max = 0.39 e Å⁻³
152 parameters	Δρ_min = −0.53 e Å⁻³

Special details top

Experimental. One distinct cell was identified using APEX2 (Bruker, 2013). Fourteen frame series were integrated and filtered for statistical outliers using SAINT (Bruker, 2013) then corrected for absorption by integration using SAINT/SADABS, v2012/1 (Bruker, 2012) to sort, merge, and scale the combined data. No decay correction was applied.

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

Refinement. Structure was phased by direct methods (Sheldrick, 2008). Systematic conditions suggested the ambiguous space group. The space group choice was confirmed by successful convergence of the full-matrix least-squares refinement on F². The final map had no significant features. A final analysis of variance between observed and calculated structure factors showed little dependence on amplitude and resolution.

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

	x	y	z	U_iso*/U_eq
Co1	0.08356 (4)	0.96491 (4)	0.63894 (3)	0.01839 (12)
O1	0.0955 (2)	1.1492 (2)	0.54669 (18)	0.0197 (4)
H1	0.182 (4)	1.158 (4)	0.530 (3)	0.030*
O2	0.0442 (2)	0.7772 (2)	0.71880 (18)	0.0244 (4)
O3	0.2682 (2)	0.9024 (2)	0.56955 (18)	0.0220 (4)
C1	0.0467 (4)	0.5042 (3)	0.7559 (3)	0.0294 (6)
H1A	0.1238	0.5263	0.8584	0.044*
H1B	0.0576	0.3969	0.7002	0.044*
H1C	−0.0808	0.4967	0.7508	0.044*
C2	0.1074 (3)	0.6460 (3)	0.6920 (2)	0.0216 (5)
C3	0.2293 (3)	0.6301 (3)	0.6154 (3)	0.0239 (5)
H3	0.2605	0.5236	0.5962	0.029*
C4	0.3092 (3)	0.7594 (3)	0.5647 (2)	0.0204 (5)
C5	0.4588 (3)	0.7360 (3)	0.5010 (3)	0.0291 (6)
H5A	0.4703	0.8171	0.4411	0.044*
H5B	0.4290	0.6201	0.4398	0.044*
H5C	0.5745	0.7556	0.5805	0.044*
O4	−0.1041 (2)	1.0298 (2)	0.70365 (18)	0.0211 (3)
O5	0.2764 (2)	1.0871 (2)	0.81009 (18)	0.0258 (4)
C6	−0.2501 (3)	1.1417 (4)	0.8641 (3)	0.0302 (6)
H6A	−0.2682	1.2526	0.8490	0.045*
H6B	−0.2371	1.1397	0.9658	0.045*
H6C	−0.3556	1.0527	0.7980	0.045*
C7	−0.0812 (3)	1.1114 (3)	0.8328 (3)	0.0216 (5)
C8	0.0873 (3)	1.1769 (3)	0.9434 (3)	0.0265 (5)
H8	0.0877	1.2323	1.0373	0.032*
C9	0.2534 (3)	1.1666 (3)	0.9258 (3)	0.0245 (5)
C10	0.4268 (4)	1.2530 (4)	1.0500 (3)	0.0383 (7)
H10A	0.4992	1.1698	1.0733	0.057*
H10B	0.3972	1.3033	1.1363	0.057*
H10C	0.4973	1.3424	1.0215	0.057*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Co1	0.01960 (18)	0.01881 (19)	0.02005 (19)	0.00636 (13)	0.01007 (13)	0.00540 (13)
O1	0.0196 (8)	0.0184 (8)	0.0237 (9)	0.0052 (7)	0.0118 (7)	0.0033 (7)
O2	0.0309 (9)	0.0253 (9)	0.0253 (9)	0.0113 (7)	0.0164 (7)	0.0102 (7)
O3	0.0223 (8)	0.0223 (9)	0.0267 (9)	0.0086 (7)	0.0130 (7)	0.0083 (7)
C1	0.0407 (15)	0.0259 (13)	0.0245 (13)	0.0060 (11)	0.0144 (11)	0.0090 (10)
C2	0.0227 (12)	0.0217 (12)	0.0162 (11)	0.0041 (9)	0.0015 (9)	0.0035 (9)
C3	0.0276 (12)	0.0198 (12)	0.0253 (13)	0.0091 (10)	0.0091 (10)	0.0041 (10)
C4	0.0199 (11)	0.0214 (12)	0.0166 (11)	0.0057 (9)	0.0023 (9)	0.0018 (9)
C5	0.0292 (13)	0.0297 (14)	0.0366 (15)	0.0149 (11)	0.0175 (11)	0.0099 (11)
O4	0.0210 (8)	0.0233 (9)	0.0218 (8)	0.0066 (7)	0.0114 (7)	0.0042 (7)
O5	0.0216 (9)	0.0323 (10)	0.0231 (9)	0.0069 (7)	0.0088 (7)	0.0033 (7)
C6	0.0301 (13)	0.0399 (15)	0.0278 (14)	0.0147 (12)	0.0167 (11)	0.0085 (12)
C7	0.0292 (12)	0.0188 (12)	0.0231 (12)	0.0075 (10)	0.0155 (10)	0.0080 (9)
C8	0.0317 (13)	0.0303 (14)	0.0196 (12)	0.0094 (11)	0.0120 (10)	0.0034 (10)
C9	0.0282 (13)	0.0260 (13)	0.0214 (12)	0.0074 (10)	0.0098 (10)	0.0074 (10)
C10	0.0313 (14)	0.0479 (18)	0.0277 (15)	0.0049 (13)	0.0074 (12)	−0.0021 (13)

Geometric parameters (Å, º) top

Co1—O3	1.8770 (16)	C4—C5	1.506 (3)
Co1—O4	1.8814 (16)	C5—H5A	0.9800
Co1—O5	1.8820 (17)	C5—H5B	0.9800
Co1—O2	1.8830 (16)	C5—H5C	0.9800
Co1—O1ⁱ	1.9087 (17)	O4—C7	1.268 (3)
Co1—O1	1.9131 (16)	O5—C9	1.279 (3)
Co1—Co1ⁱ	2.8829 (7)	C6—C7	1.495 (3)
O1—Co1ⁱ	1.9087 (17)	C6—H6A	0.9800
O1—H1	0.74 (3)	C6—H6B	0.9800
O2—C2	1.278 (3)	C6—H6C	0.9800
O3—C4	1.269 (3)	C7—C8	1.395 (3)
C1—C2	1.502 (3)	C8—C9	1.380 (3)
C1—H1A	0.9800	C8—H8	0.9500
C1—H1B	0.9800	C9—C10	1.502 (3)
C1—H1C	0.9800	C10—H10A	0.9800
C2—C3	1.387 (3)	C10—H10B	0.9800
C3—C4	1.393 (3)	C10—H10C	0.9800
C3—H3	0.9500

O3—Co1—O4	178.37 (6)	C2—C3—C4	124.5 (2)
O3—Co1—O5	85.06 (7)	C2—C3—H3	117.8
O4—Co1—O5	95.92 (7)	C4—C3—H3	117.8
O3—Co1—O2	95.73 (7)	O3—C4—C3	125.0 (2)
O4—Co1—O2	85.55 (7)	O3—C4—C5	115.1 (2)
O5—Co1—O2	91.96 (7)	C3—C4—C5	120.0 (2)
O3—Co1—O1ⁱ	90.26 (7)	C4—C5—H5A	109.5
O4—Co1—O1ⁱ	88.67 (7)	C4—C5—H5B	109.5
O5—Co1—O1ⁱ	173.53 (7)	H5A—C5—H5B	109.5
O2—Co1—O1ⁱ	92.95 (7)	C4—C5—H5C	109.5
O3—Co1—O1	88.10 (7)	H5A—C5—H5C	109.5
O4—Co1—O1	90.54 (7)	H5B—C5—H5C	109.5
O5—Co1—O1	93.29 (7)	C7—O4—Co1	124.45 (16)
O2—Co1—O1	173.75 (7)	C9—O5—Co1	123.82 (16)
O1ⁱ—Co1—O1	82.07 (7)	C7—C6—H6A	109.5
O3—Co1—Co1ⁱ	88.91 (5)	C7—C6—H6B	109.5
O4—Co1—Co1ⁱ	89.47 (5)	H6A—C6—H6B	109.5
O5—Co1—Co1ⁱ	134.10 (5)	C7—C6—H6C	109.5
O2—Co1—Co1ⁱ	133.93 (6)	H6A—C6—H6C	109.5
O1ⁱ—Co1—Co1ⁱ	41.09 (5)	H6B—C6—H6C	109.5
O1—Co1—Co1ⁱ	40.98 (5)	O4—C7—C8	125.1 (2)
Co1ⁱ—O1—Co1	97.93 (7)	O4—C7—C6	116.0 (2)
Co1ⁱ—O1—H1	103 (2)	C8—C7—C6	118.9 (2)
Co1—O1—H1	106 (2)	C9—C8—C7	124.4 (2)
C2—O2—Co1	123.65 (15)	C9—C8—H8	117.8
C4—O3—Co1	124.41 (15)	C7—C8—H8	117.8
C2—C1—H1A	109.5	O5—C9—C8	125.7 (2)
C2—C1—H1B	109.5	O5—C9—C10	114.7 (2)
H1A—C1—H1B	109.5	C8—C9—C10	119.6 (2)
C2—C1—H1C	109.5	C9—C10—H10A	109.5
H1A—C1—H1C	109.5	C9—C10—H10B	109.5
H1B—C1—H1C	109.5	H10A—C10—H10B	109.5
O2—C2—C3	125.1 (2)	C9—C10—H10C	109.5
O2—C2—C1	115.2 (2)	H10A—C10—H10C	109.5
C3—C2—C1	119.6 (2)	H10B—C10—H10C	109.5

Symmetry code: (i) −x, −y+2, −z+1.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1B···O1ⁱⁱ	0.98	2.42	3.395 (3)	174

Symmetry code: (ii) x, y−1, z.

Acknowledgements

This research was conducted under contract DEFG02- 90ER14146 with the US Department of Energy by its Division of Chemical Sciences, Office of Basic Energy Sciences.

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