Orientational disorder in the one-dimensional coordination polymer catena-poly[[bis-(acetyl-acetonato-κ(2) O,O')cobalt(II)]-μ-1,4-di-aza-bicyclo-[2.2.2]octane-κ(2) N (1):N (4)].

The title compound, [Co(C5H7O2)2(C6H12N2)] n , was obtained as a one-dimensional coordination polymer from bis-(acetyl-acetonato)di-aqua-cobalt(II), [Co(acac)2(OH2)2], and 1,4-di-aza-bicyclo-[2.2.2]octane (DABCO), a di-amine 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 anti-ferromagnetic 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.

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 n class="Chemical">metal complex bis­(acetyl­aceto­nato-κ2 O,O′)cobalt(II), [Co(acac)2], have been chosen to design a one-dimensional coordination polymer in which the paramagnetic CoII 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)] compound which exhibits weak anti­ferromagnetic exchange between the CoII ions.

Within this context, the title compound catena-poly[[bis(acetyl­acetonato-κ2 O,O′)cobalt(II)]-μ-1,4-di­aza­bicyclo­[2.2.2]octane-κ2 N 1:N 4], [n class="Chemical">Co(acac)2(DABCO)], (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.

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 n class="Chemical">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 (n class="Chemical">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 CoII atom shows an octa­hedral environment defined by four equatorial n class="Chemical">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.]

Supra­molecular features

The centrosymmetric DABCO ligand is bonded to two [n class="Chemical">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 CoII coordination requirements.

Figure 2

The mol­ecular packing of the coordination polymer chains.

Database survey

Although some polymeric complexes of the form [n class="Chemical">Co(acac)2(μ-di­amine)] [di­amine = NH2–R–NH2, with R = CH2 (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)] 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}] (Lennartson & Håkansson, 2009 ▸), [Co(acac)2(pyrazine)] and [Co(acac)2(4,4′-bi­pyridine)] (Ma et al., 2001 ▸).

Synthesis and crystallization

[Co(acac)2(H2O)2] was prepared by precipitation of CoCl2·6H2O with aqueous n class="Chemical">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 (n class="Chemical">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).

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 n class="Disease">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, P n n m
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[F 2 > 2σ(F 2)], wR(F 2), S	0.020, 0.055, 1.09
No. of reflections	1045
No. of parameters	81
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (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 n class="Disease">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.

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S205698901600428X/wm5278sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S205698901600428X/wm5278Isup2.hkl

CCDC reference: 1454848

Additional supporting information: crystallographic information; 3D view; checkCIF report

[Co(C5H7O2)2(C6H12N2)]	Dx = 1.444 Mg m−3
Mr = 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

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	Rint = 0.045
Detector resolution: 6.67 pixels mm-1	θmax = 27.5°, θmin = 3.8°
rotation method scans	h = −10→10
Absorption correction: multi-scan (MULABS in PLATON; Spek, 2003)	k = −19→19
Tmin = 0.637, Tmax = 0.960	l = −8→9
11457 measured reflections

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(Fo2) + (0.0389P)2] where P = (Fo2 + 2Fc2)/3
S = 1.09	(Δ/σ)max < 0.001
1045 reflections	Δρmax = 0.25 e Å−3
81 parameters	Δρmin = −0.39 e Å−3

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.

	x	y	z	Uiso*/Ueq	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

	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)

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)