The 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, can serve for a comparative investigation of the magnetic behaviour of analogous compounds. Space filling more symmetric than atom positions leads to pronounced orientational disorder for the DABCO ligand.
Keywords: crystal structure, one-dimensional coordination polymer, orientational disorder, acetylacetonate complexes, cobalt(II), DABCO, magnetic behaviour
Abstract
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 CoII 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 CoII 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 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)]n 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], [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.
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 CoII 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.]
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 CoII coordination requirements.
Figure 2.
The molecular packing of the coordination polymer chains.
Database survey
Although some polymeric complexes of the form [Co(acac)2(μ-diamine)]n [diamine = NH2–R–NH2, with R = CyH2y+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 ▸).
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).
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, 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 |
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.
Supplementary Material
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
supplementary crystallographic information
Crystal data
| [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 |
Data collection
| 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
| 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 |
Special details
| 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. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)
| 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 |
Atomic displacement parameters (Å2)
| 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)
| 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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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
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