Tetra­kis(μ2-2,2-dimethyl­propanoato-κ2 O,O′)bis­[(pyridine-κN)copper(II)]: a monoclinic polymorph

Lailatun Nazirah Ozair; Norbani Abdullah; Hamid Khaledi; Edward R T Tiekink

doi:10.1107/S1600536810015060

. 2010 Apr 30;66(Pt 5):m589–m590. doi: 10.1107/S1600536810015060

Tetrakis(μ₂-2,2-dimethylpropanoato-κ² O,O′)bis[(pyridine-κN)copper(II)]: a monoclinic polymorph

Lailatun Nazirah Ozair ^a, Norbani Abdullah ^a,^‡, Hamid Khaledi ^a, Edward R T Tiekink ^a,^*

PMCID: PMC2979036 PMID: 21579064

Abstract

The structure of the dinuclear title complex, [Cu₂(C₅H₉O₂)₄(C₅H₅N)₂], represents a monoclinic polymorph of the previously reported triclinic form [Blewett et al. (2006 ▶). Acta Cryst. E62, m420–m422]. Each carboxylate group is bidentate bridging and the distorted octahedral geometry about each Cu^II atom is completed by a pyridine N atom and the other Cu atom [Cu⋯Cu = 2.6139 (7) Å]. In the crystal, molecules are connected into supramolecular chains via π–π interactions formed by the pyridine rings [centroid–centroid distance = 3.552 (3) Å] and these are connected into a two-dimensional array in the ac plane by C—H⋯π contacts. One of the tert-butyl groups is disordered over two orientations in a 0.734 (6):0.266 (6) ratio.

Related literature

For the structure of the triclinic polymorph of the title compound, see: Blewett et al. (2006 ▶). For background to copper(II) carboxylates, see: Attard & Cullum (1990 ▶); Kato et al. (1964 ▶); Melnik et al. (1984 ▶); Kawata et al. (1992 ▶).

Experimental

Crystal data

[Cu₂(C₅H₉O₂)₄(C₅H₅N)₂]
M _r = 689.80
Monoclinic,
a = 9.4758 (6) Å
b = 20.0192 (12) Å
c = 18.6136 (10) Å
β = 104.515 (3)°
V = 3418.3 (4) Å³
Z = 4
Mo Kα radiation
μ = 1.29 mm⁻¹
T = 100 K
0.32 × 0.26 × 0.16 mm

Data collection

Bruker SMART APEX CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.682, T _max = 0.820
28775 measured reflections
7077 independent reflections
5583 reflections with I > 2σ(I)
R _int = 0.060

Refinement

R[F ² > 2σ(F ²)] = 0.058
wR(F ²) = 0.156
S = 1.13
7077 reflections
404 parameters
12 restraints
H-atom parameters constrained
Δρ_max = 1.26 e Å⁻³
Δρ_min = −0.75 e Å⁻³

Data collection: APEX2 (Bruker, 2008 ▶); cell refinement: SAINT (Bruker, 2008 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶) and DIAMOND (Brandenburg, 2006 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810015060/hb5416sup1.cif

e-66-0m589-sup1.cif^{(33.3KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810015060/hb5416Isup2.hkl

e-66-0m589-Isup2.hkl^{(339.3KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Cu1—O7	1.950 (3)
Cu1—O1	1.956 (3)
Cu1—O3	1.976 (3)
Cu1—O5	1.987 (3)
Cu1—N1	2.157 (3)
Cu2—O6	1.962 (3)
Cu2—O4	1.968 (3)
Cu2—O8	1.976 (3)
Cu2—O2	1.978 (3)
Cu2—N2	2.157 (3)

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Table 2. Hydrogen-bond geometry (Å, °).

Cg1 and Cg2 are the centroids of the N1,C21–C25 and N2,C26–C30 rings, respectively.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C3—H3c⋯Cg1ⁱ	0.98	2.90	3.609 (7)	130
C19b—H19f⋯Cg2ⁱⁱ	0.98	2.64	3.554 (19)	154

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

The authors thank the University of Malaya for funding this study through PPP (PS345/2010 A) and the Research University Fund (TA021/2009 A).

supplementary crystallographic information

Comment

Research on copper(II) carboxylates focuses upon their metallomesogenic properties (Attard & Cullum, 1990) and interesting magneto-structural relationship (Kato et al., 1964; Melnik et al., 1984; Kawata et al., 1992). However, the practical use of these complexes is hindered by their high melting points (greater than 523 K) and which are accompanied by thermal decomposition. Our research interest is to develop low-temperature copper(II) carboxylates as functional materials for use in the fields of catalysis, photonics, spintronics, and electronics. To realise this, we adopted the concepts of symmetry reduction by mixed ligands and the use of highly-branched alkylcarboxylates. This contribution reports the crystal structure of one of the starting materials to be used in the synthesis of such complexes, i.e. the title compound, (I).

The dinuclear structure of (I), Fig. 1, features two Cu atoms, separated by 2.6139 (7) Å, connected by four bidentate bridging carboxylate ligands. The final position in the disordered octahedral trans-CuNO₄ donor set is occupied by a pyridine-N atom in each case. The structure resembles closely that described for the triclinic polymorph but with the latter being disposed about a centre of inversion (Blewett et al., 2006). The primary differences between the molecules is found in the relative disposition of the pyridine groups. In (I), the dihedral angles formed between the least-squares planes through the four O atoms and pyridine ring = 81.5 (1) ° for Cu1 and 88.6 (1) ° for Cu2, which compares to 89.38 (8) ° found in the triclinic structure. These differences are reflected in the dihedral angle of 12.93 (15) ° formed between the pyridine rings in (I) compared to 0 ° (from symmetry) in the triclinic polymorph. These differences not withstanding, the Cu–O bond distances are experimentally equivalent in the two forms but it is noted these cover are broader range in (I), i.e. 1.950 (3) to 1.987 (3) Å, compared with 1.963 (2) to 1.977 (2) Å; the Cu–N distances are indistinguishable. The Cu···Cu distance in (I), 2.6139 (7) Å, is shorter than 2.6229 (9) Å in the triclinic form.

A common feature of the crystal packing of both forms is the presence of significant π–π interactions between the pyridine rings. In (I), these [ring centroid(N1,C21—C25)···ring centroid(N2,C26—C30)ⁱ = 3.552 (3) Å, angle between planes = 9.2 (2) °, for i: 1/2+x, 1/2-y, 1/2+z] lead to supramolecular chains which are connected into a 2-D array in the ac plane by C–H···π contacts involving methyl-H atoms (one being derived from a disordered tert-butyl residue), Fig. 2 & Table 1. The layers are stacked along the b direction as illustrated in Fig. 3.

Experimental

An aqueous solution (50 ml) of sodium carbonate (5.2 g, 0.049 mol) was added to an aqueous solution (50 ml) of 2,2-dimethylpropionic acid (10 g, 0.098 mol) and the mixture was stirred at 323 K. After 30 min, a solution of CuCl₂.2H₂O (8.33 g, 0.049 mol) dissolved in a minimum amount of water was added followed by addition of several drops of pyridine. The mixture was stirred for another 30 min. and then set aside at room temperature for a week whereupon green blocks of (I) were obtained. Both DSC and TGA data indicate that the material did not melt, but decomposed at 408 K. CHN analyses (%), Found: C, 52.17; H, 6.75; N, 4.16. Calc'd: C, 52.23; H, 6.72; N, 4.05.