Crystal structure of tetra­kis­(μ-caproato-κ2 O:O′)bis­[(4-cyano­pyridine-κN 1)copper(II)]

Sukanya Baruah; Zinnatara Islam; Sanjib Karmakar; Birinchi Kumar Das

doi:10.1107/S2056989015019052

. 2015 Oct 14;71(Pt 11):m195–m196. doi: 10.1107/S2056989015019052

Crystal structure of tetrakis(μ-caproato-κ² O:O′)bis[(4-cyanopyridine-κN ¹)copper(II)]

Sukanya Baruah ^a, Zinnatara Islam ^a, Sanjib Karmakar ^b,^*, Birinchi Kumar Das ^a,^*

PMCID: PMC4645092 PMID: 26594530

Abstract

The title dinuclear complex, [Cu₂(C₆H₁₁O₂)₄(C₆H₄N₂)₂], has a paddle-wheel structure. The two crystallographically independent Cu^II atoms are each in a distorted square-pyramidal environment, in which four O atoms from the four bridging caproate ligands form the basal plane and the pyridine N atom of the 4-cyanopyridine ligand occupies the apical position. The Cu⋯Cu distance is 2.6055 (9) Å. One of the alkyl chains of the caproate ligands is disordered over two sets of sites, with occupancies of 0.725 (5) and 0.275 (5). In the crystal, two pairs of C—H⋯N hydrogen bonds connect the molecules into chains along [11-1] and C—H⋯O hydrogen bonds link the chains into a three-dimensional network.

Keywords: crystal structure, dicopper complex, 4-cyanopyridine, hexanoic acid

Related literature

For related structures of copper(II) complexes, see: Brown & Chidambaram (1973 ▸); Petrič et al. (1995 ▸); Lomer & Perera (1974 ▸); Kozlevčar et al. (2000 ▸); Catterick & Thornton (1977 ▸). For applications as catalysts of dicopper(II) tetracarboxylates, see: Abied et al. (1987 ▸); Kozlevčar et al. (1999 ▸); Bora et al. (2007 ▸); Das et al. (2007 ▸); Sarmah et al. (2010 ▸). graphic file with name e-71-0m195-scheme1.jpg

Experimental

Crystal data

[Cu₂(C₆H₁₁O₂)₄(C₆H₄N₂)₂]
M _r = 795.92
Monoclinic,
a = 8.7740 (4) Å
b = 25.3083 (11) Å
c = 17.7893 (8) Å
β = 101.321 (2)°
V = 3873.3 (3) Å³
Z = 4
Mo Kα radiation
μ = 1.15 mm⁻¹
T = 100 K
0.42 × 0.18 × 0.14 mm

Data collection

Bruker SMART APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▸) T _min = 0.780, T _max = 0.851
29777 measured reflections
11382 independent reflections
8952 reflections with I > 2σ(I)
R _int = 0.032

Refinement

R[F ² > 2σ(F ²)] = 0.035
wR(F ²) = 0.084
S = 1.03
11382 reflections
502 parameters
155 restraints
H-atom parameters constrained
Δρ_max = 0.47 e Å⁻³
Δρ_min = −0.40 e Å⁻³

Data collection: APEX2 (Bruker, 2004 ▸); cell refinement: SAINT (Bruker, 2004 ▸); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▸); program(s) used to refine structure: SHELXL2012/9 (Sheldrick, 2015 ▸); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012 ▸) and Mercury (Macrae et al., 2008 ▸); software used to prepare material for publication: SHELXL2012/9.

Supplementary Material

Crystal structure: contains datablock(s) I, Global. DOI: 10.1107/S2056989015019052/is5420sup1.cif

e-71-0m195-sup1.cif^{(906.1KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015019052/is5420Isup2.hkl

e-71-0m195-Isup2.hkl^{(616.7KB, hkl)}

Click here for additional data file.^{(1.8MB, tif)}

. DOI: 10.1107/S2056989015019052/is5420fig1.tif

Molecular structure of the title compound drawn with 30% probability ellipsoid. H-atoms are shown as circles of arbitrary radius. Only one component of the disordered alkyl chain is shown.

Click here for additional data file.^{(2.3MB, tif)}

. DOI: 10.1107/S2056989015019052/is5420fig2.tif

A packing diagram of the title compound. Hydrogen bonds are shown by dotted lines.

CCDC reference: 1430487

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

Table 1. Hydrogen-bond geometry (, ).

DHA	DH	HA	D A	DHA
C2H2O4ⁱ	0.95	2.55	3.301(2)	137
C4H4N3ⁱⁱ	0.95	2.58	3.444(2)	151
C8H8N4ⁱⁱⁱ	0.95	2.48	3.422(2)	169
C10H10O5^iv	0.95	2.59	3.432(2)	148
C20H20BO6^v	0.99	2.66	3.479(2)	141
C26H26AO3^vi	0.99	2.56	3.532(2)	167

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) ; (vi) .

Acknowledgments

The authors thank the SAIF, Department of Instrumentation & USIC, Gauhati University, Guwahati, India, for the data collection. SB thanks the UGC, India, for a scholarship awarded under its BSR Fellowship scheme.

supplementary crystallographic information

S1. Comment

A few members of the family of dicopper(II) tetracarboxylates of the type Cu₂(µ-O₂CR)₄L₂, where R is either an alkyl or aryl group and L is pyridine or a pyridyl ligand, have been demonstrated as homogeneous catalysts in the oxidation of various alcohols (Abied et al., 1987; Kozlevčar et al., 1999; Bora et al., 2007; Das et al., 2007; Sarmah et al., 2010). In view of this it was found instructive to prepare other members of the above general formula having R = a long-chain alkyl group because the presence such alkyl groups could make the resultant dimeric carboxylates more soluble in organic solvents, and hence more effective as catalysts.

We aimed to prepare complexes of long chain carboxylic acids as only a few crystal structures of such complexes of copper(II) have been reported (Petrič et al., 1995; Lomer & Perera, 1974). The structure of the title compound, [Cu₂(µ-O₂CC₅H₁₁)₄(4-CNpy)₂], (I), is similar to that of copper(II) acetate hydrate (Brown & Chidambaram, 1973). The Cu—Cu distance of 2.6055 (9) Å is shorter than the corresponding distance in [Cu₂(µ-O₂CCH₃)₄(H₂O)₂] (2.614 Å) as well as that in [Cu₂(OOCC₅H₁₁)₄(OCN₂H₄)₂] [2.644 (2) Å] (Kozlevčar et al., 2000). The average Cu—O bond length of 1.9731 (12) Å and the longer average Cu—N distance of 2.1837 (13) Å in the title complex are considered to be normal for [Cu₂(µ-O₂CR)₄L₂] (L = axial ligand, R = alkyl group) type of structures (Catterick & Thornton, 1977). In (I), one pair of hydrocarbon chains has the common zigzag conformation while the other pair is distorted, which facilitates efficient packing.

S2. Experimental

CuSO₄·5H₂O (0.749 g, 3 mmol) was dissolved in methanol (25 ml). To this solution, sodium caproate (C₅H₁₁COONa; 0.882 g, 6 mmol) and 4-cyanopyridine (0.321 g, 3 mmol) were added and the mixture was stirred for 2 h. The resulting green product was filtered off, washed with small volumes of methanol and dried in a vacuum desiccator over fused CaCl₂ (yield 80%). The product was dissolved in acetonitrile to get a greenish homogeneous solution which was allowed to concentrate by evaporation at room temperature. Single crystals suitable for X-ray diffraction were obtained from this solution after one day and collected by filtration.