Copper(II) clofibriates, Part II. A two-dimensional coordination polymer of Cu(clofibriate)₂(3-pyridylmethanol)₂

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Abstract

A two-dimensional coordination polymer of [Cu(clof)₂(3-pymeth)₂]_n1 (clof = clofibriate anion and 3-pymeth = 3-pyridylmethanol) has been synthesized and characterized by single crystal structural analysis. The coordination environment about the copper(II) atom is tetragonal bipyramidal. The compound crystallizes in the monoclinic system, space group P2₁/c with a = 15.206(3), b = 8.029(2), c = 14.338(3) Å, β = 113.64(3)°, V = 1603.6(6) Å³ and Z = 2.

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Introduction

The coordination bonds between transition metal ions and nitrogen containing heterocyclic ligands have proved useful for the construction of solid-state architectures and inorganic crystal engineering.² Phenoxyalkanoic acids play an important role in biological processes as commercial auxin herbicide and/or anti-inflammatory agents.³ Copper(II) phenoxyalkanoate complexes have been shown to have diverse stereochemistry.^3,4 Clofibric acid {2-(4-chlorophenoxy)-2-methylpropionic acid or 2-(4-chlorophenoxy)isobutyric acid} is a very interesting anti-inflammatory agent. Four copper(II) clofibriate complexes were studied by X-ray diffraction methods. X-Ray diffraction analysis of [Cu₂(clof)₄(ampy)₂] (ampy = 2-aminopyrimidine)⁵ and [Cu₂(clof)₄(MeOH)₂]⁶ shows that the compounds are binuclear with square pyramidal geometry at each copper(II) centre. The two copper(II) atoms are bridged by four carboxylate groups in syn–syn configuration of four clofibriate anions, while the apical ligands are 2-aminopyrimidine in [Cu₂(clof)₄(ampy)₂]⁵ and methanol molecules in [Cu₂(clof)₄(MeOH)₂],⁶ respectively. The structures of [Cu(clof)₂L₂], where L = pyridine (py)⁶ or nicotinamide (nia),⁷ are mononuclear, and each copper(II) atom has a tetragonal-bipyramidal environment with the CuO₄N₂ chromophore.

This paper present the preparation of [Cu(clof)₂(3-pymeth)₂] 1 [3-pymeth = ronicol (3-pyridylmethanol)] and its crystal and molecular structures.

Experimental

Preparation of the complex

1 was prepared by addition of 3-pyridylmethanol (0.02 mol) to copper(II) clofibriate (0.01 mol) in hot methanol.⁷ The mixture was stirred, filtered and left to cool and stand at room temperature. A blue product precipitated and was collected; recrystallization from methanol–acetone (4∶1) solution gave air stable blue crystals. Anal. Found: C, 57.5; H, 4.6; Cu, 9.0; N, 4.0. Calc. for [Cu(clof)₂(3-pymeth)₂] 1: C, 57.60; H, 4.55, Cu, 8.96, N, 3.95%.

Structure determination

Data collection at 100 K using an Oxford Cryosystems cooler device⁸ and cell refinement were carried out using a four-circle diffractometer Kuma KM4CCD with graphite monochromated MoKα radiation. The diffraction intensities were corrected for Lorentz and polarization factors. The structure was solved by heavy atom methods using SHELXS-97.⁹ Geometrical analysis was performed using SHELXL-97¹⁰ and PLATON-99.¹¹ Empirical absorption correction was made by using XABS2.¹² The structure of the complex was drawn by using ORTEP-3.¹³ The Single Crystal Suite WINGX was used as an integrated system for all the crystallographic programs.¹⁴ Crystal data and conditions of data collection and refinement are reported in Table 1.

Table 1 Crystallographic data for [Cu(clof)₂(3-pymeth)₂] 1^a

a Click b109456d.txt for full crystallographic data (CCDC 167248).
Empirical formula	C32H34Cl2N2O8Cu1
Crystal dimensions/mm	0.17 × 0.15 × 0.12
M	709.05
T/K	100(2)
Crystal system	Monoclinic
Space group	P21/c
a/Å	15.206(3)
b/Å	8.029(2)
c/Å	14.338(3)
β/°	113.64(3)
Z	2
Absorption correction: Empirical	T min = 0.6945, Tmax = 1.0830
D c/Mg m^−3	1.467
μ(MoKα)/mm^−1	0.901
F(000)	734
θ Range/°	3.58–27
Reflections collected	10025
Independent reflections	3443 [Rint = 0.0312]
Final R indices [I > 2σ(I)]	R 1 = 0.0327, wR2 = 0.0787
R indices (all data)	R 1 = 0.0424, wR2 = 0.0830

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Results and discussion

The molecule of 1 lies about an inversion centre and the molecular structure of 1 is shown in Fig. 1. Selected bond lengths and bond angles are summarized in Table 2. The coordination environment of the copper(II) atom is tetragonal bipyramidal. The tetragonal plane is built up by a pair of unidentate clofibriate anions using carboxylate oxygen atoms [Cu–O1 = 1.9892(15) Å] and a pair of neutral ronicol molecules using nitrogen atoms of pyridine rings [Cu–N1 = 2.0077(15) Å] in trans positions. The axial positions are occupied by two hydroxyl oxygen atoms [Cu–O4^iv = 2.4406(14) Å] from two adjacent molecules of ronicol [x, −y − 1/2, z + 1/2]. The interatomic distance Cu⋯O2 is 3.282(2) Å, which should be regarded as non-bonding. In the mononuclear complexes [Cu(clof)₂(py)₂]⁶ and [Cu(clof)₂(nia)₂]⁷ with bidentate bi-coordinated carboxylic groups the bond lengths Cu–O2 are 2.683(1) Å and 2.614(2) Å, respectively. The intramolecular hydrogen bond O4^iv–H17^iv⋯O2 (Table 3) creates a six membered metalocycle and stabilizes the molecular structure. The torsion angle C1–C2–O3–C3 of −55.6(2)° is similar to the torsion angles in [Cu(clof)₂(py)₂]⁶ and [Cu(clof)₂(nia)₂]⁷ of −57.4° and −59.8°, respectively.

Fig. 1 Perspective view of complex [Cu(clof)₂(3-pymeth)₂]_n1, with the atom numbering scheme. Thermal ellipsoids are drawn at the 50% probability level. Click image or 1.htm to access a 3-D representation.

Table 2 Selected bond lengths (Å) and angles (°) for [Cu(clof)₂(3-pymeth)₂] 1

Symmetry code: (i) −x, −y, −z; (ii) x, −y − 1/2, z + 1/2; (iii) −x, y + 1/2, −z − 1/2; (iv) −x, y − 1/2, −z − 1/2; (v) x, −y + 1/2, +z + 1/2; (vi) x, −y − 1/2, z − 1/2; (vii) x, −y + 1/2, z − 1/2; (viii) −x − 1, y − 1/2, −z − 1/2; (ix) −x − 1, −y + 1, −z.
Cu–O1	1.9892(15)	Cu–N1	2.0077(15)
Cu–O4^iv	2.4406(14)	O1–C1	1.274(2)
O2–C1	1.243(2)	O3–C3	1.362(2)
O3–C2	1.450(2)	O4–C16	1.425(2)
C1–C2	1.549(3)
O1^i–Cu–O1	180.0	O1–Cu–N1	89.37(6)
O1–Cu–O4^iv	92.50(7)	N1–Cu–O4^iv	94.05(6)
N1–Cu–N1^i	180.0	C1–O1–Cu	127.4(1)
C3–O3–C2	121.1(1)	C11–N1–C15	118.2(2)
C11–N1–Cu	118.6(1)	C15–N1–Cu	123.2(1)
O2–C1–O1	126.7(2)	O2–C1–C2	117.6(2)
O1–C1–C2	115.6(2)	O3–C2–C1	110.6(1)
O4–C16–C12	109.5(2)	Cu–O4^iv–C16^iv	143.4(1)

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Table 3 Parameters of intermolecular interactions within the structure 1

D–H⋯A	d(D–H)/Å	d(H⋯A)/Å	d(D⋯A)/Å	<(DHA)/°
Symmetry code: (iii) −x, y + 1/2, −z − 1/2; (iv) −x, y − 1/2, −z − 1/2; (vi) x, −y − 1/2, z − 1/2; (vii) x, −y + 1/2, z − 1/2; (viii) −x − 1, y − 1/2, −z − 1/2; (ix) −x − 1, −y + 1, −z.
O4^iv–H17^iv⋯O2	0.83(3)	1.74(3)	2.599(2)	172(3)
C11–H11⋯O4^iii	0.95(2)	2.52(2)	3.033(2)	113(2)
C16–H15⋯O2^iii	1.00(2)	2.55(2)	3.248(2)	127(2)
C13–H12⋯O3^iv	0.93(2)	2.66(2)	3.462(2)	147(2)
C8–H14⋯Cl^vi	0.92(2)	2.92(2)	3.745(2)	150(2)
C10–H8⋯Cl^viii	0.95(2)	3.01(2)	3.847(3)	147(2)
C6–Cl⋯Cl^ix	—	3.359(1)	—	142.86(8)

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The crystal structure of 1 consists of 2-D sheets¹⁵ (Fig. 2). The layers are situated in the bc plane and consist of two zigzag chains crossing at the Cu(II) atom and several hydrogen-bonding interactions C–H⋯O,¹⁶ [C11–H11⋯O4ⁱⁱⁱ; C16–H15⋯O2ⁱⁱⁱ; C13–H12⋯O3^iv] (Table 3) as shown in Fig. 2. The weak hydrogen bonds are now intensively studied;¹⁶ the role of weak C–H⋯O hydrogen bonds in crystal engineering of organometallic complexes has been recently reviewed by Braga et al.¹⁷ In complex 1 C–H⋯O hydrogen bonds have the role of stabilizing the 2-D chains. In Fig. 3 a view of the packing of 1 perpendicular to the ac plane is shown. As can be seen, the layers are connected by short Cl⋯Cl contacts¹⁸ and weak C–H⋯Cl interactions,¹⁹ [C8–H4⋯Cl^vi; C10–H8⋯Cl^viii] (Table 3), resulting in a 3-D network.¹⁵ The intermolecular interactions C–H⋯Cl with organic chlorine acceptor groups were previously the subject of controversial discussion; Thallapally and Nangia^19a suggested that C–H⋯Cl are essentially van der Waals contacts, on the other hand Brammer et al.^19b suggested that C–H⋯Cl are weak hydrogen bonds. In complex 1 the weak C–H⋯Cl interactions together with the short Cl⋯Cl interactions are dominant in the created 3-D network.

Fig. 2 View perpendicular to the bc plane showing the hydrogen bonding; chlorine atoms and benzene rings of clofibriate anions are omitted for clarity.

Fig. 3 View of the packing of 1 in the cell, viewed perpendicular to the ac plane; hydrogen atoms are omitted for clarity. Click image or 3.htm to access a 3-D representation.

The crystal structure of the compound under study can be compared with those of [CuX₂(3-pymeth)₂]_n, where X = salicylate (sal)²⁰ or niflumate (nif; 2-[α,α,α-trifluoro-m-tolylamino]pyridine-3-carboxylate).²¹ The Cu–O_eq (oxygen atom of carboxylic group), Cu–N_eq (nitrogen atom of pyridine ring of ronicol) and Cu–O_ax (oxygen atom of hydroxyl group of ronicol) lengths for the former structure are 1.944(4) Å, 2.039 Å and 2.622(4) Å, respectively. In the latter structure the values are 1.946(3) Å, 2.038(3) Å and 2.573(3) Å, respectively. All three compounds have polymeric structures with axially elongated tetragonal bipyramidal geometry about each Cu(II) atom of the CuO₄N₂ chromophore, as predicted by the Jahn–Teller theorem. The T parameter (T = R_s/R_L), indicating the degree of tetragonal distortion about the copper(II) centers,²² decreases in the sequence: 0.819 1 > 0.774 [Cu(nif)₂(3-pymeth)₂]_n > 0.759 [Cu(sal)₂(3-pymeth)₂]_n. Another structure variation for [CuX₂(3-pymeth)₂]_n was found for [Cu(nif)₂(3-pymeth)₂]_n.²¹ In this structure, ambidentate 3-pyridylmethanol molecules in the 1-D infinite chains bridge copper(II) atoms.²¹

Conclusions

Analysis of the packing of molecules of 1 in the crystal shows that the strong O–H⋯O as well as the weak C–H⋯O interactions play a role in the stabilization of 2-D coordination polymers. The interlayer contacts are found to dominate in the absence of the strong hydrogen bonds. Short Cl⋯Cl and weak C–H⋯Cl interactions have been observed, which link layers of the 2-D coordination polymer.

Acknowledgements

This work was financially supported by grant 1/6106/20 from the Slovak Grant Agency for Science.

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Footnote

† Part 1: ref. 1.

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