Novel dinuclear and polynuclear copper(II)-pyrazine-2,3-dicarboxylate supramolecular complexes with 1,3-propanediamine, N,N,N′,N′-tetramethylethylenediamine and 2,2′-bipyridine
Graphical abstract
We have successfully synthesized and characterized the novel dinuclear and polynuclear Cu(II)-pyrazine-2,3-dicarboxylate complexes. The molecular structures of dinuclear (1) and polynuclear (2, 3) complexes have also been determined by the single crystal X-ray diffraction technique. The pyrazine-2,3-dicarboxylate ligand acts as a tridentate bridge between the metal ions forming one-dimensional polymeric chains, its coordination sites being the O atom of carboxylate and N atom of ring and one O atom of neighboring carboxylate group.
Introduction
The rational design and synthesis of metal-directed the supramolecular framework have received much attention in coordination chemistry in recent years owing to their novel and diverse topologies and potential applications in host–guest chemistry, catalysis, electrical conductivity, magnetism, nonlinear optics and gases sensors [1], [2], [3], [4], [5], [6], [7], [8]. In crystal engineering the cyclic dicarboxylates [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], oxocarbons [37], [38], [39] and pyrimidine bases have been used as building blocks [40], [41], [42] and many coordination polymers. Pyrazine-2,3-dicarboxylic acid (H2pzdca, Scheme 1a) generally tends toward react with metal salts to yield insoluble polynuclear materials and it behaves as a polyfunctional ligand in metal complexes and coordinates to metal ions by means of its four carboxylate oxygens and two nitrogen atoms forming monodentate [14], bidentate [15], [16], [17], [18], [19], bis(bidentate) bridging [20], [21], [22], [23], tridentate bridging [24], [25], [26], [27], [28], [29], tetradentate bridging [30], [31], [32], [33], [34], [35] and mixed chelating-bridging ligand [36]. The Pyrazine-2,3-dicarboxylate coordinated to the Cu(II) ion for the first time as a monodentate ligand in the [Cu(pdca)(H2O)(en)2] and [Cu(pdca)(H2O)(dmpen)2] [14], pzdca behaved as a bidentate ligand via O atom of carboxylate and N atom of pyrazine ring in the K2[Cu(pzdca)2(H2O)] · 6H2O [18] complexes, as a bis(bidentate) bridge ligands coordinated to metal ions through two carboxylate oxygen atoms and two nitrogen atoms of pyrazine ring in the [Cu(pzdca)(HCl)] [20] and {[Cu(pzdca)(H2O)2] · 2H2O}n [35]. The pzdca acts as a tridentate and tetradentate bridge between the metal ions forming one-dimensional polymeric chains, its coordination sites being the O atom of carboxylate and N atom of ring and one O atom (for tridentate) or two O atoms (for tetradentate) of neighboring carboxylate group in the {[Cu(pzdca)(H2O)2] · H2O}n [26], {[Cu(pzdc)2]·3(H2O)·2(idzc)}n [29], [Cu2(pzdca)2(L)]n [35].
In the present study, we describe the syntheses, spectroscopic, thermal studies (TG, DTG and DTA) and crystal structures of novel three supramolecular Cu(II)-pyrazine-2,3-dicarboxylate complexes with 1,3-propanediamine (pen), N,N,N′,N′-tetramethylethylenediamine (tmen) and 2,2′-bipyridine (bipy) (Scheme 1b–d); {[Cu(μ-pzdc)(pen)]·H2O}2 (1), {[Cu(μ-pzdc)(tmen)]·H2O}n (2) {[Cu(μ-pzdc)(bipy)]·H2O}n (3).
Section snippets
Complexes 1 and 3
A solution of pyrazine-2,3-dicarboxylic acid (0.840 g, 5 mmol) in water (25 mL) was neutralized with NaOH (0.4 g, 10 mmol) and added dropwise with stirring at 50 °C to a solution of CuCl2 · 2H2O (0.852 g, 5 mmol) in water (25 mL). The solution immediately became precipitate and was stirred for 4 h at 50 °C. The addition of the pen ligand (0.372 g, 5 mmol) or 2,2’-bipyridine (0.781 g, 5 mmol) in ethanol (10 mL) to the precipitate mixture resulted in a clear solution. The mixture was stirred for 2 h at 50 °C and
UV–Vis spectra and magnetic properties
The electronic spectra of water solutions of the complexes 1–3 display broad absorption bands at 617 (ϵ = 159 L mol−1 cm−1), 647 (ϵ = 88 L mol−1 cm−1) and 700 (ϵ= 127 L mol−1 cm−1), respectively, which are assigned to the dxz, dyz → dx2–y2 (a1 → b1) transition. The strong absorption bands below 300 nm are due to n → Π∗ and Π → Π∗ transitions of pen, tmen, bipy and pzdca ligands.
The complexes exhibit magnetic moment value of 1.57 for 2 and 1.58 for 3 which corresponds to one unpaired electron, while the dimeric
Conclusion
We have successfully synthesized and characterized the three novel dimeric and polymeric Cu(II)-pyrazine-2,3-dicarboxylate complexes. The molecular structures of dinuclear (1) and polynuclear (2 and 3) complexes have also been determined by the single crystal X-ray diffraction technique. The pyrazine-2,3-dicarboxylate behaves as a tridentate bridging ligand.
Acknowledgements
This work was supported by the Eskişehir Osmangazi University by project No. 200819042.
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