New polimeric adducts of tetrakis-u-haloaspirinato-dicopper(II)

MARIELA A. AGOTEGARAY; EDUARDO M. RUSTOY; OSCAR V. QUINZANI; GUSTAVO A. ECHEVERRÍA; OSCAR E. PIRO

Cusco

Congreso; Congreso Iberoamericano de Química ? XXIV Congreso Peruano de Química; 2008

Numerous studies have been carried out on the pharmacological properties of copper carboxylates. In particular, copper aspirinates have been found to act as anti-inflammatory, analgesic, anticarcinogenic, anticonvulsant, antithrombotic, catecholase mimetic and potential neuroprotective agents. These pharmacological studies often contain copper-aspirinate systems either involving simple mononuclear complexes or paddle-wheel dinuclear tetrakis-aspirinate complexes. In contrast with the large number of experimental and theoretical studies about aspirin, less is know about its 5-halogenated derivatives. As far as we know, there exist only a report about the synthesis and ESR spectra of the complete series of dinuclear copper-5-haloaspirinates and a study of the thermal stability of dinuclear and mononuclear copper haloaspirinates. In order to further explore the chemical and structural properties of haloaspirinate-copper complexes we started a complete study of ternary mono- and polynuclear derivatives including different kind of nitrogenated bases as additional ligands. In this work we report the synthesis, FTIR and UV-visible spectroscopic characterizations of dinuclear copper(II) complexes of the form [Cu2(Xasp)4(MeCN)2] (Xasp=haloaspirinate anion; X= F, Cl, Br) and [{Cu2(Xasp)4}(B)]n (B= pyrazine (pyz) or 4,4?-bipyridine). The FTIR spectra of all the complexes show very strong bands assignable to the nas(COO) and ns(COO) vibrations of bidentate bridging carboxylates. Vibrational bands of the MeCN and azines molecules were also observed and assigned. The solid state electronic spectra of all the complexes show broad unsymetrical bands centered at ca. 700 nm, assigned to unresolved d-d transitions of the copper atoms under the C4v symmetry of the dinuclear arrangements. We also report the X-ray diffraction study of bis(acetonitrile-kN)tetrakis{m-chloroaspirinate(k2-O,O)}dicopper(II) diacetonitrile, and poly[m-pyrazine(k2-N,N)-tetrakis{m-fluoraspirinate(k2-O,O?)}-dicopper(II)] monoacetonitrile. Both complexes are built by dinuclear units where four bidentate carboxylate anions form syn-syn bridges between metal atoms. The basal coordination of copper (II) ions is formed by four coplanar oxygen atoms from the bridging halo-aspirinate groups. The average Cu-O distances (1.943(5) and 2.002(5) Å) fall in the range of the values previously reported for Cu2(asp)4 [6]. The apical positions of each copper atom are occupied by N atoms of MeCN or pyz molecules at averaged Cu-N distances of 2.170 and 2.188 Å, respectively. In the [{Cu2(Xasp)4}(pyz)]n complex the alternating dinuclear copper fluoraspirinates and the pyrazine units form 1D infinite chains.