Síntese e caracterização de novos compostos de coordenação contendo ligantes pirazólicos funcionalizados

Abstract

Aromatic heterocycles such as pyrazoles are widely used in the construction of new molecular architectures when coordinated to ions of the d block leading to interesting biological and technological properties. In this work we describe the synthesis and characterization of two functionalized pyrazole ligands: potassium 5-amino-1-(benzothiazol-2-yl)-1H-pyrazole-4-carboxylate (L1) and potassium 5-amino-1-(pyrazin-2-yl)-1H-pyrazole-4-carboxylate (L2). The syntheses of the ligands were performed in three steps: (1) formation of the pyrazole nucleus with an ester group, (2) hydrolysis and (3) neutralization. In addition, a new azo (N=N-) photosensitive compound (E)-diazene-1,2-diylbis(4,1 phenylene)bis(hydrazinecarboxylate) (L3) was obtained. The synthesis of L3 was performed by reduction of 4-nitrophenol in alkaline conditions, affording the azo group, followed by two additions reactions in the phenol and carbonyl groups. All reactions steps were characterized by infrared, 1H-NMR and 13C-NMR spectroscopies, as well as melting point and GC-MS analyzes. The L1 and L2 ligands were used to synthesize new coordination compounds containing CoII, FeII, MnII, CuII and NiII ions. By using the slow diffusion methodology, two new families of coordination compounds wereobtained, with molecular formulas cis-[M(L1)2(OH2)4] (M= FeII, CoII and NiII) and trans-[M(L2)2(OH2)4] (MnII and CoII). The crystal structures of these complexes were solved by X ray diffraction and it was observed that the ligands are coordinated in a monodentate fashion. The crystal packing of these systems is stabilized by intra and intermolecular hydrogen bonds. The complexes cis-[M(L1)2(OH2)4] were studied by cyclic voltammetry, which theoxidation and reduction peaks were observed with respect to the FeII, CoII and NiII ions. The Mössbauer spectroscopy for cis-[Fe(L1)2(OH2)4] showed a high spin state for the FeII ion in the emperature range 4-300 K. The magnetic measurements for the compounds cis-[Fe(L1)2(OH2)4] (M = CoII, FeII) showed a key role played by the axial and rhombic anisotropy from the metal ion, since the exchange interactions are negligible. Furthermore, this family was evaluated against the inhibition of the acetylcholinesterase showing good inhibition rates in aconcentration of 10 μmol L-1. Through the slow diffusion methodology, new coordination compounds [Cu(L1)2(Py)2] and [Co(L1)2(Py)2] were obtained. The crystal structures of the compounds were elucidated by single crystal X-ray diffraction; in the [Co(L1)2(Py)2] complex, the metal ion lies on a distorted tetrahedral geometry, coordinated to two pyridine molecules and two oxygen atoms from different carboxylate groups in a monodentate fashion. The complex [Cu(L1)2(Py)2] presented the CuII ion in a distorted octahedral geometry, with two L1 ligands coordinated in a bidentate fashion the coordination sphere of the metal ion was completed by two coordinated pyridine molecules.