Síntese, estudos espectroscópicos e estruturais de complexos contendo o ligante 4,4’- bipiridina, o ânion barbiturato e os íons metálicos da primeira série de transição (Fe2+, Co2+, Ni2+, Cu2+ e Zn2+)

Abstract

This work describes the synthesis and characterization of five new transition metal complexes of general formula MB2Bipy.10H2O (where M = Fe2+, Co2+, Ni2+, Cu2+ and Zn2+, B is barbiturate anion and Bipy is 4,4’-bipyridine) . Several physical and spectroscopical techniques were used to characterize the compounds, such as elemental analysis (CHN), thermal analysis (TG/DTA), vibrational (Raman and infrared) and electronic (absorption and reflectance in the visible region) spectroscopy as well as single crystal X ray diffraction analysis. The FeB2Bipi . 10H2O (1), CoB2Bipi . 10H2O (2), NiB2Bipi . 10H2O (3), CuB2Bipi . 10H2O (4) and ZnB2Bipi . 10H2O (5) complexes give rise to polymeic basic units, where Fe(II), Co(II) and Zn(II) compounds are isomorphous belonging to P6422 space group, different from the Ni(II) and Cu(II) compounds which are also isomorphous, belonging to P6522 space group; however, all compounds present the same molecular structure. In each compound the metal site appears in a distorted octahedral geometry, coordinated by two pyridine nitrogen atoms and also to four oxygen atoms from the coordinated water molecules. Each structure shows a covalent linear [M(Bipy)(H2O)4]2+ one-dimensional chain , which interacts by hydrogen bond with the barbiturate anion and the crystallization waters, resulting in a tridimensional arrangement. The analysis of the Ni2+ and Cu2+ complexes structures shows flexible bidimensional hydrogen bonds networks being constructed by the four barbiturate anions and the two crystallization water molecules; this structure may be deemed to be the host, while the robust 1D [M(bipy)(H2O)4]2+ chains may be deemed to be the guest, in a very intriguing and interesting structure. The vibrational spectra of the compounds are very similar, in agreement to the crystallographic data. In all infrared spectra a medium intensity band at 1690 cm-1 has been observed, assigned to the CO stretch of the barbiturate anion. In the Raman spectra the most important bands referring to 4,4’-bipyridine ligand are the ones at 1616, 1290 and 1020 cm-1, assigned to νCC/CN, νring + δCH and νring modes, respectively. For characterization of barbiturate anion one medium Raman signal is observed around 680 cm-1 assigned to the ring breathing mode. The successful synthesis of the new (1), (2), (3), (4) and (5) compounds demonstrates that the introduction of mixed ligands may provide multiple binding forces such as coordinated covalent, electrostatic and hydrogen bonding interactions, which may endow an enormous potential for assembling multidimensional supramolecular architectures. Furthermore, the use of the barbiturate species, which act as H-donors by the NH and CH moieties, and H-acceptors by the CO groups, can contribute through new features and arrays to the rapidly expanding area of supramolecular chemistry by our research group.