Arranjos supramoleculares: formação de polímeros de coordenação com metais da primeira série de transição e ligantes polidentados derivados de anéis piridínicos

Abstract

This work presents the synthesis and characterization of supramolecular array with CoII, CuII and MnII first row transition metal ions and polidentate nitrogen ligands. The preparation in these compounds involved reactions between different metallic precursors MX2.xH2O (M= CoII, CuII, MnII, X= NO3- and ClO4-) with the flexible nitrogen ligands di(4-pyridyl)sulfide (4-DPS) and di(4-pyridyl)disulfide (4-DPSS). Additionally, the syntheses involving the substitution of chloride or nitrate ions in MX2 by thiocyanate anions followed by reaction with 4-DPS and 4-DPSS and the ligand N,N-4,4’-bis(4-pyridylmethylleneamino)(biphenyl) (DPBI) were carried out. The obtained compounds were characterized by means of elemental analysis (CHN), thermal analysis (TG/DTA), vibrational spectroscopies (infrared and Raman) and electron paramagnetic resonance (EPR). Initially, a brief introduction about the supramolecular chemistry (definition, interests, weak non-covalent interactions), coordination polymers (definition, different kinds, properties, covalent interactions), used nitrogen ligands (4-DPS, 4-DPSS e DPBI) and the chemistry of the pseudo-halide NCS-, was presented. Then, the synthesis and characterization of the nitrogen ligand di(4-pyridyl)sulfide (4-DPS) as well as of seven novel CoII, CuII and MnII complexes formulated as: {[Co(4-DPS)2(H2O)2](NO3)2.(4-DPS)2.4H2O}n (1), {[Co(4-DPS)2(H2O)2](NO3)2.4H2O}n (2), {[Cu(4-DPS)2(NO3)2].4H2O}n (3), {[Cu(4-DPS)2(H2O)2](NO3)2.2H2O}n (4), [Co(4-DPS)4(H2O)2](ClO4)2.H2O (5), [Mn(4-DPS)4(H2O)2](ClO4)2.H2O (6) and {[Mn(4-DPS)2(NCS)2].2H2O}n (7) were described. In the complexes (1-4) and (7) the 4-DPS ligands have coordinated the metal centers in a bridge fashion while in the complexes (5) and (6) acting in a monodentate mode, where only one of the pyridyl nitrogen donor atoms from each 4-DPS ligand is coordinated to metal centers. In this sense, the vibrational spectroscopy was a very useful tool to determine the 4-DPS and pseudo-halide coordination modes. In all cases, the thiocyanate anion is coordinated to the metal centers in terminal N-bonded fashion or isothiocyanate. The compounds (1-7), except (5), had their structures determined by single crystal X-ray diffraction analysis. In special, the compound [Mn(4-DPS)4(H2O)2](ClO4)2.H2O (6) consists in an coordination complex where the ligand 4-DPS is coordinated in the monodentate mode forming mononuclear units that expands to a two-dimensional (2-D) array through hydrogen bonding and by π-π stacking interactions extend the supramolecular arrangement in three dimensions. Another approach is related to the synthesis and characterization of five compounds containing the di(4-pyridyl)disulfide (4-DPSS) ligand namely: {[Co(C10H8N2S2)2(H2O)(NO3)]NO3.3H2O}n (8), {[Co2(C10H8N2S2)4(OCHN(CH3)2)2)](ClO4)4}n (9), {Co(C10H8N2S2)2(NCS)2}n (10), {[Mn2(C10H8N2S2)4(OCHN(CH3)2)4)](ClO4)4}n (11) and {Mn(C10H8N2S2)2(NCS)2}n (12). The X-ray diffraction data of the compounds (8-11) confirmed the structural information obtained by other characterization techniques, where it was possible to verify that both compounds (9) and (11) crystallized in the space group P2/n and monoclinic system with crystal cell parameters for (9): a=18.430(4), b=10.624(2) c=18.663(4) Å; β=93.99(3)o, Z=2 and for (11): a=18.402(4), b=10.637(2), c=18.641(4) Å; β=94.24(3)o, Z=2, and therefore are isostructural. These compounds have repeated rhomboidal structures in which the di(4-pyridyl)disulfide ligands coordinate the metal centers in a double bridged fashion. Each double chain and the metallocycle cavities are chiral and contain either the M- or the P- enantiomeric forms of 4-DPSS and are independent on recrystallization solvents or the metallic precursors. The crystal packing of these coordination polymers reveals that, in all cases, weak interactions such as classical and non-classical hydrogen bonds, as well as SS interactions, connect the polymeric chains to increase the dimensionality of the network. Finally, the syntheses involving the ligand 4,4’-bis(4-pyridylmethylleneamino)(biphenyl) (DPBI) led to the taking of three compounds named: [Co2(DPBI)(NCS)2(NO3)2].CH2Cl2 (13), [Cu(DPBI)(NCS)2].2CH2Cl2 (14) and [Mn(DPBI)2(NCS)2].4CH2Cl2 (15). In a similar way, as mentioned before, vibrational spectroscopy afforded important information about the bonding properties of NCS- anion. In these cases, two different coordination modes were observed for the pseudo-halide; symmetric bridging μ-1,3 in dimmer (13), simultaneously terminal N-bonding and symmetric bridging μ-1,3 in compound (14) and isothiocyanate in polymer (15). This work opens new possibilities to study Supramolecular Inorganic Chemistry, currently one of the most promising areas of research in chemistry. In this study we focused on some factors that can influence the dimension of the structure formed and the interactions present. The comparison between some complexes can highlight some conclusions; 1st) the synthesis conditions were essential to structural differences in compounds (1) and (2), (3) and (4), 2nd) the counter-ion effect in the formation of complexes (6) and (7) and 3rd) the solvent effect in the formation of complexes (8) and (9). The same synthesis conditions with the perchlorate counter-ion led to obtain the isostructural compounds (9) and (11) which have different metal centers. Although we can plan the structures design by selecting the determining factors, the self-assembly ability of this class of compounds led us to obtain unexpected arrangements with intriguing structural topologies. The advance Supramolecular Chemistry research will bring valuable contributions to the potential applications of these compounds in physics and chemistry as well as to understand and control the various factors that are directly related to the supramolecular architectures formation process. "Formula disponível no trabalho completo"