Síntese e análise estrutural de novos plímeros de coordenação envolvendo seleninatos de metais alcalinos e alcalinos terrosos

Abstract

Seven new compounds involving the phenylseleninato ligand and alkaline and alkaline earth metals were obtained in this work: poly-phenylseleninato lithium(I) (1), catena-polybis(aqua)-phenylseleninato sodium(I) (2), poly-phenylseleninato potassium(I) (3), polytetraquis(aqua)-bis(phenylseleninato) magnesium(II) (4c), catena-poly-bis(phenylseleninic acid)-bis(phenylseleninato) calcium(II) (5), catena-poly-acetato-phenylseleninic cidphenylseleninato strontium(II) (6) and catena-poly-bis(phenylseleninato) barium(II) (7c).Among of these compounds, the structures of (2), (4c), (5), (6) and (7c) were determined and (1) and (3) coordination polymers appeared to be amorphous. All compounds were synthesized in a mixture containing the phenylseleninic acid and the desired metal acetate using previously dried methanol as solvent, under constant mechanical stirring at room temperature for 90 minutes. Crystals were obtained directly from methanol solutions after slow evaporation after one week, except for compounds (4c) and (7c), whose powders were dissolved in concentrated ammonium hydroxide and in deionized water, respectively, yielding suitable crystals for analysis after one week. Single crystal X-ray diffraction revealed the formation of 2D coordination polymers, with the exception of compound (5), which exhibits 1D chains. The unit cell and refinement basic parameters for the five determined crystalline structures are as following: a = 6,0576(5), b = 13,8771(11), c = 6,0733(6), α = 90, β = 116,052(5), γ = 90, R1 = 0,0470 and wR2 = 0,0668 [I>2s(I)] for compound (2) (monoclinic crystal system, space group Pc); a = 13,9470(5), b = 5,0443(2), c = 11,9802(5), α = 90, β = 90,985(3), γ = 90, R1 = 0,0339 and wR2 = 0,0629 [I>2s(I)] for compound (4c) (monoclinic crystal system, space group P21/c); a = 5,9262(2), b = 10,0707(4), c = 11,2799(4), α = 91,496(2), β = 94,201(2), γ= 92,269(2), R1 = 0,0212 and wR2 = 0,0605 [I>2s(I)] for compound (5) (triclinic crystal system, space group P-1); a = 11,3610(7), b = 6,9836(4), c = 24,6038(14), α = 90, β = 90, γ = 90, R1 = 0,0493 and wR2 = 0,1280 [I>2s(I)] for compound (6) (orthorhombic crystal system, space group Pnma) and a = 6,3685(10), b = 6,8811(12), c = 15,549(3), α = 90, β= 94,436(8), γ = 90, R1 = 0,0400 10 and wR2 = 0,1269 [I>2s(I)] for compound (7c) (monoclinic crystal system, space group C2/m). Collected data using powder X-ray diffraction showed that compounds (2), (4c) and (5) have their crystalline phase modified when exposed to different moisture experimental conditions (~ 47% with variable times of exposure). Thermal analysis was performed to investigate the water content present in compounds (2) and (4c), revealing the probably formation of compound Na2SeO2 containing the SeOn2- anion (where n can be equal to 2, 3, 4 or 5). Some of these compounds containing such anions are new and very interesting for spectroscopic studies involving infrared and Raman techniques, since they presents different symmetry motifs, belonging to different point groups. Other instrumental methods used to characterize the compounds obtained were infrared spectroscopy and C/H elemental analysis.