“Síntese e estudos espectroscópicos dos compostos envolvendo metais divalentes (Mn, Co, Ni, Cu, Zn) contendo o ligante nitrogenado 1,3-bis (4-piridil) propano e o Íon esquarato”

Abstract

This work deals with the synthesis, specteroscopic characterization and crystal structure determination of coordination polymers formed by the interaction between squarate ion, 1,3-bis(4-pyridil)propane (BPP) and several transition metal ions (Mn2+, Co2+, Ni2+, Cu2+ e Zn2+). Eleven compounds have been obtained, and ten are new ones; from these new compounds, five are isostructural with general formula {(H2BPP)2+[M(C4O4)2(H2O)2]2-} (M = Mn2+, Co2+, Ni2+, Cu2+ e Zn2+) and abbreviated as MnSQH2BPP, CoSQH2BPP, NiSQH2BPP, CuSQH2BPP e ZnSQH2BPP, respectively. The other six compounds, three of them present general formula {M(C4O4)(BPP)2(H2O)2}, abbreviated as MnSQBPP, CoSQBPP e ZnSQBPP, and ZnCl2BPP is a sub product from the Zn+2 synthesis. The compounds MnSQH2BPP, CoSQH2BPP, NiSQH2BPP, CuSQH2BPP and ZnSQH2BPP crystallize in the ionic form, where the BPP ligand is not coordinated to the metal site, and the two nitrogen atoms from the pyridinic ring are protonated giving rise to a bivalent cation; the metal ion is bonded to two squarate ions and two water molecules, presenting distorted octahedral geometry. The squarate ion adopts the 1,3bis(monodentate) coordination mode, binding two metallic sites and giving rise to a bidimensional arrangement with (4,4) topology. The vibrational spectra of all compounds are very similar and agree very well with the crystallographic data, which show all them are isostructural. It can be observed in all infrared spectra one band of medium intensity at 1640 cm-1, assigned to NH deformation mode, indicative of cationic BPP formation. In the Raman spectra obtained with 1064 nm excitation a band at ca. 1800 cm-1 show up, assigned to CO stretching mode of the free ligand, whereas a band at ca. 1600 cm-1 is assigned to the CO stretching mode of the coordinated squarate ion. The MnSQBPP, CoSQBPP and ZnSQBPP compounds present the BPP and squarate ligands coordinated to the metal site, as well as two water molecules, in a distorted octahedral geometry. The squarate ligand adopts the 1,3-bis (monodentate) coordination mode, giving rise to an unidimensional arrangement in the a axis. Two bands can be observed in all infrared spectra: one of medium intensity at ca. 1620 cm-1 and one strong at 1535 cm-1, assigned to νCC/CN and νCO modes respectively, indicating the coordination of BPP and squarate ligands to the metal ion. In the Raman spectra it can be observed a very intense band at 1769 cm-1, assigned to νCO mode of the free squarate species. All these spectroscopic data are in a very good agreement with the X ray diffraction measurements. The ZnCl2BPP compound presents the metal ion in a distorted tetrahedral geometry, bonded by two chloride ions and by the BPP bridging two metal sites, exhibiting TT (trans-trans) conformation. The infrared spectra indicate this type of coordination through the CC/CN bands at 1619, 1562, 1508 and 1433 cm-1, all shifted to higher wavenumbers when compared to the free ligand. Structurally the BPP is bonding two metallic sites forming a chain in the crystallographic b axis direction, and this layer is linked to other adjacent layers by means of C-H..Cl interactions, extending in a bidimensional arrangement. The spectroscopic data obtained are also in a very good agreement with the crystallographic data for this compound.