Complexos supramoleculares baseados em manganês(II): síntese, caracterização estrutural e espectroscópica

Abstract

Supramolecular complexes are part of a class of materials which result is the result from the association of two or more chemical species held together by a variety of non-covalent intermolecular interactions including hydrogen bonds and coordination bonds. Such complexes can also be obtained from the intermolecular association of 1, 2 or 3 dimensions chains of coordination polymer which are also formed by the association of two or more chemical species, but these species are held together by covalent bonds. The interest in prepare these type of materials is due the variety of structures that can be formed and their potential applications in optics, electronics, as host materials, etc. About the supramolecular complex based on manganese(II) the interest is primarily related to the magnetic properties of these materials. In this work, from a relatively simple synthesis was obtained two crystalline products containing manganese(II): an ionic complex and a coordination polymer. The obtained products (B1 and C) were isolated and characterized by chemical and physical techniques, like X-ray diffraction crystallography, electron paramagnetic resonance spectroscopy and absorption spectroscopy in the infrared region; was also carried out a qualitative test for each product in order to confirm the presence of manganese(II) ion. The B1 product was obtained either from a reaction under reflux at 90 °C as for Teflon® reactor at 107 °C. The synthesis using reactor, in addition to being faster, resulted in a yield approximately four times greater than that for the synthesis using the reflux system. The B1 product represents a coordination polymer comprising MnII centers coordinating formate ligand generating ionic unities which can be represented by {Mn(OCHO)3}-, and the charge balance is done by dimethylammonium ion, (CH3)2NH2+, embedded in the pores of the polymer network. The C product obtained from a refluxing reaction at 95 °C, is a complex of molecular formula [Mn(NO3)2(bpy)2][Mn(NO3)(bpy)2(H2O)]NO3 which has two coordination units containing mononuclear manganese(II):one of them a neutral entity and other a cationic entity. In the neutral unit, the central manganese(II) is bound to two 2,2'- bipyridine ligands and two nitrate ligands, while in cationic unit the MnII center has two 2,2'-bipyridine ligand, a nitrate ligand and a coordinated molecule of water. The counter-ion nitrate makes the charge balance of cationic unit. The complete characterization of both systems is in progress.