SÍNTESE, CARACTERIZAÇÃO E ESTUDOS TEÓRICOS DOS COMPLEXOS DE COORDENAÇÃO [(Fen)4Fe2(Succinato)2(μ-O)](H2O)9 E [(Fen)4Fe2(Cl)2(μ-O)](H2O)4

Abstract

The development of materials is crucial for advancing solutions to modern challenges. Coordination complexes and their crystalline structures stand out due to their unique properties and multidomain applications. Their synthesis and characterization through advanced techniques enable understanding of their extent and potential, guiding toward targeted applications. In this context, this thesis reports the synthesis and characterization of the complexes [(Fen)4Fe2(Succinate)2(μ-O)](H2O)9 - “SUCFENFe” e [(Fen)4Fe2(Cl)2(μ-O)](H2O)4 – “CLOFENFe”, obtained via slow evaporation of water and methanol using 1,10- phenanthroline, succinic acid, iron(II) chloride, and iron(II,III) oxide as precursors. Structural, spectroscopic, electronic, and thermal properties were investigated using XRD, PXRD, FT-IR, Raman, UV-Vis, and TG-DTA. Theoretical features were analyzed through Hirshfeld surface analysis (Crystal Explorer 21) and computational calculations in vacuum and under solvation using Density Functional Theory (DFT) in Gaussian 16 rev. C.01 with the PBE1PBE functional and def2-SVP/def2-TZVP basis sets. The “SUCFENFe” structure is novel, patented, and deposited in the Cambridge Structural Database (CSD: 2300427). It crystallizes in the monoclinic system, space group C2/c (Z = 4), with crystal packing stabilized by C – H ••• O, C – O ••• H, C – H ••• π e π•••π interactions. It exhibits a strongly heteroleptic, low-spin coordination environment, with a stabilization energy of approximately –4.73 eV. Direct allowed electronic transitions were observed, with a maximum optical bandgap of 2.66 eV determined by fitting the Tauc and Wood equation to the UV-Vis spectrum. Characteristic vibrational modes of ligands and metal centers in IR and Raman spectra were consistent with literature. Thermal analysis revealed three main decomposition stages, with dehydration occurring between 80 and 136 °C, indicating potential for temperature-dependent applications. The “CLOFENFe” structure, originally reported by Saha et al. (2003), was synthesized via an alternative route and confirmed by Rietveld refinement of PXRD data (Rwp = 11.39%, Rp = 8.59%, S = 1.80). It also crystallizes in the monoclinic system, space group C2/c (Z = 4), with packing stabilized by C – H ••• O, C – O ••• H, C – H ••• π, H ••• Cl, e π ••• π interactions. DFT calculations in this work confirm a strongly heteroleptic, low-spin coordination environment, previously supported by Mössbauer analysis for magnetic moment by Saha and coworkers. It exhibits direct allowed electronic transitions and a maximum optical bandgap of 3.10 eV. Experimental IR and Raman vibrational modes were assigned based on DFT predictions. A strong and significant Pearson correlation (r > 0.94, p < 0.05) was observed between experimental and theoretical bond lengths and angles. Thermal analysis revealed three main decomposition stages, with dehydration between 50 and 138 °C, again suggesting suitability for temperature-sensitive applications. Global chemical reactivity descriptors, electrostatic potential, dipole moment, and optical bandgap of CLOFENFe are strongly influenced by the solvation environment. Therefore, the synthesis and characterization of SUCFENFe and CLOFENFe presented herein highlight their potential for diverse applications in materials science and chemistry, establishing them as notable multifunctional structures.