Determinação da estrutura cristalina do novo complexo de L-Glutamina com Ni(II): um estudo de difração de raios X em policristais auxiliado por análise térmica, vibracional e cálculos DFT

Abstract

In this work, the determination of the crystal structure of the L-glutamine-nickel complex through X-ray diffraction in polycrystals was carried out and aided by thermal and vibrational analysis and DFT calculations. This material was synthesized in the proportion of 2 mols of L-glutamine and 1 mol of nickel, which grew in the form of polycrystalline spheres. These spheres were ground and subjected to X-ray diffraction measurements in polycrystals. After a search at the Cambridge Crystallographic Data Center (CCDC) for materials that had a crystal structure that matched the diffraction pattern of the complex studied in this work, it was found that the available X-ray diffraction patterns did not match the pattern of the complex. glutamine with nickel. Therefore, a new material had been obtained and therefore its crystal structure had to be determined. From the thermogravimetric analysis, a loss of mass around 160 ◦C was observed, equivalent to the mass of two water molecules, which were coordinated to the metal. Thus, it was considered that the chemical formula of this new complex is: Ni(L-glutamine)2(H2O)2. DFT calculations were performed with the aim of generating an initial molecule to resolve the structure of this crystal. Initially, the analysis of five molecules of the complex was established, arranged with two molecules of glutamine and water linked to the nickel atom. These structures were optimized with the hybrid functional B3LYP with the base function def2-tzvp for the nickel atom and 6-311++G(d,p) for the other atoms, and relaxed scan calculations were performed. in order to build the potential energy surfaces, and identify the most stable structure. With the measurement of X-ray diffraction in polycrystals and with the possible configurations of the optimized molecules, the resolution of the crystal structure Ni(L-glutamine)2(H2O)2 was performed using the Simulated Annealing method. This compound crystallized in a triclinic system with space group P-1, with unit cell parameters a = 5.1308(2) Å, b = 10.6038(9) Å, c = 14.2084(14) Å, α = 104.325 ◦

, β = 96.652 ◦

, γ = 91.433 ◦

and V = 742.79(11) Å 3 . The crystal structure of Ni(L-glutamine)2(H2O)2 consists of two molecules per unit cell (Z = 2), accommodating one molecule in the asymmetric unit (Z’ = 1). The Rietveld method was used to refine the crystal structure and the fit quality indicators were: Rp = 3.53 %, Rwp = 4.77 % and the RBragg = 1.07 %.