Spherulite-like Ni(II)(l-glutaminato·H2O)2 Complex: Morphological Microstructure, DFT-Assisted Crystal Structure Determination, and Vibrational Analysis

l-glutamine complexes with transition metals have already been reported in the literature, but there have been no studies on l-glutamine complexes with Ni2+. Here, the new polycrystalline spherulite-like Ni(II)(l-glutaminato·H2O)2 complex was synthesized, and powder X-ray diffraction (PXRD) measurements and density functional theory (DFT) calculations were performed to determine its crystal structure. SEM images revealed the beautiful morphological microstructure of the new spherulite-like complex's surface and internal region. Thermogravimetric analysis (TGA) and vibrational spectroscopic techniques (infrared and Raman) were also performed. A mass loss observed at around 160 °C, equivalent to the mass of two water molecules, was determined by TGA. DFT calculations were initially performed to generate the most stable molecule and assist in crystal structure determination using the PXRD data. Five conformations of the complex were established, and these structures were optimized with the B3LYP hybrid functional and Def2-tzvp basis function for the nickel atom and 6-311++G(d,p) for the other atoms. Scanning calculations were performed to construct the potential energy surfaces and identify the most stable structure. From a PXRD measurement and the possible configurations of the optimized molecules, the Ni(II)(l-glutaminato·H2O)2 crystal structure was solved using a simulated annealing approach. The new compound crystallized in a triclinic system with a P1̅ space group.