%0 Journal Article %T The Effects of Oxidation States and Spin States of Chromium Interaction with <i>Sargassum Sp</i>.: A Spectroscopic and Density Functional Theoretical Study %A Mohammad Abdul Matin %A Md. Aftab Ali Shaikh %A Md. Anwar Hossain %A Md. Alauddin %A Tapas Debnath %A Mohammed Abdul Aziz %J Green and Sustainable Chemistry %P 125-141 %@ 2160-696X %D 2021 %I Scientific Research Publishing %R 10.4236/gsc.2021.114011 %X The study of various oxidation states of chromium with Sargassum sp. is of particular interest since hexavalent chromium is reduced to trivalent chromium in an aqueous solution. In this study, a systematic density functional theory (DFT) calculations were performed to study the interactions of transition metal chromium ion with different oxidation states and spin states with the Sargassum sp. decorated with carboxylate (acetate) at the wB97XD/6-311++ G(d,p) level of theory. The structures and binding energies of chromium metal-carboxylate complexes at various oxidation states and spin states in gas phase were examined. The coordination strength of Cr(VI) with the acetate ligand was predominantly the strongest compared to the other oxidation states. Vibrational frequency analysis, for the homoleptic monomers of tris [Cr^III(AC)₃]⁰ and [Cr^VI(AC)₃]³⁺ complexes, illustrate good harmony with the experimental and theoretical calculated frequencies. Using the time-dependent DFT (TD-DFT) at the level of CAM-B3LYP/6-311++G(d,p), the vertical excitation energies were obtained. The stabilization energies derived using the second order perturbation