Isomerism of Trimeric Aluminum Complexes in Aqueous Environments: Exploration via DFT-Based Metadynamics Simulation

Abstract

The chemistry of aluminum or oxo-aluminum in water is still relatively unknown, although it is the basis for many chemical and industrial processes, including flocculation in water treatment plants. Trimeric species have a predominant role in the formation of the Keggin cations, which are the basic building blocks of aluminum-based chemicals. Despite this, details of the structural evolution of these small solvated clusters and how this is related to the processes leading to the formation of larger aggregates are still an open issue. To address these questions, here, we have applied the metadynamics (MTD) simulation technique [ Barducci , A. ; Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2010 , 1 , 826 - 843 ] with density functional theory-based molecular dynamics to disclose the dynamics and structural conversions of trimeric aluminum complexes in an aqueous environment. The existence of a variety of competing metastable conformations, for example, book-like, cyclic boat, and linear shape conformations, is revealed in the MTD simulation. Furthermore, equilibrium simulations of the various intermediate states encountered along the MTD trajectory are used to assess their (meta)stability, determine the rearrangement of the OH ligands, and discuss the role of the solvating water.

Ab Initio Molecular Dynamics Study of the Proton Transfer in Hydroxyl Ion-Induced Hydrolysis of Aluminum Monomers

“…The stability of these products in the solution system is determined by observing whether or not a dehydration reaction occurs. Considering the cost and reasonability of the calculation, one product is considered stable in solution if no dehydration reaction occurs within 25 ps AIMD. , In the presence of one OH – ion in solution, only one product, namely, Al­(H 2 O) 5 (OH) 1 2+ , is observed. This species is stable as no changes were observed during the following 25 ps of AIMD analysis.…”

“…Aluminum compounds, such as alumina, aluminum hydroxide, and aluminum sulfate, find diverse applications in electronic devices, heat insulation, and water treatment. − The sol–gel method is widely employed for the preparation of various aluminum products due to its simplicity, economic applicability, and wide range of applications. − Nanoscale aluminum particles gradually form through hydrolysis and polymerization reactions during the sol process. Despite numerous studies conducted on large polymeric species that exist stably in solution, such as AlO 4 Al 12 (OH) 24 (H 2 O) 12 7+ and Al 30 O 8 (OH) 56 (H 2 O) 24 18+ , the mechanisms behind the formation and growth of these aluminum clusters remain unclear. − Since aluminum oligomers are the basis for the formation of polymeric species, the study of aluminum oligomers, particularly the most fundamental aluminum monomers, contributes to revealing the formation process of polynuclear aluminum clusters and provides guidance for the preparation of aluminum-based materials. − …”

Ab initio molecular dynamics free energy study of enhanced copper (II) dimerization on mineral surfaces

“…Focusing on divalent and multivalent cation dimer species, the electrostatic repulsion between cations is overcome by OH − and/ or O 2− bridges, plus the surrounding water/high dielectric media. Al 3+ dimers, which can be bridged reversibly by either two OH − or a single O 2− , have arguably received the most fundamental science studies due to their relevance to nuclear waste at high pH conditions [29][30][31][32][33][34] . In recent years divalent transition metal cation dimers and trivalent lanthanide dimers have become areas of technological significance 6,17,18 .…”