Molecular Mechanisms of [Bi₆O₄(OH)₄](NO₃)₆ Precursor Activation, Agglomeration, and Ripening towards Bismuth Oxide Nuclei

Abstract

Molecular dynamics simulations have been employed to characterize the role of [Bi6O4(OH)4](NO3)6 cage structures in DMSO solution as precursors to larger bismuth oxide aggregates. We find that the nitrate ions play a twofold role: (i) the association of [Bi6O4(OH)4](NO3)6 clusters – which are fully coordinated by six nitrate ligands – is electrostatically disfavored giving rise to stable [Bi6O4(OH)4](NO3)6 solutions; (ii) in contrast, the dissociation of a single nitrate ligand results in attractive cluster–cluster interactions. This results in the formation of oligomers, which are initially bridged by one to three nitrate ions, but then form Bi–O contacts by sharing common edges and faces and eventually ripen into nuclei of bismuth oxide. Strikingly, this process may be induced by a single activated species, the [Bi6O4(OH)4](NO3)5+ cluster, which may bind several [Bi6O4(OH)4](NO3)6 clusters.

Structural Changes during the Growth of Atomically Precise Metal Oxido Nanoclusters from Combined Pair Distribution Function and Small‐Angle X‐ray Scattering Analysis

“…We therefore attempted to fit other known cluster structures, with sizes between [Bi 6 O 8 ] to [Bi 38 O 45 ], to the intermediate PDF as shown in Figure S7. The best cluster candidates were the [Bi 18 O 36 ] and [Bi 22 O 38 ] structures, agreeing well with observations from in situ ESI‐MS analysis, molecular dynamics simulations and quantum chemical calculations [13, 15a,b] . However, to look further into the time‐dependent structural changes, and to probe a larger structural space, we developed an automated method, where all smaller cluster structures based on the [Bi 38 O 45 ] framework were tested against the experimental PDF.…”

From Solute, Fluidic and Particulate Precursors to Complex Organizations of Matter

“… Mechanistic contributions of (a–c) solute clusters and (d‐h) liquid condensed phases in nucleation and crystallization reactions. Computer simulations of (a) the termination effects of HCO 3 − ions (dotted circle) on the growth and stability of CaCO 3 clusters, (b) the contributions of nitrate ions (dotted circle) as salt bridges between [Bi 6 O 4 (OH) 4 ](NO 3 ) 6 ] related cluster species, subsequently undergoing structural rearrangements and forming dimer species during bismuth oxide nucleation and (c) Cd 13 S 4 (SH) 18 PNCs exhibiting repulsive interactions based on thiol‐stabilized surfaces and distinct coordination structures . (d) In situ observations of LCPs as precursors for amorphous and crystalline metal particles in supersaturated Au 0 solutions .…”

“…For instance, PNC‐associated ions and organic molecules presenting higher hydration contents hinder the dehydration of the ionic species, thereby enhancing the supersaturation levels required for particle nucleation ,. Thus, the nucleation process cannot be deconstructed to a simple aggregation‐based size evolution from individual ions to particles, but also is ingrained by the configurational and molecular nature of solute precursors in relation to their environment, (Figure a–c). Given the prospects of configurational motifs propagating through the reaction co‐ordinate prior to and after the nucleation event, the forces contributing to the clustering of ions, atoms and molecules are fundamentally and technologically relevant.…”

Thermodynamics and Kinetics of Prenucleation Clusters, Classical and Non‐Classical Nucleation

“…[28] Using molecular dynamics simulations we identified the mechanisms of precursor stabilization by coordinating nitrate ions. [29] For intact [Bi 6 O 4 (OH) 4 ](NO 3 ) 6 clusters the nitrate surfactants were shown to electrostatically inhibit the association of the clusters, thus giving rise to stable solutions. However, by lowering the pH, the clusters may be protonated and dissociation of a HNO 3 molecule leads to the formation of an activated species, the [Bi 6 O 4 (OH) 4 ](NO 3 ) 5 + cluster, which was found to bind several [Bi 6 O 4 (OH) 4 ](NO 3 ) 6 clusters.…”

“…Pictures were taken from molecular dynamics simulations as reported in Ref. [29]. Reproduced with permission from Wiley-VCH.…”