Theoretical Studies of Boron−Water Cluster Ions B⁺(H₂O)_n and Aluminum−Water Cluster Ions Al⁺(H₂O)_n:  Isomers and Intracluster Reactions

Abstract

With ab initio molecular orbital calculations, structures of the singly positive charged boron−water clusters B+(H2O) n and aluminum−water clusters Al+(H2O) n are determined. The insertion reaction products HBOH+(H2O) n -1 and HAlOH+(H2O) n -1 are also investigated. Structures of the dimer-core clusters [M+(H2O)2](H2O) n -2 are similar to each other for M = B and Al. In contrast, the stability and structures of [B+(H2O)](H2O) n -1 and [Al+(H2O)](H2O) n -1 are quite different. The monomer-core boron clusters [B+(H2O)](H2O) n -1 do not have stable local minima; the spontaneous proton transfer reaction takes place to form BOH(H3O)+(H2O) n -2. In other words, the acid−base reaction takes place in such small clusters. In the larger clusters, the reaction further proceeds and the clusters isomerize to the linear type HBOH+(H2O) n -1. On the other hand, in the clusters [Al+(H2O)](H2O) n -1, no such reaction takes place. The cis-form hydrated products of the insertion reaction HMOH+(H2O) n -1 are more reactive, and the acid−base reaction is seen for both M = B and Al.

Ab Initio Studies on the Mechanism of the Size-Dependent Hydrogen-Loss Reaction in Mg+(H2O)n

“…HAlOH (H 2 O) nÀ1 was also more stable than Al (H 2 O) n for n ! 2, [17] and the isomerization barrier dropped significantly as the cluster size increased. [18] In contrast, structure optimizations starting with HÀMgOH (H 2 O) nÀ1 always led to a long H ¥¥¥ Mg distance (!…”

“…Moreover, the mechanism, as well as its variation with increasing cluster size, should be a crucial part in our understanding of any size-dependent reaction. In the case of B (H 2 O) n clusters, [17] an intracluster reaction to form (HBOH) (H 2 O) nÀ1 became spontaneous for n ! 3.…”

“…One way is to place all water molecules in the first shell, as studied at the MP2/6-31G** level by Castleman et al [1] However, it is generally understood that hydrogen bonding between water molecules could be comparable in strength to the direct bonding between Mg and H 2 O, since the unpaired electron on Mg interacts repulsively with water molecules when the first shell becomes too crowded. [24] In the case of Al (H 2 O) n , [17] for which the repulsive interaction is more prominent due to the lone pair on Al , the maximum number of water molecules in the first shell was found to be three, which was termed the ™trimer core structure∫, [17] while water molecules in the second and third solvation shells would form hydrogen-bonded networks together with the first-shell ligands. Tetramer core structures were unstable.…”

Reactions of Alkaline Earth Metal Ions with Methanol Clusters

“…The number of methanol ligands in the first solvation shell is expected to be six based on the knowledge on the coordination of Mg 2+ in crystal. 32 The electron transferred from the Mg is delocalized among the methanol molecules other than the six directly ligated methanol molecules. It forms a solvated cage structure.…”

Automated exploration of stable isomers of H+(H2O)n (n = 5–7) via ab initio calculations: An application of the anharmonic downward distortion following algorithm

“…The latter is more reliable when the model potential is as accurate as ab initio calculations, although applicability and reliability of force field methods is not guaranteed for systems involving chemical bond rearrangements. 37 Hence, an automated systematic approach which can be applied to ab initio surfaces is desirable for analyses of such clusters involving an acid molecule with/ without the charge separation, [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] a neutral/zwitter-ionic amino acid, [54][55][56][57][58][59] a reactive metal cation which inserts into a water molecule, [60][61][62][63][64] and so on. The protonated water cluster also includes bond rearrangement in the reactions from the Eigen-type to the Zundel-type or vice versa.…”