Chapter 6
Cooperative Active-Sites Mechanism
Akin to the shell structures of atoms, shell-filling concepts from traditional valence
bond theory can be applied to the description of cluster stability. In view of this, the
result of a chemical interaction could be explained through the energy minimization
attained when a cluster closes an incomplete electronic shell, either by direct ionization or through the formation of a covalent/ionic bond. Also it has been widely recognized that the cluster reactivity depends on both geometric and electronic structure,
although not all reactions are subject to the same fundamental constraints. However,
unexpected stability may also exist for some clusters with neither a spherical geometry nor a closed electron shell according to the NFEG model. Understanding how a
specific size and/or shape can affect the affinity of a metal cluster toward a specific
reagent will facilitate the efforts to design either stable or reactive materials for
specific applications.
In this regard, cooperative active-sites mechanism has found reasonable research
interest for chemists to interpret novel cluster reactivitity. Originally, active sites in
biology usually refer to the region of an enzyme (a groove or pocket) where certain
substrate molecules bind and react [1–3], allowing the residues in the binding site to
form hydrogen bonds, hydrophobic interactions, or temporary covalent interactions
(van der Waals). In cluster science, complementary Lewis acid/base active sites refer
to a location on the cluster surface where one atom acts as a Lewis acid and a
second Al atom acts as a Lewis base site [4–8]. This established mechanism well
explained the size-selectivity of Al n
− in reacting with water, and has been recognized
to be highly helpful in understanding reactivities between metal clusters and polar
molecules [9–22]. In this chapter, we will introduce how the complementary active
sites (CAS) mechanism is operative in metal cluster reactivity.
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
Z. Luo and S. N. Khanna, Metal Clusters and Their Reactivity,
https://doi.org/10.1007/978-981-15-9704-6_6
81
Cooperative Active-Sites Mechanism
Akin to the shell structures of atoms, shell-filling concepts from traditional valence
bond theory can be applied to the description of cluster stability. In view of this, the
result of a chemical interaction could be explained through the energy minimization
attained when a cluster closes an incomplete electronic shell, either by direct ionization or through the formation of a covalent/ionic bond. Also it has been widely recognized that the cluster reactivity depends on both geometric and electronic structure,
although not all reactions are subject to the same fundamental constraints. However,
unexpected stability may also exist for some clusters with neither a spherical geometry nor a closed electron shell according to the NFEG model. Understanding how a
specific size and/or shape can affect the affinity of a metal cluster toward a specific
reagent will facilitate the efforts to design either stable or reactive materials for
specific applications.
In this regard, cooperative active-sites mechanism has found reasonable research
interest for chemists to interpret novel cluster reactivitity. Originally, active sites in
biology usually refer to the region of an enzyme (a groove or pocket) where certain
substrate molecules bind and react [1–3], allowing the residues in the binding site to
form hydrogen bonds, hydrophobic interactions, or temporary covalent interactions
(van der Waals). In cluster science, complementary Lewis acid/base active sites refer
to a location on the cluster surface where one atom acts as a Lewis acid and a
second Al atom acts as a Lewis base site [4–8]. This established mechanism well
explained the size-selectivity of Al n
− in reacting with water, and has been recognized
to be highly helpful in understanding reactivities between metal clusters and polar
molecules [9–22]. In this chapter, we will introduce how the complementary active
sites (CAS) mechanism is operative in metal cluster reactivity.
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
Z. Luo and S. N. Khanna, Metal Clusters and Their Reactivity,
https://doi.org/10.1007/978-981-15-9704-6_6
81