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T. Masubuchi and A. Nakajima
Keywords Sandwich complexes · Multiple-decker sandwich clusters · Mass
spectrometry · Photoionization spectroscopy · Anion photoelectron
spectroscopy · Molecular magnetism
8.1 Introduction
It was 60 years ago that Feynman [1] delivered a famous lecture named “There’s
Plenty of Room at the Bottom,” where he proposed a concept of designing
functionalities by taking full advantage of the properties of things on a small scale.
In 1962, Kubo [2] theoretically inferred that physicochemical properties of such
small materials are different from those in bulk because of discrete energy levels of
electrons. Since then, nanoscale materials have been important subjects in both basic
and applied sciences. Among them, clusters consisting of up to about 1000 atoms
have been extensively studied as they exhibit unexpected geometric and electronic
properties that are scaled as a function of cluster size [3].
In recent decades, indeed, metal clusters and molecular clusters have attracted
great attention as novel nanoscale materials of finite multifunctional systems.
For metal clusters, spectroscopic and theoretic studies have revealed the sizedependent electronic properties of metal-insulator transition [4] and the electron
shell structures based on jellium model [3, 5], the latter of which were discussed
also from the viewpoint of mimicking shell model of nucleus [5]. As well as physical
properties, chemical properties of size-specific reactivity of the metal clusters have
been greatly explored as cluster catalysts [6]. On the other hand, molecular clusters
have been extensively studied as the aggregates of weak van der Waals forces or
hydrogen bond network, revealing microscopic solvation dynamics [7], coexisting
phases [8], and electronic evolution of organic semiconductors [9].
However, studies on hybridized clusters between metal atoms and molecules,
organometallic clusters, are limited, although organometallic molecular complexes
such as an archetypal complex of ferrocene and ligated metal cluster compounds
have been well known [10]. In particular, organometallic cluster formation can
facilitate to control the dimensionality of the geometric structure through local
metal-ligand interaction [11]. Since a low-dimensional structure of organometallic clusters synergistically exploits the chemical and physical features of metal
atoms and organic molecules, leading to a dramatic change in their confinement
behavior, functional properties such as charge transfer, conductivity, and electron
spin arrangement can be designed by selecting an appropriate organic ligand which
optimizes the characteristics of the metal atoms.
Sandwich clusters, consisting of metal atoms and planar ring ligands, are typical
organometallic clusters, whose metal-ligand interactions are of fundamental interest
due to their unique structures and electronic properties [11]. In this chapter, we focus
on transition metal-benzene sandwich clusters. Followed by a general introduction
on organometallic sandwich compounds, we explain gas-phase synthesis and
characterization studies to probe the structures of transition metal-benzene clusters.
T. Masubuchi and A. Nakajima
Keywords Sandwich complexes · Multiple-decker sandwich clusters · Mass
spectrometry · Photoionization spectroscopy · Anion photoelectron
spectroscopy · Molecular magnetism
8.1 Introduction
It was 60 years ago that Feynman [1] delivered a famous lecture named “There’s
Plenty of Room at the Bottom,” where he proposed a concept of designing
functionalities by taking full advantage of the properties of things on a small scale.
In 1962, Kubo [2] theoretically inferred that physicochemical properties of such
small materials are different from those in bulk because of discrete energy levels of
electrons. Since then, nanoscale materials have been important subjects in both basic
and applied sciences. Among them, clusters consisting of up to about 1000 atoms
have been extensively studied as they exhibit unexpected geometric and electronic
properties that are scaled as a function of cluster size [3].
In recent decades, indeed, metal clusters and molecular clusters have attracted
great attention as novel nanoscale materials of finite multifunctional systems.
For metal clusters, spectroscopic and theoretic studies have revealed the sizedependent electronic properties of metal-insulator transition [4] and the electron
shell structures based on jellium model [3, 5], the latter of which were discussed
also from the viewpoint of mimicking shell model of nucleus [5]. As well as physical
properties, chemical properties of size-specific reactivity of the metal clusters have
been greatly explored as cluster catalysts [6]. On the other hand, molecular clusters
have been extensively studied as the aggregates of weak van der Waals forces or
hydrogen bond network, revealing microscopic solvation dynamics [7], coexisting
phases [8], and electronic evolution of organic semiconductors [9].
However, studies on hybridized clusters between metal atoms and molecules,
organometallic clusters, are limited, although organometallic molecular complexes
such as an archetypal complex of ferrocene and ligated metal cluster compounds
have been well known [10]. In particular, organometallic cluster formation can
facilitate to control the dimensionality of the geometric structure through local
metal-ligand interaction [11]. Since a low-dimensional structure of organometallic clusters synergistically exploits the chemical and physical features of metal
atoms and organic molecules, leading to a dramatic change in their confinement
behavior, functional properties such as charge transfer, conductivity, and electron
spin arrangement can be designed by selecting an appropriate organic ligand which
optimizes the characteristics of the metal atoms.
Sandwich clusters, consisting of metal atoms and planar ring ligands, are typical
organometallic clusters, whose metal-ligand interactions are of fundamental interest
due to their unique structures and electronic properties [11]. In this chapter, we focus
on transition metal-benzene sandwich clusters. Followed by a general introduction
on organometallic sandwich compounds, we explain gas-phase synthesis and
characterization studies to probe the structures of transition metal-benzene clusters.