268
N. Kojima and A. Okazawa
LIESST Light induced excited spin state trapping
T CT
Critical temperature of charge transfer phase transition
SP
Spiropyran
SMMs Single-molecule magnets
SCMs
Single-chain magnets
SIMs
Single-ion magnets
QTM
Quantum tunneling of magnetization.
6.1 Introduction
Transition-metal complexes consist of transition-metal elements and various kinds of
ligands with the ability to control the structural dimensionality, which have produced
wide variety of magnetic materials such as low-dimensional magnets, photo-induced
magnets, single-molecule magnets (SMMs) and so forth, which have stimulated the
theory of molecular magnetism. Thus, the development of advanced magnetic materials and the theory of molecular magnetism have mutually stimulated each other.
Especially, the discoveries of light induced excited state spin trapping (LIESST)
for spin crossover system (1984), SMM of [Mn 12 ] cluster complex (1993), and
photo-induced ferrimagnet of Prussian blue analogous complex (1996) have significantly expanded the field of molecular magnetism. These recent topics of molecular
magnetism are reviewed in the following excellent books [1].
In this chapter, we focus on the molecular magnetism and its related light-induced
phase transitions from the viewpoint of Mössbauer spectroscopy. Among various
kinds of molecular compounds, in the case of transition-metal complexes whose spin
states are situated in the spin crossover region, new types of synergetic phenomena
coupled with spin and charge are expected. Based on this viewpoint, we have
synthesized organic–inorganic hybrid systems, A[Fe
II Fe
III X 3 ] [A = (C n H 2n+1 ) 4 N,
spiropyran, etc.; X = dto (C 2 O 2 S 2 ), mto (C 2 O 3 S), tto (C 2 OS 3 )] and have found
novel multifunctional phenomena coupled with spin, charge and photon [2].
In general, the Fe
III site coordinated by six S atoms is in the low spin (LS) state,
while that coordinated by six O atoms is in the high spin (HS) state. Therefore, the
spin state of Fe
III coordinated by three S atoms and three O atoms is expected to be
situated in the spin crossover region. Based on this viewpoint, we have synthesized
(C 6 H 5 ) 4 P[Zn
II Fe
III (mto) 3 ] consisting of Fe
III O 3 S 3 and Zn
II O 6 octahedra, and the
57 Fe Mössbauer spectroscopy and the electron spin resonance (ESR) revealed the
dynamic spin equilibrium phenomenon occurs at the Fe
III O 3 S 3 site in which the HS
and LS states exchange alternately in the time scale of 10
−10 < τ < 10
−7 s [3]. On
the other hand, in the case of (C 6 H 5 ) 4 P[Mn
II Fe
III (mto) 3 ] consisting of Fe
III O 3 S 3 and
Mn
II O 6 , there exists a dynamic spin equilibrium (τ < 10
−7 s) between the HS and
LS states at the Fe
III O 3 S 3 site, which induces the frustration of internal magnetic
field between the ferromagnetic and antiferromagnetic interactions at the Mn
II O 6
site. Owing to the frustration of internal magnetic field at the Mn
II site caused by
N. Kojima and A. Okazawa
LIESST Light induced excited spin state trapping
T CT
Critical temperature of charge transfer phase transition
SP
Spiropyran
SMMs Single-molecule magnets
SCMs
Single-chain magnets
SIMs
Single-ion magnets
QTM
Quantum tunneling of magnetization.
6.1 Introduction
Transition-metal complexes consist of transition-metal elements and various kinds of
ligands with the ability to control the structural dimensionality, which have produced
wide variety of magnetic materials such as low-dimensional magnets, photo-induced
magnets, single-molecule magnets (SMMs) and so forth, which have stimulated the
theory of molecular magnetism. Thus, the development of advanced magnetic materials and the theory of molecular magnetism have mutually stimulated each other.
Especially, the discoveries of light induced excited state spin trapping (LIESST)
for spin crossover system (1984), SMM of [Mn 12 ] cluster complex (1993), and
photo-induced ferrimagnet of Prussian blue analogous complex (1996) have significantly expanded the field of molecular magnetism. These recent topics of molecular
magnetism are reviewed in the following excellent books [1].
In this chapter, we focus on the molecular magnetism and its related light-induced
phase transitions from the viewpoint of Mössbauer spectroscopy. Among various
kinds of molecular compounds, in the case of transition-metal complexes whose spin
states are situated in the spin crossover region, new types of synergetic phenomena
coupled with spin and charge are expected. Based on this viewpoint, we have
synthesized organic–inorganic hybrid systems, A[Fe
II Fe
III X 3 ] [A = (C n H 2n+1 ) 4 N,
spiropyran, etc.; X = dto (C 2 O 2 S 2 ), mto (C 2 O 3 S), tto (C 2 OS 3 )] and have found
novel multifunctional phenomena coupled with spin, charge and photon [2].
In general, the Fe
III site coordinated by six S atoms is in the low spin (LS) state,
while that coordinated by six O atoms is in the high spin (HS) state. Therefore, the
spin state of Fe
III coordinated by three S atoms and three O atoms is expected to be
situated in the spin crossover region. Based on this viewpoint, we have synthesized
(C 6 H 5 ) 4 P[Zn
II Fe
III (mto) 3 ] consisting of Fe
III O 3 S 3 and Zn
II O 6 octahedra, and the
57 Fe Mössbauer spectroscopy and the electron spin resonance (ESR) revealed the
dynamic spin equilibrium phenomenon occurs at the Fe
III O 3 S 3 site in which the HS
and LS states exchange alternately in the time scale of 10
−10 < τ < 10
−7 s [3]. On
the other hand, in the case of (C 6 H 5 ) 4 P[Mn
II Fe
III (mto) 3 ] consisting of Fe
III O 3 S 3 and
Mn
II O 6 , there exists a dynamic spin equilibrium (τ < 10
−7 s) between the HS and
LS states at the Fe
III O 3 S 3 site, which induces the frustration of internal magnetic
field between the ferromagnetic and antiferromagnetic interactions at the Mn
II O 6
site. Owing to the frustration of internal magnetic field at the Mn
II site caused by