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The spin-crossover (SC) compounds are one of the representative examples of
molecular bistability. The high-spin (HS) and low-spin (LS) states of an SC
compound are interconvertible by several different physical perturbations such as
temperature, pressure, light-irradiation as well as chemical modifications such as
variation in the nature of associated counteranion and the degree of solvation in the
crystallized salts. Some results from our laboratories on spin-crossover FeIIN6
complexes which are representative examples of molecular bistability will be
discussed.
The design and synthesis of discrete metal clusters of high-nuclearity and
coordination polymers, based on transition-metal ions bridged by carboxylate groups,
to fabricate molecule-based magnetic materials are currently under intense
investigation. Structural characterization of the newly synthesized complexes of a
group of carboxylate-appended (2-pyridyl)alkylamine ligands reveals denticitycontrolled
self-assembly process: discrete clusters CoII
4, CoII
13, NiII
4, NiII
8, NiII
13,
CuII
4, CuII
7; 1D chain-like MnII, CoII, CuII, ZnII coordination polymers. These
complexes exhibit magnetic-exchange interaction between the MII ions through
monatomic, syn-anti and anti-anti bridging carboxylate pathway. Temperaturedependent
magnetic studies reveal the presence of spin-canted antiferromagnetic,
antiferromagnetic, and ferromagnetic exchange-coupling. The successful syntheses of
these complexes enriched our knowledge not only structurally but magnetically as
well. Future efforts will investigate how the stereochemical demand of this class of
ligands would direct the molecular shape and control the magnetic properties of the
resulting complexes. Such an endeavor is on in our laboratories. In this lecture a
comprehensive account of this work will be presented.
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