Self-assembled Transition Metal Coordination Frameworks of ...

Chapter I W _ _
Traditional magnets are based on metallic or ionic systems, but recently it has
been discovered that even individual molecules can behave like tiny magnets.
Magnetic molecules are a new class of fascinating materials. These molecules contain
a finite number of interacting spin centers (e.g. paramagnetic ions) and thus provide
ideal opportunities to study basic concepts of magnetism. One of the characteristic
features of molecular magnetism is its deeply interdisciplinary character, bringing
together organic, organometallic and inorganic synthetic chemists as well as
theoreticians from both the chemistry and physics communities, and materials and
life-science specialists. This interdisciplinary nature confers a special appeal to this
field. Nobody alone can make a crucial contribution [99].
Paramagnetic metal ions with covalent radii of the order of l A (0.1 nm) can
be brought into close proximity with suitable diamagnetic single atom bridging
ligands, and with appropriate magnetic orbital overlap situations can produce parallel
or antiparallel alignment of the metal centered spins (ferromagnetic or
antiferromagnetic behavior respectively). Increasing the number of spin centers in a
polynuclear bridged arrangement is more of a challenge, but can be achieved using
polydentate ligands of various types. One approach uses well-defined polydentate
ligands to impose specific geometries on the resulting arrays, while another approach
uses simple ligands, and essentially is controlled by properties of the metal ion. An
intermediate approach uses coordinatively flexible ligands [21].
Magnetic measurements can be performed in ac or dc modes. In the dc mode
a static magnetic field H is applied, and the induced magnetization, M, is studied as a
function of this magnetic field and of temperature [99]. In the present study variable
temperature and field dependent magnetization were carried out in dc mode at the
Department of Physics, Boise State University, Boise, USA in the powder state on a
Quantum Design PPMS superconducting magnetometer at 500 Oe field strength.
Diamagnetic corrections were made using Pascal's constants [I00].
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