Self-assembled Transition Metal Coordination Frameworks of ...

-_ FIVE CHAPTER
Spectral and magnetic studies of Mn(II) molecular
frameworks of carbohydrazone and
thiocarbohydrazone ligands
5.1. Introduction
Manganese, an essential trace nutrient in all forms of life, shows oxidation
states ranging from -3 to +7 [1], however the most common oxidation states being +2
to +7. The +2 state is the most common and 1\/1112+ ions exist in the solid, in solution
and as complexes. The coordination chemistry of manganese with N and/or O
containing ligands has recently been receiving much attention, because of the variable
structures of manganese complexes, the wide occurrence of manganese enzymes in
plants and bacteria [2,3], the possibility of magnetic coupling interactions [4] and the
application of manganese compounds in industrial catalysis [3]. High spin Mn(lI)
complexes are characterized by the absence of ligand field stabilization energy and
this has two main consequences: (i) the possibility to obtain various coordination
geometries and (ii) a lower stability of Mn(H) complexes compared with those of
other divalent 3d metals. With regard to second point, there are lesser number of
reports for Mn(lI) complexes compared to complexes ofNi(]1), Cu(H), Zn(II), etc.
The name manganese originates from the Latin word ‘magnes’ meaning
magnet. The magnetochemistry of manganese complexes has been the subject of
interest from their very beginning. The synthesis and magnetic properties of discrete
polynuclear molecules of manganese are of considerable interest to the field of
molecular magnetism, as the first single-molecule magnet was an MH12 complex [5].
Polynuclear manganese clusters have received attention in recent years as potential
precursors to molecular magnetic materials or as single-molecule magnets. The