Self-assembled Transition Metal Coordination Frameworks of ...

_ _ _ M __ _ g__g _g_ Introduction
frameworks and the redox or magnetic properties of the metals [l5]. Also, with their
potential application as functional materials and molecular devices of interdisciplinary
area made a rapid development in the synthesis and structural characterization of
novel compounds. The inclusion of magnetic metal ions with these polynuclear
complexes added a new dimension, which leads nanometer-sized magnetic clusters of
versatile magnetic properties. Of these, the grid stmctures are of special interest in
information storage and processing technology [16]. At the same time, the self­
assembly process driven by noncovalent interactions are considered as crucial in the
proliferation of all biological organisms [17], they can serve as biological models.
Stang et al.[l7] have reported many different molecular square complexes based on
square planar coordinated metal centers. The most frequently used metal ions for
octahedral centers include Fe(ll), Co(ll) and Ni(II) [15] and are rare for self­
assembled molecular squares of multidentate ligands.
Wurthner er al. in 2004 [13] have reported a valuable account of
metallosupramolecular squares from their structure to function in detail. One of the
main attractive features of molecular squares is their suitability for various functional
applications. On the one hand, functionalities can be readily introduced onto
metallosupramolecular squares by employing functional ligands and/or metal corners
in the assembly processes. Upon square formation these functions may interact
leading to a higher level of functionality. Additionally, cavities are created which may
accommodate guest molecules. On the other hand, macrocycles containing transition
metals are generally more sensitive and responsive on electro- and photochemical
stimuli compared to metal-free organic macrocyclic molecules. Therefore, the
employment of metallosupramolecular squares may open up new opportunities to
develop novel molecular switches and devices [13]. Different molecular functional
squares include: (a) squares for molecular recognition by varying the cavity sizes, (b)
chiral molecular squares for enantioselective recognition, sensing and catalysis, (c)
photolumineseent molecular squares for molecular sensing and as artificial light
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