Self-assembled Transition Metal Coordination Frameworks of ...

Chapter I _ _ _
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Scheme 1.2. Different tautomeric forms of (thio)carbohydrazones.
The geometrical constraints that prevails within the self-assembly of metals
are of greatest importance for controlled assembly process. Suitably substituted
thiocarbohydrazone ligands favors cyclic tetramers for octahedral metal centers as the
most possible compound [31]. The bridging sulfilr donor requires pairs of metal ions
to assemble in a syn manner when coordinated within each MQL (or MZHL or MZHQL)
moiety. It follows that, for six-coordination to be achieved at each center, only an
equal and even number of metal ions and thiocarbohydrazones can lead to closure of a
cyclic oligomer. All other combinations of metals and ligands must be open-chain.
However only a 4:4 metal/ligand assembly enables an orthogonal coordination of the
two tridentate N, N, X units, leading to the least distorted six-coordinate geometry
[31]. For example, a 6:6 cyclic hexamer would require a 30° twist of each N, N, X
chelate away from orthogonality (with respect to its companion ligand), which would
introduce considerable non-bonded repulsion.
Crystal structures of all thiocarbohydrazone ligands reported so far
[29,65,68,87] are in amidothioketone tautomeric form. Similar is the case with
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