Self-assembled Transition Metal Coordination Frameworks of ...

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CHAPTER
Self-assembled Zn(II) and Cd(ll) molecular
frameworks: Structural and spectral properties
6.1. Introduction
Zn and Cd are not typical members of transition elements and they are stable
with their only significant oxidation state of +2 with completely filled d shell. Their
coordination chemistry, however, can be considered along with that of typical
transition metals. Both metal ions form stable complexes with N, O or S donor ligands
well. Cd(ll) is a soft ion and preferred to bond to sulfur compared to nitrogen atoms.
Stable complexes of Zn(lD and Cd(H) with NNS and NNO donor ligands like
thiosemicarbazones [1-6] and semicarbazones [7,8] have been reported. However,
there are only very few reports of Zn(ll) and Cd(ll) coordination compounds of
carbohydrazones and thiocarbohydrazones [8-14]. Some theoretical and dipole
moment studies of closely similar Zn(II) carbazone complexes have been reported by
Siddalingaiah et al. [15-18]. The stereochemistry of Zn(lI) complexes mainly depends
on the nature of the coordinating ligands as the d 10 configuration is well stable.
Zn(Il) usually favors tetrahedral coordination; in that respect one review cited over six
hundred Zn(H) complexes which are predominantly tetrahedral [19]. Among the less
common five coordinate complexes, trigonal bipyramidal geometry occurs more
frequently than square pyramidal [20]. There are many reports of six coordinated
octahedral complexes, normally with two tridentate ligands. Reports of tetranuclear
Zn(H) complexes having six coordinated octahedral centers are also found but very
rare [21]. There are few reports of 2>