Acetate, ligand structure

The molecular structures of several [TpBut]ZnX derivatives have been determined by x-ray diffraction. For example, x-ray diffraction studies confirm that the acetate ligand in [TpBut]Zn(r)1-02CMe) is bound to zinc in a unidentate mode, similar to that proposed for [TpBut]Mg(7j1-02CMe), but in contrast to the bidentate coordination proposed for the copper analogue [TpBut]Cu(T)2-02CMe) (86,87). Such a change in coordination mode for copper and zinc derivatives is to be anticipated on the basis of structural studies on the nitrate derivatives [TpBut]M(N03) (M = Co, Ni, Cu, Zn), as described in Section V,B,2,e. The thioacetate [TpPh]-Zn V-SC(0)Me (81), and cyanoacetate [Tp lZnlr -C CCH N) (88) derivatives also exhibit unidentate coordination. 

Ligands with more than one coordination site have been synthesized. A superstructured porphyrin ligand with an additional binding site for a second zinc ion was synthesized. The X-ray structure shows a bridging acetate ligand between the porphyrin cavity-bound zinc and the zinc bound to the appended tripodal chelator.778... 

This emphasizes that iron(II) complexes bearing more bulky bis(pyrazol-l-yl)acetate ligands should be good structural models to mimic mononuclear non-heme iron dependent enzymes. 

The acetate type structure can also occur with nitrogen ligands, but is only of limite occurrence. It occurs in [Cu2(NPhCPhNPh)4] (319),700 where bridging NPhCPhNPh ligarn result in an even shorter Cu—Cu distance of 2.45 A. 

Rh(0H)3H20 (161, 236) and hexachlororhodate(III) have also been reported (19). The carboxylates are initially isolated as the solvent adduct, but heating under vacuum is adequate to prepare the anhydrous product. A variety of donors can occupy the terminal positions of the copper acetate type structure found in these rhodium dimers. No simple explanation of the bond order in these compounds seems adequate to describe the metal-metal attractive force in view of the number of electrons available and the prominent role of axial ligands in the total bonding scheme (200). 

The copper-acetate-type structure has been shown by x-ray diffraction.5,6 The complex is diamagnetic it is only slightly soluble in water, methanol, acetone, etc., giving green solutions. Adducts with a variety of ligands have been characterized.2-4... 

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