Diketones tridentate bonding

Interesting coordination modes have been discovered in derivatives containing Pd and Pt metal ions or nonmetallic elements, where extra negative charge of the (diketonate)2- arises from removal of one of the methyl protons. In (XIX) the (diketonate)2- is //3-C3-tridentate to Pd through Cl5 C2, and C3, in an allylic fashion, whereas in (XX) the donor is additionally 0,0-bidentate chelating toward another metal. In (XXI) the (diketonate)2- is C,0-bonded to Pt, and in (XXII) is 0,0-bonded to a metal and C-bonded to another metal via a terminal CH2. 

Of other solvents, alcohols such as ethanol are used most often for polymerization. Since the structure of nonsolvated Cu acrylate is unknown, it may be expected that upon desolvation of its complex with ethanol, some of the bidentate carboxyl groups become tridentate (see above). Thus they can act simultaneously as a ligand and a solvation agent, which is absent. The increase in the dentate number of the P-diketonate groups leads to a distortion of the oxygen environment about Cu in particular, the Cu-O distances and, hence, the C-O bond lengths. 

---