Complexes of Oxalic Acid and Related Compounds

The oxalato anion (ox ) coordinates to a metal as a unidentate (I) or bidentate (II) ligand  

The bidentate chelate structure (II) is most common. Fujita et al. carried out normal coordinate analyses on the 1 1 (metal-ligand) model of the [M(ox)j] and [M(ox)3) series, and obtained the band assignments listed in Table 111-21. In the divalent metal series, z (C=0) (average of Vy and Vy) becomes higher, and r(C—O) (vy and i g) becomes lower, as p4(MO) becomes higher in the order Zn(ll) Cu(II) Pd(ll) Pt(ll) (see Fig. 111-30). This relation holds in spite of the fact that 4, nd I g are all coupled with other 

In the trivalent metal series, Hancock and Thornlon found that v, (MO stretching) follow,s the same trend as the crystal field stabilization energies (CFSE) of these metals, namely  

The Raman spectra of metal oxalato complexes have also been examined to investigate the solution equilibria and the nature of the M-O bond. Vibrational assignments have been made on metal oxamido complexes of V , symmetry  

III-30. M-O stretching frequency vs C O and C—O stretching frequencies in oxalato complexes of divalent metals. 

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