Twenty-six new coordination compounds are reported with methyl formate, ethyl acetate and diethyl malonate as the ligands, viz. [M(HCOOCH3)62+] [FeCl4−]2, [M(HCOOCH3)62+] [InCl4−]2, [M(CH3COOC2H5)62+] [SbCl6−]2, and [M(CH2(COOC2H5)2)32+] [SbCl6−]2, where M is Mg(II), Mn(II), Fe(II), Co(II), Ni(II), and Zn(II), and for the ethyl acetate and diethyl malonate solvates M is also Ca(II).
In the complexes the carbonyl stretching vibration is shifted to lower frequencies with regard to this vibration in the free ligands. The magnitudes of these shifts are dependent on the metal ions. Frequency-shifts of other ligand vibrations are also observed. When the shifts are dependent on the metal ions, the magnitudes of the shifts follow the Irving-Williams sequence.
For the methyl formate and ethyl acetate solvates a metal-dependent absorption band appears in the far infrared, which is attributed to the metal-ligand stretching vibration. This band could not be located for the diethyl malonate solvates.
Investigation of ligand field spectra indicates the presence of octahedral species M(O)62+ in the solid compounds. Values for Dq and B for the Co(II) and Ni(II) compounds are reported, and the ligands are placed in the spectro-chemical and nephelauxetic series.