Cu(II)–bis[4-ethoxyphenyl-O-alkyl]-dithiophosphonate and Cr(III)–tris[4-ethoxyphenyl-O-alkyl]-dithiophosphonate complexes (alkyl=methyl, ethyl, isopropyl) were prepared and studied by magnetic measurements, and electronic, IR and EPR spectroscopic studies. The valence vibrations of the PS2 group show that this group coordinates isobidentate. The electronic spectra of copper(II) complexes display two weak bands at 15 200 and 18 500cm−1, (2B1g→2A1g and 2B1g→2Eg) and an intense band at 23 000cm−1 (L→M charge-transfer). The powder EPR spectra of Cu (II) complexes are typical for square-planar monomeric species and present hyperfine and superhyperfine structure. These results suggest that the copper(II) complexes have D4h symmetry. Two bands were observed in the UV-Vis spectra of the chromium complexes at 14 320 and 18 640cm−1 (4A2g(F)→4T2g(F) and 4A2g(F)→4T1g(F)). The EPR bands of the Cr(III) complexes may be attributed to isolated metallic ions in pseudoocthaedral surroundings and to Cr(III) ions coupled by dipole–dipole interaction.