The electron paramagnetic resonance spectra of copper monochloroacetate 2.5 hydrate, Cu(O2CCH2Cl)2.2.5H2O, [Cu(ClAc)2], and zinc-doped Cu(ClAc)2 have been observed at both K-band and X-band frequencies. The EPR spectrum of the pure material was characteristic of a species with a spin of one, while the spectrum from zinc-doped Cu(ClAc)2 revealed an additional spectrum due to a species with a spin of 1/2 . The g values for both the copper—copper pairs and the copper—zinc pairs were identical with values gz=2.38 and gx=gy=2.07. The hyperfine coupling constant for the copper—copper pairs was about 84×10-4 cm-1, while in the copper—zinc spectrum it was about 158×10-4 cm-1. These results are consistent with the assumption of a weakly coupled interaction. The temperature variation of the doubly integrated intensity of the derivative spectrum indicated that the triplet state lies some 230 cm-1 above the singlet ground state. In the optical absorption spectrum of Cu(ClAc)2 three bands were observed. A very intense band was found at 14 000 cm-1, while two other bands were centered at 11 000 cm-1 and 26 000 cm-1.