Solid solutions of composition M1/3CO2/3C2O4 (.) 2H(2)O (M = Fe, Ni, Zn, Cd) were synthesized. Isothermal diagrams for the M1/3Co2/3C2O4 (.) 2H(2)O-N2H4-H2O (C2H5OH) systems were constructed. Two new hydrazineoxalato complexes with one or two hydrazine molecules are formed in each of these systems. X-ray diffraction patterns and IR spectra were recorded for these complexes, their density was measured, and their structure discussed.