ON SOLID-SOLUTION FORMATION IN THE CU(HCOO)2-CO(HCOO)2-H2O SYSTEM

Solubility in the Cu(HCOO)2-Co(HCOO)2-H2O system has been studied at 25 and 50°C. Three series of solid solutions are formed in the system at 50°C: solid solutions having the Co(HCOO)2 · 2H2O crystal structure as a matrix and solid solutions having the Cu(HCOO)2 · 2H2O crystal structure as a matrix. It was established that the crystal structure of the monoclinic Cu(HCOO)2 · 2H2O undergoes a change into a new crystal structure (solid solutions) in the concentration range Cu0.83Co0.17(HCOO)2 · 2H2O-Cu0.74Co0.26(HCOO)2 · 2H2O. The same phenomenon was observed in the Cu(HCOO)2-Mg(HCOO)2-H2O system at 50°C. The X-ray diffraction spectra of the samples Cu0.74Co0.26(HCOO)2 · 2H2O and Cu0.73Mg0.27(HCOO)2 · 2H2O are proved to be identical. Since the new crystal phase contains a copper formate dihydrate as a main component a hypothesis has been made that a new polymorphous modification of Cu(HCOO)2 · 2H2O is probably formed due to included cobalt and magnesium ions in the copper formate dihydrate crystal structure. The new polymorphous modification of Cu(HCOO)2 · 2H2O is supposed to be built up by the structural element Cu(HCOO)4(H2O)2. Two type of solid solutions are formed in the Cu(HCOO)2-Co(HCOO)2-H2O system at 25°C: solid solutions based on Cu(HCOO)2 · 4H2O and solid solutions based on Co(HCOO)2 · 2H2O. Cobalt formate dihydrate retains its crystal structure up to a maximum of 50 mol% copper formate. © 1993 Academic Press. All rights reserved.