DETERMINATION OF THE CRYSTAL-FIELD PARAMETERS IN SOLIDS BY SIMULATIONOF THE PARAMAGNETIC-SUSCEPTIBILITY OF 3D(7) COBALT - APPLICATION TO THE HYDRATED BIS (CYCLOTRIPHOSHPHATE) OF COBALT (II) AND MONOVALENT CATIONS (NA, K, RB, CS, NH4)

In the family of phosphates of general formula MI4Co(P3O9)2, xH2O (M=N a,K,Rb,Cs,NH4), Co2+ are located in octahedral sites with large distan ces between Co2+ nearest neighbors (approximately 6.8 angstrom). This arrangement allow a basic study of the physical properties of 'isolate d' Co2+ in such oxygenated coordination. The EPR and absorption spectr a have been analyzed in the context of the ABRAGAM and PRYCE formalism . The use of the complete free atom and crystal field hamiltonian of t he d7 configuration has led to the determination of the crystal field parameters by simulating the EPR data and the thermal dependence of th e magnetic susceptibility. As general result Co2+ can be considered as extremely sensitive to its close environment.