Experimental determination and modelization of a unique phase diagram: solid solutions of antiferromagnetic organometallic radical cation salts [Cp2Mo(dmit)(+center dot)][X-]((x)) [PF6-]((1-x)) (X- = AsF6- or SbF6-)

The physical properties of paramagnetic Mo(V) organometallic radical cation salts, [Cp2Mo(dmit)(+.)][X-], are investigated through the study of two se ries of solid solutions [Cp2Mo(dmit)(+.)][X-]((x))[PF6-]((1-x)) incorporati ng two kinds of anions (AsF6-/PF6- or SbF6-/PF6-). The combination of EPR a nd X-ray diffraction is used to specify the nature of the structural phase transitions which occur in the paramagnetic phase and to determine the corr esponding (T, x) phase diagrams. Finally, antiferromagnetic resonance is st udied to probe the low temperature antiferromagnetic ground state. In the l ast part of the paper, the observed complex phase diagram is analyzed by co nsidering a compressible model with at least two independent modes of compr ession. We conclude that the larger compressibilities are associated with t he smaller anions.