Experimental determination and modelization of a unique phase diagram: solid solutions of antiferromagnetic organometallic radical cation salts C

The physical properties of paramagnetic Mo(V) organometallic radical cation salts, $\rm [Cp_2Mo(dmit)^{+\bullet}][ X^-]$, are investigated through the study of two series of solid solutions $\rm [Cp_2Mo(dmit)^{+\bullet }][X^-]_{({\it x})}[PF_6^-]_{(1-{\it x})}$ incorporating two kinds of anions ($\rm AsF_6^-/PF_6^-$ or $\rm SbF_6^-/PF_6^-$). The combination of EPR and X-ray diffraction is used to specify the nature of the structural phase transitions which occur in the paramagnetic phase and to determine the corresponding (T, x) phase diagrams. Finally, antiferromagnetic resonance is studied to probe the low temperature antiferromagnetic ground state. In the last part of the paper, the observed complex phase diagram is analyzed by considering a compressible model with at least two independent modes of compression. We conclude that the larger compressibilities are associated with the smaller anions