Eur. Phys. J. B 9, 431(1999)
https://doi.org/10.1007/s100510050785

Dramatic anion size effect on structural and magnetic properties within a series of novel antiferromagnetic organometallic radical cation salts: [ Cp₂Mo(dmit)^+⋅][X^-](X^-=PF^-₆, AsF^-₆, SbF^-₆)

¹ Centre de Recherche Paul Pascal, CNRS, avenue du Dr. Schweitzer, 33600 Pessac, France
² Institut Jean Rouxel, CNRS-Université de Nantes, 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 03, France
³ Institut de Chimie de la Matière Condensée de Bordeaux, avenue du Dr. Schweitzer, 33600 Pessac, France
⁴ Laboratoire de Physique des Solides, CNRS-Université Paris-Sud, Bât. 510, 91405 Orsay Cedex, France

Received: 20 July 1998
Published online: 15 June 1999

Abstract

Electrocrystallization of CH₂Cl₂ solutions of Cp₂Mo(dmit), dmit^2- = 2-thioxo-1,3-dithiole-4,5-dithiolate, in the presence of n-Bu₄NX (X^- = PF, AsF, SbF) affords the corresponding 1:1 cation radical salts [ Cp₂Mo(dmit)] [ X^-] . The three isostructural salts crystallize in the orthorhombic system, space group Cmcm. In the three salts, a second-order transition at a temperature T₁, identified by EPR measurements and low-temperature X-ray Weissenberg photographs reveals also a splitting of some principal reflections and the twinned character of the crystals, whose room temperature structure may also be described in the monoclinic P2₁/m space group. The second order monoclinic triclinic transition is associated with the apparition of a superlattice characterized by the critical wave vector when expressed in the monoclinic system. A second transition at a lower temperature T₂, of first order character, is observed only in the PF salt. This triclinic triclinic transition leads to a novel superlattice of wave vector while the superlattice is conserved down to 10 K in the AsF and SbF salts. Finally, a third transition to an antiferromagnetic ground state is observed for the three salts and investigated by static susceptibility measurements and Antiferromagnetic Resonance (AFMR) experiments. The detailed analysis of the AFMR rotation patterns confirms the twinned nature and the low temperature triclinic symmetry of the crystals as well as the peculiar behaviour of the PF salt, when compared with the two other members of these novel series.