Magnetic Properties of a New Hexahalorhenate({IV}) Compound and Structural Comparison with Its Hexahaloplatinate({IV}) Analog

Two mononuclear complexes of formula (Et(3)BzN)(2)[ReCl6] (1) and (Et(3)BzN)(2)[PtCl6] (2) (Et(3)BzN(+) = triethylbenzylammonium cation) have been synthesized in good yield (70 and 75 %, respectively) and structurally characterized. From a structural point of view, they both crystallized in the monoclinic centrosymmetric P2(1)/n space group and the two molecular structures are almost perfectly superimposable, with only minor differences in the M-Cl bond lengths. Solid-state direct-current (dc) magnetic susceptibility analysis in the temperature range 1.9-300 K for 1 reveal the occurrence of magnetically isolated rhenium(IV) ions with a significant zero-field splitting (zfs), D = +6.7 cm(-1) (2D being the energy gap between the M-S = +/- 3/2 and M-S = +/- 1/2 Kramers doublets). DFT, CASSCF and CASSCF/NEVPT2 theoretical calculations were carried out on the experimental geometry of the complex [ReCl6](2-) in 1 to substantiate the parameters defining the zfs tensor. Alternating current (ac) magnetic susceptibility measurements of 1 in the temperature 2.0-10 K show incipient frequency-dependence of the out-of-phase signals below 3.0 K under non-zero applied dc fields supporting a field-dependent Single Ion Single Molecule Magnet (SISMM) behaviour of this rhenium(IV) derivative.