X-ray absorption fine structure spectroscopic study of (NH4)2ReF6

Abstract

The (NH 4) 2 ReX 6 (X = F, Cl, Br, I) salts have been investigated by x-ray absorption fine structure spectroscopy. The ReF distance determined by EXAFS in (NH 4) 2 ReF 6 (i.e., 1.95 Å) is in good agreement with the one determined by single crystal x-ray diffraction in A 2 ReF 6 salts (A = K, Rb, Cs). The XANES studies of (NH 4) 2 ReX 6 (X = F, Cl, Br, I) indicates that the positions of the absorption edge and of the white line are shifted to higher energy when moving from I to F. These shifts have been explained in terms of the crystal field splitting parameter and covalent charge carried by the Re atoms. Calculations of the XANES spectra of the ReX 6 2− (X = F, Cl, Br, I) anions at the Re-L 3 edge have been performed and the calculated shifts and intensity of the white lines reproduce well the experimental observations.

Coexistence of metamagnetism and slow relaxation of magnetization in ammonium hexafluoridorhenate

“…Recently, an optimized method for the preparation of A 2 [ReX 6 ] salts has been developed from the solid-state melting reaction of (NH 4 ) 2 [ReX 6 ] (X = Cl, Br) with excess NH 4 HF 2 . 7,9,27 Using this method, 1 was prepared and separated after washing with a water–methanol mixture. After centrifugation and precipitation, the pink compound was obtained in 60% yield.…”

“…Colorless single crystals of 1 could be obtained by recrystallization in water or in aqueous HF. The purity and homogeneity of the bulk sample of 1 was confirmed by EXAFS 7 spectroscopy and powder XRD. The XRD pattern ( Fig.…”

“…However, the isolation of the subsequent water-soluble A 2 [ReF 6 ] salt has shown to be challenging. 4,5 Recently, detailed procedures for the preparation of K [ReF 6 ] has been studied by X-ray absorption spectroscopy, 7 thermal gravimetric analysis 14,15 and was used as a precursor for preparing materials with remarkable magnetic properties, 9,11,12 up to now there is no available single crystal Xray data of the salt. In salts containing the [ReX 6 ] 2À (X ¼ F, Cl, Br, I) anions, the Re(IV) ion (5d 3 ) forms a hexakis-monodentate coordination with the halogen atoms resulting in either a regular or slightly distorted octahedral geometry.…”

“…In this context, the (NH 4 ) 2 [ReF 6 ] salt was prepared and characterized by X-ray diffraction (single crystal and powder), IR and Raman spectroscopies, DC and AC magnetic susceptibility measurements, and computational methods. 7,9,27 Using this method, 1 was prepared and separated aer washing with a water-methanol mixture. Aer centrifugation and precipitation, the pink compound was obtained in 60% yield.…”

“…However, the isolation of the subsequent water-soluble A 2 [ReF 6 ] salt has shown to be challenging. 4,5 Recently, detailed procedures for the preparation of K 2 [ReF 6 ] 6 and (NH 4 ) 2 [ReF 6 ] 7 have been reported. Currently, only eleven compounds containing the [ReF 6 ] 2− anion have been characterized by single crystal X-ray diffraction: K 2 [ReF 6 ], 6,8 A 2 [ReF 6 ] (A = Rb, Cs), 6 (AsPh 4 ) 2 [ReF 6 ]·2H 2 O, (PPh 4 ) 2 [ReF 6 ]·2H 2 O (Ph = C 6 H 5 : tetraphenylphosphonium), 9,10 [M(viz) 4 (ReF 6 )] ∞ (M = Zn, Ni; viz = C 5 H 6 N 3 : 1-vinylimidazole), 9 [Co 3 (dpa) 4 ][ReF 6 ]·2DMF (DMF = HCON(CH 3 ) 2 and dpa = C 10 H 8 N 3 : 2,2′-dipyridylamine anion), 11 (PPh 4 ) 2 [ReF 6 ]·CH 3 CN, 11 (BEDO) 4 [ReF 6 ]·6H 2 O (BEDO = C 10 H 8 O 4 S 4 : bis(ethylenedioxo)tetrathiafulvalene) 12 and [Co(NH 3 ) 6 ] 3 [ReO 4 ][ReF 6 ] 4 ·6H 2 O.…”