Synthesis, crystal structure, thermal analysis and dielectric properties of Rb4(SO4)(HSO4)2(H3AsO4) compound

A new inorganic Rb-4(SO4)(HSO4)(2)(H3AsO4) compound was prepared. It was found to crystallize in the monoclinic system (P2(1) space group) with the following lattice parameters: a = 5868 (1) angstrom, b = 13,579(2) angstrom, c = 11,809 (3) angstrom and beta = 94,737 (1)degrees. The structure is characterized by SO42-, HSO4- and H3AsO4 tetrahedra connected by hydrogen bridge to form two types of dimmer (H(8)S(2)O-4(-) S(1)O-4(2-) and H(12)S(2)O-4(-)center dot center dot center dot H3AsO4). These dimmers are interconnected by both hydrogen bonds O(14)-H(14)center dot center dot center dot O(4) and O(15)-H(15)center dot center dot center dot O(2). They are also linked by the hydrogen bridge assured by the hydrogen atoms H(2), H(3) and H(4) of the H3AsO4 group to build the chain S(1)O-4 center dot center dot center dot H3AsO4 which are parallel to the a,direction. The rubidium cations are coordinated by eight oxygen atoms with Rb-O distance ranging from 2893(8) to 3.415(6) angstrom. The existence of O-H and (S/As)-O bonds in the structure at room temperature has been confirmed by IR and Raman spectroscopy in the frequency ranges 4000-400 cm(-1) and 1200 - 50 cm(-1), respectively. Thermal analysis of Rb-4(HSO4)(HSO4)(2)(H3AsO4) showed that the transformation to high temperature phase occurs at 407 K by one-step process. Thermal decomposition of the product takes place at much higher temperatures, with an onset of approximately 522 K. The first transition detected by differential scanning calorimetry (DSC) was also analyzed by dielectric and conductivity measurements using the impedance spectroscopy techniques. The conductivity in the high temperature phase at 428 K is 1.04 x 10(-3) Omega(-1) cm(-1), and the activation energy for the proton transport is 036 eV. The conductivity relaxation parameters associated with the high disorder protonic conduction have been examined from analysis of the M ''/M '' max spectrum measured in a wide temperature range. Transport properties of this material appear to be due to the proton hopping mechanism. The obtained results show that this transition is protonic by nature. (C) 2017 Elsevier B.V. All rights reserved.