Ag Ion-Exchange Reactions of Cu 2 P 3 I 2 and Cu 2 P 1.8 As 1.2 I 2
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Ag Ion-Exchange Reactions of Cu2P3I2 and Cu2P1.8As1.2I2 Buddhimathie Jayasekera and Stephanie L. Brock Wayne State University, Detroit, MI 48202, U.S.A. ABSTRACT A variety of ion exchange techniques for Cu2P3I2 and its mixed pnictogen analog Cu2P1.8As1.2I2 have been studied. Ag2P3I2 is an existing material, previously prepared from Cu2P3I2 by ion exchange of Ag+ for Cu+ in aqueous medium. This method is compared to nonaqueous (ionic liquid) and solid state routes for ion exchange. Additionally, the new compound Ag2P1.8As1.2I2 with cell parameters a = 15.838(17) Å, b = 13.684(10) Å, c = 15.580(17) Å and β = 117.63(7)°, has been prepared by reaction of Cu2P1.8As1.2I2 with AgNO3 in aqueous solution.
INTRODUCTION Cu2P3I2 is one of only a handful of compounds that feature neutral, one-dimensional phosphorus chains in the solid state. These chains are surrounded by copper atoms, all located on partially occupied sites, which are in turn surrounded by iodine atoms (Figure 1). Cu+ ion mobility in this phase has been suggested by the facile exchange of Cu+ for Ag+ in aqueous solution, producing Ag2P3I2, [1,2] and was later confirmed, and quantified, by impedance spectroscopy [3]. Recently, a mixed pnictogen analog, Cu2P1.8As1.2I2, with an unprecedented 40 % As substitution into the neutral chain, has been synthesized [4]. This new phase has a larger number of partially occupied copper sites relative to the parent compound, and some of the sites are located outside of a normal bonding distance to P/As. Accordingly, copper ion mobility is expected to be as good, if not better, in the mixed pnictogen material. In order to qualitatively probe ion mobility in this phase, and to prepare, for the first time, the related silver phase, ion exchange reactions were explored. Herein, the results of Ag+ ion-exchange reactions of Cu2P1.8As1.2I2 and Cu2P3I2 conducted in aqueous media (with and without KCN additives) are presented. Additionally, attempts to conduct the ion-exchange in non-aqueous media (room temperature ionic liquids) and in the solid state, will be discussed.
EXPERIMENTAL DETAILS The reaction of Cu2P1.8As1.2I2 with Ag+ was conducted in an analogous manner to that reported for Cu2P3I2 [1]. A 10 wt% solution of AgNO3 was prepared and ground crystals of Cu2P1.8As1.2I2 were subsequently introduced and permitted to react for 15 minutes. The product was filtered, washed several times with water, and allowed to air dry. In order to prevent formation of elemental Ag on the surface of the crystals, another set of reactions were done with excess KCN added to the 10 wt% AgNO3 solution [1]. Reactions with Cu2P1.8As1.2I2 and Cu2P3I2 were conducted for periods of 15 minutes to 2 hours, and then the products were isolated, washed, and dried.
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Figure 1. Two parallel infinite chains of P/As in Cu2P1.8As1.2I2 (isostructural to Cu2P3I2) surrounded by Cu and I atoms. Phosphorus/arsenic, copper and iodine atoms are shown as filled, shaded and open, respectively. (For clarity purpose some of the I atoms have been removed)
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