Crystal structures of Ag2ZrF6•8NH3 and Ag2HfF6•8NH3 and their synthesis by the "Reactive Fluoride Route" in liquid ammonia

Starting from the ternary transition-metal fluorides Ag3M2F14 (M = Zr, Hf) and dry liquid ammonia, [Ag(NH3)(4)(mu-NH3)(-) Ag(NH3)(3)]ZrF6 (1) and [Ag(NH3)(4)(mu-NH3)Ag(NH3)(3)]HfF6 (2) have been prepared as colorless single crystals crystallizing isotypically in the space group Pnma-D-2h(16) (No. 62). The compounds feature weak Ag center dot center dot center dot Ag interactions known as argentophilicity, which is yet unknown in fluorides. It is also shown that ionic silver(II) fluorides are suitable starting materials for fluorine chemistry in liquid ammonia and are easily reduced to Ag-I by oxidizing ammonia. This driving force bypasses the generally high lattice energy of ionic fluorides, so that they can be dissolved easily. We would like to introduce the term "reactive fluoride route" for this method of dissolving reactive ionic fluorides in liquid ammonia. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).