InF3(H2O)2 : An indium fluoride dihydrate phase with direct O-H...F hydrogen bonding between isolated columns of InF4(OH2)2 corner-sharing octahedra

Abstract

InF3(H2O)2 is a new monoclinic C2/m phase [a = 5.774(2) Å, b = 10.239(3) Å, c = 4.1150(8) Å, β = 118.16(2)°]. It is obtained fortuitously as very few single crystals during the synthesis in sealed tubes of the phases in the system InF3-TeO2. It can also be prepared by direct dissolution of InF3 or In2O3 in HF 40 %, followed by a slow evaporation of the solution about 50–70 °C. It corresponds to an intermediate unstable dihydrate in the process of hydration of InF3 at air to a stable trihydrate InF3(H2O)3.InF3(H2O)2 structure is composed of trans-chains [InF3(H2O)2]n of InF4(OH2)2 octahedra sharing F vertices, interconnected via strong OH···F hydrogen bonds between equatorial O/F of adjacent chains with short O···F bonds of 2.57 Å and 2.60 Å. A medium range order between F(1) and O(1) equatorial anions is proposed. InF3(H2O)2 seems to be the first simple dihydrate of trivalent metal fluorides. It is compared to InF3(H2O)3 and to other trihydrates presenting some similar structural features.