Conservation of [(C 2H 4NH 3) 3N] 2·(ZrF 7) 2·H 2O layers during the topotactic dehydration of [(C 2H 4NH 3) 3N] 2·(ZrF 7) 2·9H 2O

Abstract

Tren amine cations [(C 2H 4NH 3) 3N] 3+ and zirconate or tantalate anions adopt a ternary symmetry in two hydrates, [H 3 tren] 2·(ZrF 7) 2·9H 2O and [H 3 tren] 6·(ZrF 7) 2·(TaOF 6) 4·3H 2O, which crystallise in R32 space group with a H = 8.871 (2) Å, c H = 38.16 (1) Å and a H = 8.758 (2) Å, c H = 30.112 (9) Å, respectively. Similar [H 3 tren] 2·(MX 7) 2·H 2O (M = Zr, Ta; X = F, O) sheets are found in both structures; they are separated by a water layer (O w(2)–O w(3)) in [H 3 tren] 2·(ZrF 7) 2·9H 2O. Dehydration of [H 3 tren] 2·(ZrF 7) 2·9H 2O starts at room temperature and ends at 90 °C to give [H 3 tren] 2·(ZrF 7) 2·H 2O. [H 3 tren] 2·(ZrF 7) 2·H 2O layers remain probably unchanged during this dehydration and the existence of one intermediate [H 3 tren] 2·(ZrF 7) 2·3H 2O hydrate is assumed. O w(1) molecules are tightly hydrogen bonded with –NH 3 + groups and decomposition of [H 3 tren] 2·(ZrF 7) 2·H 2O occurs from 210 °C to 500 °C to give successively [H 3 tren] 2·(ZrF 6)·(Zr 2F 12) (285 °C), an intermediate unknown phase (320 °C) and ZrF 4.