Solvothermal Synthesis and Luminescent Properties of Two Organically Templated Chain-Structure Fluorides, [C₄H₁₄N₂][MF₅] (M = In, Sc)

Abstract

The solvothermal syntheses and crystal structures of organically templated indium fluoride, [C 4 H 14 N 2 ][InF 5 ] 1, and its scandium analogue, [C 4 H 14 N 2 ][ScF 5 ] 2, are reported. Compound 1 represents the first indium fluoride with extended inorganic connectivity prepared using an organic amine, 1,4-diaminobutane (DAB), as a structure-directing agent. 1 is orthorhombic, space group Ibam, with cell parameters a = 9.324(2) Å, b = 11.391(2) Å, c = 8.401(2), and Z = 4 (for isostructural 2: a = 9.353(3) Å, b = 11.433 (1) Å, c = 8.226 (4) Å). The structure of 1 consists of infinite trans vertex sharing (InF 5 ) ∞ chains running parallel to the c- axis, which are linked via H-bonded organic moieties. The photoluminescence properties of the doped compounds, of nominal composition [C 4 H 14 N 2 ][In 1-x Ln x F 5 ] (Ln=Tb and/or Eu), have been explored. For x = 0.05 Eu 3+, 1 exhibits a dominant orange emission at 592.5 nm from the 5 D 0 → 7 F 1 magnetic dipole transition within Eu 3+ . For x = 0.08 Tb 3+, 1 shows strong down-conversion fluorescence corresponding to 5 D 4 → 7 F 5 (green at 543.5 nm). In addition, a Tb 3+ /Eu 3+ co-doped sample exhibits a combination of green (Tb 3+ ) and orange (Eu 3+ ) luminescence, with Tb 3+ enhancing the emission of Eu 3+ in this host. The dependence of luminescence intensity on dopant concentration for 1 has been analyzed. The scandium and fluorine local environments in 2 have been characterized by 19 F and 45 Sc solid-state magic-angle spinning (MAS) NMR, which confirms a single scandium site together with discrete bridging and planar fluorine sites.