cm0607029_si_002.cif (11.19 kB)
Synthesis and Characterization of Tb[N(CN)2]3·2H2O and Eu[N(CN)2]3·2H2O: Two New Luminescent Rare-Earth Dicyanamides
dataset
posted on 2006-11-28, 00:00 authored by Abanti Nag, Peter J. Schmidt, Wolfgang SchnickTwo new rare-earth dicyanamides, namely, Tb[N(CN)2]3·2H2O and Eu[N(CN)2]3·2H2O, have been
prepared by ion exchange in aqueous solution, followed by evaporation of the solvent at room temperature.
The structures of both compounds have been solved and refined from single-crystal and powder X-ray
diffraction data, respectively. The two compounds are isostructural and are built up from irregular quadratic
antiprismatic LnN6O2 polyhedra connected to each other by three crystallographically independent
dicyanamide ([N(CN)2]3-) ions (Tb[N(CN)2]3·2H2O, P21/n, Z = 4, a = 7.4632(15) Å, b = 11.523(2) Å,
c = 13.944(3) Å, β = 94.06(3)°, V = 1196.2(4) Å3; Eu[N(CN)2]3·2H2O, P21/n, Z = 4, a = 7.4780(3) Å,
b = 11.5429(5) Å, c = 13.9756(7) Å, β = 93.998(4)°, V = 1203.41(10) Å3). Annealing of the hydrated
phases of Ln[N(CN)2]3·2H2O (Ln = Eu, Tb) at 150 °C under an argon atmosphere leads to the formation
of nonhydrated Ln[N(CN)2]3 (Ln = Eu, Tb). Both the hydrated (Eu[N(CN)2]3·2H2O) and nonhydrated
(Eu[N(CN)2]3) europium(III) dicyanamides show red luminescence due to the dominant intensity of 5D0−7FJ (J = 1, 2, 4) emission lines by excitation at 365 nm. The broad excitation band of europium(III)
dicyanamide (fwhm = 8000 cm-1) ranging between 260 and 420 nm with λmax ≈ 30000 cm-1 is ascribed
to a Eu−N charge-transfer transition, which is significantly shifted to lower energy compared to that of
oxo compounds due to the nephalauxetic effect. Similarly, both the hydrated (Tb[N(CN)2]3·2H2O) and
nonhydrated (Tb[N(CN)2]3) terbium(III) dicyanamides show green emission at λexc = 365 nm, arising
mainly from the dominant 5D0−7F4 transition. However, unlike europium(III) dicyanamide, the broad
excitation band of terbium(III) dicyanamide ranging between 250 and 400 nm with a maximum at 33000
cm-1 can be assigned to the 4f8−4f75d1 transition of Tb3+.