Synthesis, Crystal Structure, Magnetism, and Optical Properties of Gd3[SiON3]O—An Oxonitridosilicate Oxide with Noncondensed SiON3 Tetrahedra

Abstract

The novel oxonitridosilicate oxide (sion oxide) Gd3[SiON3]O was obtained by the reaction of gadolinium metal with its carbonate oxide and silicon diimide in a radiofrequency (r.f.) furnace at a temperature of 1400°C. The crystal structure of Gd3[SiON3]O (I4/mcm, a=649.1(2) pm, c=1078.8(6) pm, Z=4, R1=0.0411, wR2=0.0769, 405 F2 values, 19 parameters, 123 K) is isotypic with that of Ba3[SiO4]O and Cs3[CoCl4]Cl. It can be derived from the perovskite structure type by a hierarchical substitution: Ti4+→O2–, O2–→Gd3+, Ca2+→[SiON3]7– resulting in the formation of large [OGd6]16+ octahedra, which are twisted by ξ=16.47(1)° around [001]. The low-temperature single-crystal data investigation led to a crystallographic splitting of the central O atom which could not be resolved at room temperature. The UV–Vis absorption spectra in reflection geometry of the yellow title compound revealed two overlaying broad bands, one peaking at almost the same wavelength as observed in gadolinium oxide (340 nm) and a second red-shifted band at approximately 400 nm indicating a strong influence of nitrogen on the ligand field splitting of the 5d states of Gd3+. Temperature-dependent magnetic susceptibility measurements of Gd3[SiON3]O show Curie–Weiss behavior from 2 to 300 K with an experimental magnetic moment of 7.68(5) μB/Gd, indicating trivalent gadolinium. There is no evidence for magnetic ordering down to 2 K. According to the paramagnetic Curie temperature of −7(1) K, the exchange between the gadolinium magnetic moments is supposed to be only weak. The vibrational spectroscopic data (IR and Raman) are reported.