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

The novel oxonitridosilicate oxide (sion oxide) Gd₃SiON₃]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 Gd₃SiON₃]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 Ba₃SiO₄]O and Cs₃CoCl₄]Cl. It can be derived from the perovskite structure type by a hierarchical substitution: Ti⁴⁺→O^2-, O^2-→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 Gd₃SiON₃]O show Curie-Weiss behavior from 2 to 300 K with an experimental magnetic moment of 7.68(5) μ_B/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.