High-temperature synthesis, crystal structure, optical properties, and magnetism of the carbidonitridosilicates Ho2[Si4N6C] and Tb2[Si4N6C]

The novel carbidonitridosilicates Ho-2[Si4N6C] and Tb-2[(SiNC)-N-4-C-6] were obtained by the reaction of the respective lanthanoid metal with carbon and Si(NH)(2) in a radiofrequency furnace at the temperature of 1700 degreesC. According to the single-crystal structure analysis of Ho-2[Si4N6C] (P2(1)/c, Z=4, a=593.14(1), b=989.74(1), c=1188.59(2) pm, beta =119.58(4)degrees, R1=0.0355, wR2=0.0879, 2187 F-2 values, 119 parameters) the compound contains a condensed network of corner-sharing star like [C(SiN3)(4)] units. The holmium ions are situated in channels along [100]. The UV-VIS absorption spectrum of Ho-2[Si4N6C] shows the typical Ho3+ absorption bands. The spectroscopic results show that the 4f states remain almost unaffected by the coordination sphere and thus it is impossible to distinguish between the two crystallographic sites of Ho3+ in the UV-VIS spectrum. Magnetic susceptibility measurements of Tb-2[Si4N6C] and Ho-2[Si4N6C] show Curie-Weiss behaviour above 150 K with experimental magnetic moments of 9.57(6) mu (B)/Tb and 10.27 (4) mu (B)/Ho. The Weiss constants are -15(1) K and -11(1) K for the terbium and holmium compounds, respectively. Down to 2 K no magnetic ordering could be detected. The magnetization curves at 2 K show an increase of the magnetization with increasing flux density, indicating partial parallel spin alignments. At 5 T the magnetizations reach values of 4.15(5) mu (B)/Tb and 4.75(5) mu (B)/Ho, respectively.