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Free keywords:
lanthanides; nitride sulfides; crystal structures; magnetism
Abstract:
Nitride sulfides of the trivalent lanthanides with the composition
M3NS3 (M = La - Nd, Sm, Gd - Dy) can be prepared by the oxidation of
the respective lanthanide metal with sulfur, sodium azide (NaN3) and
the corresponding lanthanide tribromide (MBr3) when an additional flux
(NaBr) is used. Temperature ranges from 800 to 900 degrees C for the
thermal treatment of the reaction mixtures in evacuated silica tubes
secure the formation of bright to dark brown, transparent, lath shaped
single-crystals. The orthorhombic crystal structure (Pnma, Z = 4) was
determined from single-crystal X-ray diffraction data (La3NS3: a =
1215.13(5), b = 415.90(2), c = 1322.12(5) pm, Ce3NS3: a = 1206.28(4), b
= 410.16(1), c = 1307.18(5) pm, Pr3NS3: a = 1205.45(7), b = 405.35(2),
c = 1297.58(8) pm, Nd3NS3: a = 1207.82(5), b = 401.31(1), c =
1295.20(4) pm, Sm3NS3: a = 1201.58(6), b = 394.84(2), c = 1285.63(7)
pm, Gd3NS3: a = 1197.17(7), b = 388.22(3), c = 1286.92(8) pm, Tb3NS3: a
= 1191.62(7), b = 385.07(3), c = 1282.44(8) pm, and Dy3NS3: a =
1187.66(7), b = 382.55(3), c = 1276.77(8)pm). There are three
crystallographically different M3+ cations present in coordination of
both the N3- and the S2- anions. However, [NM4](9+) tetrahedra
connected via two common corners (c) to form linear chains
(1)(infinity){[N(M1)(1/1)(t)(M2)(1/1)(t)(M3)(2/2)(c)](6+)} along [010]
build up the main structural feature. A non-linear behaviour for the
decreasing lattice constants of the pseudo-isotypic series from La3NS3
to Dy3NS3 concerning the a- and c-axes is observed along with the
lanthanoid contraction caused by the diminishing coordination sphere of
(M1)(3+) (CN = 7) and (M3)(3+) (CN = 7) moving from the light to the
heavier lanthanides. Curie-Weiss-type magnetic behaviour for Dy3NS3
with mu(eff) = 10.3(1) mu(B) for DyN1/3S corresponding to a H-6(15/2)
groundstate for Dy3+ at higher temperatures and antiferromagnetic
ordering of the Dy3+ moments below 5 K is observed.
