ChemInform Abstract: Crystal Structure Determination of the Misfit Layer Compound (HoS)1. 23NbS2.

Abstract

Abstract Single-crystal X-ray diffraction has shown that (HoS)1.23NbS2 is a misfit layer compound built of alternate double layers of HoS, approximately a {001} slice of NaCl-type HoS, and sandwiches of NbS2 with niobium in trigonal prisms of sulphur like niobium in 2HNbS2. The unit cell dimensions of the HoS subsystem are a1 = 5.396(1) A, b1 = 5.661(1) A, c1 = 22.195(8) A, β1 = 89.81(2)°, space group F2, Z = 8. The NbS2 lattice with unit cell dimensions a2 = 3.312(1) A, b 2 = 5.661(1) A , c2 = 11.125(7) A, β2 = 86.99(3)°, space group C2, Z = 2 shows twinning, the twin plane being (001). Corresponding a and b axes in the layers of the two subsystems are parallel, while the c axes diverge slightly. The two subsystems have a common ( b∗, c∗ ) reciprocal lattice plane which corresponds in real space to a common projection along [100]. Refinements were performed of the subsystem reflections (Okl excluded) and the common Okl reflections to fix the origin of one subsystem with respect to the other. The HoS distances in the HoS double layer are 2.743(4), 2.754(4), 2.765(4), 2.83(1) and 2.95(1) A; holmium is also coordinated to one or two sulphur atoms of NbS2 (the coordination varies because of the incommensurateness along [100]). The shortest distance is 2.72 A for coordination with one sulphur atom (two other sulphur atoms at distances of 3.18 A) and 2.86 A for coordination with two sulphur atoms of NbS2, holmium atoms in rows parallel to [100] lying in between rows of sulphur atoms of NbS2 sandwiches. The Ho-S distances point to Ho(III). The Nb-S distances are 2.453(8) A (4X) and 2.472(8) A (2X).