Impact of the chemical vapor transport agent on polymorphism in the quasi-1D NbS3 system

The discovery of another monoclinic polymorph in the niobium trisulfide system expands the structural possibilities for quasi-1D transition metal trichalcogenide materials. We describe here NbS3-VI prepared by chemical vapor transport (CVT) using ammonium chloride as the transport agent rather than the typical iodine or excess chalcogen. This example establishes precedent for transport agent control over CVT product polymorphism, thereby opening an alternative avenue for structural engineering. The single crystal x-ray diffraction structure of NbS3-VI shows that this polymorph unexpectedly incorporates features of both NbS3-IV and NbS3-V; specifically, NbS3-VI contains corrugated chains with paired Nb–Nb and uniform chains with unpaired, equidistant Nb centers. We also use single crystal x-ray diffraction to compare NbS3-VI with (Nb0.6Ti0.4)S3, which contains solely uniform chains with slightly shorter metal–metal distances than those of uniform NbS3-VI chains.