Synthesis and Structural Anisotropy of Single-Crystalline 2D AgEPh (E = S, Se, Te)

Silver
phenylchalcogenides (AgEPh; E = S, Se, Te) are emerging
two-dimensional (2D) semiconductors belonging to a broader class of
hybrid organic–inorganic materials, known as metal organochalcogenolates
(MOCs). However, it has been challenging to synthesize crystals of
AgSPh and AgTePh that are sufficient for fundamental and applied research.
Moreover, assignment of the crystal structure of AgSePh is debated
(C2/c vs P21/c). Here, we report the growth of up to
millimeter-sized single-crystalline 2D AgEPh (E = S, Se, or Te) having
a macroscopic parallelogram shape. Transmission electron microscopy
and electron diffraction studies reveal the relationship between their
macroscopic morphology and microscopic crystal structure, which is
essential for understanding in-plane anisotropic properties. We report
three new crystal structures through single-crystal X-ray diffraction:
2D AgSPh in P21 and 2D AgTePh in P21/c, as well as 1D AgTeC6.27H5.62N0.09 (1D AgTePh + 0.089C3H7N) in P1̅. Significantly, our space group assignment of all
three 2D AgEPh compounds in primitive lattices is different from that
of the previously reported C-centered lattices. Using temperature-dependent
powder X-ray diffraction and temperature-dependent absorption and
photoluminescence spectroscopy of 2D AgEPh prepared by different synthetic
methods, we reconcile discrepancies in their structural assignment,
which is needed for the accurate theoretical prediction of electronic
and vibrational properties.