  Layered materials with kagome lattice have attracted a lot of attention due
to the presence of nontrivial topological bands and correlated electronic
states with tunability. In this work, we investigate a unique van der Waals
(vdW) material system, $A_{2}M_{3}X_{4}$ ($A$ = K, Rb, Cs; $M$ = Ni, Pd; $X$ =
S, Se), where transition metal kagome lattices, chalcogen honeycomb lattices
and alkali metal triangular lattices coexist simultaneously. A notable feature
of this material is that each Ni/Pd atom is positioned in the center of four
chalcogen atoms, forming a local square-planar environment. This crystal field
environment results in a low spin state $S$ = 0 of Ni$^{2+}$/Pd$^{2+}$. A
systematic study of the crystal growth, crystal structure, magnetic and
transport properties of two representative compounds, Rb$_{2}$Ni$_{3}$S$_{4}$
and Cs$_{2}$Ni$_{3}$Se$_{4}$, has been carried out on powder and single crystal
samples. Both compounds exhibit nonmagnetic $p$-type semiconducting behavior,
closely related to the particular chemical environment of Ni$^{2+}$ ions and
the alkali metal intercalated vdW structure. Additionally,
Cs$_{2}$Ni$_{3}$Se$_{4}$ undergoes an insulator-metal transition (IMT) in
transport measurements under pressure up to 87.10 GPa without any structural
phase transition, while Rb$_{2}$Ni$_{3}$S$_{4}$ persists in its semiconducting
behavior.
