  To accelerate development of innovative materials, their modelings and
predictions with useful functionalities are of vital importance. Here, based on
a recently developed crystal structure prediction method, we find a new family
of stable two-dimensional crystals with an open-channel tetrahedral bonding
network, rendering a potential for electronic and energy applications. The
proposed structural prototype with a space group of Cmme hosts at least
thirteen different freestanding T$_{3}$X compounds with group IV (T=C, Si, Ge,
Sn) and VI (X=O, S, Se, Te) elements. Moreover, the proposed materials display
diverse electronic properties ranging from direct band gap semiconductor to
topological insulator at their pristine forms, which are further tunable by
mechanical strain.
