  In this work, we foresee the structure of a new class of borophenes with
smaller 2D densities of atoms than those explored so far for 2D boron crystals.
Boron atoms in the porous borophenes tend to be $5$-coordinated in contrast to
commonly investigated structures with hexagonal holes for which the number of
nearest neighbors of each atom varies from $3$ to $6$. High metallic character
is the usual feature of borophenes, however, we have also identified a
semimetallic borophene that turns into semiconductor upon unit cell expansion.
A $10\%$ increase in lattice constant of this structure gives rise to an energy
gap of $0.3\,\textnormal{eV}$. This extends to semiconductor industry the
possible application of 2D boron crystals.
