  The hourglass fermions in solid-state materials have been attracting
significant interest recently. However, realistic two-dimensional (2D)
materials with hourglass-shaped band structures are still very scarce. Here,
through the first-principles calculations, we identify the monolayer
Pb(ClO$_{2}$)$_{2}$ and Sr(ClO$_{2}$)$_{2}$ materials as the new realistic
materials platform to realize 2D hourglass Weyl nodal loop. We show that these
monolayer materials possess an hourglass Weyl nodal loop circling around the
$\Gamma$ point and Weyl nodal line on the Brillouin zone (BZ) boundary in the
absence of spin-orbit coupling (SOC). Through the symmetry analysis, we
demonstrate that the hourglass Weyl nodal loop and Weyl nodal line are
protected by the nonsymmorphic symmetries, and are robust under the biaxial
strains. When we include the SOC, a tiny gap will be opened in the hourglass
nodal loop and nodal line, and the nodal line can be transformed into the
spin-orbit Dirac points. Our results provide a new realistic material platform
for studying the intriguing physics associated with the 2D hourglass Weyl nodal
loop and spin-orbit Dirac points.
