  Using inelastic neutron scattering, x-ray, neutron diffraction, and the
first-principle calculation techniques, we show that the crystal structure of
the two-dimensional quantum spin system (CuCl)LaNb$_2$O$_7$ is orthorhombic
with $Pbam$ symmetry in which CuCl$_4$O$_2$ octahedra are tilted from their
high symmetry positions and the Cu$^{2+} (s = 1/2)$ ions form a distorted
square lattice. The dominant magnetic interactions are the fourth nearest
neighbor antiferromagnetic interactions with a Cu-Cl--Cl-Cu exchange path,
which lead to the formation of spin singlets. The two strongest interactions
between the singlets are ferromagnetic, which makes (CuCl)LaNb$_2$O$_7$ the
first system of ferromagnetically coupled Shastry-Sutherland quantum spin
singlets.
