  While much is known about isoelectronic materials related to carbon
nanostructures, such as boron nitride layers and nanotubes, rather less is
known about equivalent silicon based materials. Following the recent discovery
of phosphorene, we herein discuss isoelectronic silicon monosulfide monolayers.
We describe a set of anisotropic ground state structures that clearly have a
high stability with respect to the near isotropic silicon monosulfide
monolayers. The source of the layer anisotropy is related to the presence of
Si-S double chains linked by some Si-Si covalent bonds, which lye at the core
of the increased stability, together with a remarkable spd hybridization on Si.
The involvement of d orbitals brings more variety to silicon-sulfide based
nanostructures that are isoelectronic to phosphorene, which could be relevant
for future applications, adding extra degrees of freedom.
