Complex sentence: Roussin's red salt anion is an edge-shared bitetrahedron, wherein a pair Fe (NO) 2 units are bridged by a pair of sulfide ligands.
Split into simpler sentences: Roussin's red salt anion is an example of a ligand-bridged metal dimer. Its structure is described as an edge-shared bitetrahedron, wherein a pair Fe (NO) 2 units are bridged by a pair of sulfide ligands.