Pairs of octahedra can be fused in a way that preserves the octahedral coordination geometry by replacing terminal ligands with bridging ligands.  Two motifs for fusing octahedra are common: edge-sharing and face-sharing.  Edge- and face-shared bioctahedra have the formulas [ML(μ-L)] and ML(μ-L), respectively. Polymeric versions of the same linking pattern give the stoichiometries [ML(μ-L)] and [M(μ-L)], respectively.
The sharing of an edge or a face of an octahedron gives a structure called bioctahedral. Many metal pentahalide and pentaalkoxide compounds exist in solution and the solid with bioctahedral structures. One example is niobium pentachloride. Metal tetrahalides often exist as polymers with edge-sharing octahedra. Zirconium tetrachloride is an example.  Compounds with face-sharing octahedral chains include MoBr, RuBr, and TlBr.