text: Bond stretch isomerism is confirmed for complexes subject to spin crossover transitions.  In some octahedral complexes of d configuration, the depopulation of e orbitals causes significant contractions of the metal-ligand bond distances.  The phenomenon is mainly manifested in the solid forms of the compounds.
  Although no example of bond stretch isomerism has been established in solution, two isomers have been crystallized for pentamethylcyclopentadienyl ruthenium dichloride dimer ([Cp*RuCl]).  One has an Ru-Ru bond (2.93 Å) and the other has a long intermetallic distance of 3.75 Å.   The former isomer is thought to be diamagnetic, and the latter is magnetic.