Delta/Lambda-(delta/lambda-1,1’-biisoquinoline)bis(2,2’-bipyridine)metal(II) bis(hexafluorophosphate), 1(M = Ru, Os), exists in two diastereomeric forms. The crystal structures of the major diastereomers, (Delta,delta/Lambda,lambda)-1(M = Ru) and (Delta,delta/ Lambda/lambda)-1(M = Os), have been determined. The 1,1’-biisoquinoline ligand is nonplanar, which is a result of a transannular steric interaction between H-8 and H-8’ The conformation of the five-membered chelate ring formed by the 1,1’-biisoquinoline ligand in the solid-state is lambda when the configuration at the metal is A. As expected due to the lanthanide contraction effect, the molecular structure of 1(M = Os) is comparable with the analogue 1(M = Ru) with statistically-equivalent M-N bond distances. Diastereoisomerization of 1(M = Ru, Os) in solution is facile. Spin perturbation NMR experiments demonstrate that the interconversion of the two diastereomers of 1(M = Ru) and 1(M = Os) is the result of an intramolecular process of C-2 symmetry that does not change the cis/trans relationship between the 1,1’-biisoquinoline and 2,2’-bipyridine ligands.