Relationship between H−D Spin−Spin Coupling and Internuclear Distance in Molecular Hydrogen Complexes

An essentially identical linear relationship between the spin−spin coupling constant J HD and internuclear separation r HH in closed-shell “eighteen electron” η 2 -H 2 molecular hydrogen complexes is both predicted by quantum chemical calculations for complexes of the type [ Os(II)(NH 3 ) 4 L(η 2 -H 2 )] for a wide range of trans ligands L and found experimentally for a series of complexes of Fe, Cr, Ru, and Os, also containing a variety of ligands. Simple electronic structural considerations are proposed in order to provide a preliminary interpretation of these remarkable results.