H−D Spin−Spin Coupling in Stretched Molecular Hydrogen Complexes of Osmium(II): Density Functional Studies of JHD

Using density functional techniques the H−D spin−spin coupling constant J HD has been calculated for a range of osmium(II)−dihydrogen complexes [Os(NH 3 ) 4 L z (η 2 -H 2 )] ( z +2)+ in which properties of the H−H bond are modulated by variation of the trans ligand L z (L z = (CH 3 ) 2 CO, H 2 O, CH 3 COO -, Cl -, H -, C 5 H 5 N, CH 3 CN, NH 3, NH 2 OH, and CN - ). The results of the calculations are compared with the available experimental values. A high degree of correlation between the calculated J HD, H−H bond length r HH, and Os−H 2 interaction energy is demonstrated. Consistent with the experimentally established trends in a wide variety of complexes, J HD varies inversely with r HH . This behavior, opposite to that in free HD, is explained in terms of the metal−dihydrogen bonding mechanism.