NEAR DOUBLING OF H-H BOND-LENGTH IN THE STRETCHED OSMIUM MOLECULAR-HYDROGEN COMPLEX [OS(NH3)4OAC(ETA-2-H2)]- A THEORETICAL-STUDY( )

Using ab initio quantum chemical methods the structure of the osmium c omplex [Os(NH3)4OAc-(eta2-H-2)]+ has been studied. The hydrogen is fou nd to bind to the Os in a sideways fashion. The potential energy surfa ce with respect to the H-H stretch is predicted to be extremely shallo w; thus, electron correlation accounted for at the MP2 level of theory has a large effect on bot-h the H-H bond length and the stretching fo rce constant. The predicted (MP2) H-H and Os-H distances are 1.39 and 1.58 angstrom respectively, and compare favorably with the analogous e xperimental values of 1.34 +/- 0.0.02 and 1.60 +/- 0.01 angstrom obser ved for [Os(en2)4OAc(eta2-H-2)]+ (Hasegawa, T.; Koetzle, T. J.; Li, Z. ; Parkin, S.; McMullan. R.; Taube. H. 29th International Conference on Coordination Chemistry; Lausanne, Switzerland 1992).