Effect of high pressure on the vibrational frequencies of the .alpha.-pyridyl moiety in HOs3(CO)10(.mu.,.eta.2-NC5H4)

The effect of high pressure on the vibrational frequencies of the {alpha}-pyridyl-substituted triosmium cluster HOs{sub 3}(CO){sub 10}({mu},{eta}{sup 2}-NC{sub 5}H{sub 4}) has been measured in a crystalline environment to more than 70 kbar. The pressure shifts observed for well-characterized infrared bands associated with {alpha}-pyridyl moiety show agreement with the trend established previously for C{sub 2}-substituted triosmium clusters, namely, dv/dP of v(CC) > {delta}(C-H). The pressure shift of the band assigned to the antisymmetric ring breathing mode (v{sub 8}) of the pyridyl fragment of this cluster is significantly different than that observed previously for pyridine adsorbed onto gold sols. With increasing pressure, new bands are observed in the region 740-760 cm{sup {minus}1} (assigned as {gamma}(C-H)), and the various bands show distinctly different pressure shifts.