An X-ray structural analysis of ruthenium carbonyl, Ru3(CO),,. has been completed using 936 independent reflexions in a least-squares refinement (R = 0.079). The molecule has essentially D3i, symmetry with a mean Ru-Ru bond length of 2.848 A. The crystal structure is very similar to that of Os,(CO),,.A good deal of structural data on transiton-metal carbonyls has accumulated during the last decade or so. More recently, the structure and bonding in hydridometal carbonyls has been of interest following their preparation and characterisation by a number of workers. The hydridoruthenium carbonyl, Ru,(CO),,H, (x = 2 or 3) has been isolated,l the hydride being identified from the characteristic high field shift of the protons in the n.m.r. spectrum. One rather large and irregular crystal (average cross section ca. 2 mm.) crystallised out when the solution in the n.m.r. sample tube was set aside over a period of several days. A chip of this crystal of dimensions 0-15 x 0.1 x 0.1 mm., was subjected to X-ray analysis which showed that it was, in fact, a sample of the ruthenium carbonyl, Ru,(CO),,, rather than of the hydrido-complex ; clearly the original solution contained the carbonyl as an impurity.
EXPERIMENTALThe unit-cell dimensions were measured by least-squares analysis of high angle reflexions on 30" precession photographs taken using Mo 1-Ka X-radiation and are: a = , Q = 110.61 f 0.03" where the errors quoted are standard deviations obtained from the least-squares residuals. No corrections have been made for film shrinkage. The space group is uniquely determined as P2,,, from the systematic absences {hOZ) for 1 = 2n $-1 and {OkO} for K = 2x2 + 1.Assuming four molecules in the unit cell, the cell dimensions lead to a calculated density of 2.75 gm. om.?.The intensity data were collected using a ' Pailred ' automatic diffractometer. The crystal was oriented with its a axis along the w axis of the instrument and all layers of reflexions from (OK,!}-{ 8kl) measured by the stationary counter-moving crystal method. Monochroniatised Mo-Ka X-radiation was used with a maximum value of 20 equal to 50". The w scan through reflexions varied from 1.0" on the zero layer to 2.2" on the eighth layer with a scan speed of 1.0" per minute. The background was measured by counting with the counter and crystal both stationary for 24 sec. ; independent measurements were taken on each
