The non-carbido decaosmium cluster dianion [H40~,0(C0)24]2-(1 ) has been prepared in low yield by heating several trinuclear osmium clusters in isobutyl alcohol; X-ray analysis of the [ (Ph,P),N] + salt shows that the tetrahydrido-dianion (1) is very similar in structure to the carbido-dianion [OS,~C(CO)~~]~- (2) indicating that the four hydrido-ligands in (1) may possibly be interstitial in the solid state.The tetrahydrido-dianion [H40~lo(C0)24]2-(I), which has been obtained in low yield by heating Os,(CO),,, Os,(CO),,-(OEt),,' HOs,(CO),,CI, or Os,(CO),,/sodium benzoate in isobutyl alcohol is the first example of a new type of decaosmium cluster which does not contain a central carbidoatom. The first Oslo cluster species to be isolated was the dianion [OS~~C(CO),~]~-(2) in which, for the first time, a carbon atom was located in an octahedral Os, cavity.2 Since then several derivatives of this species have been isolated3p4 and until now all have been found to contain the same basic carbido-centred octahedral Os, unit.We recently reported that a range of high nuclearity cluster compounds is obtained when Os,(CO),, is heated in KOH/ Bu'OH.~ We now find that, when the reaction is carried out in BuiOH under reflux (108 "C) in the absence of base,? ? At 130 "C in 2-methylbutan-1-01 or on prolonged reflux in Bu'OH the carbido-dianion is formed showing that the reaction may be very sensitive to small changes in reaction conditions.
