Carbonyl ligand semibridging

The product (40% yield) contains semibridging carbonyl ligands ... 

The metallic isosceles triangle (Pdl-Pd2, Pd2-Col, 2.55 A Pdl-Col, 2.62 A) is capped at opposite sides by carbonyl ligands. At each side, one of the Pd-C(capping) distances results in semibridging carbonyls (Pdl-C51,2.36 A Pd2-... 

Numerous palladium-osmium clusters have been prepared and characterized through the reaction of osmium carbonyl clusters with palladium(O) and palladium(ii) complexes. The simplest of these is probably (bipy)Pd 20s3(G0)i2, which is prepared from Os3(/i-H)2(GO)io and Pd(OAc)2(bipy). This cluster is made up of a triangular arrangement of Os3(GO)s, with two (/x-GO)2Pd(bipy) units attached to two of the osmium atoms (43, terminal osmium carbonyls omitted for clarity). Each palladium atom has one symmetrically bound and one semibridging carbonyl ligand associated with it (Pd-GO= 1.98(2) and 2.34(2) A). 

Weakly semibridging carbonyls, such as those in Os4(CO),4, are nearly linear but show some distortion toward the second metal. Of course it is not always clear whether departures from linearity arise from interaction with the metal or because of packing forces in the crystalline solid. All CO ligands are fully nonbridging in the puckered 034(00),, described as a metal carbonyl analogue of cyclobutane. 5 The dark red crystals of Os4(CO) j possess nearly planar OS4 units with only terminal CO ligands. 

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