Crystal structures and luminescence properties of osmium complexes of cis-1,2-vinylenebis(diphenylarsine) and pyridyl ligands: Possible evidence for metal d, ligand d backbonding

Divalent osmium complexes of the form [Os(N-N)2L-L](PF6-)2 where N-N was a polypyridyl, and L-L was either cis-1,2-bis(diphenylphosphino)ethene (dppene) or cis-1,2-vinylenebis(diphenylarsine) (dpaene) have been synthesized and characterized. X-ray structures were determined for three complexes and for the free dpaene molecule. It was observed that the P-C bond lengths, and C-P-C bond angles do not change significantly when complexed to osmium. It was observed the As-C bond lengths shorten by 2.3 pm and the C-As-C bond angles broaden by 5.6°when dpaene was complexed to osmium. These changes in the arsine structure may indicate a different method of backbonding between arsenic and osmium. It was found that the arsine complexes had absorption and emission that were to the red of analogous phosphine complexes. In violation of "energy gap law", the dpaene complexes were found to have higher quantum yields. This may be due to the way that the arsenic atoms bond to osmium.