The ditopic ligands 4'-(diphenylphosphino)-2,2':6',2''-terpyridine L-1 and 4'-(oxodiphenylphosphanyl)-2,2':6',2''-terpyridine L-2: co-ordination to iron(II), ruthenium(II), cobalt(II) and palladium(II); crystal structures of [RuL22][PF6](2) H2O MeCN and trans[PdCl2L21]center dot 2.5CH(2)Cl(2)

The new compound 4'-(diphenylphosphino)-2,2':6',2 ''-terpyridine L-1 has been prepared; in solution it readily oxidises to the corresponding phosphine oxide, L-2. The reaction between L-1 and FeCl2 . 4H(2)O yielded salts containing [FeL21](2+), however, oxidation resulted in the formation of [FeL22](2+). The corresponding ruthenium(II) complex of L-2 has also been prepared and structurally characterised as the hexafluorophosphate salt; attempts to prepare [RuL21](2+) always resulted in oxidation of the ligand to L-2. The reaction of L-1 with cobalt(II) acetate gave [CoL21](2+) which has been isolated as the hexafluorophosphate salt. The complexes have been characterised by IR and NMR spectroscopies, mass spectrometry and elemental analysis. Compound L-1 also reacts with [PdCl2(NCMe)(2)] to give trans-[PdCl2L21] which has been fully characterised; results of an X-ray diffraction study confirm the trans configuration of the complex.