Metal-directed synthesis and photophysical studies of trinuclear V-shaped and pentanuclear X-shaped ruthenium and osmium metallorods and metallostars based upon 4`-(3,5-dihydroxyphenyl)-2,2`: 6`,2``-terpyridine divergent units

A new series of V-shaped trinuclear metallorods and X-shaped pentanuclear metallostars has been prepared by the reaction of metal complexes bearing pendant phenolic functionalities with complexes containing electrophilic ligands. Specifically, M(tpy)(2) motifs (M=Ru or Os; tpy= 2,2`:6,2``-terpyridine) bearing one or two pendant 3,5-dihydroxyphenyl substituents at the 4-position of the central ring of the tpy have been reacted with the complexes [Ru(tpy)(Xtpy)](2+) (X= Cl or Br) to form new ether-linked species. The energy transfer from ruthenium to osmium in these complexes has been investigated in detail and the efficiency of transfer shown to be highly temperature dependent; the energy transfer is highly efficient at low temperature, whereas at room temperature nonradiative and nontransfer deactivation of the excited RU(tPY)2* domains is most significant