Mixed-metal supramolecular complexes coupling phosphine-containing Ru(II) light absorbers to a reactive Pt(II) through polyazine bridging ligands

Supramolecular bimetallic Ru(II)/Pt(II) complexes [(tpy)Ru(PEt2Ph)(BL)PtCl2](2+) and their synthons [(tpy)Ru(L)(BL)](n+) (where L = Cl-, CH3CN, or PEt2Ph; tpy = 2,2':6',2-terpyridine; and BL = 2,2'-bipyrimidine (bpm) or 2,3-bis(2-pyridyl)pyrazine (dpp)) have been synthesized and studied by cyclic voltammetry, electronic absorption spectroscopy, mass spectral analysis, and P-31 NMR. The mixed-metal bimetallic complexes couple phosphine-containing Ru chromophores to a reactive Pt site. These complexes show how substitution of the monodentate ligand on the [(tpy)RuCl(BL)](+) synthons can tune the properties of these light absorbers (LA) and incorporate a P-31 NMR tag by addition of the PEt2Ph ligand. The redox potentials for the Ru(III/II) couples occur at values greater than 1.00 V versus the Ag/AgCl reference electrode and can be tuned to more positive potentials on going from Cl- to CH3CN or PEt2Ph (E-1/2 = 1-01, 1.55, and 1.56 V, respectively, for BL = bpm). The BL0/- couple at -1.03 (bpm) and -1.05 V (dpp) for [(tpy)Ru(PEt2Ph)(BL)](2+) shifts dramatically to more positive potentials upon the addition of the PtCl2 moiety to -0.34 (bpm) and -0.50 V (dpp) for the [(tpy)Ru(PEt2Ph)(BL)PtCl2](2+) bridged complex. The lowest energy electronic absorption for these complexes is assigned as the Ru(dpi) --> BL(pi*) metal-to-ligand charge transfer (MLCT) transition. These MLCT transitions are tuned to higher energy in the monometallic synthons when Cl- is replaced by CH3CN or PEt2Ph (516, 452, and 450 nm, for BL = bpm, respectively) and to lower energy when (PtCl2)-Cl-II is coordinated to the bridging ligand (560 and 506 nm for BL = bpm or dpp). This MLCT state displays a broad emission at room temperature for all the dpp systems with the [(tpy)Ru(PEt2Ph)(dpp)PtCl2](2+) system exhibiting an emission centered at 750 nm with a lifetime of 56 ns. These supramolecular complexes [(tpy)Ru(PEt2Ph)(BL)PtCl2](2+) represent the covalent linkage of TAG-LA-BL-RM assembly (TAG = NMR active tag, RM = Pt(II) reactive metal).