New bimetallic [(Cl)3Pt(dpop′)M(dpop′)](PF6) (M = Ru(II) and Os(II); dpop′ = dipyrido (2,3-a:3′,2′-j)phenazine) complexes using dpop′ as a novel mixed denticity bridging ligand

The dpop′ (dipyrido (2,3-a:3′,2′-j)phenazine) ligand structurally displays the possibility of a mixed denticity bridging ligand (BL) with low lying π∗ orbitals. Previously prepared complexes with Fe(II); Ru(II); Os(II) and Re(I) have only demonstrated tridentate coordination to dpop′ and it’s use as a terminal ligand (TL). In this study two new bimetallic complexes [(Cl)3Pt(dpop′)M(dpop′)](PF6) (M = Ru(II) and Os(II)) were synthesized and are the first to use dpop′ as a bridging ligand (BL), with monodentate coordination to Pt(II) and tridentate coordination to Ru(II) and Os(II). The electronic absorption spectra display Ru(II) and Os(II) (dπ) → dpop′ (π∗) (BL) MLCT transitions shifted to lower energy due to stabilization of the bridging dpop′ (π∗) acceptor orbitals. Cyclic voltammetry shows the reversible Ru+2/+3 and Os+2/+3 redox couples are at the same potentials as the respective [M(dpop′)2](PF6)2 complexes while the bridging dpop′0/−1 reversible reductions are shifted to less negative potential by 0.2 V. NMR data show downfield shifts for protons bound to the dpop′ (BL) versus dpop′ (TL) ligands.