Ruthenium complexes containing 2,2'-bipyridine and PTA (PTA = 1,3,5-triaza-7-phosphaadamantane)

Abstract

The water soluble complexes cis-[Ru(bpy)2(PTA)2]Cl2 (1Cl2), cis-[Ru(bpy)2(PTA)2](PF6)2 (1(PF6)2), trans-[Ru(bpy)2(PTA)2](CF3SO3)2 (2(CF3SO3)2), cis-[Ru(bpy)2(PTA)(H2O)](CF3SO3)2 (3(CF3SO3)2), cis-[Ru(bpy)2(PTAH3)(H2O)](CF3SO3)5 (4(CF3SO3)5), cis-[Ru(bpy)2(PTAH3)2](CF3SO3)8 (5(CF3SO3)8) and trans-[Ru(bpy)2(PTAH3)2](CF3SO3)8 (6(CF3SO3)8) have been synthesized and characterized by elemental analysis, NMR and IR spectroscopy. The crystal structures of 1(PF6)2, 2(CF3SO3)2, 4(CF3SO3)5 were obtained by single-crystal X-ray diffraction. Both experimental and computational techniques were utilized to perform a thorough analysis of the structural and electronic properties of the complexes 1 and 2 in water in both the deprotonated and protonated state and under N2 and air. UV/Visible absorbance spectroscopy revealed the sensitiveness of complex 1 and 2 to the pH. Both Ligand-to-Metal Charge Transfer (LMCT) and Metal-to-Ligand/Ligand-to-Ligand Charge Transfer (MLCT/LLCT) transisions were observed in the absorption spectrum. Luminescence studies showed that these complexes are active fluorescence compounds, despite the presence of monofosfines in their structure. The pH sensitiveness of the emission band of both complexes was studied. The photohydrolisis of 1 and 2 in acid water solution was also studied, showing that both complexes release a PTA molecule under selective irradiation in acidic water to give rise to the complex 4. Cyclic voltammetry showed that, in water, irreversible anodic oxidation corresponding to the Ru(II)/Ru(III) redox process occurs for 1, whereas for 2 the process is quasi-reversible. In DMF the redox Ru(II)/Ru(III) wave for both complexes are irreversible and occur at lower potential than in water.