Reversible and pH dependent photophysical properties of mixed-ligand Ru(II) complexes containing 2,2′-bipyridine and nitrosobarbiturate: Experimental and theoretical approach

• Two new Ru(II) complexes with a ligand that can be reversibly protonated/deprotonated were synthesized.
• The complexes were found susceptible to pH of the medium.
• Theoretical calculations supported electron transfer from ligand to metal ion.

A ruthenium(II) complex of type [Ru(bpy)2(L′H)]·PF61 (L′H = 5-Nitroso-pyrimidine-2,4,6-trione, is prepared by the reaction of [1,5-dihydro-5-[5-pyrimidine-2,4(1H,3H)-dionyl]-2H-chromeno[2,3-d] pyrimidine-2,4(3H)-dione)]) LH4 with [Ru(bpy)2(NO3)2] (prepared in situ). It is characterized using elemental analyses, spectroscopic and single crystal X-ray diffraction techniques. This complex is converted in another complex of type [Ru(bpy)2(L′)] 2 by the addition of an aqueous solution of NaOH. The complex 2 turns back to complex 1 after its neutralization by the addition of an aqueous solution of HCl. The reversible conversion of complexes 1 and 2 in each other is monitored using their UV–Vis and luminescence spectra. Quantum chemical calculations using density functional theory (DFT) method corroborates transfer of electron density from nitrosobarbiturate to metal ion leading the formation of complex 2.

Two pH dependent inter-convertible Ru(II) 2,2′-bipyridyl complexes containing 5-nitroso-pyrimidine-2,4,6-trione ligand are synthesized and characterized. Their pH dependent inter-conversion is supported using spectroscopic as well as by DFT calculations.Figure optionsDownload as PowerPoint slide