Ruthenium Complexes of Substituted Terpyridine and Pyridyl–quinoline Based Ligands with Ancillary Ligands: Synthesis, Characterization, Electrochemical Study and DFT Calculation

• Published in: ChemistrySelect (Weinheim) Vol. 1; no. 12; pp. 3276 - 3287
• Main Authors: Mongal, Binitendra N., Naskar, Sumita, Pal, Arunava, Bhattacharya, Sayantani, Mandal, Tarun K., Datta, Jayati, Naskar, Subhendu
• Format: Journal Article
• Language: English
• Published: 01-08-2016
• Subjects: aqua complexes; Pourbaix diagram; Ruthenium; TDDFT; terpyridine
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.201600483

Herein we report three novel ruthenium(II) complexes of general formula [Ru(LL′L“)](PF6)n (where L= 4’‐(9‐Anthryl)‐2,2’:6’,2”‐terpyridine, L′=2‐(2‐pyridyl)‐4‐carboxyquinoline (pcqH) and L”=Cl, n=1 (for 1), L“=SCN, n=1 (for 2) and L”=H2O, n=2 (for 3)). All the complexes were characterized by routine spectroscopic techniques e. g., FTIR, UV‐Vis, mass and NMR. A detailed pH based spectroscopic and electrochemical analysis for the complexes 1,2 and 3 were carried out to determine the pka of carboxyl and aqua moiety coordinated to ruthenium centre. The COOH group in complex 2 (pkCOOH=3.13) is slightly more acidic than in complex 3 (pkCOOH=3.98). Whereas pkH2O for complex 1 (12.33) and 3 (12.27) are comparable as expected. A Pourbaix diagram for the aqua complex has been reported. The lability of the Chloro moiety in aqueous medium has been corroborated with D2O exchange 1H‐NMR study. Photovoltaic measurements for the Chloro and thiocyanato complex are also carried out. During the pH based spectrochemical and electrochemical study we find in‐situ conversion of the aqua complex into hydroxo complex. A detailed TDDFT analysis of all the three synthesized complexes and in‐situ generated hydroxo complex in the aqueous medium at higher pH has been performed to explain the various experimental findings. In the electronic spectrum all the molecules show a MLCT transition in the visible region (1: 529 nm, 2: 511 nm, 3: 488 nm). The remarkable blue shift on going from 1 to 2 to 3 is because of the decreasing stabilizing effect of the dπ (Ru) orbital (H2O > SCN > Cl). All the electronic transitions have been nicely correlated with the TDDFT analysis. Preliminary electrochemical experiment indicates that the aqua complex 3, may act as a promising catalyst for light driven water oxidation.
Three Ruthenium(II) complexes based on the ligands 4′‐(9‐Anthry)l‐2,2′:6′,2“‐terpyridine and 2‐(2‐pyridyl)‐4‐carboxyquinoline with ancillary ligands ‐Cl, ‐NCS and H2O‐ are synthesized and fully characterized. Pourbaix diagram for the aqua complex has been reported. A detailed TDDFT analysis of all the three synthesized complexes and in‐situ generated hydroxo complex in the aqueous medium at higher pH has been performed to explain the various experimental findings. Preliminary electrochemical experiment indicates that the aqua complex may act as a promising catalyst for light driven water oxidation.