96517-97-4Relevant articles and documents
Definition of an intramolecular Eu-to-Eu energy transfer within a discrete [Eu2L] complex in solution
Nonat, Aline,Regueiro-Figueroa, Martin,Esteban-Gomez, David,De Blas, Andres,Rodriguez-Blas, Teresa,Platas-Iglesias, Carlos,Charbonniere, Loic J.
, p. 8163 - 8173 (2012)
Ligand L, based on two do3a moieties linked by the methylene groups of 6,6'-dimethyl-2,2'-bipyridine, was synthesized and characterized. The addition of Ln salts to an aqueous solution of L (0.01 M Tris-HCl, pH 7.4) led to the successive formation of [LnL] and [Ln2L] complexes, as evidenced by UV/Vis and fluorescence titration experiments. Homodinuclear [Ln2L] complexes (Ln=Eu, Gd, Tb, Yb, and Lu) were prepared and characterized. The 1H and 13C NMR spectra of the Lu and Yb complexes in D2O solution (pD=7.0) showed C1 symmetry of these species in solution, pointing to two different chemical environments for the two lanthanide cations. The analysis of the chemical shifts of the Yb complex indicated that the two coordination sites present square antiprismatic (SAP) coordination environments around the metal ions. The spectroscopic properties of the [Tb2L] complex upon ligand excitation revealed conventional behavior with τH2O=2.05(1) ms and φH2O=51 %, except for the calculation of the hydration number obtained from the luminescent lifetimes in H2O and D2O, which pointed to a non-integer value of 0.6 water molecules per TbIII ion. In contrast, the Eu complex revealed surprising features such as: 1) the presence of two and up to five components in the 5D0→7F0 and 5D0→7F1 emission bands, respectively; 2) marked differences between the normalized spectra obtained in H2O and D2O solutions; and 3) unconventional temporal evolution of the luminescence intensity at certain wavelengths, the intensity profile first displaying a rising step before the occurrence of the expected decay. Additional spectroscopic experiments performed on [Gd 2-xEuxL] complexes (x=0.1 and 1.9) confirmed the presence of two distinct Eu sites with hydration numbers of 0 (site I) and 2 (site II), and showed that the unconventional temporal evolution of the emission intensity is the result of an unprecedented intramolecular Eu-to-Eu energy-transfer process. A mathematical model was developed to interpret the experimental data, leading to energy-transfer rates of 0.98 ms-1 for the transfer from the site with q=0 to that with q=2 and vice versa. Hartree-Fock (HF) and density functional theory (DFT) calculations performed at the B3LYP level were used to investigate the conformation of the complex in solution, and to estimate the intermetallic distance, which provided Foerster radii (R0) values of 8.1 A for the energy transfer from site I to site II, and 6.8 A for the reverse energy transfer. These results represent the first evidence of an intramolecular energy-transfer equilibrium between two identical lanthanide cations within a discrete molecular complex in solution. Copyright
Novel ruthenium complexes bearing bipyridine-based and N-heterocyclic carbene-supported pyridine (NCN) ligands: The influence of ligands on catalytic transfer hydrogenation of ketones
Piyasaengthong, Akkharadet,Walton, James W.,Williams, Luke J.,Yufit, Dmitry S.
, p. 340 - 351 (2021/12/27)
Transfer hydrogenation (TH) is a powerful synthetic tool in the production of secondary alcohols from ketones by using a non-H2hydrogen source along with metal catalysts. Among homogeneous catalysts, Ru(ii) complexes are the most efficient catalysts. In our research, six novel ruthenium(ii) complexes bearing bipyridine-based ligands [Ru(L1)Cl2] (1), [Ru(L1)(PPh3)Cl]Cl (2) and [Ru(L2)Cl2] (3) and N-heterocyclic carbene-supported pyridine (NCN) ligands [RuCp(L3)]PF6(4), [RuCp*(L3)]PF6(5), and [Ru(p-cymene)(L3)Cl]PF6(6) (whereL1= 6,6′-bis(aminomethyl)-2,2′-bipyridine,L2= 6,6′-bis(dimethylaminomethyl)-2,2′-bipyridine andL3= 1,3-bis(2-methylpyridyl)imidazolium bromide) were synthesised and characterised by NMR spectroscopy, HRMS, and X-ray crystallography. The catalytic transfer hydrogenation of 28 ketones in 2-propanol at 80 °C in the presence of KOtBu (5 mol%) was demonstrated and the effect of ligands is highlighted. The results show that catalyst1exhibits improved TH efficiency compared to the commercially available Milstein catalyst and displays higher catalytic activity than2due to the steric effect from PPh3. From a combination of kinetic data and Eyring analysis, a zero-order dependence on the acetophenone substrate is observed, implying a rate-limiting hydride transfer step, leading to the proposed inner-sphere hydride transfer mechanism.
Dynamic Helicates Self-Assembly from Homo- and Heterotopic Dynamic Covalent Ligand Strands
Santoro, Antonio,Holub, Jan,Fik-Jaskó?ka, Marta A.,Vantomme, Ghislaine,Lehn, Jean-Marie
, p. 15664 - 15671 (2020/10/21)
The understanding and the application of reversible covalent reactions and coordination chemistry together with the proper design of the molecular frameworks, allow to achieve not only well-defined output architectures but also different grades of complex behavior. In this work, the dynamic nature of the helical systems offers an additional level of complexity by combining self-sorting on two levels: 1) the build-up of the ligand strand constituents from their components through dynamic covalent chemistry; 2) the assembly of the helicates from the ligands and the metal cations through dynamic metallo-supramolecular chemistry. The information encoded in the ligands constituent molecule was read differently (and accurately at the same time) by metal cations that varied in the coordination algorithms. It enabled the selective formation of a specific type of helicates from a wide library of helicates formed by the possible combination of subcomponents. Ligands containing dynamic tridentate and/or bidentate binding motifs in the same strand were studied to explore the helicates self-assembly with appropriate metal cations.
Design and synthesis of new Ru-complexes as potential photo-sensitizers: Experimental and TD-DFT insights
Sharmoukh,Hassan, Walid M. I.,Gros, Philippe C.,Allam, Nageh K.
, p. 69647 - 69657 (2016/08/05)
We report density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations on a novel organic ligand and a novel class of ruthenium complexes; cis-RuL2X2 with L = 2,2′-bipyridine-6,6′-bis ethyl ester phosphonate and phosphonic acid, X = Cl, CN or NCS. The calculations show that cis-configurations are more stable than the trans-counterparts. The DFT results have been used to help design such novel complexes for potential use as sensitizers. We demonstrate the opportunity to synthesize such complexes with high purity. The synthesis of these complexes relies on the preparation of the key intermediates cis-Ru(2,2′-bipyridine-6,6′-bisdiethyl ester phosphonate)Cl2. These complexes were characterized by 1H, 13C, and 31P NMR, elemental analysis and FTIR spectroscopy. The NCS complex shows the smallest optical band gap followed by the Cl and CN complexes, respectively, with the highest performance upon use as a sensitizer in dye-sensitized solar cells.
