Structural and Spectroscopic Properties of New Chiral Quinoline-based Ln(III) Complexes

Synthesis and Applications of Asymmetric Catalysis Using Chiral Ligands Containing Quinoline Motifs

In the past decade, asymmetric synthesis of chiral ligands containing quinoline motifs, a family of natural products displaying a broad range of structural diversity and their metal complexes have become the most significant methodology for the generation of enantiomerically pure compounds of biological and pharmaceutical interest. This review provides comprehensive insight on the plethora of nitrogen-based chiral ligands containing quinoline motifs and organocatalysts used in asymmetric synthesis. However, it is circumscribed to the synthesis of quinoline-based chiral ligands and metal complexes, and their applications in asymmetric synthesis as a homogeneous and heterogeneous catalyst.

Eu(iii) and Tb(iii) complexes of 6-fold coordinating ligands showing high affinity for the hydrogen carbonate ion: a spectroscopic and thermodynamic study

In the present contribution, four classes of Ln(iii) complexes (Ln = Eu and Tb) have been synthesized and characterized in aqueous solution. They differ by charge, Ln(bpcd)+ [bpcd2- = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate] and Ln(bQcd)+ (bQcd2- = N,N'-bis(2-quinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate) being positively charged and Ln(PyC3A) (PyC3A3- = N-picolyl-N,N',N'-trans-l,2-cyclohexylenediaminetriacetate) and Ln(QC3A) (QC3A3- = N-quinolyl-N,N',N'-trans-l,2-cyclohexylenediaminetriacetate) being neutral. Combined DFT, spectrophotometric and potentiometric studies reveal the presence, under physiological conditions (pH 7.4), of a couple of equally and highly stable isomers differing by the stereochemistry of the ligands (trans-N,N and trans-O,O for bpcd2- and bQcd2-; trans-O,O and trans-N,O for PyC3A3- and QC3A3-). Their high log β values (9.97 < log β < 15.68), the presence of an efficient antenna effect and the strong increase of the Ln(iii) luminescence intensity as a function of the hydrogen carbonate concentration in physiological solution, render these complexes as very promising optical probes for a selective detection of HCO3-in cellulo or in extracellular fluid. This particularly applies to the cationic Eu(bpcd)+, Tb(bpcd)+ and Eu(bQcd)+ complexes, which are capable of guesting up to two hydrogen carbonate anions in the inner coordination sphere of the metal ion, so that they show an unprecedented affinity towards HCO3- (log K for the formation of the adduct in the 4.6-5.9 range).

Rare earth metal-organic complexes constructed from hydroxyl and carboxyl modified arenesulfonate: syntheses, structure evolutions, and ultraviolet, visible and near-infrared luminescence

The reaction of 2-hydroxyl-4-carboxylbenzenesulfonic acid (H₃L) and rare earth (RE) metal nitrates together with two N-heterocyclic ligands gives rise to the formation of 38 complexes, namely, [La(H₂L)₂(ox)_0.5(H₂O)₄]_n·2nH₂O (1-La) (ox = oxalate), [RE₂(H₂L)₂ (ox)(H₂O)₁₂]·2(H₂L)·8H₂O (2-RE) (RE = Nd, Sm, Eu, Gd, Tb, Dy), [RE(SO₄)(H₂O)₇]·(H₂L)·3H₂O (3-RE) (RE = Ho, Er, Tm, Yb, Lu and Y), [RE(L)(H₂O)₃]_n·nH₂O (4-RE) (RE = Er, Tm, Yb and Lu), [RE(L)(2,2'-bipy)(H₂O)]_n (5-RE) (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Y, 2,2'-bipy = 2,2'-bipyridine), [RE(L)(1,10-phen)(H₂O)]_n (6-RE) (RE = La, Pr, Nd, Sm, Eu, 1,10-phen = 1,10-phenanthroline), and [RE(L')(1,10-phen)₂(H₂O)]_n (7-RE) (RE = Gd, Tb, Ho, Er, Yb and Lu, H₃L' = 2-hydroxy-3-nitro-4-carboxybenzenesulfonic acid), which have been characterized by elemental analysis, IR, TG, PL, powder and single-crystal X-ray diffraction. Complexes 1-La, 2-RE and 3-RE present zigzag chain, di- and mono-nuclear structures, in which H₂L^- acts as a counterion and monodentate and μ₂-bridging monoanions. For the three species, light RE metal cations tend to induce the formation of oxalate while heavy RE metal cations tend to induce the formation of sulfate. Complexes 4-RE and 5-RE exhibit layer structures incorporating helical chains, in which the L^3- trianion presents μ₃ and μ₄ coordination modes. Complexes 6-RE containing light RE metal cations show layer structures incorporating helical chains, while complexes 7-RE containing heavy RE metal cations have helical chain structures supported by the bridging of in situ generated L'^3-. Remarkably, the in situ generated oxalates in 1-La and 2-RE, as well as the in situ generated L'^3- in 7-RE, also play a crucial role in determining the structures of these complexes. Structure evolutions make these complexes present various luminescent emissions. Complexes 3-Tm, 3-Yb, 3-Lu, 3-Y and 4-Lu exhibit ultraviolet emissions from 354 to 370 nm. Complexes 1-La and 6-La present blue emissions at 442 and 463 nm. Complexes 2-Eu, 2-Tb, 5-Tb and 7-Tb exhibit characteristic red and green emissions while the complex 5-Y presents a green emission at 501 nm. Meanwhile, complexes 2-Nd, 3-Yb, 4-Yb, 5-Nd, 6-Nd, and 7-Yb show near-infrared (NIR) emissions. Moreover, 2-Eu, 2-Tb, 5-Tb, 7-Tb and 5-Y show longer luminescence lifetimes from 390.47 to 1211.57 μs.