Kesheng Shen

Synthesis, crystal structure, antioxidation and fluorescence of two lanthanide complexes with a noncyclic polyether Schiff base ligand

Abstract Two lanthanide (Sm and La) complexes with the Schiff base ligand bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine (Bod) have been synthesized and characterized by physico-chemical and spectroscopic methods. [Sm(Bod)(NO3)3] {bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine samarium(III) trinitrate} (1) is a discrete mononuclear species and [La(Bod)(NO3)3(DMF)]n {bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine dimethylformamide lanthanum(III) trinitrate}n (2) formed an inorganic coordination polymer. In the two complexes, the metal ions are both ten-coordinate and the geometric structure around the Ln(III) ions can be described as distorted hexadecahedral. An antioxidant assay in vitro shows that complexes 1 and 2 exhibit better scavenging activity than both the ligand and the usual antioxidants on hydroxyl and superoxide radicals. Under excitation at room temperature, a red shift in the fluorescence band of the ligand in the complexes compared with that of the free ligand can be attributed to coordination of the rare earth ions to the ligand. Furthermore, 1 produced characteristic Sm(III) luminescence, which indicates the ligand Bod is a good organic chelator to absorb energy and transfer it to the Sm3+ ion.

Synthesis, crystal structures, and biological properties of a new naphthalimide Schiff base and its copper(II) complex

Abstract A new naphthalimide Schiff base N-allylamine-4-(ethylenediamine-3-methoxysalicylidene)-1,8-naphthalimide (HL) and its copper(II) complex {N-allylamine-4-(ethylenediamine-3-methoxysalicylidene)-1,8-naphthalimide copper(II)} (CuL2) have been synthesized and characterized. The crystal structure of CuL2 has been determined by X-ray single crystal diffraction. The central Cu(II) ion is four-coordinate with an N2O2 donor set which is afforded by two L ligands, forming a slightly distorted square planar geometry. The interactions of HL and CuL2 with calf thymus DNA were investigated using electronic absorption titration, fluorescence titration, and viscosity measurements. The results indicate that free HL and CuL2 bind to DNA in an intercalation mode, and their binding affinity for DNA takes the order CuL2 > HL. Moreover, the antioxidant assay in vitro also shows that HL and CuL2 possess significant antioxidant activities and CuL2 is more effective than free HL.

A new modification of [Ag4Br4(PPh3)4]: synthesis, structure and properties

Abstract A new modification of the homometallic silver(I) cluster [Ag4Br4(PPh3)4] has been prepared and characterized by elemental analysis, UV/Vis and IR spectroscopy, and X-ray crystallography. The tetramer shows a polycyclic structure with a chair conformation. The bromine atoms adopt μ2- and μ3-bridging modes. The shortest Ag–Ag distance in the cluster is 3.159(2) Å, which indicates significant Ag–Ag interactions. A supramolecular structure is arranged by hydrogen bonds (C–H···Br). Cyclic voltammograms of the cluster indicate a quasi-reversible Ag+/Ag couple. The fluorescence properties of the ligand and the Ag(I) cluster were studied in the solid state. The emission peaks of the Ag(I) cluster are attributed to ligand-centered luminescence.

Synthesis, crystal structure, fluorescence and electrochemical properties of two Ag(I) complexes based on 2-(4'-pyridyl)-benzoxazole/SPPh3 ligands

Abstract To explore the luminescence properties of silver complexes in the solid state, two Ag(I) complexes, [Ag(4-PBO)2(NO3)] {di[2-(4′-pyridyl)-benzoxazole]silver(I) nitrate} (1) and [Ag2(SPPh3)4](ClO4)2 {[tetra(triphenylphosphine sulfide)disilver(I)] diperchlorate} (2) (4-PBO =2-(4′-pyridyl)-benzoxazole, SPPh3 = triphenylphosphine sulfide), have been synthesized and characterized by elemental analysis, FT-IR and UV-Vis spectroscopy. Single-crystal X-ray diffraction revealed that 1 is three-coordinate by two nitrogen atoms from two 4-PBO ligands and an oxygen atom from the coordinated nitrate anion forming a triangular plane configuration. In 2, the SPPh3 ligands adopt a monodentate coordinated and monoatomic bridging mode to connect two Ag(I) ions, resulting in a three-coordinate symmetrical binuclear structure. In the solid state, the luminescence properties of the ligands 4-PBO, SPPh3 and their complexes were investigated. The results demonstrated that 1 results in the fluorescence quenching of aggregates due to the strong π–π stacking effect. The fluorescence enhancement of 2 may be attributed to the “aggregation-induced emission” (AIE) effect of restricted intramolecular rotations of the peripheral phenyl rings against the central core. In addition, cyclic voltammograms of 1 and 2 indicated an irreversible Ag+/Ag couple. Graphical Abstract

Synthesis, structure, electrochemical properties, and antioxidant activities of copper(II) and zinc(II) complexes with N,N-bis(N-ethyl-2-ylmethylbenzimidazol)allylamine ligand

Abstract N,N-bis(N-methyl-2-ylmethylbenzimidazole)aniline (EtAIDB) and its transition metal complexes, [Cu(EtAIDB)Br2]·EtOH {dibromo[N,N-bis(N-methyl-2-ylmethylbenzimidazole)aniline] copper(II) ethanol} (1) and [Zn(EtAIDB)Br2] {dibromo[N,N-bis(N-methyl-2-ylmethylbenzimidazole)aniline] zinc(II)} (2), have been synthesized and characterized by elemental analysis, molar conductivity, UV–visible, and IR spectroscopy. The X-ray crystallographic studies of 1 and 2 have shown two different arrangements: 1 is distorted square-based pyramidal, while 2 can be treated as distorted tetrahedral. The cyclic voltammogram of 1 represents quasi-reversible Cu2+/Cu+ pairs. In vitro antioxidant tests showed that 1 had significant antioxidant activity against superoxide and hydroxy radicals.