Xiao-Peng Zhang

Distinct magnetic dynamic behavior for two polymorphs of the same Dy(III) complex

Two polymorphs of the same Dy(III) complex show distinct slow magnetic relaxation behaviors due to the different local environments of Dy(III) in the crystal. This work represents the first example where the magnetic dynamic property of neutral rare earth complexes could be tuned by growing polymorphic crystals without changing the ligand.

Solvent-Induced Single-Crystal-to-Single-Crystal Transformation in Multifunctional Chiral Dysprosium(III) Compounds

Two new enantiomeric ionic chiral dysprosium(III) compounds were designed and synthesized. These compounds show simultaneously the optical activity, ferroelectric effects, nonlinear-optical effects, and slow magnetic relaxation behavior. More interestingly, these compounds exhibit reversible single-crystal-to-single-crystal transformations associated with the release or absorption of solvent molecules. The structure transformations are accompanied by distinct changes in the physical properties.

Mechano-induced luminescent and chiroptical switching in chiral cyclometalated platinum(II) complexes

A couple of enantiomeric chiral cyclometalated platinum(II) complexes [Pt((−)-L1)(Dmpi)]Cl ((−)-1) and [Pt((+)-L1) (Dmpi)]Cl ((+)-1) [(−)-L1 = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine, (+)-L1 = (+)-4,5-pinene-6′-phenyl-2,2′-bipyridine, Dmpi = 2,6-dimethylphenylisocyanide] were synthesized. Two polymorphs (Form-Y and Form-R) of the complex (−)-1 were obtained. The crystallographic studies of both forms revealed that the emission and electronic circular dichroism (ECD) spectra of these complexes at solid state were sensitive to the intermolecular effects and to the molecular surrounding environments. The yellow forms (Form-Y) of the complexes (−)-1 and (+)-1 were found to undergo crystal-to-amorphous transformation upon mechanical grinding, resulting in luminescent and chiroptical switching behaviours as evidenced by emission and ECD spectra. The mechanochromic process can be reversed repeatedly by the addition of a few drops of dichloromethane. When the counteranion Cl− in 1 was replaced with trifluoromethanesulfonate (OTf−), complexes [Pt((−)-L1)(Dmpi)]OTf ((−)-2) and [Pt((+)-L1)(Dmpi)]OTf ((+)-2) were obtained. Complexes (−)-2 and (+)-2 showed a more pronounced luminescent switching behaviour, suggesting that the switching properties can be tuned by the counteranions.

Potential switchable circularly polarized luminescence from chiral cyclometalated platinum(II) complexes.

A series of chiral cyclometalated platinum(II) complexes, [Pt((−)-L1)(Dmpi)]Cl ((−)-1), [Pt((+)-L1)(Dmpi)]Cl ((+)-1), [Pt((−)-L2)(Dmpi)]Cl ((−)-2), [Pt((+)-L2)(Dmpi)]Cl ((+)-2), [Pt3((−)-L2)2(Dmpi)4](ClO4)4 ((−)-3), and [Pt3((+)-L2)2(Dmpi)4](ClO4)4 ((+)-3) [(−)-L1 = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine, (+)-L1 = (+)-4,5-pinene-6′-phenyl-2,2′-bipyridine), (−)-L2 = (−)-1,3-bis(2-(4,5-pinene)pyridyl)benzene, (+)-L2 = (+)-1,3-bis(2-(4,5-pinene)pyridyl)benzene, Dmpi = 2,6-dimethylphenyl isocyanide], have been designed and synthesized. In aqueous solutions, (−)-1 and (+)-1 aggregate into one-dimensional helical chain structures through Pt···Pt, π–π, and hydrophobic–hydrophobic interactions. (−)-3 and (+)-3 represent a novel helical structure with Pt–Pt bonds. The formation of helical structures results in enhanced and distinct chiroptical properties as evidenced by circular dichroism spectra. Circularly polarized luminescence (CPL) was observed from the aggregates of (−)-1 and (+)-1 in water, as well as (−)-3 and (+)-3 in dichloromethane. The CPL activity can be switched reversibly (for (−)-1 and (+)-1) or irreversibly (for (−)-3 and (+)-3) by varying the temperature.

Vibrational and electronic circular dichroism monitoring of copper(II) coordination with a chiral ligand.

Novel copper(II) coordination compounds with chiral macrocyclic imine ligands derived from R-/S-camphor were asymmetrically synthesized and characterized with the aid of chiroptical spectroscopies. Crystal structures of both enantiomers were determined by single crystal X-ray diffraction analysis. Circular dichroism (CD) spectra were analyzed using a simplified exciton model as well as quantum chemical computations. The absolute configuration of the copper(II) coordination compounds determined from CD was found consistent with the crystal data. The copper(II) complexes were further investigated by vibrational CD (VCD) measurement combined with density functional theory calculation. The complex formation was evidenced by spectral shifts of the characteristic bands in the CD and VCD spectra.

Vapor-induced chiroptical switching in chiral cyclometalated platinum(II) complexes with pinene functionalized C^N^N ligands

A new couple of enantiomeric chiral cyclometalated platinum(II) complexes Pt(La)(CC–Ph) (1a) and Pt(Lb)(CC–Ph) (1b) (La = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine, Lb = (+)-4,5-pinene-6′-phenyl-2,2′-bipyridine) have been designed and synthesized. These complexes were found to undergo crystal transformation upon exposure to dichloromethane vapor, resulting in slight changes of vapochromism/vapoluminescence but very distinct chiroptical switching behaviour. Single crystal X-ray diffraction studies revealed that the two polymorphs (Form-Y and Form-O) of complexes 1a/1b display dissimilar molecular arrangements as well as inter-molecular interactions, which are responsible for the switching behaviour in electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectra. The vapor-induced chiroptical switching behaviour in these platinum(II) complexes is unique and may lead to novel chiroptical sensing applications.

High Adsorption of Sulfamethoxazole by an Amine-Modified Polystyrene–Divinylbenzene Resin and Its Mechanistic Insight

Sulfamethoxazole (SMZ) adsorption by a series of amine-modified polystyrene-divinylbenzene resins (PSA/B/C/D) was investigated. All resins showed a similar pH dependent adsorption of SMZ but their capacities were linearly related with the contents of primary amines (-NH2) rather than secondary amines (-NH-). Mechanisms of SMZ adsorption by PSA (highest -NH2 content) were discussed as an example. Due to comparable pKa, H-bonding interactions of -NH2(0) with SMZ(0) (regular H-bond) and SMZ(-) (negative charge-assisted H-bond, (-)CAHB) successively contributed most adsorption (pH 4-9). At weakly acidic pH, -NH2(0) was partially protonated and electrostatic attraction between -NH3(+) and SMZ(-) occurred concurrently, but could be hindered by increased loading of SMZ(0). Hydrophobic/ π-π interactions were not major mechanisms as phenanthrene and nitrobenzenes had little effect on SMZ adsorption. At alkaline pH, where SMZ(-) and -NH2(0) prevailed, adsorption was accompanied by the stoichiometric (∼1.0) proton exchange with water, leading to OH(-) release and the formation of (-)CAHB [SO2N(-)···H···NH2]. The interaction and SMZ spatial distribution in the resin-phase were further confirmed by FTIR and Raman spectra. SMZ was uniformly adsorbed on external and interior surfaces. SMZ adsorption by PSA had low-interference from other coexistent matter, but high stability after multiple regenerations. The findings will guide new adsorbent designs for selectively removing target organics.

Citric Acid Enhanced Copper Removal by a Novel Multi-amines Decorated Resin

Cu removal by a novel multi-amines decorated resin (PAMD) from wastewater in the absence or presence of citric acid (CA) was examined. Adsorption capacity of Cu onto PAMD markedly increased by 186% to 5.07 mmol/g in the presence of CA, up to 7 times of that onto four commercial resins under the same conditions. Preloaded and kinetic studies demonstrated adsorption of [Cu-CA] complex instead of CA site-bridging and variations of adsorbate species were qualitatively illustrated. The interaction configuration was further studied with ESI-MS, FTIR, XPS and XANES characterizations. The large enhancement of Cu adsorption in Cu-CA bi-solutes systems was attributed to mechanism change from single-site to dual-sites interaction in which cationic or neutral Cu species (Cu2+ and CuHL0) coordinated with neutral amine sites and anionic complex species (CuL− and Cu2L22−) directly interacted with protonated amine sites via electrostatic attraction, and the ratio of the two interactions was approximately 0.5 for the equimolar bi-solutes system. Moreover, commonly coexisting ions in wastewaters had no obvious effect on the superior performance of PAMD. Also, Cu and CA could be recovered completely with HCl. Therefore, PAMD has a great potential to efficiently remove heavy metal ions from wastewaters in the presence of organic acids.

Circular Dichroism Spectroscopy Study of Crystalline-to-Amorphous Transformation in Chiral Platinum(II) Complexes

Two couples of enantiomeric platinum(II) complexes: Pt(L1a )Cl (1a), Pt(L1b )Cl (1b) and Pt(L1a )(C ≡ C - Ph) (2a), Pt(L1b )(C ≡ C - Ph) (2b) (L1a  = (+)-1,3-di-(2-(4,5-pinene)pyridyl)benzene, L1b  = (-)-1,3-di-(2-(4,5-pinene)pyridyl)benzene) were synthesized and characterized. Their absolute configurations were determined by single crystal X-ray diffraction and further verified by circular dichroism (CD) spectra (including electronic circular dichroism [ECD] and vibrational circular dichroism [VCD]). These complexes show interesting mechanoluminescence and/or vapoluminescence due to crystalline-to-amorphous transformation. The crystalline solids, grinding-induced amorphous powders, and vapor-induced amorphous powders of complexes 2a and 2b were comparatively investigated by solid-state ECD and VCD spectra. The transformation from crystalline solids to amorphous powders was accompanied by significant variances of the spectral feature in both ECD and VCD spectra.

A novel tetraethylenepentamine functionalized polymeric adsorbent for enhanced removal and selective recovery of heavy metal ions from saline solutions

A series of multi-amine functionalized polymeric adsorbents with polymethacrylate–divinylbenzene as the substrate were facilely prepared for the enhanced removal and selective recovery of Cu(II) and Ni(II) from saline solutions. The optimal experiment of suspension polymerization between divinylbenzene and methylacrylate was designed by response surface methodology. The multi-amine was successfully grafted on polymethacrylate–divinylbenzene beads as evidenced by N–H deformation vibrations in Fourier-transform infrared spectrometry and characteristic absorption peaks of nitrogen in X-ray photoelectron spectroscopy. Among the newly-synthesized multi-amine adsorbents, the tetraethylenepentamine decorated resin (PAMD) exhibited the highest content of N, reaching as high as 20.38%. The maximum adsorption capacity of PAMD for Cu(II) was up to 1.21 mmol g−1, which is obviously superior to such commercial multi-amine resins as Purolite S984. With increasing concentration of NaNO3 in the solutions, the uptake of Cu(II) and Ni(II) onto PAMD was significantly enhanced by up to 74.28% and 75.51%, respectively. It is noteworthy that the separation factor towards Cu(II) became infinite with the help of NaNO3 despite the moderate one (1160.19) in a Cu(II)/Ni(II) salt-free solution, and such interesting characteristics could be potentially applied to prepare high-purity nickel. The salt-promotion effect of PAMD was expressed by the promotion index (Kp). Furthermore, based on the model of a compressed electric double layer, the quantitative simulation of salt-enhanced adsorption was illuminated for the first time. PAMD has also been successfully applied to treat the actual saline effluent, and a greater volume of wastewater can be decontaminated by PAMD (330 BV) compared with S984 (220 BV) under the same conditions. These interesting findings suggest that PAMD could be satisfactorily applied in the advanced treatment of actual saline effluents with low-cost, high-efficiency and good-reproducibility.