Yan-Hui Chi

π–π Stacking, spin density and magnetic coupling strength

The π-π stacking interaction, one of the main intermolecular forces, sometimes leads to amazing magnetic properties. Although the concept has been raised that spin density is one of the main factors that contribute to the magnetic coupling strength in intermolecular magnetic coupling systems, it has not been confirmed either experimentally or theoretically to date. Herein we present a study on the magnetostructural data of seven unpublished Cu(II) complexes and ten reported radicals. It is confirmed for the first time that the spin density on short contact atoms is a major factor that contributes to the π-π stacking magnetic coupling strength. Based on the reported data to date, when the short contact distance is larger than the default contact radius, medium or relatively strong magnetic coupling strength could be obtained only if the spin density on the short contact atoms is greater than 0.1350; when the C···C short contact is less than the default contact radius of 3.4 Å, but not less than 3.351 Å, and the spin density is less than 0.1, neither medium nor strong magnetic coupling strength could be observed. Further, when the short contact distance decreases with a temperature drop, the spin densities on the relevant short contact atoms increase. In the complexes reported the small spin densities on the relevant short contact atoms are the major factors that result in the weak π-π magnetic coupling strength.

Synthesis, crystal structure, and magnetism of a 1-D CuII chain complex with a mono-bromide bridge

A 1-D CuII chain, [Cu(μ-Br)(phenmp)2]n·(ClO4)n (phenmp = 2-(4-methyl-pyrazol-1H-yl)-1,10-phenanthroline), was synthesized and its crystal structure was determined by X-ray crystallography. CuII is located in a distorted square-pyramidal geometry, with the mono-bromide – a bridge linking two adjacent CuII ions with a separation of 3.788 Å. The result is a uniform 1-D chain that lies along the c axis. Mono-halide-bridged models have not been reported very often. The fitting for the data of the variable-temperature (2.00–330 K) magnetic susceptibilities gave a ferromagnetic interaction of J = 5.11 cm−1 (H = −2JS 1 S 2) for adjacent-bridged CuII ions. Comparing mono-halide bridged CuII complexes, trigonal-bipyramidal geometry has strong magnetic interactions, whereas square-pyramidal geometry has weak magnetic interactions. In mono-bromide bridged CuII complexes, the Cu–Br–Cu angle is related to the magnetic coupling signs with small Cu–Br–Cu angle favoring ferromagnetic interaction, while large Cu–Br–Cu angle results in antiferromagnetic interactions.

Highly efficient electrochemical recognition and quantification of amine enantiomers based on a guest-free homochiral MOF

We facilely synthesized a novel guest-free homochiral metal–organic framework, (Cu4L4)n [H2L = N-(2-hydroxybenzyl)-L-leucine] in space group P1. The (Cu4L4)n nanocrystals exhibit high electrochemical activity for rapidly discriminating chiral α-methylbenzylamine enantiomers and quantitatively determining the enantiomeric excess in the chiral amine mixture.

Intermolecular interaction and magnetic coupling mechanism of a mixed-valence CuIICuI tetranuclear complex with iodide bridge

A tetranuclear CuICuII mixed oxidation state complex, [CuII 2(μ-I)2CuI 2(μ-I)2(phenP)2I2] (phenPE: 2-(1H-pyrazol-1-yl)-1,10-phenanthroline), has been prepared and its crystal structure is determined by X-ray crystallography. In the complex, CuII is a distorted square pyramid and CuI is a distorted trigonal planar coordination environment; CuII and CuI are bridged by iodide. It is rare to form a CuII-iodide bond and for CuII and CuI to be bridged by iodide. In the crystal, there is a slipped π–π stacking between adjacent CuII complexes, which resulted in the formation of the 1-D chain along the c axis. The fitting for the variable-temperature magnetic susceptibility data gave magnetic coupling constant 2J = −1.16 cm−1 and it may be ascribed to the intermolecular π–π magnetic coupling pathway.

Intermolecular interaction and magnetic coupling mechanism between adjacent mononuclear NiII complexes

A new mononuclear complex, [Ni(dpphen)(NCS)2] [dpphen = 2,9-di(1H-pyrazol-1-yl)-1,10-phenanthroline], has been prepared and its crystal structure is determined by X-ray crystallography. In the NiII complex, NiII is a distorted octahedral geometry. The crystal structure analysis shows that there exist π−stacking interactions and an intermolecular interaction among adjacent complexes. The fitting to the variable-temperature magnetic susceptibility data gave the magnetic coupling constant J = −1.37 cm−1 ( ). Theoretical calculations reveal that the π-stacking magnetic coupling pathway resulted in an antiferromagnetic interaction with 2 J = −0.22 cm−1 ( ), whereas the magnetic coupling pathway of the intermolecular interaction led to a ferromagnetic interaction with 2 J = 0.10 cm−1 ( ). The calculations also display that there occur both spin delocalization and spin polarization in the π-stacking magnetic coupling system and the magnetic coupling system of the intermolecular interaction.

Facile preparation of a hierarchically porous metal–organic nanocomposite with excellent catalytic performance

Herein, we report a strategy to prepare a hierarchical micro–meso–macro porous metal–organic nanocomposite, hpCuL (L = 2,4,6-tris(3,5-dicarboxylatephenylamino)-1,3,5-triazine), using a facile gel-aging process. The effect of pH values and aging time on the growth morphologies was monitored. This 3-D material, comprised of continuous metal–organic framework nanocrystallines serving as pore walls, exhibits high catalytic activity and stability towards the reduction of 4-nitrophenol by NaBH4 in water.

Novel fluorescent probes for the fluoride anion based on hydroxy-substituted perylene tetra-(alkoxycarbonyl) derivatives

The fluoride anion (F−) sensing abilities of 1-hydroxyl-3,4,9,10-tetra (n-butoxyloxycarbonyl) perylene (probe 1) and 1-hydroxyl-mono-five-membered S-heterocyclic annulated tetra (n-butoxyloxycarbonyl) perylene (probe 2) were studied through visual detection experiments, UV-Vis, fluorescence, and 1H NMR titrations. The probes were sensitive and selective for distinguishing F− from other anions (Cl−, Br−, I−, SO4−, PF6−, H2PO4−, BF4−, ClO4−, OH−, CH3COO−, and HPO42−) through a change of UV-Vis and fluorescence spectra. The absorption and fluorescence emission properties of the probes arise from the intermolecular proton transfer (IPT) process between a hydrogen atom on the phenolic O position of probe and the F− anion. The sensing mechanism was supported by theoretical investigation. Moreover, probe-based test strips can conveniently detect F− without any additional equipment, and they can be used as fluorescent probes for monitoring F− in living cells.

Synthesis, crystal structure, and magnetism of the binuclear radical complex [N-hydrogenpyridinium]2[Ni(tdas)2]2

The binuclear radical complex [N-hydrogenpyridinium]2[Ni(tdas)2]2 (tdas = 1,2,5-thiazole-3,4-dithiolate) has been prepared and its crystal structure determined by X-ray crystallography. In the binuclear radical complex, the two nickel ions assume a distorted pyramidal geometry and are bridged by two sulfurs of different tdas anionic ligands. ESR spectra and the theoretical calculations reveal a very strong antiferromagnetic interaction in the binuclear radical complex, leading to diamagnetic crystals. The theoretical calculations also reveal a very weak antiferromagnetic interaction between adjacent radical complexes. This study is the first to report the magnetism of a binuclear radical nickel complex with tdas as ligand. This study is the first to report the magnetism of a binuclear radical nickel complex with tdas as ligand.