Yuan-Yuan Zhu

Zero-field slow magnetic relaxation from single Co(II) ion: a transition metal single-molecule magnet with high anisotropy barrier

An air-stable star-shaped CoIICoIII3 complex with only one paramagnetic Co(II) ion in the D3 coordination environment has been synthesized from a chiral Schiff base ligand. Magnetic studies revealed that this complex exhibits slow magnetic relaxation in the absence of an applied dc field, which is one of the main characteristics of single-molecule magnets (SMMs). The relaxation barrier is as high as 109 K, which is quite large among transition-metal ion-based SMMs. The complex represents the first example of zero-field SMM behavior in a mononuclear six oxygen-coordinate Co(II) complex.

An enantiopure Fe(III)4 single-molecule magnet.

A pair of enantiopure star-shaped Fe(III)(4) clusters were constructed from simple chiral ligands. AC field frequency dependence and a hysteresis loop, which are very important features of SMMs, were observed. Circular dichroism (CD) spectra demonstrated that the chirality was successfully transferred from the ligand to the coordination environment of Fe(3+) ions.

A Family of CoIICoIII3 Single-Ion Magnets with Zero-Field Slow Magnetic Relaxation: Fine Tuning of Energy Barrier by Remote Substituent and Counter Cation

The synthesis, structures, and magnetic properties of a family of air-stable star-shaped Co(II)Co(III)3 complexes were investigated. These complexes contain only one paramagnetic Co(II) ion with the approximate D3 coordination environment in the center and three diamagnetic Co(III) ions in the peripheral. Magnetic studies show their slow magnetic relaxation in the absence of an applied dc field, which is characteristic behavior of single-molecule magnets (SMMs), caused by the individual Co(II) ion with approximate D3 symmetry in the center. Most importantly, it was demonstrated that the anisotropy energy barrier can be finely tuned by the periphery substituent of the ligand and the countercation. The anisotropy energy barrier can be increased significantly from 38 K to 147 K.

Cobalt(II) coordination polymer exhibiting single-ion-magnet-type field-induced slow relaxation behavior.

A one-dimensional cobalt(II) coordination polymer, [Co(btm)2(SCN)2·H2O]n [btm = bis(1H-1,2,4-triazol-1-yl)methane], was synthesized and magnetically characterized. The isolated slightly distorted octahedral Co(II) ion displays field-induced slow relaxation with a big positive axial and a negative rhombic magnetic anisotropy (D = 93.9 cm(-1) and E = -10.5 cm(-1)), and the anisotropy energy barrier is 45.4 K.

Polypeptide-b-Poly(Phenyl Isocyanide) Hybrid Rod-Rod Copolymers: One-Pot Synthesis, Self-Assembly, and Cell Imaging

Hybrid rod-rod diblock copolymers, poly(γ-benzyl L-glutamate)-poly(4-cyano-benzoic acid 2-isopropyl-5-methyl-cyclohexyl ester) (PBLG-PPI), with determined chirality are facilely synthesized through sequential copolymerization of γ-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) and phenyl isocyanide monomers bearing chiral menthyl pendants using a Ni(cod)(bpy) complex as the catalyst in one-pot. Circular dichroism and absorption spectra reveal that each block of the block copolymers possesses a stable helical conformation with controlled helicity in solution due to the induction of chiral pendants. The two diastereomeric polymers self-assemble into helical nanofibrils with opposite handedness due to the different chiral induction of the L- and D-menthyl pendants, confirmed by transmission electron microscopy (TEM). Deprotection of the benzyl groups of the PBLG segment affords biocompatible amphiphilic diblock copolymers, poly(L-glutamic acid)-poly(4-cyano-benzoic acid 2-isopropyl-5-methyl-cyclohexyl ester) (PLGA-PPI), that can self-assemble into well-defined micelles by cosolvent induced aggregation. Very interestingly, a chiral rhodamine chromophores RhB(D) can be selectively encapsulated into the chiral polymeric micelles, which is efficiently internalized into living cells when directly monitored with a confocal microscope. This contribution will be useful for developing novel rod-rod biocompatible hybrid block copolymers with a controlled helicity, and may also provide unique chiral materials for potential bio-medical applications.

Facile synthesis of stereoregular helical poly(phenyl isocyanide)s and poly(phenyl isocyanide)-block-poly(L-lactic acid) copolymers using alkylethynylpalladium(II) complexes as initiators

The development of novel synthetic methods for the facile preparation of well-defined stereoregular helical polyisocyanides and their block copolymers in a living/controlled fashion is of great interest. In this contribution, a family of air-stable alkylethynyl Pd(II) complexes was unexpectedly found to promote the living polymerization of phenyl isocyanide, affording poly(phenyl isocyanide)s with controlled molecular weights, narrow molecular weight distributions and high stereoregularity. Interestingly, such alkylethynyl Pd(II) complexes exhibit very high helix-sense-selectivity in the living polymerization of an optically active phenyl isocyanide bearing an L-alanine pendant with a long decyl chain, and a single handed helical poly(phenyl isocyanide) with controlled helical sense was selectively produced. Moreover, a Pd(II) complex bearing a hydroxyl group can initiate the living polymerization of both phenyl isocyanide and L-lactide in one-pot, leading to the formation of well-defined poly(phenyl isocyanide)-b-poly(L-lactic acid) copolymers in high yields with controlled molecular weights and tunable compositions. Although the two monomers were polymerized via distinct mechanisms, the block copolymerization was revealed to proceed under living/controlled manners.

Fabrication of SERS-active conjugated copolymers/gold nanoparticles composite films by interface-directed assembly

We report a new type of functional composite films by taking advantage of the interface-directed assembly between thiol groups functionalized poly(4-isocyano benzoic acid⋯pyridine-4-thiol)-b-poly(3-hexylthiophene) (PPI(–SH)-b-P3HT) conjugated copolymers and gold nanoparticles (Au NPs) at the chloroform/water interface. The PPI(–SH)-b-P3HT copolymers were synthesized through hydrogen bonding induced micellization and subsequent thiol–disulfide exchange reaction. Transmission electron microscopic (TEM) and atomic force microscopy (AFM) observations showed the film was uniform on a large scale and the integrity of surface morphology was not affected by the Au NPs concentration. Interestingly, the film substrate not only exhibited a strongly Au NPs concentration dependent surface-enhanced Raman scattering (SERS) activity but also allowed detection of model molecule, IR-792 perchlorate (IR-792), in the SERS measurement. This proof-of-concept suggests the interfacial assembly route is effective in integrating the properties of organic polymers and inorganic nanoparticles, and for further application.

Field-induced Slow Magnetic Relaxation In A Hydrogen-Bonding Linked Co(II) 1D Supramolecular Coordination Polymer

We have investigated the dynamic behaviour of the magnetization of a hydrogen-bonding linked Co(II) 1D supramolecular coordination polymer. In the structure, two different mononuclear Co(II) species are linked by O–H···N hydrogen bonding through coordinated H2O and . Field-induced slow magnetic relaxation effect is observed and the anisotropy energy barrier is 33 K. Ab initio calculations reveal that Co(II) ion in [Co(bpm)2(N3)2] species is uniaxial anisotropic with a negative axial zero-field splitting parameter of D = − 82.4 cm− 1. The Co(II) ion in [Co(bpm)2(H2O)2]2+ species, however, is easy-plane anisotropic with a positive D and negative E value (D = 46.3 cm− 1, E = − 7.8 cm− 1). This is an interesting complex in which slow magnetic relaxation stems from the combination contribution of uniaxial anisotropy and easy plane anisotropy.

Fabrication of a multi-charge generable poly(phenyl isocyanide)-block-poly(3-hexylthiophene) rod–rod conjugated copolymer

A facile construction of diverse polymeric nanostructures was reported by simple quaternization reaction and UV irradiation starting from the same rod–rod conjugated poly(4-isocyano-benzoic acid 5-(2-dimethylamino-ethoxy)-2-nitro-benzyl ester)-b-poly(3-hexylthiophene) (PPI(-DMAENBA)-b-P3HT) diblock copolymers, which were prepared by sequential living copolymerization of 4-isocyano-benzoic acid tert-butyl ester (PI) and 3-hexylthiophene (3HT) using Ni(dppp)Cl2 as a catalyst in a one-pot process with a subsequent chemical modification. The facile quaternization reaction and UV irradiation upon PPI(-DMAENBA)-b-P3HT could afford quaternized PPI(-DMAENBA)-b-P3HT (PPI(-QDMAENBA)-b-P3HT) and poly(4-isocyano-benzoic acid)-b-poly(3-hexylthiophene) (PPI(-AA)-b-P3HT) copolymers. Two different polymeric micellar supramolecular structures with cationic and anionic surface properties could be obtained by direct dispersion of positively charged PPI(-QDMAENBA)-b-P3HT and negatively charged PPI(-AA)-b-P3HT copolymers into water. Interestingly, the resultant PPI(-QDMAENBA/DMAENBA)-b-P3HT block copolymers with a 40% degree of quaternization were found to exhibit unique light emissions with the color transformed from luminous yellow to pink depending on the solvent ratio of THF and water used. An almost neutral and ordered thin film was achieved on the exact stoichiometric charge balance between these two types of oppositely charged micelles, which highlights the potential to incorporate conjugated copolymers into the assembled block copolymer micelles (BCMs) to yield multifunctional ordered films and relevant applications.

The solvent effect in an axially symmetric Fe-4(III) single-molecule magnet

A pair of enantiopure Fe(III)4 SMMs with axial symmetry was synthesized and characterized by magnetization and high-frequency electron paramagnetic resonance methods. The results reveal that the axial symmetry of the structure is broken by the interaction of Fe(III)4 with the disordered solvent molecules.