Two pseudotetrahedral cobalt(II) complexes exhibiting slow magnetic relaxation under an applied direct-current field are investigated. The weak easy-plane anisotropy is accurately determined by high-field/high-frequency electron paramagnetic resonance spectroscopy as D = 2.57 cm–1 and E = 0.82 cm–1 for 1 and D = 5.56 cm–1 and E = 1.05 cm–1 for 2. In addition, hysteresis loops are observed for the two compounds at very low temperatures.

We herein report on the synthetic, structural, magnetic, and computational studies of six air-stable mononuclear Co(II) complexes with distorted octahedral geometry from PyBox type ligands. Magnetic and theoretical studies reveal that these complexes all exhibit field-induced type single-molecule magnet behaviour and a large energy splitting between the ground and first excited Kramers doublets. Dynamic magnetic property analysis shows that the Raman relaxation process is the predominant process in all six compounds. For complexes 1, 2, 3, 5, and 6, the contribution of the direct process also existed. Importantly, the axial zero-field splitting parameter D in this series varies from positive to negative with the increased distortion of the octahedral geometry for the Co(II) center, indicating that the fine-tuning of the molecular symmetry is an effective approach to manipulate the magnetic anisotropy in SIMs.

AbstractThe synthesis of two linear terpy-based metallo-supramolecular fluorescent coordination polymers through 1∶1 complexation of Zn2+ and Cd2+ ions with ditopic terpyridine ligand was reported. The dispersibility of P1 and P2 was significantly improved in organic solvent and water through the introduction of hydrophilic oligo-ethyoxy side chain. Two polymers displayed yellow light emission both in solution and the solid state due to the intra-ligand charge transfer (ILCT) between the d10 metal ions and the conjugated spacer unit. These coordination polymers were explored as fluorescent chemosensors for detecting picric acid in aqueous media, displaying high sensitivity and good selectivity. In addition, test strips were prepared from these polymers and exhibited the practical potential of detecting the NACs pollutants in the outdoor water for public safety and security.

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 CoII 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.

The synthesis, structures, and magnetic properties of a family of air-stable star-shaped CoIICoIII3 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.

Herein, we report the investigation of a mononuclear spin-crossover complex [FeIIL2][ClO4]2 (L = 2,6-bis{4,4-dimethyl-4,5-dihydrooxazol-2-yl}pyridine). This compound undergoes a structural phase transition around 173 K, accompanying with an abrupt spin-transition process. Interestingly, it exhibits a multi-induced spin-crossover behavior mediated by heat, light, pressure and solvent.

A series of chiral aryl amide compounds bearing peptide pendants have been investigated as low molecular weight gelators. A mechanistic study reveals that complementary hydrogen bonding from peptide pendants is the main driving force for the formation of organogels. This new class of organogels can exhibit multi-stimuli-responsive behavior upon applying (1) thermal, (2) pH, (3) enantiomeric purity, and (4) fluoride anion stimuli. Enantiomeric purity as a new external stimulus displays sensitive stimuli-responsiveness; only 0.02 equiv. of the enantiomer can completely disassemble the gel aggregate. They will serve as excellent smart materials with potential applications in chiral sensors, recognition, and separation.

Herein, we investigate the spin transition properties in a series of mononuclear Fe(II) complexes constructed by two pybox ligands and four counter anions. 1(BF4) undergoes an abrupt spin-transition at around 150 K, which proceeds to 50% completeness and is accompanied by a structural phase transition. 1(BPh4)·MeCN, 2(ClO4), and 2(BF4) all display gradual and complete SCO behaviours around or above ambient temperature. The desolvated compound 1(BPh4) exhibits a gradual but incomplete SCO. 2(PF6)·MeCN, 2(PF6) and 2(BPh4) show a two-step SCO. The well-defined two-step SCO of 2(BPh4) takes place at 100–200 K (T1/2 = 150 K) and 400–500 K (T1/2 = 446 K). In contrast, compounds 1(BF4)·MeCN, 1(PF6)·MeCN·Et2O and 1(PF6) remain high-spin at the measured temperatures. The LIESST (light induced excited spin state trapping) effect of several SCO compounds are also investigated, which display photo-conversion during light irradiation at low temperature at a relatively high level. Our results demonstrate that the [Fe(pybox)2]2+ series of complexes will become a new versatile system in spin-crossover research.

Herein, we report the investigation of a mononuclear spin-crossover complex [FeIIL2][ClO4]2 (L = 2,6-bis{4,4-dimethyl-4,5-dihydrooxazol-2-yl}pyridine). This compound undergoes a structural phase transition around 173 K, accompanying with an abrupt spin-transition process. Interestingly, it exhibits a multi-induced spin-crossover behavior mediated by heat, light, pressure and solvent.