Structural elucidation, EPR and magnetic property of a Co(III) complex salt incorporating 4,4′-bipyridine and 5-sulfoisophthalate

Proton-Induced Switching of Paramagnetism: Reversible Conversion between a Low and High Spin CoIII Center within a Heterobimetallic Core

The development of molecular species with switchable magnetic properties has been a long-standing challenge in chemistry. One approach involves binding an analyte, such as protons, to a compound to trigger a change in magnetism. Transition metal complexes have been targeted for this type of magnetic modulation because they can undergo changes in their spin states. However, heterobimetallic complexes have had limited utility because of a lack of ligands that create differentiated structures around each metal center that are often necessary to regulate the electronic and magnetic properties. To circumvent this problem, we have used a tripodal ligand with phosphinic amido groups to prepare a complex with a discrete [CoIII(μ-OH)FeIII] core and an overall system spin of ST = 5/2. Deprotonation readily produces a species with a unique [CoIII(μ-O)FeIII] core and an ST = 1/2 system spin. X-ray diffraction studies, electron paramagnetic resonance spectroscopy, and Mössbauer spectroscopy pinpoint the hexacoordinate CoIII center as the cause of this spin change: the typical SCo = 0 spin state of the CoIII center in the [CoIII(μ-OH)FeIII] complex switches to a rare SCo = 2 spin state in the [CoIII(μ-O)FeIII] analogue; this change turns on antiferromagnetic coupling between the two metal centers. Computational studies link an increase in π bonding within the Co-oxido unit to the change in the CoIII spin state. The conversion is reversible and provides a blueprint for using oxido/hydroxido ligands within a heterobimetallic core to regulate the spin state of a metal site and thus modulate the paramagnetism of a system.

Bent-bis(triazolyl)-based coordination polymers tuned by dicarboxylate ligands: syntheses, structures and properties

Seven new coordination polymers based on the bent 1,1'-(oxybis(1,4-phenylene))-bis(1H-1,2,4-triazole) ligand, with diverse structures and novel topologies, that are directed by the dicarboxylate ligands.

Auxiliary ligand-modulated trisimidazole-based coordination polymers: syntheses, structures and photoluminescence properties

Five coordination polymers having 1,3,5-tris(1-imidazolyl)benzene and the varied O-donor auxiliary ligands were designed and synthesized. Further, the auxiliary ligands modulated these complexes with structural diversities and novel topologies.

Band gap, sorption properties and fluorescence sensing behaviour of a novel 1D→2D cathenane-like cobalt(II)–organic framework

A novel hydrolytic stable CoII–organic framework, namely poly[[bis(2-amino-4-sulfonatobenzoato-κO 1)tetraaquatris{μ-1,4-bis[(imidazol-1-yl)methyl]benzene-κ2 N 3:N 3′}dicobalt(II)] tetrahydrate], {[Co(C7H5NO5S)(C14H14N4)1.5(H2O)2]·2H2O} n , (1), based on multifunctional 2-amino-5-sulfobenzoic acid (H2asba) and the auxiliary flexible ligand 1,4-bis[(imidazol-1-yl)methyl]benzene (bix), was prepared using the solution evaporation method. The purity of (1) was confirmed by elemental analysis and powder X-ray diffraction (PXRD) analysis. Complex (1) shows a novel 1D→2D interpenetrating network, which is further extended into a 3D supramolecular framework with channels occupied by the lattice water molecules. The 2-amino-4-sulfonatobenzoate (asba2−) ligand adopts a monodentate coordination mode. The bix ligands exhibit gauche–gauche (GG) and trans–trans (TT) conformations. A detailed analysis of the solid-state diffuse-reflectance UV–Vis spectrum reveals that an indirect band gap exists in the complex. The band structure, the total density of states (TDOS) and the partial density of states (PDOS) were calculated using the CASTEP program. The calculated band gap (E g) matches well with the experimental one. The complex exhibits a reversible dehydration–rehydration behaviour. Interestingly, gas sorption experiments demonstrate that the new fully anhydrous compound obtained by activating complex (1) at 400 K shows selective adsorption of CO2 over N2. Complex (1) retains excellent framework stability in a variety of solvents and manifests distinct solvent-dependent fluorescence properties. Moreover, the complex shows multiresponsive fluorescence sensing for some nitroaromatics in aqueous medium.