Guest-Driven Light-Induced Spin Change in an Azobenzene Loaded Metal-Organic Framework.

Stimuli-responsive materials that can be reversibly switched by light are of immense interest. Among them, photo-responsive spin crossover (SCO) complexes have great promises to combine the photoactive inputs with multifaceted outputs into switchable materials and devices. However, the reversible control the spin-state change by photochromic guests is still challenging. Herein, we report an unprecedented guest-driven light-induced spin change (GD-LISC) in a Hofmann-type metal-organic framework (MOF), [Fe(bpn){Ag(CN)2 }2 ]⋅azobenzene. (1, bpn=1,4-bis(4-pyridyl)naphthalene). The reversible trans-cis photoisomerization of azobenzene guest upon UV/Vis irradiation in the solid-state results in the remarkable magnetic changes in a wide temperature range of 10-180 K. This finding not only establishes a new switching mechanism for SCO complexes, but also paves the way toward the development of new generation of photo-responsive magnetic materials.

Chiral Erbium(III) Complexes: Single-Molecule Magnet Behavior, Chirality, and Nuclearity Control.

The reactions of chiral ligand (R)/(S)-1,1'-binaphthyl-2,2'-diyl phosphate (R-HL/S-HL) and ErCl3·6H2O afford two pairs of di- and tetranuclear enantiomers [Er2(R/S-L)4(EtOH)6]Cl2·6.5EtOH (R-1, S-1) and [Er4(PO4)(R/S-L)8(EtOH)3(H2O)]2Cl(OH)·15EtOH·11H2O (R-2, S-2). The nuclearity of these complexes is controllable and depends on the reaction temperature with a template effect. Their chirality was evidenced by circular dichroism (CD) spectra. R-1 exhibits two magnetic relaxation pathways under a zero field, with an apparent barrier of 40 K. Ab initio calculations revealed a ferromagnetic dipolar interaction between these two Er(III) ions, the equatorial nature of the ligand field, and the probable origin of the two relaxations.

Cyanometallic charge engineering in spin crossover metal-organic frameworks.

In this study, we successfully synthesize cationic/neutral/anionic inverse-Hofmann-type spin crossover (SCO) frameworks with 1,1,2,2-tetrakis(4-(pyridine-4-yl)phenyl)-ethene ligand by means of cyanometallic charge engineering strategy. The cationic and neutral frameworks exhibit single-step thermally induced spin transition behaviors, while the SCO capability of anionic framework can be aroused by partial desolvation. This strategy provides a new idea to construct ionic SCO frameworks and extends the toolkit for SCO materials.

Opening magnetic hysteresis via improving the planarity of equatorial coordination by hydrogen bonding.

Through a mixed-ligand strategy, the structural change from a discrete dinuclear DyIII cluster to a one-dimensional polymeric chain was achieved, maintaining the two magnetic entities with the same {Dy(dppbO2)2(H2O)5} (dppbO2 = 1,4-butylenebis(diphenylphosphine oxide)) core structure. Since the hydrogen bonding between the equatorial coordinated water molecules and the guests/solvents/anions is distinct, the local geometry and the equatorial planarity of the first coordination sphere of the central DyIII ion become slightly different caused by the second coordination sphere. As a result, the dinuclear compound shows typical butterfly-shaped hysteresis loops, while it significantly opens at zero magnetic field up to 11 K for the 1D polymer, which is unprecedented in coordination polymers. Our experimental observations and theoretical analysis indicate that the hydrogen bonding leads to the fine-tuning of certain bond lengths and angles of the coordination environment, as well as the crystal field to a certain extent, revealing that the second coordination sphere affects the first coordination sphere by hydrogen bonding.

Tuning luminescence of didysprosium single-molecule magnets with a π-conjugated/non-conjugated bridging ligand.

Herein, we reported two didysprosium single-molecule magnets constructed with {Dy(bbpen)(MeOH)} subunits and a π-conjugated tpb or non-conjugated tpcb bridging ligand. The former exhibits extremely weak luminescence that makes it difficult to simulate its emission spectra. However, the later shows obviously enhanced and well-resolved luminescence, which helps us to gain knowledge about the magneto-optical correlation and the relevant magnetic energy levels.

Spin-crossover in an organic-inorganic hybrid perovskite.

The first spin-crossover (SCO) complex with an organic-inorganic hybrid perovskite structure (PPN)[Fe{Au(CN)2}3] (1) is reported, which displays three-step SCO behaviour. The light-induced excited spin-state trapping measurement gives T0 = 134 K for a three-dimensional FeL3-type (L = bis-monodentate ligand) SCO complex. Moreover, spin-state dependent fluorescence is observed in 1.