Reversible coordination-induced spin-state switching in complexes on metal surfaces.

Molecular spin switches are attractive candidates for controlling the spin polarization developing at the interface between molecules and magnetic metal surfaces, which is relevant for molecular spintronics devices. However, so far, intrinsic spin switches such as spin-crossover complexes have suffered from fragmentation or loss of functionality following adsorption on metal surfaces, with rare exceptions. Robust metal-organic platforms, on the other hand, rely on external axial ligands to induce spin switching.

Crystal structure of (15,20-bis-(2,3,4,5,6-penta-fluoro-phen-yl)-5,10-{(4-methyl-pyridine-3,5-di-yl)bis-[(sulfanediyl-methyl-ene)[1,1'-biphen-yl]-4',2-di-yl]}porphyrinato)nickel(II) di-chloro-methane -solvate ( > 1/2).

The title compound, [Ni(CHFNS)]·CHCl, consists of discrete Ni porphyrin complexes, in which the five-coordinate Ni cations are in a distorted square-pyramidal coordination geometry. The four porphyrin nitro-gen atoms are located in the basal plane of the pyramid, whereas the pyridine N atom is in the apical position. The porphyrin plane is strongly distorted and the Ni cation is located above this plane by 0.

Crystal structure of (15,20-bis-(2,3,4,5,6-penta-fluoro-phen-yl)-5,10-{(pyridine-3,5-di-yl)bis-[(sulfane-diyl-methyl-ene)[1,1'-biphen-yl]-4',2-di-yl]}porph-yrin-ato)nickel(II) di-chloro-methane -solvate ( > 1/2) showing a rare CN5 coordination.

The crystal structure of the title compound, [Ni(CHFNS)]·CHCl ( > 1/2), consists of Ni-porphyrin complexes that are located in general positions and di-chloro-methane solvent mol-ecules that are disordered around centers of inversion. The Ni ions are in a square-pyramidal (CN5) coordination, with four porphyrin N atoms in the equatorial and a pyridine N atom in the apical position and are shifted out of the porphyrine N plane towards the coordinating pyridine N atom. The pyridine substituent is not exactly perpendicular to the N plane with an angle of inter-section between the planes planes of 80.

Structure and Properties of a Five-Coordinate Nickel(II) Porphyrin.

Axial coordination in nickel(II) porphyrins has been thoroughly investigated and is well understood. However, isolated five-coordinate nickel(II) porphyrins are still elusive after 50 years of intense research, even though they play a crucial role as intermediates in enzymes and catalysts. Herein we present the first fully stable, thoroughly characterized five-coordinate nickel(II) porphyrin in solution and in the solid state (crystal structure).

Photoswitchable Magnetic Resonance Imaging Contrast by Improved Light-Driven Coordination-Induced Spin State Switch.

We present a fully reversible and highly efficient on-off photoswitching of magnetic resonance imaging (MRI) contrast with green (500 nm) and violet-blue (435 nm) light. The contrast change is based on intramolecular light-driven coordination-induced spin state switch (LD-CISSS), performed with azopyridine-substituted Ni-porphyrins. The relaxation time of the solvent protons in 3 mM solutions of the azoporphyrins in DMSO was switched between 3.

Coordination-induced spin-state-switch (CISSS) in water.

We present a non-ionic water-soluble porphyrin that does not exhibit measurable aggregation even at high concentrations in water. The spin state of the corresponding nickel(II) complex changes from completely diamagnetic (low-spin) to paramagnetic (high-spin) upon addition of a strong axial ligand. This leads to a strongly reduced NMR relaxation time of the water protons even at low concentrations of the complex.