Species Equilibria in Nickel(II) Porphyrin Solutions: Effect of Porphyrin Structure, Solvent and Temperature

Coordination‐Induced Spin‐State Switching with Nickel(II) salpn Complexes: Electronic versus Steric Effects and Influence of Intermolecular Interactions

“…This effect was first seen for Ni II , as described by Herges et al It is general knowledge that the spin state of nickel(II) complexes depends on the coordination number and geometry. In square‐planar complexes, Ni II shows diamagnetic behavior, with S = 0, but if the geometry changes to tetrahedral,, or the coordination number increases to five or six, the spin state changes to S = 1, resulting in a paramagnetic complex . If the coordination of the axial ligand(s) is triggered by light, the effect is more specifically termed light‐driven coordination‐induced spin‐state switching (LD‐CISSS).…”

Azoimidazole functionalized Ni-porphyrins for molecular spin switching and light responsive MRI contrast agents

“…spintronics, data storage, 3,4 switchable diamagnetic levitation 5 or responsive ("smart") contrast agents for magnetic resonance imaging (MRI). [15][16][17][18][19][20][21] We have demonstrated highly efficient and fatigue resistant light-driven coordinationinduced spin state switching (LD-CISSS) by adding photodissociable ligands [22][23][24] to a solution of a Ni 2+ -porphyrin (PDL approach) as well as by tethering azopyridines directly to the porphyrin ("record player" approach). [11][12][13][14] Ni 2+ complexes change their spin state from diamagnetic (S = 0) to paramagnetic (S = 1) when the coordination sphere is changed from square planar (CN = 4) to square pyramidal (CN = 5) or square bipyramidal (CN = 6).…”

Coordination‐Induced Spin‐State Switching of an Aminyl‐Radical‐Bridged Nickel(II) Porphyrin Dimer between Doublet and Sextet States

“…[6] Porphyrin-based radicals,such as mesooxy, meso-aminyl, and meso-carbon-centered radicals,h ave been explored and characterized as rather stable molecules that can be manipulated like usual closed-shell molecules. [8] Further,c oordination-induced spin-state switching (CISSS) [9] has been demonstrated for Ni II porphyrin meso-oxy radical 3 that becomes aquartet (S = 3/2) upon coordination of two pyridines as ac onsequence of ferromagnetic interaction between the meso-oxy radical (S = 1/2) and the resultant high-spin Ni II center (S = 1). [8] Further,c oordination-induced spin-state switching (CISSS) [9] has been demonstrated for Ni II porphyrin meso-oxy radical 3 that becomes aquartet (S = 3/2) upon coordination of two pyridines as ac onsequence of ferromagnetic interaction between the meso-oxy radical (S = 1/2) and the resultant high-spin Ni II center (S = 1).…”

“…[9] Bis(Ni II -porphyrinyl)amine 10 was synthesized by Buchwald-Hartwig amination of meso-bromoporphyrin 7 with meso-aminoporphyrin 9 (Scheme 1). [9] Bis(Ni II -porphyrinyl)amine 10 was synthesized by Buchwald-Hartwig amination of meso-bromoporphyrin 7 with meso-aminoporphyrin 9 (Scheme 1).…”

“…Hyperfine coupling constants were determined to be (A N1 , A N2 , A N3 ) = (14.1 MHz, 1.3 MHz, 0.4 MHz), which are similar to the previously reported diporphyrinylaminyl radical;( A N1 , A N2 , A N3 ) = (13.6 MHz, 1.8 MHz, 1.0 MHz). [9,12] Magnetic properties of 11-13 were studied by aS QUID apparatus.T he observed cT-T curve of 11 was almost temperature-independent with aplateau of 0.34 emu Kmol À1 and reproduced by the Curie-Weiss model with aC urie constant of 0.34 emu Kmol À1 and aW eiss temperature of À4.2 K (Figure 3). , g // ) = (6.29, 2.08) was observed at 4K (Figures 2b,c).…”