Coordination-Induced Spin-State Switching with Nickel Chlorin and Nickel Isobacteriochlorin

We present the first coordination-induced
spin-state switching with nickel chlorin and nickel isobacteriochlorin.
The spin-state switching was monitored by UV–vis spectroscopy
and NMR titration experiments. The association constants (K1 and K2) and thermodynamic
parameters (ΔH and ΔS) of the coordination of pyridine were determined. The first X-ray
analyses of a paramagnetic nickel chlorin and a nickel isobacteriochlorin
provide further information about the structure of the octahedral
complexes. Nickel chlorin and even more pronounced nickel isobacteriochlorin
exhibit stronger coordination of axial ligands compared to the corresponding
nickel porphyrin and thus provide the basis for more efficient spin-switching
systems.