No abstract

The field strength of the axial ligands determines the spin state of saddled iron(III) porphyrin complexes (see picture). Strong axial ligands (L), such as imidazole and 4‐dimethylaminopyridine, lead to the formation of complexes with a pure S=1/2 state, while weak ligands, such as THF, give complexes with a pure S=3/2 state. Intermediate strength ligands, such as pyridine and 4‐cyanopyridine, give complexes that show a novel spin crossover between the S=1/2 and S=3/2 states.

The seminal formalism ML l X x (M = transition metal, L = 2e-donor ligand, X = 1e-donor ligand) provides a unified description for transition-metal complexes. Besides the wellknown L-and X-type ligands, the ability of Lewis acids to act as zero-electron donors/two-electron acceptors was recognized early on, [1] and these ligands were referred to as Z-type ligands in ML l

No abstract

Simple cationic sandwich complexes that contained alkyl- or halogen substituents provided ionic liquids (ILs) with the bis(perfluoroalkanesulfonyl)imide anion. Ferrocenium- and cobaltocenium ILs [M(C(5)H(4)R(1))(C(5)H(4)R(2))][Tf(2)N] (M=Fe, Co) and arene-ferrocenium ILs [Fe(C(5)H(4)R(1))(C(6)H(5)R(2))][Tf(2)N] were prepared and their physical properties were investigated. A detailed comparison of their thermal properties revealed the effects of molecular symmetry and substituents on their melting points. Their viscosity increased on increasing the length of the substituent on the cation and the perfluoroalkyl chain length on the anion. Upon cooling, ILs with low viscosities exhibited crystallization, whereas those with higher viscosities tended to exhibit glass transitions. Most of these salts showed phase transitions in the solid state. A magnetic-switching phenomenon was observed for the paramagnetic ferrocenium IL, which was associated with a liquid/solid transformation, based on the magnetic anisotropy of the ferrocenium cation. (57)Fe Mössbauer spectroscopy was applied to [Fe(C(5)H(4)nBu)(2)][Tf(2)N] to investigate the vibrational behavior of the iron atom in the crystal and glassy states of the ferrocenium IL.