Pogo-Stick Iron and Cobalt Complexes: Synthesis, Structures, and Magnetic Properties.

The synthesis, structures, and magnetic properties of monomeric half-sandwich iron and cobalt imidazolin-2-iminato complexes have been comprehensively investigated. Salt metathesis reactions of [Cp'M(μ-I)] (, M = Fe, Co; Cp' = η-1,2,4-tri--butylcyclopentadienyl) with [ImNLi] (ImN = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato) furnishes the terminal half-sandwich compounds [Cp'M(NIm)] (, M = Fe, Co), which can be regarded as models for elusive half-sandwich iron and cobalt imido complexes. X-ray diffraction analysis confirmed the structure motif of a one-legged piano stool. Complex can also be prepared by an acid-base reaction between [Cp'Co{N(SiMe)}] () and ImNH. The electronic and magnetic properties of and were probed by Fe Mössbauer spectroscopy (M = Fe), X-band EPR spectroscopy (M = Co), and solid-state magnetic susceptibility measurements. In particular, the central metal atom adopts a high-spin ( = 2) state in , while the cobalt complex represents a rare example of a Co(II) species with a coordination number different from six displaying a low-spin to high-spin spin-crossover (SCO) behavior. The experimental observations are complemented by DFT calculations.