Spectroscopy at Very High Pressures. 36. an Infrared Study of Spin-state Equilibria in Some Iron(II) Complexes

The complexes cis-[Fe(o-phen)2X2] (X = I, NCS, NCSe, and N3) have been studied under hydrostatic pressures of up to 40 kbar in a diamond-anvil cell. The spectra of these, and of the related complexes [M(o-phen)3]n+, are interpreted by deriving the skeletal modes from those of the free-ligand translations and rotations. The spectrum of the iodide is consistent with the presence of a mixture of high-spin and low-spin isomers in roughly equal proportions at 30 kbar, but the azido complex appears to be almost entirely converted to low-spin at this pressure. The new data for the thiocyanato and isocyanato complexes indicate that the spin-state transitions occur near 8 and 6 kbar, respectively, lower than previous estimates based upon samples under shear stress, and are quite sharp. © 1982 American Chemical Society