Magnetism, Electronic State, and Local Structure of Iron-Containing Organometallic Polymers

Schiff-base polymers were synthesized by the reaction of 2,6-pyridinedicarbaldehyde with 1,4-butane-, 1,6-hexane-, 1,8-octane-, and 1,12-dodecanediamine. Each of the polymers, when combined with iron(II) sulfate or iron(II) chloride, exhibited anomalously large magnetization and a nonlinear relation of the magnetization curve at room temperature. These iron-containing solids were found to be amorphous and, hence, the local structures around the iron atoms in the compounds were determined by the measurements of Fe K-edge X-ray absorption spectra. It was found that the iron atoms were each surrounded by six nitrogen atoms with the almost equivalent distance of 1.93±0.02Å. This was consistent with a possible geometry in which the tridentate ligand moieties of the polymers were coordinated with the iron atoms in a ratio 2 : 1. It was also found from the results of X-ray photoelectron and Mössbauer spectroscopies that the iron atoms in the solid obtained from the reaction between poly(2,6-pyridinediylmethylidynenitrilohexamethylenenitrilomethylidyne) and iron(II) sulfate were in two valence states consisted of the high spin (S=5⁄2) irons(III) which were responsible for the observed magnetism and the low-spin (S=0) irons(II) which gave no contribution to the magnetism.