Salts of the tris(isonitrosomalonamido)ferrate(II) ion: Crystal structures and anomalous magnetism of the potassium and caesium salts of the tris(isonitrosomalonamido)ferrate(II) anion

Colin L. Raston, Allen H. White, Raymund M. Golding

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Abstract

Complexes of the type M[FeL3]·xH2O [M+ = alkali-metal cation, L- = NH2·COC(NO)-·CO·NH2] have been prepared. The sodium and rubidium salts are diamagnetic; the potassium and caesium salts are paramagnetic, their room temperature magnetic moments being 2.16 and 2.66 B.M. respectively with only a slight temperature dependence. Mössbauer spectra are indicative of the presence of both singlet and quintet states. The crystal structure of the potassium salt, K[FeL3]·2H2O, has been determined from diffractometer data and refined by least squares to R 0.040 for 3 981 observed reflections. Crystals are monoclinic, space group C2/c, a = 29.89(1), b = 9.780(2), c = 13.980(3) Å, β = 106.68(2)°, Z = 8. The cell contents comprise infinite zig-zag chains of K+ cations and [FeL3]- anions, the ligands co-ordinating through one of the amide oxygens and the nitrosyl nitrogen in a fac-configuration, interspersed by potassium cations, the co-ordination sphere of the latter being the three nitrosyl oxygens from one anion, and the three remaining amide oxygens from the next; the chains are parallel to c; mean distances: Fe-N 1.882, Fe-O 1.972 Å. The crystal structure of Cs[FeL3]·2H2O has also been determined by X-ray diffraction and refined by least squares to R 0.12 for 5 126 observed reflections. Crystals are monoclinic, space group Aa, a = 33.312(6), b = 24.792(5), c = 13.323(2) Å, β = 91.55(1)°. Z = 20 (for Cs[FeL3]). As with K[FeL3]·2H2O, the cell contents comprise parallel independent chains of [FeL3]-anions alternating with Cs cations, the chains being almost linear in this case; one of the chains is interrupted by a region of considerable disorder which adversely affects the accuracy of determination of the metal-atom geometries. Neither structure determination is helpful in understanding the anomalous magnetism of these two complexes.

Original languageEnglish
Pages (from-to)329-338
Number of pages10
JournalJournal of the Chemical Society, Dalton Transactions
Issue number4
DOIs
Publication statusPublished - 1977
Externally publishedYes

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