Correlation of FeII low-spin Mössbauer quadrupole splittings and the 1T1 splitting in the electronic spectra of iron(II) isocyanide compounds. The oxidation state of tin in the tin trichloride ligand

Abstract

The electronic spectra of five iron(II)-isocyanide complexes of general formula trans-and cis-FeX₂(ArNC)₄(X = Cl and/or SnCl₃; ArNC =p-methoxyphenyl isocyanide) and the cationic complex [Fe(SnCl₃)(ArNC)₅]⁺ClO₄^– have been recorded and assigned. Splitting of the excited ¹T_1g state has been observed for the first time in Fe^II low-spin compounds. As predicted previously, the splitting of the ¹T₁ state (Δ¹T₁) correlates with the ⁵⁷Fe quadrupole splitting. In the compounds containing the SnCl₃ ligand, the Sn has a formal oxidation state of Sn^II, yet the ¹¹⁹Sn Mössbauer centre shift (c.s.) lies in the ‘Sn^IV region’. The value of the Sn Mössbauer c.s. for assigning the oxidation state and valency of Sn in Sn-metal compounds is discussed.