(18-crown-6)potassium [(1,2,5,6-η)-cycloocta-1,5-diene][(1,2,3,4-η) -naph-thalene]ferrate(-I)

The title salt, [K(C₁₂H₂₄O₆)][Fe(C ₈H₁₂)(C₁₀H₈)], is the only known naphthalene complex containing iron in a formally negative oxidation state. Each (naphthalene)(1,5-cod)-ferrate(-I) anion is in contact with one (18-crown-6)potas-sium cation via K···C contacts to the outer four carbon atoms of the naphthalene ligand (cod = 1,5-cyclooctadiene, 18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane). When using the midpoints of the coordinating olefin bonds, the overall geometry of the coordination sphere around iron can be best described as distorted tetrahedral. The naphthalene fold angle between the plane of the iron-coordinating butadiene unit and the plane containing the exo-benzene moiety is 19.2 (1)°.