Synthesis, crystal structure and polymorphism of a µ-oxo bridged binuclear iron(III) complex of 2,2′∶ 6′,2″∶6″,2‴-quaterpyridine

Abstract

Aqueous solutions of iron(III) perchlorate and 2,2′∶6′2″∶6″,2‴-quaterpyridine (L, C₂₀H₁₄N₄) in the presence of triethylamine gave deep red crystals of two polymorphic phases of [{FeL(H₂O)}₂(µ-O)][ClO₄]₄·2H₂O 1, a µ-oxo derivative of iron(III). One has been identified as a monoclinic phase, space group P2₁/n, with unit cell a = 13.080(3), b = 14.045(3), c = 13.778(3) Å, β = 105.52(3)° and the other as an orthorhombic one, space group Pbca with unit cell a = 14.175(2), b = 16.463(1) and c = 20.949(3) Å. The crystal structures of both polymorphs have been studied and shown to correspond to slightly different geometries of the same cation. To reduce some degree of disorder in the perchlorate anions, the monoclinic phase has also been studied at –150 °C, giving an ordered pattern. The crystal structures of the two phases are compared. The two iron atoms are at the centre of corner-sharing octahedra, with the water trans to the µ-bonded oxide.