A missing high-spin molecule in the family of cyanido-bridged heptanuclear heterometal complexes, [(LCuII)6FeIII(CN)6]3+, and its CoIII and CrIII analogues, accompanied in the crystal by a novel octameric watercluster

Abstract

Three isostructural cyanido-bridged heptanuclear complexes, [{Cu^II(saldmen)(H₂O)}₆{M^III(CN)₆}](ClO₄)₃·8H₂O (M = Fe^III2; Co^III, 3; Cr^III4), have been obtained by reacting the dinuclear copper(II) complex, [Cu₂(saldmen)₂(μ-H₂O)(H₂O)₂](ClO₄)₂·2H₂O 1, with K₃[Co(CN)₆], K₄[Fe(CN)₆], and K₃[Cr(CN)₆], respectively (Hsaldmen is the Schiff base resulting from the condensation of salicylaldehyde with N,N-dimethylethylenediamine). A unique octameric water cluster, with bicyclo[2,2,2]octane-like structure, is sandwiched between the heptanuclear cations in 2, 3 and 4. The cryomagnetic investigations of compounds 2 and 4 reveal ferromagnetic couplings of the central Fe^III or Cr^III ions with the Cu^II ions (J_CuFe = +0.87 cm⁻¹, J_CuCr = +30.4 cm⁻¹). The intramolecular Cu⋯Cu exchange interaction in 3, across the diamagnetic cobalt(III) ion, is −0.3 cm⁻¹. The solid-state ¹H-NMR spectra of compounds 2 and 3 have been investigated.