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 water cluster

Abstract

Three isostructural cyanido-bridged heptanuclear complexes, [{Cu(II)(saldmen)(H₂O)}₆{M(III)(CN)₆}]-(ClO₄)₃·8H₂O (M= Fe(III) 2; Co(III), 3; Cr(III) 4), 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.