Syntheses, structural characterisation and magnetic properties of Fe(ii) and Mn(ii) compounds with the pentacyanopropenido ligand; structural characterisation of a substituted pyrazolo[1,5-a]pyrimidine

Abstract

Reactions between the metal(II) salts [M(CH₃CN)_n](BF₄)₂ (M = Fe, n = 6; M = Mn, n = 4) and some organic anionic polynitriles were studied. With the pentacyanopropenide anion pcp⁻ [pcp⁻ = (NC)₂CC(CN)C(CN)₂⁻], were obtained, according to the experimental conditions, the new complexes [M(pcp)₂(H₂O)₄] (1, M = Fe; 2, M = Mn) and [M(pcp)₂] (3, M = Fe; 4 = Mn). Use of the hexacyano-3,4-diazahexadienediide anion [(NC)₂CC(CN)NNC(CN)C(CN)₂²⁻] instead of pcp⁻ did not afford polynitrile metal complexes but led to a new organic derivative 5, of formula C₁₀N₈H₂. Crystallographic studies indicated that the isostructural compounds 1 and 2 involve discrete monomeric units with pcp ligands acting with a monodentate coordination mode and having the metal in a pseudooctahedral trans-MN₂O₄ environment; however, a rich hydrogen bond system gives rise to a 3D array. Complex 3, which presents metal in a pseudooctahedral MN₆ environment, has a 3D structure arising from pcp ligands having an unprecedented μ₃-coordination mode. Compound 5 is a bicyclic derivative with a pyrazolo[1,5-a]pyrimidine skeleton. In all derivatives, the organic part is essentially planar and involves a strongly delocalized π system. The magnetic properties of the inorganic complexes have been studied in the 2–300 K range. Fit of the magnetic data indicates high spin complexes with weak antiferromagnetic interactions in 2, 3 and 4 and the presence of a significant zero field splitting of the Fe(II) ion in 1.