Reaction chemistry of 1,1′-ferrocene dicarboxylate towards M(ii) salts (M = Co, Ni, Cu): solid-state structure and electrochemical, electronic and magnetic properties of bi- and tetrametallic complexes and coordination polymers

Abstract

The synthesis and characterisation of a series of novel complexes of type [((tmeda)M-OC(O)-fc-(μ-CO₂))₂(μ-H₂O)] (M = Co, 4; M = Ni, 5), zwitter-ionic [((pmdta)(H₂O)Cu⁺-OC(O)-fc-CO₂⁻)(CH₃OH)] (9), and coordination polymer [(tmeda)Cu((OC(O))₂fc)]_n (7) (fc = ferrocene-1,1′-diyl, (η⁵-C₅H₄)₂Fe; tmeda = N,N,N′,N′-tetramethylethylenediamine; pmdta = 1,1,4,7,7-N,N,N′,N″,N″-pentamethyldiethylenetriamine) composed of ferrocene dicarboxylates and [(tmeda)/(pmdta)M]²⁺ entities is reported. These complexes could be prepared from [M(NO₃)₂(tmeda)] (M = Co, 2; M = Ni, 3; M = Cu, 6) and [Cu(NO₃)₂(pmdta)] (8), respectively, with stoichiometric amounts of 1,1′-ferrocene dicarboxylic acid (1) in presence of [n-Bu₄N]OH–H₂O. The molecular structures of 4, 5, 7, and 9 in the solid state have been determined by single-crystal X-ray structure analysis. Electrochemical and UV-vis–NIR spectroscopic studies of these complexes are discussed in terms of electronic communication between the redox-active transition metals. In addition, the magnetic properties of 4 and 5 have been studied by susceptibility measurements vs. temperature. In complex 4, the two cobalt(II) ions are antiferromagnetically coupled, while in 5 the Ni–Ni coupling is ferromagnetic with J≈ +2.2(1) cm⁻¹.