Cation-Induced Structural Diversity in the Cobalt(II)/Nitranilato System: A Monomer, a Dimer, a Trimer and a Chain

Herein, we show how it is possible to prepare a monomer, a dimer, a trimer and a chain with cobalt(II) and the ligand nitranilato (3,6-dinitro-2,5-dihydroxy-1,4-benzoquinone dianion = C₆O₄(NO₂)₂^2– = NA^2–) by simply changing the counter-cations. Thus, we show that when we combine the ligand NA^2– with cobalt(II) in the presence of a bulky cation as PPh₄⁺, we obtain compound (PPh₄)₄[Co(NA)₃] (1), which contains the first monomeric anion of the type [Co(L)₃]^4– (L = any anilato ligand). With a smaller cation as NMe₄⁺, we obtain (NMe₄)₂[Co₂(NA)₃(H₂O)₄] (2), a rare example of anilato-containing dimer based on a transition metal (TM). With a larger cation as NPr₄⁺, we obtain a trinuclear cobalt–nitranilato complex formulated as (NPr₄)₂[Co₃(NA)₄(H₂O)₆] (3) and finally, when using the small NH₄⁺ cation, we obtain the neutral chain: [Co(NA)(H₂O)₂] (4). This work presents the synthesis and structure of these compounds and the magnetic characterization of compounds 2–4 that show the presence of very weak antiferromagnetic interactions between the cobalt centers through the anilato bridges.