Manganese(III) in a pseudo-compressed mixed-donor octahedral environment: Synthesis, X-ray crystal structure and physicochemical properties

The compound [C₅H₁₀NH₂][MnL₂] [H₂L = N-(2-hydroxynaphthalen-l-yl)sarcosine] has been synthesised and characterised using single-crystal X-ray crystallography, spectroscopy and magnetic susceptibility measurements. The crystallographic asymmetric unit displays two similar, independent [MnL₂]^- complex ions linked via piperidinium cations through hydrogen bonding. The complex ions are alternating and arranged in two non-interacting parallel chains. Each of the complex ions is six-co-ordinate with the donor atoms, provided by the two bifunctional tridentate sarcosinato ligands, being amine nitrogen atoms and carboxylate and naphtholate oxygen atoms. The anionic ligands are co-ordinated facially and are related by a crystallographic centre of inversion at the manganese ion. The mean bond distances Mn-O_naphtholate (1.885 Å), Mn-O_carboxylate (2.069 Å) and Mn-N_amine (2.198 Å) for the two molecules point to a pseudo-compressed octahedral geometry about the Mn(III) ion consistent with a pseudo-Jahn-Teller compression. IR spectroscopy corroborates the unidentate co-ordination fashion of the carboxylate group of the sarcosinato ligand and confirms the presence of the piperidinium cation. The room temperature effective magnetic moment, (8χT)^1/2, is indicative of spin-only paramagnetism. As shown by the temperature dependence of the reciprocal of the magnetic susceptibility (χ^-1), the magnetic behaviour of [C₅H₁₀NH₂][MnL₂] in the temperature range 5-300 K is in conformity with the Curie-Weiss law, χ = C/(T-θ), with θ = -0.12 K.