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-1-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 Angstrom), Mn-O-carboxylate (2.069 Angstrom) and Mn-N-amine (2.198 Angstrom) 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, (8 chiT)(1/2), is indicative of spin-only paramagnetism. As shown by the temperature dependence of the reciprocal of the magnetic susceptibility (chi (-1)), the magnetic behaviour of [C5H10NH2][MnL2] in the temperature range 5-300 K is in conformity with the Curie-Weiss law, chi = C/(T - theta), with theta = -0.12 K. (C) 2001 Elsevier Science Ltd. All rights reserved.