Chemistry of polydentate ligands. Part 7. Synthesis, characterisation, and properties of some manganese(II) complexes of quinquedentate macrocyclic ligands based on 1,10-phenanthroline. Crystal and molecular structure of a complex with pentagonal-pyramidal coordination geometry about the MnII

Abstract

Complexes of quinquedentate macrocyclic ligands with Mn^II have been prepared by condensation of 2,6-diformylpyridine and 2,6-diacetylpyridine with 2,9-di(1-methylhydrazino)-1,10-phenanthroline monohydrochloride in the presence of manganese(II) templates. Electrical conductivity and i.r. spectra are reported and evaluated to distinguish between ring closure and polymer formation, while magnetic susceptibility data show the complexes to be high spin. Evidence is presented for co-ordination of unidentate ligands in one axial site thereby completing the pentagonal-pyramidal co-ordination geometry about the Mn^II ions. This is confirmed by a single-crystal X-ray structure determination of [MnC₂₃H₂₁N₇Cl][BF₄], which is monoclinic with a= 11.717(8), b= 14.403(9), c= 15.316(9)Å, β= 116.42(6)°, Z= 4, space group P2₁/n. Metal–donor nitrogen bond lengths are 2.167(11), 2.168(11), 2.204(11), 2.312(11), and 2.348(11)Å and the metal–chlorine distance is 2.353(6)Å. The Mn^II is 0.53 Å out of the N₅ donor plane, towards the chlorine. The structure is compared with other pentagonal pyramids and distortions from the symmetric shape are discussed. Structural similarities between the current ligand and porphyrins, particularly in cavity sizes, are noted.