With complements of the ligands: an unusual S-shaped [Mn7]2 assembly from tethered calixarenes

Abstract

The reaction between MnCl₂·4H₂O, 2,2′-bis-p-^tBu-calix[4]arene (H₈L1) and 2-(hydroxymethyl)pyridine (hmpH) in a basic dmf/MeOH solution results in the formation of the complex [Mn^III₁₀Mn^II₄(L1)₃(hmp)₄(μ₃-O)₄(μ₃-OH)₂(MeOH)₄(dmf)₆](dmf)₄ (6) upon vapour diffusion of petroleum ether into the mother liquor. The crystals are in the monoclinic space group C2/c, with the asymmetric unit (ASU) comprising one half of the molecule. The structure describes a large S-shaped cluster (∼40 Å top to tail) where the unusual syn and anti conformations of the calixarene ligands results in two binding pockets each containing a [Mn^III₅Mn^II₂] moiety comprised of two perpendicular, vertex-sharing [Mn₄] butterflies. One butterfly possesses a [Mn^III₄O₄] core and the second a [Mn^III₂Mn^II₂O₃] unit with the Mn^II ions in the central body positions. Magnetic susceptibility and magnetisation measurements reveal weak exchange interactions between the metal centres.