From monomeric to polymeric manganese complexes bearing bis(imino)pyridine and related ligands

Abstract

Reactions of MnX₂ with the tridentate nitrogen donor ligands [2,6-{(2,4,6-Me₃C₆H₂)NCMe}₂C₅H₃N], [2,6-{(Me)(Ph)NNCMe}₂C₅H₃N] and [2-{(2,6-Prⁱ₂C₆H₃)NCH}-6-{(2,6-Prⁱ₂C₆H₃)NHCH(Me)}C₅H₃N] in refluxing acetonitrile yield the high spin divalent monometallic manganese complexes, [2,6-{(2,4,6-Me₃C₆H₂)NCMe}₂C₅H₃N]MnX₂ (X = Br 1), [2,6-{(Me)(Ph)NNCMe}₂C₅H₃N]MnX₂ (X = Cl 2) and [2-{(2,6-Prⁱ₂C₆H₃)NCH}-6-{(2,6-Prⁱ₂C₆H₃)NHCH(Me)}C₅H₃N]MnX₂ (X = Cl 3), respectively, in good yield. Crystallographic studies on 1–3 reveal all three complexes to be pentacoordinate with geometries that can be best described as distorted trigonal bipyramidal (1, 2) or square pyramidal (3). Conversely, treatment of MnCl₂ with [2-{(2″-H₂NC₆H₄–C₂H₄–2″-C₆H₄)NCMe}-6-{OCMe}C₅H₃N] (prepared from the incomplete condensation reaction of the diamine [{2,2″-(NH₂)C₆H₄}₂(CH₂CH₂)] with 2,6-diacetylpyridine) under similar reaction conditions results in self-assembly to afford the antiferromagnetically coupled polymetallic salt [{2,6-{(2′,2″-C₆H₄–CH₂)₂(NCMe)₂}₂(C₅H₃N)₂}Mn₂Cl₃(NCMe)₂][{2,6-{(2′,2″-C₆H₄–CH₂)₂(NCMe)₂}₂(C₅H₃N)₂}Mn₂Cl₃(MnCl₄)]_n (4). The molecular structure of 4 shows a discrete dimanganese cation and polymeric manganese anion with each ionic unit supported by a 26-membered macrocyclic hexadentate nitrogen donor ligand.