Constructing "Closed" and "Open" {Mn 8 } Clusters.

Use of the 1,3,5-tri(2-hydroxyethyl)-1,3,5-triazacyclohexane ligand, LH 3 , in manganese chemistry affords access to two structurally related {Mn 8 } clusters: a "closed" {Mn III 6 Mn II 2 } puckered square wheel of formula [Mn 8 L 2 (LH)O 3 (OH) 2 (MeO) 2 Br(imH)(H 2 O) 3 ](Br) 3 ( 1 ; imH = imidazole) and an "open" {Mn III 8 } rod of formula [Mn ΙΙΙ 8 L 2 O 4 (aibH) 2 (aib) 2 (MeO) 6 (MeOH) 2 ](NO 3 ) 2 ( 2 , aibH = 2-amino-isobutyric acid). In each case the triaza ligands, L/LH, direct the formation of {Mn 3 } triangles with their N atoms preferentially bonding to the Jahn-Teller axes of the Mn III ions. Subsequent self-assembly is dependent on the anion of the Mn salt and the identity of the organic coligand employed-the terminally bonded imidazole and the chelating/bridging amino acid. The {Mn 3 } triangles fold up on themselves in 1 , forming a wheel. However, the syn, syn-bridging carboxylates in 2 prevent this from happening, instead directing the formation of a linear rod. Magnetic susceptibility and magnetization measurements reveal competing ferro- and antiferromagnetic interactions in both complexes, the exchange being somewhat weaker in 1 due to the presence of Mn II ions.