The [Mn(μ‐O)(μ‐PhBO₂)₂]²⁺ Unit: A New Structural Model for Manganese‐Containing Metalloproteins

Abstract

By employing boronato instead of carboxylato bridges in the dication [Mn 2IV(μ‐O)‐(μ‐PhBO2)2L2]2+ (L = 1,4,7‐trimethyl‐1,4,7‐triazacyclononane), a Mn 2IV unit has been stabilized for the first time. Together with the di‐μ‐carboxylato‐μ‐oxodimanganese complexes of analogous structure, there is now an “isostructural series” available containing Mn 2II, MnIIMnIII, Mn 2III, MnIIIMnIV, Mn 2IV units. The Mn K‐edge energy of the corresponding complexes increases linearly with increasing oxidation level. This is of importance for EXAFS investigations of metalloproteins containing manganese.

Dinuclear manganese complexes containing 1,4-dimethyl-1,4,7-triazacyclononane ligands as well as carboxylato and oxo bridges

“…The molecular structure of 4 is presented in Fig. 3 (3.193(1) Å ) [34]. Interestingly, all complexes show intermolecular interactions with solvent molecules or anions, owing to the presence of an N-H moiety within the ligand L-Me 2 .…”

Amphiphilic Iron(II) and Nickel(II) Complexes Based on Alkylated Diazaoxa‐ and Triazacyclononane

“…Analogous to 4, the structure of this complex was proposed on the basis of the mass spectrum (field desorption) of its solution in CH 2 Cl 2 which showed only a strong signal attributable to [Ni 2 (µ-Cl) 3 …”

“…In principle, an alternative structure is [Ni 2 Cl 2 (µ-Cl) 2 (L) 2 ] and this would be composed from a pair of edge-sharing octahedra. However, previous studies [29] have indicated that for dinuclear metal halide adducts of 1,4,7-trimethyl-1,4,7-triazacyclononane, structures containing edge-sharing octahedra exhibit unfavourable steric interactions so that structures containing face-sharing octahedra (as in [Ni 2 (µ-Cl) 3 (Lx) 2 ]Cl) are formed in preference. Regardless of the metal used, TACN ligands bestow a defined shape on the resultant complexes since these ligands always coordinate in a facial manner.…”

“…In addition, the advantage of their synthetic flexibility is mostly used to prepare low-molecular weight compounds of bioinorganic importance. [3][4][5] Large macrocycles (15-membered rings) show limited affinity for metal ions, Ni II , Cu II and Zn II in particular, and this affinity is even lower than for open chain ligands with comparable structures. The reason is the large diameters of the cavities which exceed those of the small ions.…”

“…Therefore, we decided not to study large macrocycles but turned instead to the use of smaller nine-membered rings which would yield more stable complexes with the envisaged metal ions. The Fe(R 3 TACN) moiety is very robust and tolerates the introduction of various reactive co-ligands in contrast to monodentate (R 3 N) 3 -Fe derivatives.…”