Tuning tetranuclear manganese-oxo core electronic properties:: Adamantane-shaped complexes synthesized by ligand exchange

A series of aclamantane-s h aped [Mn4O6](4+) aggregates has been prepared. Ligand substitution reactions of [Mn4O6-(bpea)(4)](ClO4)(4) (1) with tridentate amine and iminodicarboxylate ligands in acetonitrile affords derivative clusters [Mn4O6(tacn)(4)](ClO4)(4) (4), [Mn4O6(bpea)(2)(dien)(2)](ClO4)(4) (5), [Mn4O6(Medien)(4)](ClO4)(4) (6), [Mn4O6(tach)(4)](ClO4)(4) (7), [Mn4O6(bpea)(2)(me-ida)(2)] (8), [Mn4O6(bpea)(2)(bz-ida)(2)] (9), [Mn4O6(bpea)(2)((1)bu-ida)(2)] (10), and [Mn4O6(bpea)(2)((c)pent-ida)(2)] (111) generally on the order of 10 min with retention of core nuclearity and oxidation state. Of these complexes, only 4 had been synthesized previously. Characterization of two members of this series by X-ray crystallography reveals that compound 7 crystallizes as [Mn4O6(tach)(4)](ClO4)(4)-3CH(3)CN-4.5H(2)O in the cubic space group Fm3m and compound 11 crystallizes as [Mn4O6(bpea)(2)((c)pent-ida)(2)]-7MeOH in the monoclinic space group C2/c. The unique substitution chemistry of 1 with iminodicarboxylate ligands afforded asymmetrically ligated complexes 8-11, the mixed ligand nature of which is most likely unachievable using self-assembly synthetic methods. A special feature of the iminodicarboxylate ligand complexes 8-11 is the substantial site differentiation of the oxo bridges of the [Mn4O6](4+) cores. While there are four site-differentiated oxo bridges in 8, the solution structural symmetry of 8H(+) reveals essentially a single protonation isomer, in contrast to the observation of two protonation isomers for 1H(+), one for each of the site-differentiated oxo bridges in 1. Magnetic susceptibility measurements on 4, 7, 8, and 9 indicate that each complex is overall ferromagnetically coupled, and variable-field magnetization data for 7 and 9 are consistent with an S = 6 ground state. Electrochemical analysis demonstrates that ligand substitution of bpea affords accessibility to the Mn-V(Mn-IV)(3) oxidation state.