Tuning tetranuclear manganese-oxo core electronic properties: adamantane-shaped complexes synthesized by ligand exchange.
A series of adamantane-shaped [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((t)bu-ida)2] (10), and [Mn4O6(bpea)2((c)pent-ida)2] (11) 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 x 3CH3CN x 4.5H2O in the cubic space group Fmm 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.
Department of Chemistry, Eugene F. Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467-3860, USA.
Christopher E
CE
Dubé
Sumitra
S
Mukhopadhyay
Peter J
PJ
Bonitatebus
Richard J
RJ
Staples
William H
WH
Armstrong
D000218:Adamantane / Q000031:analogs & derivatives / Q000138:chemical synthesis*; D001665:Binding Sites; D002264:Carboxylic Acids / Q000737:chemistry; D018360:Crystallography, X-Ray; D004583:Electrons; D007097:Imines / Q000737:chemistry; D007536:Isomerism; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008345:Manganese / Q000737:chemistry*; D017895:Manganese Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011522:Protons; D013696:Temperature
D002264:Carboxylic Acids; D007097:Imines; D008024:Ligands; D017895:Manganese Compounds; D011522:Protons; D008345:Manganese; D000218:Adamantane; D010100:Oxygen