Synthesis, Structure, Electronic, Redox, and Magnetic Properties of a New Mixed-Valent Mn-Oxo Cluster: [Mn2III,IVO2(N,Nbispicen)2]3+ (N,Nbispicen =N,N-bis(2-pyridylmethyl)-1,2-diaminoethane)

Preparation of Highly Efficient Manganese Catalase Mimics

“…The half wave potentials for the Mn 2 III,III /Mn 2 III,IV and Mn 2 III,IV /Mn 2 IV,IV redox couples in 3 are E 1/2 = 0.23 V (Δ E = 80 mV) and E 1/2 = 1.10 V (Δ E = 140 mV), respectively. The values for these quasireversible steps are in good accordance with potentials reported previously for similar complexes. ,,, The cyclic voltammogram of complex 4 exhibits two quasireversible redox processes at E 1/2 = 0.61 V (Δ E = 90 mV) and E 1/2 = 1.53 V (Δ E = 90 mV) for the Mn II /Mn III and the Mn III /Mn IV couples, respectively. The Mn 2 II,III /Mn 2 III,III , Mn 2 III,III /Mn 2 III,IV , and Mn 2 III,IV /Mn 2 IV,IV quasireversible redox couples of complex 5 have values of E 1/2 = 0.63 V (Δ E = 80 mV), E 1/2 = 1.09 V (Δ E = 80 mV), and E 1/2 = 1.54 V (Δ E = 90 mV).…”

“…This is analogous to the UV−vis spectra reported for the aforementioned complexes [Mn 2 (TMIMA) 2 (μ-O)(μ-OAc)](ClO 4 ) 3 ·2CH 3 CN and [Mn 2 (bispicen) 2 (μ-O)(μ-OAc)](ClO 4 ) 3 . , The spectrum of 2 resembles the one reported for manganese catalase from Thermus thermophilus (TTC) in the (III,III) oxidation state with a band at 492 nm and a broad tail going into the near-IR region . The spectrum of 3 exhibits a shoulder at 382 nm (1710 L·mol -1 ·cm -1 ) and three bands at 442 nm (1300 L·mol -1 ·cm -1 ), 557 nm (610 L·mol -1 ·cm -1 ), and 647 nm (502 L·mol -1 ·cm -1 ); the features are comparable to those of other Mn 2 III,IV O 2 compounds. ,, Especially, the latter three absorptions are in very good accordance with the UV−vis bands of 433, 555, and 654 nm reported for the [Mn( N , N -bispicen)(μ-O)] 2 3+ system ( N , N -bispicen = N , N -bis(2-pyridylmethyl)-1,2-diaminoethane) . Therefore, the following assignments for the bands in 3 are made: the absorption at 442 nm is attributed to partial contributions of LMCT oxo Mn IV and Mn IV d−d transitions, and the band at 557 nm corresponds to a Mn IV d−d transition while the one at 654 nm originates from a LMCT oxo Mn IV transition.…”

“…This spectrum is characteristic of the Mn 2 III,IV O 2 core with an S = 1 / 2 ground state that arises from antiferromagnetic coupling of a Mn III nucleus with a Mn IV nucleus, which suggests that the nuclei in this compound are valence localized. The average hyperfine coupling constant for 3 is A = 79 G. Similar spectra for analogous compounds have been reported in the literature. ,,, For complex 1 , EPR spectra have been recorded in different solvents. In a frozen methanol solution (77 K), 1 exists as a mononuclear Mn II species indicated by the six line signal centered at g = 2.02 with a hyperfine coupling constant of A = 90 G, a pattern typical for this type of compound (Figure F1a, Supporting Information).…”

Dioxo-Bridged Dinuclear Manganese(III) and -(IV) Complexes of Pyridyl Donor Tripod Ligands: Combined Effects of Steric Substitution and Chelate Ring Size Variations on Structural, Spectroscopic, and Electrochemical Properties

“…The general features of the spectra observed here, including the wavelengths, are close to those reported for the Mn IV 2 complex of tpa which has been prepared by the electrochemical oxidation of the Mn III Mn IV complex . The appearance of an intense absorption in the 400−500 nm region has been reported as resulting from the electrolytic oxidation of the dioxo-bridged Mn III Mn IV to Mn IV 2 complexes of other similar pyridyl donor ligands where the Mn III Mn IV precursors show significantly weaker absorptions. − …”

Symmetric and Asymmetric Dinuclear Manganese(IV) Complexes Possessing a [MnIV2(μ-O)2(μ-O2CMe)]3+ Core and Terminal Cl- Ligands

“…However, close inspection of the metrical parameters shows that these differences lead to the cations of 2 and 3 not being superimposable. The Mn(1)−OH 2 bond length [Mn(1)−O(3) = 2.002(3) Å] of 3 is typical of literature values, 11l,13b,c as mentioned above, but is significantly longer than the corresponding value in 2 [1.959(3) Å]. In addition, the Mn···Mn separation in 3 ·MeCN [2.6524 (8) Å] is also similar to reported values 12e,13 but nevertheless is slightly shorter than that in 2 [2.6702(13) Å].…”