| Abstract
| - A mixed-valence Mn(III)−Mn(II)−Mn(III) trinuclear complex of stoichiometry MnIIIMnIIMnIII(Hsaladhp)2(Sal)4·2CH3CN (1), where H3saladhp is a tridentate Schiff-base ligand, has been structurally characterized with X-raycrystallography. The Mn(III)Mn(II)Mn(III) angles are strictly 180° as required by crystallographic inversionsymmetry. The complex is valence-trapped with two terminal Mn(III) ions in a distorted square pyramidal geometry.The Mn(III)···Mn(II) separation is 3.495 Å. The trinuclear complex shows small antiferromagnetic exchange Jcoupling. The magnetic parameters obtained from the fitting procedure in the temperature range 10−300 K areJ1 = −5.7 cm-1, g = 2.02, zJ = −0.19 cm-1, and R = 0.004. The EPR spectrum was obtained at 4 K in CHCl3and in tetrahydrofuran glasses. The low-field EPR signal is a superposition of two signals, one centered aroundg = 3.6 and the other, for which hyperfine structure is observed, centered around g = 4.1 indicating an S = 3/2state. In addition, there is a 19-line signal at g = 2.0. The multiline signal compares well with that observed forthe S2 or S0* states of the oxygen-evolving complex. 1H NMR data reveal that the trinuclear compound keeps itsintegrity into the CHCl3 solution. Crystal data for complex 1: [C54H52N4O18Mn3], M = 1209.82, triclinic, spacegroup P1̄, a = 10.367(6) Å, b =11.369(6) Å, c = 13.967(8) Å; α = 112.56(1)°, β = 93.42(2)°, γ = 115.43(1)°,Z = 1.
- A mixed-valence Mn(III)−Mn(II)−Mn(III) trinuclear complex that is NMR and EPR active is reported. The trinuclear complex shows a 19-line signal at g = 2.0. The multiline signal compares well with that observed for the S2 or S0* states of the OEC. 1H NMR data reveal that the trinuclear compound maintains its integrity into the CHCl3 solution. The trinuclear complex shows small antiferromagnetic exchange J coupling with S = 3/2 ground state.
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