Dianionic States of Trithiadodecaazahexaphyrin Complexes with Homotrinuclear MII3O Clusters (M = Ni and Cu): Crystal Structures, Metal- Or Macrocycle-Centered Reduction, and Doublet-Quartet Transitions in the Dianions

Metal complexes of trithiadodecaazahexaphyrin (Hhp) that contain M^II₃O clusters inside a π-extended trianionic (Hhp^3-) macrocycle have been prepared. Studies of the magnetic properties of Ni^II₃O(Hhp) and Cu^II₃O(Hhp) reveal a diamagnetic and EPR-silent trianionic (Hhp^3-) macrocycle and diamagnetic Ni^II₃(O^2-) or paramagnetic Cu^II₃(O^2-) tetracations. The positive charge of M^II₃O(Hhp) is compensated by one acetate anion {M^II₃O(Hhp)}⁺(CH₃CO₂^-). The three-electron reduction of {M^II₃O(Hhp)}⁺ yields {cryptand(Cs⁺)}₂{Ni^II₂Ni^IO(Hhp^5-)}^2-·2C₇H₈ (1) and {cryptand(Cs⁺)}₂{Cu^II₃O(Hhp^•6-)}^2-·C₇H₈ (2) crystalline salts. The magnetic properties of 1 reveal the formation of Hhp^5- and the reduction of nickel(II) to the paramagnetic Ni^I ion (S = 1/2), which is accompanied by the formation of the {Ni^II₂Ni^IO(Hhp^5-)}^2- dianion. As a result, the magnetic moment of 1 is 1.68 μ_B in the 20-220 K range, and a broad EPR signal of Ni^I was observed. The Hhp^5- macrocycle has a singlet ground state, but the increase in the magnitude of the magnetic moment of 1 above 220 K is attributed to the population of the triplet excited state in Hhp^5-. The {Ni^II₂Ni^IO(Hhp^5-)}^2- dianion is transferred from the doublet excited state to the quartet excited state with an energy gap of 1420 ± 50 K. Salt 1 also shows an unusually strong low-energy NIR absorption, which was observed at 1000-2200 nm. In 2, a highly reduced Hhp^•6- radical hexaanion (S = 1/2) coexists with a Cu^II₃(O^2-) cluster (S = 1/2) in the {Cu^II₃O(Hhp^•6-)}^2- dianions. The dianions have a triplet ground state with antiferromagnetic exchange between two S = 1/2 spins with J = -6.4 cm^-1. The reduction of Hhp in both salts equalizes the initially alternated C-N bonds, supporting the increase in the Hhp macrocycle electron delocalization.