(μ-Phenoxo)2CoIIMII (M = Mn, Co, Zn) Complexes with a Co(salen) Entity in a Macrocyclic Framework: Core Structures and Neighboring MII Effects upon Oxygenation at the Co(salen) Center

Abstract

The phenol-based macrocyclic ligands (L2,3)2- and (L2,4)2-, derived from the [2:1:1] condensation of 2,6-diformyl-4-methylphenol, ethylenediamine, and 1,3-trimethylenediamine or 1,4-tetramethylenediamine, have a salen-like metal-binding site (salen = N,N‘-ethylenedisalicylideneaminate) and a saltn- or salbn-like metal-binding site (saltn = N,N‘-trimethylenedisalicylideneaminate, salbn = N,N‘-tetramethylenedisalicylideneaminate) sharing the phenolic moieties. They form the (μ-phenoxo)2CoIIMII complexes [CoMn(L2,3)(AcO)]ClO4·DMF (1), [CoMn(L2,4)(AcO)]ClO4 (2), [CoCo(L2,3)(AcO)]ClO4 (3), [CoCo(L2,4)(AcO)]ClO4 (4), [CoZn(L2,3)(AcO)]ClO4 (5), and [CoZn(L2,4)(AcO)]ClO4 (6). Complex 1 crystallizes in the monoclinic space group P21/c, with a = 10.027(3) Å, b = 11.713(3) Å, c = 26.821(9) Å, β = 93.85(2)°, V = 3142(1) Å3, and Z = 4. The Co and Mn ions are bridged by the two phenolic oxygens of the macrocycle and an acetate group in the syn-syn mode. The CoII in the salen site is of low-spin and assumes a square-pyramidal geometry with an acetate oxygen at the axial site. The MnII has a cis six-coordinate geometry with respect to the acetate oxygen and the DMF oxygen. The Mn is displaced 0.955 Å from the basal N2O2 least-squares plane. [CoMn(L2,4)(AcO)]ClO4·DMF (2‘) crystallizes in the monoclinic space group P21/c, with a = 10.166(5) Å, b = 11.934(4) Å, c = 27.380(8) Å, β = 93.97(3)°, V = 3313(1) Å3, and Z = 4. It has a dinuclear core similar to that of 1, with square-pyramidal CoII in the salen site and cis six-coordinate MnII in the salbn site. Complex 3 crystallizes in the triclinic space group P1̄, a = 12.118(3) Å, b = 12.156(2) Å, c = 9.977(1) Å, α = 112.49(1)°, β = 99.22(2)°, γ = 77.63(2)°, V = 1321.1(5) Å3, and Z = 2. Both CoII ions in the salen and saltn sites assume a square-pyramidal geometry with a bridging acetate group in the syn-syn mode. The displacement of the Co in the saltn site, from the basal N2O2 least-squares plane toward the apical acetate oxygen, is 0.53 Å. Complex 5 is found to be isostructural with 3. The complexes 1, 2, 4, 5, and 6 are reversibly oxygenated in DMF at 0 °C to afford a μ-peroxo dimer complex [{CoIIIMII(L)(AcO)}2(O22-)]2+. Complex 3 also forms such a μ-peroxo dimer complex but is irreversibly oxidized through an intramolecular-type μ-peroxo complex [CoIIICoIII(L2,3)(AcO)(O22-)]+.