Metal Ion Binding to Octakis(dimethylamino)porphyrazine: Core Coordination of Mn(III) and Peripheral Coordination of Pd(II)
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The synthesis and X-ray structural characterization of two manganese(III) porphyrazine (tetraazaporphyrin) complexes are reported: [Mn(Et2dtc)ODMAPz] (1) and [Mn(Cl)ODMAPz] (2) (Et2dtc = diethyldithiocarbamato; ODMAPz = 2,3,7,8,12,13,17,18-octakis(dimethylamino)porphyrazinato). In both 1 and 2, the Mn(III) ion sits ∼0.3 Å out of the plane of the pyrrolic nitrogen atoms toward the axial ligand. The structural data reveal that for both 1 and 2 the Mn(III) ions are isolated from each other, simplifying the interpretation of the magnetic behavior of these compounds. Cyclic voltammetry shows that the peripheral dimethylamino groups make these metalloporphyrazines extremely electron-rich, with the Mn(III)/Mn(II) couple at -1.3 V (versus ferrocenium/ ferrocene), shifted approximately 0.6-0.9 V more negative than those of related manganese macrocycles. Temperature-dependent magnetic susceptibility measurements show that the ground state is S = 2 with axial zero-field splitting, and |D| = 3.1-3.3 cm-1 for both 1 and 2. These bulk magnetic measurements are compared to the magnetic behavior of Mn(III) porphyrin-type complexes, as well as recent direct resonance measurements on 1 and 2 by high-field EPR spectroscopy. The related metalloporphyrazine NiODMAPz, with an internally bound Ni(II) ion, coordinates 4 equiv of PdCl2 to the peripheral dimethylamino sites to give [Ni(ODMAPz)-(PdCl2)4] (5). Compound 1 crystallizes in C2/c, with a = 22.480(3) Å, b = 20.128(2) Å, c = 19.423_(3) Å, β= 102.97(1)°, V = 8564(2) Å3, and Z = 8 (R1 = 0.074, wR2 = 0.169). Compound 2 crystallizes in P1̄ with a = 10.216(6) Å, b= 13.426(8) Å, c = 15.683(14) Å, α = 114.59(5)°, β= 96.82(6)°, γ = 101.87(5)°, V= 1863(2) A°3, and Z = 2 (R1 = 0.067, wR2 = 0.183).
author list (cited authors)
Goldberg, D. P., Montalban, A. G., White, A., Williams, D. J., Barrett, A., & Hoffman, B. M.