High-frequency EPR study of a new mononuclear manganese(III) complex: [(Terpy)Mn(N3)3] (terpy = 2,2′:6′,2′-terpyridine)

J. Limburg, J. S. Vrettos, R. H. Crabtree, G. W. Brudvig, J. C. De Paula, A. Hassan, A. L. Barra, C. Duboc-Toia, M. N. Collomb

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The isolation and structural characterization of [(terpy)MnIII(N3)3], complex 1, is reported (terpy = 2,2′:6′,2-″terpyridine). Complex 1, a product of the reaction between the mixed-valence dimer[(terpy)(H2O)MnIII(O) 2-MnIV(OH2)(terpy)] (NO3)3 and NaN3, crystallizes in a triclinic system, space group P1, a = 8.480(1) Å b = 8.9007(2) Å, c = 12.109(2) Å, α = 93.79(1)°, β = 103.17(1)°, γ = 103.11(1)° and Z = 2. Complex 1 exhibits a Jahn-Teller distortion of the octahedron characteristic of a six-coordinated high-spin Mn(III). A vibrational spectroscopic study was performed. The vasym(N3) mode of complex 1 appears in the IR as a strong band at 2035 cm-1 with a less intense feature at 2072 cm-1, and in the FT-Raman as a strong band at 2071 cm-1 with a weaker broad band at 2046 cm-1. The electronic properties of complex 1 were investigated using a high-field and high-frequency EPR study (190-475 GHz). The different spin Hamiltonian parameters have been determined (D = -3.29 (±0.01) cm-1, E = 0.48 (±0.01) cm-1, E′= 0.53 (±0.01) cm-1, gx = 2.00 (±0.005), gy = 1.98 (±0.005), gz = 2.01 (±0.005)). These parameters are in agreement with the geometry of complex 1 observed in the crystal structure, a D < 0 related to the elongated distortion, and a value of E/D close to 0.2 as expected from the highly distorted octahedron. The two values of the E-parameter are explained by the presence of two slightly different structural forms of complex 1 in the crystal lattice. A second hypothesis was explored to explain the experimental data. The calculation for the simulation was done taking into account that the g and D tensors are not collinear due to the low symmetry of complex 1. In that case, the spin Hamiltonian parameters found are D = -3.29 (±0.01) cm-1, E = 0.51 (±0.01) cm-1, gx = 2.00 (±0.005), gy = L98 (±0.005), and g, = 2.01 (±0.005).

Original languageEnglish
Pages (from-to)1698-1703
Number of pages6
JournalInorganic Chemistry
Issue number7
Publication statusPublished - Mar 26 2001

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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