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|標題:||ESR, zero-field splitting, and magnetic exchange of exchange-coupled copper(II)-copper(II) pairs in copper(II) tetraphenylporphyrin N-oxide||作者:||Yang, F.A.
|關鍵字:||electron-paramagnetic-res;metal-complexes;molecular-structure;spin-resonance;meso-tetraphenylporphyrin;anisotropic exchange;porphyrin;nickel(ii);crystal;dimers||Project:||Inorganic Chemistry||期刊/報告no：:||Inorganic Chemistry, Volume 46, Issue 2, Page(s) 578-585.||摘要:||
The crystal structures of the dimer form of copper(II) tetraphenylporphyrin N-oxide, [Cu(tpp-N-O)](2) (3-dimer), and zinc(II) tetraphenylporphyrin N-oxide, [Zn(tpp-N-O)](2) (4-dimer), were established. The geometry at the copper ion in 3-dimer is essentially square-pyramidal with one oxygen bridge [O(1A)] occupying the apical site, giving a much larger Cu - O bond distance compared to those at the basal plane. The respective Cu center dot center dot center dot Cu distance and Cu-O-Cu angle in the core of 3-dimer are 3.987(4) angstrom and 148.1(3)degrees. The Zn(1) atom in 4-dimer has a distorted square-pyramidal [4 + 1] coordination geometry that gives a tau-value of 0.19. The respective Zn center dot center dot center dot Zn distance and Zn-O - Zn angle in the dimeric unit of 4-dimer are 4.025( 3) angstrom and 148.1( 2)degrees. The 3-dimer displays axial X-band electron paramagnetic resonance spectral features (E-s = 0) in the powder state at 4 K, giving g(parallel to) = 2.51 (A(parallel to,s) = (9.6 +/- 0.2) x 10(-3) cm(-1)) and g(perpendicular to) = 2.11 and in the same powder state at 293 K giving D-s = 0.0731 cm(-1) ( as derived from Delta M-s = 1 lines) or 0.0743 cm(-1) ( as derived from the Delta M-s = 2 lines). In addition, 3-dimer displays a Delta M-s = 2 transition at g = 4.17 indicating the presence of spin-exchange coupling. The anisotropic exchange interaction ( D-s(ex) = 0.132 cm(-1)) gives the main contribution to D-s in 3-dimer. The theoretical fit of the susceptibility and effective magnetic moment data of 3-dimer in the temperature range of 5 - 300 K gives 2 J = 68 cm(-1), g = 2.01, p = 0.06, and a temperature-independent paramagnetism of 10(-6) cm(3) mol(-1). This magnetic susceptibility data indicates that the copper(II) ions in 3-dimer are coupled in a ferromagnetic manner with the ground-spin triplet stabilized by 68 cm(-1) with regard to the singlet.
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