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Low Spin S = 1/2 n = 1 PowerPoint Presentation
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Low Spin S = 1/2 n = 1

Low Spin S = 1/2 n = 1

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Low Spin S = 1/2 n = 1

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  1. How will the spin state of Fe(porphyrin) complexes change on binding imidazole? Intermediate Spin S = 3/2 n = 3 High Spin S = 5/2 n = 5 Low Spin S = 1/2 n = 1

  2. Solution Magnetic susceptibility by Evan’s Method Complex g/mL meff (noimid) meff (withimid) FeTPPCl MN/TH 0.0075 5.17 (185 hz) 2.72 (31 Hz) KG/LC 0.007065.52 (201 hz) 2.40 (19 Hz) ave 5.30 2.56 FeTTPCl AM/MS 0.0076 5.57 (203 Hz) 2.94 (37 Hz)** note reported values reversed AK 0.0076 5.57 (203 hz) 2.96 (36 Hz) RK/JH 0.00675 5.57 (180 hz) 2.44 (17 Hz) CB/SK 0.00763 5.66 (211 Hz) 2.84 (32 Hz) ave5.59 2.80 FeTClPPCl AK/JV 0.00816 5.47 (188 hz) 2.39 (24 Hz) JH/BL 0.00537 3.58 (46 hz) no observed shifted resonance ave4.52

  3. Characterization by Cyclic Voltammetry 1. How will the Ered of Fe(porphyrin) complexes vary with the porphyrin? 2. How will the Ered of Fe(porphyrin) complexes change on binding imidazole? 3. Will the Ered potentials also reflect a change in spin state? High Spin S = 5/2 n = 5 Low Spin S = 1/2 n = 1 Intermediate Spin S = 3/2 n = 3

  4. Shift of signal, in Hz mass susceptibility of solvent -a diamagnetic contribution, a (-) value Mass susceptibility (+) Magnetic field (400 MHz, or 400 x 106 Hz) Concentration of sample, in g/mL How does shift, , relate to a magnetization of paramagnetic sample? g = 3  0 c

  5. NMR Spectrum from Evans’ Method Inside capillary: sample in CHCl3, produces broad singlet for paramagnetically shifted CHCl3 below 7.3 ppm Outside capillary: 99.5 %D CDCl3 produces usual sharp singlet for 0.5% CHCl3 at 7.3 ppm 

  6. How does mass susceptibility, g , relate to unpaired electrons in a paramagnetic sample? Mass susceptibility g x (Mol. Wt.) = M Molar susceptibility corr= M - diamagnetic corrections where diamagnetic corrections for Fe, porphyrin, Cl, imidazole, a negative number! eff = 3 R T corr1/2 = 2.828 (T corr) 1/2 N 2 eff = (n(n+2))1/2

  7. Diamagnetic Corrections (cgs units) Xo (CHCl3) = - 4.97 x 10-7 cgs Porphyrin: TPP= -700 x 10-6cgs TTP= -753 x 10-6cgs TClPP= -760 x 10-6cgs Fe = -13 x 10-6cgs Cl = -20 x 10-6cgs Imidazole = -38 x 10-6cgs

  8. 3d orbitals on Fe Spin State of Fe affects size of ion

  9. Large, high spin Fe(2+): In T state, transmitted by His on protein helix Small, low spin Fe(2+): In R state, transmitted to His on protein helix