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

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Presentation transcript:

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

Solution Magnetic susceptibility by Evan’s Method Complexg/mL  eff (no imid)  eff (with imid) FeTPPCl MN/TH (185 hz)2.72 (31 Hz) KG/LC (201 hz)2.40 (19 Hz) ave FeTTPCl AM/MS (203 Hz)2.94 (37 Hz)** note reported values reversed AK (203 hz)2.96 (36 Hz) RK/JH (180 hz)2.44 (17 Hz) CB/SK (211 Hz)2.84 (32 Hz) ave FeTClPPCl AK/JV (188 hz)2.39 (24 Hz) JH/BL (46 hz)no observed shifted resonance ave 4.52

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

How does shift, , relate to a magnetization of paramagnetic sample?  g = 3  0     c Mass susceptibility (+) Shift of signal, in Hz mass susceptibility of solvent -a diamagnetic contribution, a (-) value Magnetic field (400 MHz, or 400 x 10 6 Hz) Concentration of sample, in g/mL

NMR Spectrum from Evans’ Method Inside capillary: sample in CHCl 3, produces broad singlet for paramagnetically shifted CHCl 3 below 7.3 ppm Outside capillary: 99.5 %D CDCl 3 produces usual sharp singlet for 0.5% CHCl 3 at 7.3 ppm 

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

Diamagnetic Corrections (cgs units) X o (CHCl 3 ) = x cgs Porphyrin: TPP= -700 x cgs TTP= -753 x cgs TClPP= -760 x cgs Fe = -13 x cgs Cl = -20 x cgs Imidazole = -38 x cgs

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

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