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 Complex g/mL meff (no imid) meff (with imid)FeTPPClMN/TH 0.0075 5.17 (185 hz) 2.72 (31 Hz)KG/LC 0.00706 5.52 (201 hz) 2.40 (19 Hz)  ave 5.30 2.56FeTTPClAM/MS 0.0076 5.57 (203 Hz) 2.94 (37 Hz)** note reported values reversedAK 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)    ave 5.59 2.80FeTClPPClAK/JV 0.00816 5.47 (188 hz) 2.39 (24 Hz)JH/BL 0.00537 3.58 (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 Ered of Fe(porphyrin) complexes change on binding imidazole?

3. Will the Ered potentials also reflect a change in spin state?

1. How will the Ered 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 106 Hz)

Concentration of sample,in g/mL

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

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 = 2.828 (T corr ) 1/2

N 2

eff = (n(n+2))1/2

Mass susceptibility Molar susceptibility

Diamagnetic Corrections (cgs units)

Xo (CHCl3) = - 4.97 x 10-7 cgs

Porphyrin: TPP= -700 x 10-6 cgs TTP= -753 x 10-6 cgs TClPP= -760 x 10-6 cgs

Fe = -13 x 10-6 cgs

Cl = -20 x 10-6 cgs

Imidazole = -38 x 10-6 cgs

3d orbitalson 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