Skip to main content
. Author manuscript; available in PMC: 2011 Aug 1.
Published in final edited form as: Inorg Chem. 2010 Aug 2;49(15):7197–7215. doi: 10.1021/ic1010677

Table 3.

Geometric and vibrational properties of [Fe(Porphyrin)(L)(NO)] complexes where L is either vacant or 1-methylimidazole (MI) as axial ligand trans to NO.

Molecule a Geometric Parameters [Å] Vibrational Frequencies [cm−1]
Fe-N N-O ∠Fe-N-O Fe-NP Fe-NIm Ref ν(N-O) ν(Fe-NO) δip(Fe-N-O) Ref Condition
Five-Coordinate [Fe(Porphyrin(NO)] Complexes
[FeII(OEP)(NO)]
Monoclinic (form I)
Triclinic (form II)
1.722
1.731
1.167
1.168
144
143
2.004
2.010
-
-
61 		1671 522 d 388 d 28 KBr (N-O), solid
[FeII(OEP)(15N18O)] - 1597 508 d 381 d
[FeII(TPP)(NO)] b 1.72 1.12 149 2.00 - 62 1697 532 371 7b KBr
[FeII(TPP)(15N18O)] 1625 515 365
[FeII(TPP)(NO)] - 1678 524 63 benzene
[FeII(TPP)(NO)] - 538 27a solid
[FeII(P)(NO)] Calc: BP86/TZVP 1.705 1.179 146 2.019 - 7b 1703 595 427 7b -
[FeII(P)(NO)] Calc: BP86/LanL2DZ* 1.688 1.188 144 2.021 - 28 1726 619 428 28 -
[FeII(P)(NO)] Calc: B3LYP/TZVP 1.718 1.161 142 2.021 - 28 1790 585 444 28 -
[FeII(P)(NO)] Calc: B3LYP/LanL2DZ* 1.712 1.169 141 2.020 - 28 1826 538 435 28 -
Fe-N N-O ∠Fe-N-O Fe-NP Fe-NIm Ref ν(N-O) δip(Fe-N-O)/ν(Fe-NO) ν(Fe-NO) Ref Condition
Six-Coordinate [Fe(Porphyrin(MI)(NO)] Complexes
[FeII(TPP)(MI)(NO)] (1) 1.750 1.182 138 2.008 2.173 9 1630 563 d 437 d 7b, c KBr (N-O), solid
[FeII(TPP)(MI)(15N18O)] 1556 551 d 429 d
[FeII(TPP)(MI)(NO)] 1.743 1.121 142 2.008 2.180 5 1625 5 KBr
[FeII(TPP)(MI)(NO)] 1.749 1.184 137 2.007 2.170 64 1631 64
[FeII(TPP)(MI)(NO)] 1.745 1.163 138 2.006 2.186 64 1629 64
[FeII(To-F2PP)(MI)(NO)] 1.752 1.202 138 2.012 2.188 7b 1624 7b KBr
[FeII(TPP)(MI)(NO)] Calc: BP86/TZVP 1.741 1.186 140 2.018 2.204 c 1661 606/485 e c -
[FeII(TPP)(MI)(NO)] Calc: BP86/LanL2DZ* 1.717 1.194 140 2.023 2.195 c 1687 623/481 e c -
[FeII(P)(MI)(NO)] Calc: BP86/TZVP 1.734 1.186 140 2.022 2.179 7b 1662 609/482 e 7b -
[FeII(TPP)(MI)(NO)] Calc: B3LYP/TZVP 1.790 1.165 140 2.024 2.156 c 1787 550/416 f c -
[FeII(TPP)(MI)(NO)] Calc: B3LYP/LanL2DZ* 1.776 1.173 140 2.030 2.127 c 1817 543/406 f c -
[FeII(P)(MI)(NO)] Calc: B3LYP/LanL2DZ* 1.780 1.172 140 2.032 2.138 c 1824 539/417 f c -
a

MI = 1-methylimidazole; P = Porphine ligand used for calculations; values for Fe-NP (Fe-N(porphyrin) bond distances) are averaged.

b

Highly disordered structure.

c

This work.

d

Determined from NRVS using 57Fe. Compared to natural abundance isotopes (n.a.i.) Fe, the modes ν(Fe-NO) and δip(Fe-N-O) appear about 1 – 2 cm−1 shifted to lower energy.

e

From the potential energy distribution (PED) matrix, the 606 cm−1 mode has 58% Fe-NO stretching and 26% Fe-N-O bending contribution, whereas the 485 cm−1 vibration has roughly equivalent Fe-NO stretching and Fe-N-O bending character (BP86/TZVP). The BP86/LanL2DZ* result is similar to this. The calculation based on the porphine approximation also delivers equivalent results.

f

From the PED, the mode around 400 – 420 cm−1 has 30 – 40% Fe-NO stretching and ~2% Fe-N-O bending character, whereas the feature at around 550 cm−1 has roughly 30 % Fe-N-O bending and 20 % Fe-NO stretching character in the B3LYP calculations.