. Author manuscript; available in PMC: 2020 Oct 21.

Published in final edited form as: Inorg Chem. 2019 Sep 30;58(20):13933–13944. doi: 10.1021/acs.inorgchem.9b01840

Table 4.

Calculated Fe_a3-O and O-O Mayer Bond Orders (MBO) and Comparison of the Calculated and Observed (Exp) Vibrational Frequencies (cm⁻¹) of the Fe_a3-O and O-O Stretching Modes and the O-Fe_a3-Porphyrin Bending Modes in CcO DNC Sates A, Peroxo, Hydroperoxo, P_M, P_R, F, F_H, and O_H.^a

State	Structure	Fe-O MBO	ν(Fe-O)			O-O MBO	ν(O-O) or ν(O-Fe-Por) ^c
State	Structure	Fe-O MBO	Anal. Partial-H	Num. MBH	Exp ^b	O-O MBO	Anal. Partial-H	Num. MBH	Exp
A	Fe_a3^3+,LS-O₂^−•⋯-Cu_B⁺,Y-OH	0.480	518	520	571²¹⁻²⁴	1.282	1142	1145	1159,^d 1148^e
Peroxo	Fe_a3^3+,LS-O₂²⁻-Cu_B²⁺,Y-OH	0.544	577	584		1.063	906	907	870^f
Hydroperoxo	Fe_a3^3+,LS-⁻OOH-Cu_B²⁺,Y-O⁻	0.586	666	672		0.911	664	673
P_M	Fe_a3^4+,IS=O²⁻⋯HO⁻-Cu_B²⁺,Y-O^•	1.191	838	830	804⁴³⁻⁴⁵		357	367
P_R	Fe_a3^4+,IS=O²⁻⋯HO⁻-Cu_B²⁺,Y-O⁻	1.196	844	842	804⁴⁰		378	372	356^g
F	Fe_a3^4+,IS=O²⁻⋯H₂O-Cu_B²⁺,Y-O⁻	1.144	823	822	785^{36,44,55–58}		374	381	356^g
F_H	Fe_a3^4+,IS=O²⁻⋯Cu_B²⁺,Y-O⁻	1.118	775	774			375	396
O_H	Fe_a3^3+,HS-OH⁻-Cu_B²⁺,Y-O⁻	0.518	452/458	471/476	450⁵⁶

^a.

Other calculated properties of these structures are given in Table 3. The vibrational frequencies were calculated with two methods: analytical frequency calculations with partial Hessian (Anal. Partial-H) and numerical frequency calculations with mobile block Hessian (Num. MBH).

^b.

Different groups^21–24 reported a little different values of the Fe_a3-O stretch modes (cm⁻¹) observed from resonance Raman (rR) experiments for a certain state. For simplicity, we only cite the commonly agreed values used in the review article of Ref. 5.

^c.

These are the O-O stretch modes for states A, Peroxo, and Hydroperoxo. For other states, these are the O-Fe-Porphyrin bending modes.

^d.

O-O stretching mode observed in a picket-fence oxyporphyrin.⁸³

^e.

O-O stretching mode observed in a cobalt-superoxide complex CoO₂/Cu[NMePr]⁺.^84,85

^f.

O-O stretching mode observed in a synthetic Fe³⁺-O₂²⁻-Cu²⁺ complex, which is structurally analogous to the Peroxo state of the DNC.⁸⁶

^g.

A rR band that was observed and was suggested to be the His-Fe_a3⁴⁺=O²⁻ bending mode for a DNC structure between states P_R and F.^5,62,63 Our calculations show that this is likely an O-Fe_a3-Porphyrin bending mode.