Detection of Indistinct Fe−N Stretching Bands in Iron(V) Nitrides by Photodissociation Spectroscopy

Abstract

We report for the first time infrared spectra of three non‐heme pseudo‐octahedral iron(V) nitride complexes with assigned Fe−N stretching vibrations. The intensities of the Fe−N bands in two of the complexes are extremely weak. Their detection was enabled by the high resolution and sensitivity of the experiments performed at 3 K for isolated complexes in the gas phase. Multireference CASPT2 calculations revealed that the Fe−N bond in the ground doublet state is influenced by two low‐lying excited doublet states. In particular, configuration interaction between the ground and the second excited state leads to avoided crossing of their potential energy surfaces along the Fe−N coordinate, which thus affects the ground‐state Fe−N stretching frequency and intensity. Therefore, DFT calculated Fe−N stretching frequency strongly depends on the amount of Hartree–Fock exchange potential. As a result, by tuning the amount of Hartree–Fock exchange potential in the B3LYP functional, it was possible to obtain theoretical spectra perfectly consistent with the experimental data. The theory shows that the intensity of the Fe−N stretching vibration can almost vanish due to strong coupling with other stretching modes of the ligands.

Electron Paramagnetic Resonance Signature of Tetragonal Low Spin Iron(V)-Nitrido and -Oxo Complexes Derived from the Electronic Structure Analysis of Heme and Non-Heme Archetypes

“…17 Complexes 2 and 3 have been characterized by 57 Fe Mössbauer and X-ray absorption spectroscopy coupled with DFT calculations. 13,14,16 It has been concluded that both complexes are best described as genuine low spin iron(V)-nitrido compounds. In addition to these tetragonal species, Smith, Meyer, and co-workers reported synthesis and spectroscopic and structural characterization of a trigonal iron(V)-nitrido compound, [Fe V (N)(PhB( t BuIm) 3 )] + ( 4 , PhB( t BuIm) 3 – = phenyltris(3- tert -butylimidazol-2-ylidene borate).…”

“…24 Similarly, complexes 2 and 3 also undergo facile decay by dimerization of the Fe V =N groups, eventually yielding monomeric ferrous complexes and releasing N 2 . 16,25 Because complexes 1 – 3 cannot persist in fluid solutions, their reactivity studies relied on in situ spectroscopic methods. For instance, complexes [Fe V (N)L] 2+ , 2 and 3 were shown to be capable of activating C—H or C=C bonds of organic substrates on the basis of the mass fragmentation analysis.…”

“…For instance, complexes [Fe V (N)L] 2+ , 2 and 3 were shown to be capable of activating C—H or C=C bonds of organic substrates on the basis of the mass fragmentation analysis. 16,17,26 Nitride addition to CO and tri- n -butylphosphine for complexes 2 and 2″ , respectively, was monitored by time-resolved Fourier-transform infrared spectroscopy. 27 Furthermore, it was reported that treating complex 4 , the most stable iron(V)-nitrido compound, with cobaltocene and water leads to formation of ammonia.…”

Closed Shell Iron(IV) Oxo Complex with an Fe–O Triple Bond: Computational Design, Synthesis, and Reactivity

“…Our calculations can also reproduce the Fermi doublet arising from the coupling between the Fe‐ 18 O stretching band and the ligand band at 926 cm −1 . To compensate for the incorrect prediction of the ν(Fe‐O) force constant, we increased the mass of the O atom in 1 1 + to 19.1, which moved the ν(Fe‐O) vibration to the correct position [53] of ≈960 cm −1 (Figure 4 b, second panel, red trace). Then increasing this mass by the 18/16 ratio to a value of 21.5, we can clearly observe the Fermi doublet like in the IRPD experiment (compare Figure 4 a, red trace and Figure 4 b, second panel, red trace).…”

Bimetallic Oxide Hollow Structures Induced by Surface Coordination of ZIF‐67

“…Furthermore, the peaks at 2929 and 3135 cm –1 could be due to the stretching mode of C–H from the aromatic ring and the aliphatic chain in 2‐MIM, respectively , . According to the literature, the IR peaks of Cu–N, Fe–N and Ni–N stretch at 460, 855 and 525 cm –1 respectively . We tried to use FT‐IR to analyze the coordination modes between metal and unsaturated ligands on ZIF‐67 surface, but there is no obvious difference between metal derivatives and ZIF‐67 because the amount of Fe/Cu/Ni in the sample is too low to be detected.…”