Toward Binary Nitrosyls:  Distinctly Bent Fe−N−O Linkages in Base-Stabilized Fe(NO)₃⁺ Complexes

Abstract

Air- and moisture-sensitive Fe(NO)(3)(eta(1)-PF(6)) (1) may be conveniently prepared by treating Fe(NO)(3)Cl with 1 equiv of [Ag][PF(6)] in CH(2)Cl(2) or by reacting [NO][PF(6)] with excess iron filings in MeNO(2). Complex 1 is thermally sensitive both as a solid and in solutions, and is best handled below -20 degrees C. To isolate 1 reproducibly from MeNO(2) solutions it is necessary to remove all traces of propionitrile, which often occurs as an impurity in MeNO(2), because it reacts with Lewis-acidic 1 to form [Fe(NO)(3)(EtCN)][PF(6)] (2). If trace H(2)O is present during the synthesis of 1, some of the PF(6)(-) is converted to PO(2)F(2)(-), which is sufficiently Lewis basic that it captures two Fe(NO)(3)(+) fragments and forms [(ON)(3)Fe(mu-PO(2)F(2))Fe(NO)(3)][PF(6)] (3). Finally, Fe(NO)(3)(eta(1)-BF(4)) (4) can be obtained as a green microcrystalline powder by employing the same synthetic methodologies used to prepare 1. The new complexes 1-4 have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 2, 3, and 4 and their parent compound, Fe(NO)(3)Cl, have been established by X-ray diffraction methods. The iron centers in the Fe(NO)(3) fragments in all these structures exhibit approximately tetrahedral coordination geometries, and the Fe-N-O linkages are distinctly nonlinear with bond angles in the range of 159 to 169 degrees. DFT calculations on Fe(NO)(3)(eta(1)-BF(4)) (4) confirm that its bent Fe-N-O links have an electronic origin and need not be attributed to other factors, such as packing forces in the crystal. Interestingly, the bending of the NO ligands results in an increase in the energy of the HOMO, relative to the linear case, but at the same time causes a decrease in energy of the HOMO-1 and the HOMO-2 molecular orbitals. This more than compensates for the higher energy of the HOMO, resulting in a lower energy structure.

Neutral and reduced Roussin's red salt ester [Fe2(μ-RS)2(NO)4] (R = n-Pr, t-Bu, 6-methyl-2-pyridyl and 4,6-dimethyl-2-pyrimidyl): synthesis, X-ray crystal structures, spectroscopic, electrochemical and density functional theoretical investigations

“…The main difference between the X-ray data and the calculated data is that the FeN–O angle is underestimated by an average of 2.5° in calculation. This difference is usually very common for metal nitrosyls and it is thought to have an electronic origin,20 and thus cannot be attributed to packing forces, bearing in mind that calculations were carried out in the gas phase. Even when using very large basis sets, this structural characteristic of metal nitrosyls is difficult to calculate accurately 17.…”

New precursor for the post-synthesis preparation of Fe-ZSM-5 zeolites with low iron content

“…[15,17,18,35,48,[50][51][52] for Fe 2+ (NO) 2 ; Refs. [15,17,18,30,35,48,50,53] Fe 2+ (NO) 3 ones. Part (b): FTIR spectra of NO dosed at room temperature (decreasing P NO from 15 Torr, dashed line spectrum to 10 )3 Torr, dotted line spectrum) on Fe-ZSM-5 oxa sample previously activated in vacuo at 773 K. 2 1918 and 1807 cm )1 isolated sites Fe 2+ (NO) 3 1846 and 1767 cm )1 isolated sites Note: The reported frequencies were measured on sample Fe-ZSM-5 oxa previously activated in vacuo at 773 K.…”

Endlich homoleptisch: Synthese und vollständige Charakterisierung stabiler Salze des Mangantetranitrosylkations

“…[4] Einige Jahre später wurde das [Fe 2 (NO) 6 ] 2+ -Kation postuliert, [5] was letztlich 2003 zu Fe(NO) 3 (h 1 -PF 6 )k orrigiert wurde (Tabelle 1). [8,9] So gesehen ermçglichte also der Einsatz der (immer noch zur Koordination fähigen) schwach koordinierenden Anionen (WCAs) [BF 4 ] À und [PF 6 ] À die Synthese und Stabilisierung dieser Metallnitrosylfragmente -v erhinderte dadurch allerdings auch die Herstellung reiner Nitrosylkationen. [8,9] So gesehen ermçglichte also der Einsatz der (immer noch zur Koordination fähigen) schwach koordinierenden Anionen (WCAs) [BF 4 ] À und [PF 6 ] À die Synthese und Stabilisierung dieser Metallnitrosylfragmente -v erhinderte dadurch allerdings auch die Herstellung reiner Nitrosylkationen.…”

“…[Fe(NO) 4 ] À [3] A Cr(NO) 4 [4] "[Mo(NO) 2 ][BF 4 ]" [7,9] "[Fe 2 (NO) 6 ][PF 6 ] 2 " [5] [a] Fe(NO) 3 In Hinblick auf die Bildung eines stabilen 18-Valenzelektronen(VE)-Nitrosylkations schien Mangan das vielversprechendste 3d-Metall auf Basis der Annahme,d ass NO wahrscheinlich als (formaler) Drei-Elektronen-Donor gegenüber dem elektronenarmen Metallkation auftreten würde. Dennoch konnten wir diese Substitution nie beobachten, was zu der Schlussfolgerung führt, dass der vermutlich assoziative Substitutionsmechanismus des strukturell stabilen oktaedrischen [Mn(CO) 6 ] + kinetisch gehemmt sein muss.D ies ist im Einklang mit den Erkenntnissen aus dem isoelektronischen Cr(CO) 6 -System. Abinitio-Rechnungen auf dem aufwendigen CCSD(T)/TZ!…”

“…Ausgehend von kommerziell erhältlichem Mn 2 (CO) 10 4 ] + auf maximal 50 %l imitiert. [13] Experimentell gesehen konnten nach zwei Wochen Kristallisation bei À4 8 8Cn ur etwa 30 %d es reinen [Mn(NO) 4 ] + [Al(OR F ) 4 ] À nach sorgfältigem manuellem Abtrennen der roten Kristalle (Schema 1a)v on den farblosen [Mn(CO) 6 ] + [Al(OR F ) 4 ] À -Kristallen isoliert werden. QZ-Niveau (siehe Hintergrundinformationen, S.I.,K apitel 11) zeigen, dass die Gasphasenreaktion von [Mn(CO) 6 ] + mit 4NO (g) zu [Mn(NO) 4 ] + und 6CO (g) um D r H8 8 Gas = + 52 kJ mol À1 benachteiligt sein sollte.Allerdings sollte durch den entropischen Beitrag der Freisetzung von sechs Molekülen CO diese Reaktion nach der Gibbs-Energie D r G8 8 Gas = À34 kJ mol À1 bei Raumtemperatur (r.t.) ablaufen.…”