Single‐Crystal EPR Spectroscopy on [⁵⁷Fe(NO)(S₂CNEt₂)₂]: The “Triplet Signal” in the EPR Spectrum of [Fe(S₂CNEt₂)₃]

Abstract

COMMUNICATIONSwere assigned. From the chemical shifts and the coupling constants of 2.5 Hz, 17-H, 18-H, and 19-H were assigned to the protons of a pyrrole ring. This pyrrole ring carries the octatetraenyl and bromo substituents in the 2-and 3-positions, respectively. as confirmed by the chemical shifts in the 13C spectrum and by the COLOC spectrum (COLOC = correlation by longrange couplings). This substitution pattern is also apparent from the strong NOES (NOE = nuclear Overhauser enhancement effect) between 19-H and 13-H/18-H, and between 17-H and 18-H. The remaining C,H,O, fragment is a 4-hydroxy-2pyrone. which is connected to the octatetraenyl residue at C-6, and carries a methyl group in the 3-position. This assignment was contirmed by the COLOC spectrum and by a strong NOE between 5-H and 7-H. Keronopsin B, therefore has structure lc, and is present predominantly in the conformation depicted.From the isotope pattern of the M f signal in the FD mass spectrum ( m / z : 456/454/452), keronopsin B, (Id) contains a second bromine atom. This is found at C-17, since the ' H and I3C N M R spectra of the two compounds were identical, apart from the absence of the 17-H signal. The same is true for keronopsins A , ( l a ) and A, (Ib), which also have one and two bromo substituents, respectively, at C-16 and C-17 of the pyrrole ring. Keronopsins A and A, differ from B, and B, only in the pyrone ring. The signal for the 4-hydroxy group is missing, the signal for 5-H is shifted by A6 = 0.6 downfield, and the signal for C-3 is moved by AS = 5 downfield-the signals for C-2 and C-4 are shifted by A6 = 4-6 upfield, which suggests the presence of a 4-acyloxy substituent. From elemental analysis and negative-

Coordination and Organometallic Chemistry of Metal−NO Complexes

“…Magnetic susceptibility and Mössbauer measurements on [Fe(NO)(salen)] 2+ have detected transitions between the S = 3/2 and S = 1/2 spin states . In contrast to this behavior, the isoelectronic five-coordinate iron(I) complexes Fe(NO)(E 2 CNR 2 ) 2 (E = S, Se) and [Fe(NO)(S 2 CC(CN) 2 ) 2 ] 2- have been found to be pure low-spin species by ESR spectroscopic and magnetic susceptibility methods. − Kirmse and co-workers have utilized isotopic labeling techniques to prove that trace amounts of Fe(NO)(S 2 CNEt 2 ) 2 are responsible for a previously ill-explained triplet at g = 2.0 in the ESR spectrum of Fe(S 2 CNEt 2 ) 3 . The nitrosyl-containing impurity is present as a result of traces of nitrate ions in the FeCl 3 starting materials .…”

“…In contrast to this behavior, the isoelectronic five-coordinate iron(I) complexes Fe(NO)(E 2 CNR 2 ) 2 (E = S, Se) and [Fe(NO)(S 2 CC(CN) 2 ) 2 ] 2- have been found to be pure low-spin species by ESR spectroscopic and magnetic susceptibility methods. − Kirmse and co-workers have utilized isotopic labeling techniques to prove that trace amounts of Fe(NO)(S 2 CNEt 2 ) 2 are responsible for a previously ill-explained triplet at g = 2.0 in the ESR spectrum of Fe(S 2 CNEt 2 ) 3 . The nitrosyl-containing impurity is present as a result of traces of nitrate ions in the FeCl 3 starting materials . Only one example of the chemical reactivity of an Fe(NO)(E 2 CNR 2 ) 2 system has been reported to date, namely the displacement of a dithiocarbamate ligand by donor molecules (L) to generate the dichloromethane adducts Fe(NO)(S 2 CNR 2 )L· n CH 2 Cl 2…”

“…The nitrosyl-containing impurity is present as a result of traces of nitrate ions in the FeCl 3 starting materials. 664 Only one example of the chemical reactivity of an Fe(NO)(E 2 CNR 2 ) 2 system has been reported to date, namely the displacement of a dithiocarbamate ligand by donor molecules (L) to generate the dichloromethane adducts Fe(NO)(S 2 CNR 2 )L‚nCH 2 Cl 2 . 663 Various Fe(NO)(L 2 )(PPh 3 ) 2 and Fe(NO)(L 2 ) 2 complexes (L 2 ) cysteine, phenanthroline, dithiolene, bipyridine) have been found to exhibit no antibacterial activity.…”

Super reduced Fe4S4 cluster of Balch's dithiolene series

“…A super hyperfine interaction based on the low abundance of the naturally occurring 13 C nuclei in the paramagnetic ion, Mo(CN) 8 ] 3− is known. [21][22][23] Reaction of complex 1 with acids…”