Fe CH Research Articles

Excited States versus Reaction Intermediates as Active Species in Photoinduced Redox Reactions of Cyrhetrenyl and Ferrocenyl Chalcones: A 351 nm Flash Photolysis Study.

The photoinduced redox reactions of two organometallic chalcones: trans, E, (η5-C5H4C(O)CH═CH-4-benzo-15-crown-5)Re(CO)3, 1, and trans, E, (η5-C5H4C(O)CH═CH-4-benzo-15-crown-5)Fe(η5-C5H4C(O)CH═CH-4-benzo-15-crown-5), 2, were investigated in fluid solution using the flash photolysis technique. For a better understanding of the photoinduced redox processes of these organometallic chalcones, an electron donor, triethylamine (TEA), and an electron acceptor, methylviologen dichloride (MVCl2), were chosen. Two parallel reaction paths for the decay of the intermediate 1-I, that is, the anion radical of 1, were observed in the presence of TEA. One generates a radical anion, while the other reaction path produces the Z isomer. Instead, the photoinduced reaction of 2 with TEA in MeOH generates an intense absorption band at λmax = 660 nm, which is attributed to a 2-I·MeOH adduct. The oxidative process between 1-I and MV2+ in CH3CN generates transient spectra consistent with the formation of the radical cation MV•+. In contrast, the photoinduced reaction between 2 and MV2+ showed that the generation of MV•+ occurs through a complex mechanism. MV•+ is formed in two steps where the first one is the formation of an adduct between the long-lived metal-to-ligand charge transfer (MLCT)Fe→Chalcone excited state and MV2+. These results have shown that intermediates 1-I and 2-I can function as photo-oxidants and photoreductants better than the chalcone short-lived excited states.

Methylene insertion into an Fe2S2 cluster: formation of a thiolate-bridged diiron complex containing an Fe-CH2-S moiety.

Reduction of a thiolate-bridged FeIIFeIII complex leads to the cleavage of an Fe-S bond by the insertion of the methylene unit from CH2Cl2 to give a neutral FeIIFeIII complex with a novel Fe-CH2-S fragment. The structural and electrochemical differences of the alkylated and the non-alkylated Fe2S2 complexes are also examined.

Synthesis of Diferrocenyl Hydrazone–Enone Receptor Molecules – Electronic Communication, Metal Binding, and DFT Study

Four new diferrocenyl hydrazone–enone compounds were obtained through a two‐step reaction process involving 1,1′‐diacetylferrocene, hydrazides, and ferrocenecarboxaldehyde. The structural characterization of two compounds, 6 and 7, through single‐crystal X‐ray diffraction showed the presence of a stable eclipsed conformation with the two ferrocenyl moieties oriented in trans geometries. The electrochemical and metal‐ion sensing properties of the diferrocenyl‐bifunctionalized compounds were explored to understand their potential in electronic communication and as receptor molecules. Compounds 1,1′‐[(η5‐C5H5)Fe(η5‐C5H4)CH=CHC(O)(η5‐C5H4)Fe{(η5‐C5H4)C(CH3)=N–N(H)C(O)–R}] [R = C6H4OH (6), C6H4N‐p (7)], showed selective interactions with Pb2+ cations and distinct binding interactions with bovine serum albumin (BSA) protein. The mode of the metal–receptor interaction was established through DFT studies. The redox properties of the diferrocenyl compounds with variable end groups revealed distinct electronic communication between the two electroactive groups.

The effect of a paramagnetic metal ion within a molecule: comparison of the structurally identical paramagnetic [3,3-Fe(1,2-C2B9H11)2]- with the diamagnetic [3,3-Co(1,2-C2B9H11)2]- sandwich complexes.

Derivatives of the ferrabisdicarbollide [3,3'-Fe(1,2-C(2)B(9)H(11))(2)](-) have been produced starting from the zwitterion [3,3'-Fe(8-(OCH(2)CH(2))(2)-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))], 1, upon reaction with nucleophiles: alkoxides, halides and hydrosulfide ions HS(-). The result has been the preparation of [3,3'-Fe(8-(OCH(2)CH(2))(2)R/X-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))] (R = OMe, [2](-); OEt, [3](-); OCH(2)CH(2)OCH(3), [4](-); and X = Cl, [5](-); Br, [6](-); I, [7](-); and SH, [8](-)). The reaction behavior of is comparable to the well-studied cobalt equivalent, [3,3'-Co(8-(OCH(2)CH(2))2-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))], and the yields and stability of the resulting complexes are similar. These results are relevant taking into account that [3,3'-Fe(1,2-C(2)B(9)H(11))(2))(-) is a paramagnetic anion. Implications of this are observed in the (11)B-, (1)H and (13)C NMR spectra of [3,3'-Co(1,2-C(2)B(9)H(11))(2)](-) and [3,3'-Fe(1,2-C(2)B(9)H(11))(2)](-) that having identical sandwich molecular structures and the same negative charge have absolutely different widths of the NMR field, between 15 and -25 ppm for [3,3'-Co(1,2-C(2)B(9)H(11))(2)](-) and in the range 150 to -550 ppm for [3,3'-Fe(1,2-C(2)B(9)H(11))(2)](-). The sharpness of both spectra is on the other hand comparable, although no B-H couplings are observed in the Fe metallacarborane or its derivatives. Remarkable is the comparative influence vs. [3,3'-Co(1,2-C(2)B(9)H(11))(2)](-) of replacing Co by Fe on the elements of the cluster layer nearest to the metal. The two equivalent C cluster (Cc) atoms are influenced at 36 840 Hz, the two equivalent B atoms that are adjacent to the two Cc are influenced at 38 157 Hz and the single B that is adjacent to the two B atoms is influenced at 44 062 Hz. Remarkable is the similar influence on B and on C, taking into account that the values have been obtained from two distinct NMR spectra of (11)B and (13)C. The {(11)B-(11)B} COSY NMR and {(1)H-(11)B} HETEROCOSY NMR spectra of [3,3'-Fe(1,2-C(2)B(9)H(11)(2)](-) have been obtained and are reported for the first time.

Trends in structural, electronic properties and Fermi surface topology of 15 tetragonal ThCr2Si2-type phases AFe2Ch2, where A = Li, Na, K, Rb, and Cs; Ch = S, Se, and Te, as parent systems of new ternary iron–chalcogenide superconductors

By means of the first principles FLAPW-GGA approach, a systematic study of the structural and electronic properties of full series of 15 synthesized and hypothetical tetragonal ThCr2Si2-type phases in the system A–Fe–Ch, where A=Li, Na, K, Rb, and Cs; Ch=S, Se, and Te, was performed. We find that for the tuning of the structural parameters of conducting [Fe2Ch2] blocks the replacements of Ch2− ions will be most effective, whereas for the tuning of the inter-blocks separation [Fe2Ch2]–[Fe2Ch2] the replacements of the alkaline ions seem more useful. The trends in the electronic properties and Fermi surface topology of AFe2Ch2 phases are analyzed in relation to their structural parameters to explore whether these materials can be as the parent systems for new ternary iron–chalcogenide superconductors. For all these systems, similar multi-sheet Fermi surfaces consist exclusively of electronic-like sheets, two of which are 2D-like sheets in the corners of the Brillouin zone, and the third one is a closed pocket around Z. The total DOSs at the Fermi level are related with the type of anion Ch2− and their values grow in the sequence AFe2S2→AFe2Se2→AFe2Te2. Thus we assume that AFe2Se2 and AFe2Te2 phases may be considered as favorable parent systems for the search of new ternary iron–chalcogenide SCs.

Determination factors of magnetic anisotropy in a layered iron-based pnictide and its related compounds

From magnetic orientation under static and rotating magnetic fields for RE OFeAs, RE OCuS and Fe Ch , we discuss determination factors of magnetic anisotropies for the above compounds. Behaviours of the magnetic orientation were quite different between RE OFeAs and RE OCuS, and revealed that FeAs layers and RE3+ ions played main roles as determination factors of magnetic anisotropies in RE OFeAs and RE OCuS, respectively. Furthermore, FeSe and FeTe compounds with the same crystal structure possess different magnetic axes, and we clarified that FeTe was the one and only compound with the easy axis parallel to the c -axis among the Fe- based layered compounds.

A re-investigation of [Fe(l-cysteinate)2(CO)2]2−: an example of non-heme CO coordination of possible relevance to CO binding to ion channel receptors

[Fe(L-cysteinate)(2)(CO)(2)](2-) is a CO releasing molecule which has low cytotoxicity to RAW264.7 macrophages. It provides an example of CO binding using ligands available to ion channels which use CO as a signalling molecule in the absence of heme. Previous work has shown that this compound consists of five isomers and it was proposed that the two isomers with trans-dicarbonyls are dominant. In this work the isomers are re-assigned and shown to be capable of releasing CO, albeit too slowly to act as a signalling receptor. It is shown that by linking the two L-cysteines together to form [Fe(SCH(2)CH{CO(2)H}NHCH(2))(2)(CO)(2)], only one isomer is isolated.

Spectroscopic and Functional Characterization of the Nitric Oxide Adducts of the Fe(III) and Fe(II) States of the CO‐Sensing Transcription Factor, CooA, from Carboxydothermus Hydrogenoformans

CooA is a carbon monoxide (CO) sensing transcription factor that is found in several bacteria and regulates CO metabolism. CO binding to CooA's heme groups initiates a conformation change that activates protein DNA binding. This study investigates the reaction of Fe(III) Carboxydothermus hydrogenoformans CooA (Ch CooA) with nitric oxide (NO). Previously, Clark and coworkers reported Fe(II) Ch CooA bound NO to form a 6‐coordinate (6‐C) Fe(II)‐NO adduct that was active for DNA binding in vivo and in vitro. This is in contrast to the best studied CooA homolog from R. rubrum (Rr) that was exquisitely specific for CO and formed an inactive 5‐coordinate (5‐C) Fe(II)‐NO adduct. In the current study, when Fe(III) Ch CooA was incubated with NO, a final 5‐C Fe(II)‐NO species resulted. This species had an electronic absorbance spectrum similar to Rr CooA; however, unlike Rr CooA, the 5‐C Fe(II)‐NO Ch CooA adduct retained some DNA‐binding activity. Results from mutagenesis studies suggest that S‐nitrosylation of a Cys residue located in the heme pocket may account for the unexpected reactivity differences of Fe(III) and Fe(II) Ch CooA with NO. Based on these data, it is proposed the ability of Ch CooA (and failure of Rr CooA) to be activated by NO is due to the binding of NO to the correct (i.e. distal) heme face. The authors wish to thank the Valparaiso University College of Arts and Sciences for financial support.

Impact of nitric oxide (NO) treatment on the spectroscopic properties and DNA binding activity of the carbon monoxide‐sensing heme transcription factor, CooA

CooA is a carbon monoxide (CO)‐sensing heme transcription factor that regulates CO metabolism in several bacteria including Carboxydothermus hydrogenoformans (Ch). The goal of this research was to investigate the spectroscopic properties and DNA binding activity of Fe(III) Ch CooA that was reacted with NO. Based on electronic absorbance spectra, addition of NO to Fe(III) CooA resulted in the formation of a 6‐coordinate (6‐C) Fe(III)‐NO intermediate species, which slowly converted to a 5‐coordinate (5‐C) Fe(II)‐NO complex. A fluorescence anisotropy assay revealed appreciable DNA binding activity by the 6‐C Fe(III)‐NO form and lesser activity by the 5‐C adduct. DNA binding by 5‐C Fe(II)‐NO CooA was unexpected because this species has a much different coordination structure than the native 6‐C Fe(II)‐CO form or the 6‐C Fe(III)‐NO adduct. Based on these findings, we propose that the most important factor required for activating CooA's DNA binding function is the presence of a gas molecule (CO or NO) that is bound to the correct (i.e. distal) face of the heme. The authors wish to thank the Valparaiso University College of Arts and Sciences for financial support.

Synthesis of an ionic liquid with an iron coordination cation

An iron-based ionic liquid, Fe((OHCH(2)CH(2))(2)NH)(6)(CF(3)SO(3))(3), is synthesized in a single-step complexation reaction. Infrared and Raman data suggest NH(CH(2)CH(2)OH)(2) primarily coordinates to Fe(iii) through alcohol groups. The compound has T(g) and T(d) values of -64 degrees C and 260 degrees C, respectively. Cyclic voltammetry reveals quasi-reversible Fe(iii)/Fe(ii) reduction waves.

The water-soluble Roussin's red ester acting as a potential photochemical NO-delivery agent: Photolysis reactions, DNA cleavage and anticancer activity

The water-soluble Roussin's red ester [(NO)(2)Fe(mu-SCH(2)CH(2)P(O)(CH(2)OH)(2))(2)Fe(NO)(2)] (1), a potential photochemical prodrug of an NO precursor, was synthesized from the reaction of HSCH(2)CH(2)P(O)(CH(2)OH)(2) (F) and [Fe(CO)(2)(NO)(2)]. The IR v(NO) stretching frequencies of complex 1 appear at 1759 (s), 1784 (s) and 1816 (w) cm(-1) in buffer (pH = 7.4). NO was released with a stoichiometry ratio Delta[NO]/Delta[1] = 3.6 +/- 0.2 when complex 1 was exposed to UV in deaerated aqueous phosphate buffer solution. Here light acts as an On/Off switch for NO release. Incubation of pBR322 supercoiled DNA with complex 1, followed by irradiation, produced DNA strand breakage. In contrast to the addition of carboxy-PTIO (NO radical scavenger), DNA strand breakage was not inhibited when the scavengers of hydroxyl radical and singlet oxygen were added. Complex 1 irradiated under a N(2) atmosphere exhibited the same cleavage efficiency as complex 1 irradiated under air. The results show that DNA strand cleavage efficiency depends on the concentration of complex 1, the pH value of the buffer, and the duration of the photolysis of complex 1. The conversion rate from supercoiled (SC form) to nicked circular (NC form) of complex 1 was 2.96 x 10(-2) s(-1). The results of a T4 ligase enzymatic assay reveals the nonhydrolytic DNA breakage mechanism. The NO-release ability of complexes 1, 2, and 3 follows the order 1 > 2 > 3. Upon UV-irradiation, complex 1 exhibits cytotoxicity against B16-F10 mouse melanoma cells.

Teaching & Learning Guide for: Moral Realism and Moral Nonnaturalism

Teaching & Learning Guide for: Moral Realism and Moral Nonnaturalism

Coordination chemistry of acrylamide 6: Formation and structural characterization of [Fe( O-OC(NH 2)CH [dbnd]CH 2) 6][Fe 2OCl 6

The new acrylamide iron(II)/iron(III) complex [Fe( O-OC(NH 2)CH CH 2) 6][Fe 2OCl 6] ( 1) was obtained by the reaction of a mixture of anhydrous FeCl 2 and anhydrous FeCl 3 with acrylamide (molar ratio 1:2:6) in 98% pure commercial nitromethane under nitrogen atmosphere. According to an X-ray structural analysis, the acrylamide ligands in the cation are coordinated via the amide-oxygen atoms. The formation of the (μ-oxo)bis[trichloroferrate(III)] 2− anion presumably resulted from partial hydrolysis of FeCl 3 or [FeCl 4] − by small amounts of water in the nitromethane and/or by the nitromethane itself.

Thermal decomposition and stability of [Fe(η4-enone)(CO)2L] complexes (L=CO and PPh3)

The compounds [Fe(bda)(CO)2L] and [Fe(ch)(CO)2L], (bda=benzylideneacetone; ch=chalcone; L=CO, PPh3) were investigated by thermogravimetry and derivative thermogravimetry (TG and DTG). The fragmentation patterns suggest that the iron atom protects the enone fragment, so that the organic ligands break up with the loss of the pendant aromatic rings.

Synthesis and reactivity of [2]ferrocenophanes containing C–Pb and C–Zr bridges

The synthesis, characterization and reactivity of novel carbometalla[2]ferrocenophanes (η-C 5Me 4)Fe(η-C 5H 4)CH 2ER 2 ( 14) and ( 15) (E = Pb, R = Ph or E = Zr, R = (η-C 5H 5)) are reported. Compounds 14 and 15 were prepared by the reaction of the dilithiated species (η-C 5Me 4)Fe(η-C 5H 4Li)CH 2Li · xTMEDA with the appropriate dichlorodiorganoplumbane or dichlorozirconocene in low yields (ca. 20%). The Pb species 14 was characterized by 1H and 13C NMR, and MS, however it could not be cleanly separated from pentamethylferrocene. Moreover, it was found that the C–Pb bonds of 14 underwent facile cleavage, and under ambient light or at room temperature, 14 decomposed to Pb 2Ph 6 and pentamethylferrocene. Compound 15, on the other hand, was stable and readily purified; this species was characterized by 1H and 13C NMR, UV–Vis, MS, and elemental analysis. Single crystal X-ray diffraction studies of this compound revealed the presence of a moderate degree of ring-tilt with a value of α = −5.5(2)° (a negative value is used to denote tilting away from the bridging elements), and a potentially moderate degree of strain due to a large β(Zr) of 31.6(1)° (angle between Cp′(Fe) plane and ipso-Cp′–Zr bond). Attempted thermal ring-opening polymerization (ROP) of 15 resulted only in decomposition and attempted transition metal-catalyzed and photolytic ROP were also unsuccessful. The reaction of 15 with HCl · Et 2O resulted in cleavage of the C–Zr bonds, and led to the formation of pentamethylferrocene.

Structure and reactivity in the selective oxidation of methane to formaldehyde of low-loaded FeO x/SiO 2 catalysts

The structure of low-loaded (0.09–0.73 Fe wt%) FeO x /SiO 2 catalysts prepared by adsorption–precipitation of Fe 2+ precursor on silica (AP) has been assessed by DR UV–Vis and Mössbauer techniques in comparison with counterpart incipient wetness (IW) systems. Spectroscopic findings indicate the speciation of the active phase into isolated Fe 3+ species, oligomeric 2-d FeO x patches , and 3-d Fe 2O 3 nanoparticles , characterised by decreasing interaction strength with silica carrier. The reduction pattern of the above surface structures has been probed by temperature-programmed reduction (TPR) measurements, and a deconvolution analysis of spectra allowed the concentration of the various surface species to be highlighted. The catalytic activity in the selective oxidation of CH 4 to HCHO with oxygen (MPO) has been systematically evaluated by batch (BR) and continuous-flow (CF) measurements in the range of 400–750 °C. Direct relationships among Fe dispersion and specific atomic rate of CH 4 conversion ( Fe CH 4 , s −1) and HCHO formation (Fe HCHO, s −1) confirm the superior catalytic performance of AP systems. After a poor reactivity of “ isolated species” and the unselective behaviour of 3-d Fe 2O 3 particles, 2-d oligomeric patches feature the best catalytic pattern, owing to an optimum Fe O bond strength. Sintering and surface reconstructuring phenomena affect the catalyst stability during the MPO reaction.

Synthetic models of the reduced active site of superoxide reductase.

We report the synthesis, structural and spectroscopic characterization, and magnetic and electrochemical studies of a series of iron(II) complexes of the pyridyl-appended diazacyclooctane ligand L(8)py(2), including several that model the square-pyramidal [Fe(II)(N(his))(4)(S(cys))] structure of the reduced active site of the non-heme iron enzyme superoxide reductase. Combination of L(8)py(2) with FeCl(2) provides [L(8)py(2)FeCl(2)] (1), which contains a trigonal-prismatic hexacoordinate iron(II) center, whereas a parallel reaction using [Fe(H(2)O)(6)](BF(4))(2) provides [L(8)py(2)Fe(FBF(3))]BF(4) (2), a novel BF(4)(-)-ligated square-pyramidal iron(II) complex. Substitution of the BF(4)(-) ligand in 2 with formate or acetate ions affords distorted pentacoordinate [L(8)py(2)Fe(O(2)CH)]BF(4) (3) and [L(8)py(2)Fe(O(2)CCH(3))]BF(4) (4), respectively. Models of the superoxide reductase active site are prepared upon reaction of 2 with sodium salts of aromatic and aliphatic thiolates. These model complexes include [L(8)py(2)Fe(SC(6)H(4)-p-CH(3))]BF(4) (5), [L(8)py(2)Fe(SC(6)H(4)-m-CH(3))]BF(4) (6), and [L(8)py(2)Fe(SC(6)H(11))]BF(4) (7). X-ray crystallographic studies confirm that the iron(II)-thiolate complexes model the square-pyramidal geometry and N(4)S donor set of the reduced active site of superoxide reductase. The iron(II)-thiolate complexes are high spin (S = 2), and their solutions are yellow in color because of multiple charge-transfer transitions that occur between 300 and 425 nm. The ambient temperature cyclic voltammograms of the iron(II)-thiolate complexes contain irreversible oxidation waves with anodic peak potentials that correlate with the relative electron donating abilities of the thiolate ligands. This electrochemical irreversibility is attributed to the bimolecular generation of disulfides from the electrochemically generated iron(III)-thiolate species.

The origin of diastereoselectivity in cyclopropanation reactions of the iron carbene complex [(η5-C5H5)(CO)2FeCH[(η6-o-CH3OC6H4)Cr(CO)3]

Abstract The origin of diastereoselectivity in cyclopropanation reactions of the iron carbene complex [(η 5 -C 5 H 5 )(CO) 2 FeCH[(η 6 - o -CH 3 OC 6 H 4 )Cr(CO) 3 ]] + has been investigated. The chromium participation has been proved by the upfield shifts of both 1 H- and 13 C-NMR for C α  H and C α , which stabilized the iron carbene and may result in a late transition-state for the cyclopropanation reaction via tricarbonylchromium-complexed iron carbene. Hence, trans selectivity is expected. However, when using aromatic alkenes, a π stacking effect may exist during the transition-state, resulting in the cis selectivity for cyclopropanation.

Methyl bonding to Fe and Fe(CO) n: : reactions of Fe − and Fe(CO) n− with methyl halides

Rate constants for atomic iron anion and successively ligated anions Fe(CO) n − (n = 0–4) reacting with CH 3X (X = F, Cl, Br, I) were measured using a selected-ion flow tube apparatus. The results indicate that X − formation occurs as the dominant channel when exothermic. Other observed reaction channels are ligand exchange (with CH 3 and X replacing two CO), halogen-atom abstraction and adduct formation. Fe(CO) 4 − is too stable for a reaction with CH 3X to develop by any channel. Fe(CO) 2 − displays a rich chemistry. Information on the bond strengths, D[Fe(CO) n CH 3], is deduced from the results. Under the assumption that the X − product channel is observed if exothermic, we calculate the homolytic iron–methyl bond energies 0.13 eV ≤ D[FeCH 3] ≤ 1.76 eV, D[Fe(CO)CH 3] = 1.2 ± 0.2 eV, D[Fe(CO) 2CH 3] = 1.3 ± 0.3 eV, D[Fe(CO) 3CH 3] < 1.4 eV, and D[Fe(CO) 4CH 3] < 2.1 eV.

Synthesis, X-ray structural determination and Mössbauer characterization of Schiff bases bearing ferrocene groups, their reduced analogues and related complexes

[1+1], [1+2], [2+1] or [3+1] acyclic and [1+1] or [2+2] cyclic Schiff bases (L A⋯L S), containing ferrocene moieties, have been prepared by reaction of formyl- or 1,1′-diformylferrocene and the appropriate amines. Formyl- and 1,1-diformylferrocene form respectively the acyclic [2+1] L W and [2+2] n L Z compounds by reaction with 1,4-diaminomethylbenzene. Similar compounds (L T⋯L V) have been obtained by condensation of aminomethylferrocene and 2,6-diformylpyridine, 2,6-diformyl-4-chlorophenol and 3-methoxy-2-hydroxybenzaldehyde. By reduction of these compounds with NaBH 4 the corresponding ferrocene–amine derivatives (L′) have been synthesized. All these compounds have been characterized by physico–chemical measurements (IR, NMR, Mössbauer spectroscopy and FAB mass spectrometry) and L H, derived by the condensation of ferrocene–aldehyde and 1,5-diamino-3-oxa-pentane, also by an X-ray structural determination. The X-ray analysis of crystals of L H, grown from a diethyl ether solution, shows that two independent molecules are present in the asymmetric unit; these two molecules are chemically equivalent with the ferrocenyl groups in the eclipsed form. The coordination ability of these compounds towards d metal ions as copper(II), nickel(II), platinum(II) and rhodium(III) was investigated; while the Schiff bases (L) may suffer hydrolysis, their reduced analogues (L′) form stable, well-defined complexes of the type M(L′)(Cl) n ( n=2, 3). The Mössbauer spectra of the prepared compounds show signals with δ at 0.44 and Δ E Q 2.30 mm s −1 for the Schiff bases L A⋯L S and 0.52 and 2.40 mm s −1 for the reduced analogues and hence may be diagnostic of the presence of Fe–CHN– or Fe–CH 2–NH– groups. The signals with δ at 0.51–0.55 and Δ E Q at 2.34–2.38 mm s −1 for the Schiff bases L T⋯L V, having Fe–CH 2–NCH groups, resemble those of the reduced analogues.