N2S2 Ligands Research Articles

Modulating the reduction potential and ligand basicity of Ni(II) HER catalysts with highly conjugated N2S2 ligands

Molecular catalysts with N2S2 chelates and earth abundant metals have been used in different applications. With their versatile nature to modulate activity through changes in the ligand framework, they are excellent candidates to generate low-cost and sustainable energy as electrocatalysts for the hydrogen evolution reaction (HER). Herein we demonstrate the modulation of the reduction potential and basicity across a series of six square planar Ni(II) complexes with bis(thiosemicarbazonato) (BTSC), hybrid thiosemicarbazonato-alkylthiocarbamato (TSTC), and bis(alkylthiocarbamato) (BATC) ligands and evaluate their activity as homogenous HER catalysts. The redox active ligands have been designed to modulate the electronic structure of the N2S2Ni core and to systematically alter their respective pKa values. Cyclic voltammograms of all six complexes show two reversible reduction events in acetonitrile that systematically shift to more anodic potentials when the pendent methylthiosemicarbazonato (–NN=C(S)NHMe) groups are substituted with ethylthiocarbamato (–NN=C(S)OEt) groups and/or when the 2,4-butanedione backbone is replaced by 1-phenyl-1,2-propandione. Ligand basicity was evaluated by spectroscopic titration in acetonitrile and found to vary systematically across the series. Within the series of complexes the reduction potentials vary over an ∼ 500 mV range and the ligand basicity over ∼ 7 pKa units. Density functional theory (DFT) computations are consistent with experimental changes in redox potential and pKa values across the series of complexes. The results demonstrate a unique example in which electronic properties of the complexes are modulated via small ligand structure variations. The complexes are stable under acidic conditions or upon reduction, but they degrade upon reduction in the presence of acid limiting their application as homogeneous HER electrocatalysts.

Modulation of Fe-Fe distance and spin in diiron complexes using tetradentate ligands with different flanking donors.

Here we report the synthesis and characterization of diiron complexes containing triaryl N4 and N2S2 ligands derived from o-phenylenediamine. The complexes display significant differences in Fe-Fe distances and magnetic properties that depend on the identity of the flanking NMe2 and SMe donor groups.

Bond Trading: Intramolecular Metal and Ligand Exchange within a NO/Ni/Co Complex.

With the goal of generating hetero-redox levels on metals as well as on nitric oxide (NO), metallodithiolate (N2 S2 )CoIII (NO- ), N2 S2 = N,N- dibenzyl-3,7-diazanonane-1,9-dithiolate, is introduced as ligand to a well-characterized labile [Ni0 (NO)+ ] synthon. The reaction between [Ni0 (NO+ )] and [CoIII (NO- )] has led to a remarkable electronic and ligand redistribution to form a heterobimetallic dinitrosyl cobalt [(N2 S2 )NiII ∙Co(NO)2 ]+ complex with formal two electron oxidation state switches concomitant with the nickel extraction or transfer as NiII into the N2 S2 ligand binding site. To date, this is the first reported heterobimetallic cobalt dinitrosyl complex.

Mono- and Bimetallic Aluminum Complexes Supported by Thioether-Amide Ligands: Synthesis, Characterization, and Application in the Ring Opening Polymerization of l-Lactide

Mono- and bimetallic aluminum complexes bearing bidentate NS or tetradentate NSSN ligands have been synthesized via reaction of AlMe3 with the corresponding proligand and spectroscopically characterized. In these complexes the aluminum centers are surrounded by anionic nitrogen and neutral sulfur atoms that, together with the carbon atoms of the alkyl groups, produce tetrahedral coordination geometries. In the bimetallic complexes the two metal centers are linked by a thioether-bridge of different lengths. The solid state structure of the complexes featuring the thioethyl or thiopropyl bridge were determined by X-ray diffraction studies. Both mono- and bimetallic aluminum complexes display fluxional behaviors in solution. After proper activation, all complexes were able to promote the ring opening polymerization of l-lactide in toluene solution. The polymerizations were well controlled as testified by the linear increase of the molecular weights with the conversions and the narrow polydispersity indexes. The highest activity was observed for the bimetallic complex bearing the NSSN ligand with the shortest bridge (ethyl bridge) with a turnover frequency of 11.6 molLA·molAl–1·h–1 (toluene, 80 °C). The activity decreased as the distance between the two metal centers increased. Moreover, the activity of the bimetallic complex with the ethyl bridge was higher than those of the monometallic ones. These findings suggest that a cooperative interaction between two aluminum centers is operative in the bimetallic complex with the shortest bridge.

BSA Interaction, Molecular Docking, and Antibacterial Activity of Zinc(II) Complexes Containing the Sterically Demanding Biomimetic N3S2 Ligand: The Effect of Structure Flexibility.

Two zinc(II) complexes, DBZ and DBZH4, that have (ZnN3S2) cores and differ in the bridging mode of the ligating backbone, effectively bind to BSA. The binding affinity varies as DBZ > DBZH4 and depends on the ligand structure. At low concentrations, both complexes exhibit dynamic quenching, whereas at higher concentrations they exhibit mixed (static and dynamic) quenching. The energy transfer mechanism from the BSA singlet excited state to DBZ and DBZH4, is highly likely according to steady-state fluorescence and time-correlated singlet photon counting. Molecular docking was used to support the mode of interaction of the complexes with BSA and showed that DBZ had more energy for binding. Furthermore, antibacterial testing revealed that both complexes were active but to a lesser extent than chloramphenicol. In comparison to DBZH4, DBZ has higher antibacterial activity, which is consistent with the binding constants, molecular docking, and particle size of adducts. These findings may have an impact on biomedicine.

Evaluation of 186WS2 target material for production of high specific activity 186Re via proton irradiation: separation, radiolabeling and recovery/recycling

Abstract Enriched tungsten disulfide (186WS2) was evaluated at increasing proton beam currents (20–50 μA) and times (up to 4 h) on a GE PETtrace cyclotron for production of high specific activity (HSA) 186Re. The HSA 186Re was separated from the irradiated target as [186Re][ReO4]– by a liquid–liquid extraction method and radiolabeled with a new N2S2 ligand (222-MAMA-N-ethylpropionate). The enriched 186W was recovered from the extraction process, analyzed for purity and enrichment, and converted back to the disulfide (186WS2). The results demonstrate that the 186WS2 is an easily pressed target material that can withstand relatively high currents and can be readily recovered and recycled. The 186Re produced was isolated in high specific activity and readily formed the radiotracers [186Re][ReO(222-MAMA-N-ethylpropionate)] and [186Re][Re(CO)3(OH2)3] +.

A new bis(thioether)-dipyrrin N2S2 ligand and its coordination behaviors to nickel, copper and zinc.

Tetradentate N2S2 coordination platforms are widespread in biological systems and have endowed metalloenzymes and metalloproteins with abundant reactivities and functions. However, there are only three types of N2S2 scaffolds respectively based on the bipyridine, aryl and alkyl amine derivatives, which are significantly underdeveloped for coordination chemistry. With the objective of developing a new N2S2 coordination platform to assemble a series of first-row transition metal complexes, we have designed a novel tetradentate N2S2 ligand containing a central dipyrrin donor functionalized with two thioether-substituted aryl units. Interestingly, complexation of the N2S2 ligand with the chloride salts of Ni(II), Cu(II) and Zn(II) yields various geometries with various coordination numbers. The reaction between the ligand and NiCl2 readily forms two chloride-bridged centrosymmetric dinickel complexes in which the nickel centers are hexacoordinated by an N2S2Cl2 coordination environment in distorted octahedron geometry. In contrast, metalation of the ligand with CuCl2 gives a mononuclear copper complex consisting of a pentacoordinated copper center in a trigonal bipyramidal geometry with an N2S2Cl coordination sphere. Unexpectedly, the complexation of the ligand with ZnCl2 forms a homoleptic zinc complex in which the zinc center is surrounded by an N4 coordination sphere from two dipyrrin units in a non-planar pseudo-tetrahedral geometry despite the steric hindrance of two bulk thioether-substituted aryl units. These various geometries illustrate the potential structural flexibility of this new ligand. In addition, the optical properties of these compounds were also examined. This work thus provides a new N2S2 coordination platform with geometric flexibility.

Synthesis, spectral characterization, optical properties and X-ray structural studies of S centrosymmetric N2S2 or N2S2O2 donor Schiff base ligand and its binuclear transition metal complexes

A new chelate namely 2,2′-thiobis(N\\-thiophen-2-ylmethyylene) acetohydrazide) (H2TTAH) was synthesized and its metal complexes with Co (II), Ni (II), Cu (II), and Zn (II) ions. The isolated complexes were characterized by conventional spectroscopic (IR, UV-visible, ESR, 1H, 13C-NMR, and mass), elemental analysis, and magnetic as well as thermal measurements. H2TTAH binds either as neutral tetra-dentate and mono- or dibasic NNOOSS hexadentate coordinating two metal ions. The metal complexes afforded the formulae: [Cu2(TTAH)Cl3(C2H5OH)3]0.5C2H5OH.H2O (1), [Co2(TTAH)(C5H5N)]Cl2.2.5C2H5OH (2), [Ni2(TTAH)(C5H5N)2(OH)2(C2H5OH)2] (3) and [Zn2(TTAH)2)(OH)4(C5H5N)2].C2H5OH (4). On the premise of their electronic spectra and magnetic moments data; tetrahedral for Co (II) and octahedral geometries for other complexes were suggested. X-ray powder diffraction technique was used to obtain more details of the chemical constitution of (2) complex. The geometries of all studied compounds were further affirmed by DFT method calculations. Also, all compounds were examined for their antibacterial and superoxide dismutase (SOD)-like activities.

Synthesis, Structures, and Reactivity of [NiFe]-H2ase Mimics Containing One Square-Planar N2S2 Ligand Bridged between Their Ni/Fe Centers through One or Two S Atoms

To develop the biomimetic chemistry of [NiFe]-H2ases, we have successfully prepared 2 types of 16 biomimetic models for [NiFe]-H2ases by various synthetic methods. These models are new cationic complexes that contain one square-planar N2S2 ligand coordinated to a Ni atom to form a metalloligand (dsdm)Ni (H2 dsdm = N,N′-dimethyl-N,N′-bis(2-sulfanylethyl)ethylenediamine) or (dmpn)Ni (H2 dmpn = N,N′-dimethyl-N,N′-bis(2-mercaptoethyl)-1,3-propanediamine), and in turn, one or two S atoms of their metalloligands are bridged to one Fe moiety with different ligands such as t-Cl, t-I, t-PhS, t-MeO, t-MeCN, μ-H, η2-1,2-C2H2(PPh2)2(dppv), and/or η2-1,2-C6H4(PPh2)2(dppb). While all the prepared 16 model complexes are fully characterized by elemental analysis and various spectroscopic techniques, the molecular structures for 6 of the prepared models are unambiguously confirmed by X-ray crystallography, and particularly, 2 of the prepared models have been found to activate H2 under mild conditions to give the dithiolato-bridged μ-H model complexes.

Detection and Characterization of Mononuclear Pd(I) Complexes Supported by N2S2 and N4 Tetradentate Ligands.

Palladium is a versatile transition metal used to catalyze a large number of chemical transformations, largely due to its ability to access various oxidation states (0, I, II, III, and IV). Among these oxidation states, Pd(I) is arguably the least studied, and while dinuclear Pd(I) complexes are more common, mononuclear Pd(I) species are very rare. Reported herein are spectroscopic studies of a series of Pd(I) intermediates generated by the chemical reduction at low temperatures of Pd(II) precursors supported by the tetradentate ligands 2,11-dithia[3.3](2,6)pyridinophane (N2S2) and N,N'-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane (tBuN4): [(N2S2)PdII(MeCN)]2(OTf)4 (1), [(N2S2)PdIIMe]2(OTf)2 (2), [(N2S2)PdIICl](OTf) (3), [(N2S2)PdIIX](OTf)2 (X = tBuNC 4, PPh3 5), [(N2S2)PdIIMe(PPh3)](OTf) (6), and [(tBuN4)PdIIX2](OTf)2 (X = MeCN 8, tBuNC 9). In addition, a stable Pd(I) dinuclear species, [(N2S2)PdI(μ-tBuNC)]2(ClO4)2 (7), was isolated upon the electrochemical reduction of 4 and structurally characterized. Moreover, the (tBuN4)PdI intermediates, formed from the chemical reduction of [(tBuN4)PdIIX2](OTf)2 (X = MeCN 8, tBuNC 9) complexes, were investigated by EPR spectroscopy, X-ray absorption spectroscopy (XAS), and DFT calculations and compared with the analogous (N2S2)PdI systems. Upon probing the stability of Pd(I) species under different ligand environments, it is apparent that the presence of soft ligands such as tBuNC and PPh3 significantly improves the stability of Pd(I) species, which should make the isolation of mononuclear Pd(I) species possible.

Ruthenium(II) Phosphine/Mercapto Complexes: Their in Vitro Cytotoxicity Evaluation and Actions as Inhibitors of Topoisomerase and Proteasome Acting as Possible Triggers of Cell Death Induction.

In this paper, a series of new ruthenium complexes of the general formula [Ru(NS)(dpphpy)(dppb)]PF6 (Ru1-Ru3), where dpphpy = diphenyl-2-pyridylphosphine, NS ligands = 2-thiazoline-2-thiol (tzdt, Ru1), 2-mercaptopyrimidine (pySm, Ru2), and 4,6-diamino-2-mercaptopyrimidine (damp, Ru3), and dppb = 1,4-bis(diphenylphosphino)butane, were synthesized and characterized by elemental analysis, spectroscopic techniques (IR, UV/visible, and 1D and 2D NMR), and X-ray diffraction. In the characterization, the correlation between the phosphorus atoms and their respective aromatic hydrogen atoms of the compounds in the assignment stands outs, by 1H-31P HMBC experiments. The compounds show anticancer activities against A549 (lung) and MDA-MB-231 (breast) cancer cell lines, higher than the clinical drug cisplatin. All of the complexes are more cytotoxic against the cancer cell lines than against the MRC-5 (lung) and MCF-10A (breast) nontumorigenic human cell lines. For A549 tumor cells, cell cycle analysis upon treatment with Ru2 showed that it inhibits the mitotic phase because arrest was observed in the Sub-G1 phase. Additionally, the compound induces cell death by an apoptotic pathway in a dose-dependent manner, according to annexin V-PE assay. The multitargeted character of the compounds was investigated, and the biomolecules were DNA, topoisomerase IB, and proteasome, as well as the fundamental biomolecule in the pharmacokinetics of drugs, human serum albumin. The experimental results indicate that the complexes do not target DNA in the cells. At low concentrations, the compounds showed the ability to partially inhibit the catalytic activity of topoisomerase IB in the process of relaxation of the DNA plasmid. Among the complexes assayed in cultured cells, complex Ru3 was able to diminish the proteasomal chymotrypsin-like activity to a greater extent.

Copper Complexes of Benzoylacetone Bis-Thiosemicarbazones: Metal and Ligand Based Redox Reactivity

Bis-thiosemicarbazones derived from the β-diketone benzoylacetone (H3banR, R=Me, Et, Ph) are potentially tetradentate N2S2 ligands whose coordination chemistry with copper is reported. In the absence of oxygen and in the presence of base they form anionic CuII complexes of the fully deprotonated ligands [CuII(banR)]–. Upon exposure to atmospheric oxygen they undergo a complex series of reactions leading to two types of products; one a ligand oxidised ketone complex [CuII(banRO)] and the other an unprecedented dimeric di-CuIII complex [(CuIII(banR))2] depending on the R substituent. Time-resolved UV-vis spectroscopy, cyclic voltammetry, spectroelectrochemistry, and electron paramagnetic resonance (EPR) spectroscopy have been used to identify intermediates on the way to stable products formed under both anaerobic and aerobic conditions. It is found that both ligand-centred and Cu-centred oxidation reactions are occurring in parallel leading to this unusually complicated mixture of products.

Influence of Multisite Metal-Ligand Cooperativity on the Redox Activity of Noninnocent N2S2 Ligands.

Metal-ligand cooperativity (MLC) relies on chemically reactive ligands to assist metals with small-molecule binding and activation, and it has facilitated unprecedented examples of catalysis with metal complexes. Despite growing interest in combining ligand-centered chemical and redox reactions for chemical transformations, there are few studies demonstrating how chemically engaging redox active ligands in MLC affects their electrochemical properties when bound to metals. Here we report stepwise changes in the redox activity of model Ru complexes as zero, one, and two BH3 molecules undergo MLC binding with a triaryl noninnocent N2S2 ligand derived from o-phenylenediamine (L1). A similar series of Ru complexes with a diaryl N2S2 ligand with ethylene substituted in place of phenylene (L2) is also described to evaluate the influence of the o-phenylenediamine subunit on redox activity and MLC. Cyclic voltammetry (CV) studies and density functional theory (DFT) calculations show that MLC attenuates ligand-centered redox activity in both series of complexes, but electron transfer is still achieved when only one of the two redox-active sites on the ligands is chemically engaged. The results demonstrate how incorporating more than one multifunctional reactive site could be an effective strategy for maintaining redox noninnocence in ligands that are also chemically reactive and competent for MLC.

Synthesis and comparative study of the anticancer activity of η3-allyl palladium(II) complexes bearing N-heterocyclic carbenes as ancillary ligands

In this paper we report the synthesis and characterization (NMR, IR, elemental analysis and XRD) of fifteen new Pd(II) allyl complexes containing at least one N-heterocyclic carbene ligand.The synthesized compounds and others previously published by our research group, have been tested against the six tumor lines OVCAR5, A2780, A2780cis (ovarian cancer), DLD1 (colon cancer), A549 (lung cancer) and A375 (malignant melanoma).This comparative study, involving also complexes coordinating NS and NP heteroditopic ligands, shows that most of the tested compounds exhibit a much powerful antitumor activity than cisplatin on all tumor cell lines examined.In many cases, the antiproliferative activity on the A2780 (cisplatin-sensitive) and A2780cis (cisplatin-resistant) lines is comparable, suggesting a different mechanism of action of this class of molecules as compared to cisplatin and its derivatives.Moreover, a selected number of compounds among those reported are particularly promising since exhibit a markedly lower activity toward normal cells than to cancer cells.

Synthesis and characterization of Pd(II) complexes bearing NS, CS, SNS and SCS ligands. Evaluation of their microwave assisted catalytic activity in C[sbnd]C coupling reactions

A series of coordination (Pd-NS,Pd-SNS, Pd-SNS-O) and organometallic (Pd-C and Pd-SCS) Pd(II) complexes supported by bidentate and tridentate ligands featuring sulphur moieties have been prepared. All ligands and their palladium complexes were fully characterized by various analytical techniques, including the unequivocal determination of the solid-state structures of the ligand L-SNS-O and the Pd-CS and Pd-NS complexes by single crystal X-ray diffraction analysis. Complexes Pd-NS,Pd-SNS,Pd-CS,Pd-SCS containing thioether groups were used as efficient catalysts in microwave-assisted Suzuki-Miyaura and Mizoroki-Heck C–C cross-coupling reactions, showing the organometallic catalysts (Pd-CS, Pd-SCS) to produce the better conversions, most likely due to enhanced thermal stability provided by the Pd–C bonds.

Spectroscopic Characterisation of a Bio-Inspired Ni-Based Proton Reduction Catalyst Bearing a Pentadentate N2 S3 Ligand with Improved Photocatalytic Activity.

Inspired by the sulfur-rich environment found in active hydrogenase enzymes, a Ni-based proton reduction catalyst with pentadentate N2 S3 ligand was synthesised. When coupled with [Ru(bpy)3 ]2+ (bpy=2,2'-bipyridine) as photosensitiser and ascorbate as electron donor in a 1:1 mixture of dimethylacetamide and aqueous ascorbic acid/ascorbate buffer, the catalyst showed improved photocatalytic activity compared with a homologous counterpart bearing a tetradentate N2 S2 ligand. The mechanistic pathway of photoinduced hydrogen evolution was comprehensively analysed through optical transient absorption and time-resolved X-ray absorption spectroscopy, which revealed important electronic and structural changes in the catalytic system during photoirradiation. The NiII catalyst undergoes a photoinduced metal-centred reduction to form a NiI intermediate with distorted square-bipyramidal geometry. Further kinetic analyses revealed differences in charge-separation dynamics between the pentadentate and tetradentate forms.

Zn Complex of Diaminedithiol Tetradentate Ligand as a Stable Precursor for 99mTc-Labeled Compounds

The diaminedithiol (N2S2) tetradentate ligand constitutes a useful chelating molecule for preparing 99mTc-labeled compounds of high in vivo stability in high radiochemical yields. However, since the thiol groups in the N2S2 ligand are easy to be oxidized to disulfide bonds, they need to be protected with an appropriate protecting group, which hinders the broad applications of the N2S2 ligand for radiopharmaceuticals. In this study, a Zn chelate of N2S2 was evaluated as a precursor for purification-free 99mTc-labeled N2S2 under the mild and simple procedure. Zn-N2S2 was prepared by reacting Zn acetate with N2S2, and the Zn-N2S2 remained stable under aerobic conditions at room temperature. 99mTc-N2S2 was obtained over 90% radiochemical yields at room temperature by a one-pot reaction, consisting of Zn-N2S2 (10−5 M), 99mTcO4−, ethylenediaminetetraacetic acid (EDTA), and a reducing agent (Sn2+) at pH = 5.5 to 7.5. 99mTc-N2S2 was also obtained over 90% radiochemical yields when the reaction was conducted in the presence of an equimolar amount of IgG antibody. These findings indicate the Zn complex of N2S2 ligand constitutes a stable and useful precursor to prepare 99mTc-labeled N2S2 compounds in high yields under the mild and simple procedure.

Synthesis and physicochemical, DFT, thermal and DNA-binding analysis of a new pentadentate N3S2 Schiff base ligand and its [CuN3S2]2+ complexes.

A new N3S2 pentadentate Schiff base ligand derived from 5-bromothiophene-2-carbaldehyde, (E)-N1-((5-bromothiophen-2-yl)methylene)-N2-(2-((E)-((5-bromothiophen-2-yl)-methylene amino) ethyl ethane-1,2-diamine, is prepared. The ligand and its complexes are subjected to extensive physical and theoretical analyses and the results are consistent with their predicted compositions. Dicationic Cu(ii) complexes ([CuN3S2]X2) with a coordination number of 5 are proposed on the basis of the spectral data with N3S2 serving as a pentadentate ligand. The prepared complexes display a square pyramidal geometry around the Cu(ii) center. TG shows different thermal behavior for the N3S2 ligand and its complexes. Solvatochromism of the complexes is promoted by the polarity of the solvent used. A one-electron transfer Cu(ii)/Cu(i) reversible redox reaction is promoted by CV. SEM and EDS of the free ligand and its complexes support the morphology and composition changes observed upon the complexation of Cu(ii). As an outstanding goal to develop anticancer new metal chemotherapy, preliminary studies of the binding of the desired complexes with DNA were carried out, as it is through judging the strength of interactions that a future drug can be designed and synthesized. The viscosity and absorption results obtained for complex 1 indicated its enhanced CT-DNA binding properties as compared to those of complex 2 with Kb values of 3.2 × 105 and 2.5 × 105 M−1, respectively.

Connecting Main-Group Metals (Al, Ga, In) and Tungsten(0) Carbonyls via the N2S2 Metallo-Ligand Strategy

Tetradentate N2S2 ligands (such as bismercaptoethanediazacycloheptane in this study) have seen extensive use in combination with transition metals. Well-oriented N2S2 binding sites are ideal for d8 transition metals with square planar preferences, especially NiII, but also as a square pyramidal base for those metals with pentacoordinate preferences, such as [V≡O]2+, [Fe(NO)]2+, and [Co(NO)]2+. Further reactivity at the thiolate sulfurs generates diverse bi, tri, and tetra/heterometallic compounds. Few N2S2 ligands have been explored to investigate the possibility of binding to main group metals, especially group III (MIII) metals, and their utility as synthons for main group/transition metal bimetallic complexes. To open up this area of chemistry, we synthesized three new five-coordinate main group XMN2S2 complexes with methyl as the fifth binding ligand for M = Al, and chloride for M = Ga and In. The seven-membered diazacycle, dach, was engaged as a rigid stabilized connector between the terminal thiolate sulfurs. The pentacoordinate XMN2S2 complexes were characterized by 1H-NMR, 13C-NMR, +ESI-Mass spectra, and X-ray diffraction. Their stabilities and reactivities were probed by adding NiII sources and W(CO)5(THF). The former replaces the main group metals in all cases in the N2S2 coordination environment, demonstrating the weak coordinate bonds of MIII–N/S. The reaction of XMN2S2 (XM = ClGaIII or ClInIII) with the labile ligand W(0) complex W(CO)5(THF) resulted in Ga/In–W bimetallic complexes with a thiolate S-bridge. The synthesis of XMN2S2 complexes provide examples of MIII–S coordination, especially Al–S, which is relatively rare. The bimetallic Ga/In–S–W complex formation indicates that the nucleophilic ability of sulfur is retained in MIII–S–R, resulting in the ability of main group MIII–N2S2 complexes to serve as metalloligands.

Structural and Electronic Responses to the Three Redox Levels of Fe(NO)N2S2‐Fe(NO)2

The nitrosylated diiron complexes, Fe2 (NO)3 , of this study are interpreted as a mono-nitrosyl Fe(NO) unit, MNIU, within an N2 S2 ligand field that serves as a metallodithiolate ligand to a dinitrosyl iron unit, DNIU. The cationic Fe(NO)N2 S2 ⋅Fe(NO)2 + complex, 1+ , of Enemark-Feltham electronic notation {Fe(NO)}7 -{Fe(NO)2 }9 , is readily obtained via myriad synthetic routes, and shown to be spin coupled and diamagnetic. Its singly and doubly reduced forms, {Fe(NO)}7 -{Fe(NO)2 }10 , 10 , and {Fe(NO)}8 -{Fe(NO)2 }10 , 1- , were isolated and characterized. While structural parameters of the DNIU are largely unaffected by redox levels, the MNIU readily responds; the neutral, S= , complex, 10 , finds the extra electron density added into the DNIU affects the adjacent MNIU as seen by the decrease its Fe-N-O angle (from 171° to 149°). In contrast, addition of the second electron, now into the MNIU, returns the Fe-N-O angle to 171° in 1- . Compensating shifts in FeMNIU distances from the N2 S2 plane (from 0.518 to 0.551 to 0.851 Å) contribute to the stability of the bimetallic complex. These features are addressed by computational studies which indicate that the MNIU in 1- is a triplet-state {Fe(NO)}8 with strong spin polarization in the more linear FeNO unit. Magnetic susceptibility and parallel mode EPR results are consistent with the triplet state assignment.