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The uranyl complexes UO2(OAc)(L) and UO2Cl(L) of the redox-active, acyclic diamido–dipyrrin anion L– are reported and their redox properties explored. Because of the inert nature of the complexes toward hydrolysis and oxidation, synthesis of both the ligands and complexes was conducted under ambient conditions. Voltammetric, electron paramagnetic resonance spectroscopy, and density functional theory studies show that one-electron chemical reduction by the reagent CoCp2 leads to the formation of a dipyrrin radical for both complexes [Cp2Co][UO2(OAc)(L•)] and [Cp2Co][UO2Cl(L•)].

International audience; The uranyl complex UVIO2Cl(LMes) of the redox-active, acyclic dipyrrin–diimine anion LMes– [HLMes = 1,9-di-tert-butyl-imine-5-(mesityl)dipyrrin] is reported, and its redox property is explored and compared with that of the previously reported UVIO2Cl(LF) [HLF = 1,9-di-tert-butyl-imine-5-(pentafluorophenyl)dipyrrin] to understand the influence of the meso substituent. Cyclic voltammetry, electron paramagnetic resonance spectroscopy, and density functional theory studies show that the alteration from an electron-withdrawing meso substituent to an electron-donating meso substituent on the dipyrrin ligand significantly modifies the stability of the products formed after reduction. For UVIO2Cl(LMes), the formation of a diamond-shaped, oxo-bridged uranyl(V) dimer, [UVO2(LMes)]2 is seen, whereas in contrast, for UVIO2Cl(LF), only ligand reduction occurs. Computational modeling of these reactions shows that while ligand reduction followed by chloride dissociation occurs in both cases, ligand-to-metal electron transfer is favorable for UVIO2Cl(LMes) only, which subsequently facilitates uranyl(V) dimerization.

Metallodithiolene complexes of the type [(R

The oxidative dehydrogenation (ODH) of 1-butene to 1,3-butadiene was studied over a series of AFe2O4 catalysts, where A = Zn, Mn, Ni, Cu, Mg and Fe. The catalysts were characterised by XPS, EPR spectroscopy, BET surface area analysis, Raman spectroscopy and XRD. All the ferrites were active for ODH and gave an order of activity after 80 h on-stream of ZnFe2O4 > NiFe2O4 > MnFe2O4 > MgFe2O4 > CuFe2O4 > FeFe2O4. All catalysts lost significant surface area (up to ~ 80%) under reaction conditions of 0.75:1:15 oxygen:1-butene:steam with an overall GHSV of 10,050 h−1 at 693 K. Fe3O4 was unstable under reaction conditions and was converted to Fe2O3, which showed very low activity. Nickel ferrite was the only material that gave carbon dioxide as a significant product, all others were selective to 1,3-butadiene. Zinc ferrite gave a steady-state yield of 1,3-butadiene of ~ 80%. Inversion parameters were determined for the ferrites from XPS and a correlation was obtained between 1,3-butadiene yield and inversion parameter, indicating that Fe3+ in an octahedral hole is a key species in the mechanism of oxidative dehydrogenation. Butene isomerisation and ODH were shown to occur on different sites.

The enhancement of reactivity inside supramolecular coordination cages has many analogies to the mode of action of enzymes, and continues to inspire the design of new catalysts for a range of reactions. However, despite being a near-ubiquitous class of reactions in organic chemistry, enhancement of the reduction of carbonyls to their corresponding alcohols remains very much underexplored in supramolecular coordination cages. Herein, we show that encapsulation of small aromatic aldehydes inside a supramolecular coordination cage allows the reduction of these aldehydes with the mild reducing agent sodium cyanoborohydride to proceed with high selectivity (ketones and esters are not reduced) and in good yields. In the absence of the cage, low pH conditions are essential for any appreciable conversion of the aldehydes to the alcohols. In contrast, the specific microenvironment inside the cage allows this reaction to proceed in bulk solution that is pH-neutral, or even basic. We propose that the cage acts to stabilise the protonated oxocarbenium ion reaction intermediates (enhancing aldehyde reactivity) whilst simultaneously favouring the encapsulation and reduction of smaller aldehydes (which fit more easily inside the cage). Such dual action (enhancement of reactivity and size-selectivity) is reminiscent of the mode of operation of natural enzymes and highlights the tremendous promise of cage architectures as selective catalysts., Herein, we use a supramolecular coordination cage as a catalyst for the reduction of aldehydes to the corresponding alcohols using a weak hydride donor in neutral water, with a mode of action reminiscent of natural enzymes.

We report the experimental and computational investigations of the reactions of aryl and vinyl triflates with a model nickel(0) complex. Oxidative addition rates decrease in the order naphthyl > vinyl > phenyl, although 4-acetylphenyl triflate reacts most quickly due to favourable ketone coordination. Two possible reaction mechanisms are explored using DFT calculations.

Spectroscopic and computational examination of the neutral tris-dioxolene complex [V(dbcat)(3)] (dbcat(2−) = 3,6-di-tert-butylcatecholate) reveals a Class III mixed-valent ground state. The radical is stabilised by delocalisation across the ligands mediated by the energy matched d orbital manifold of the V(V) centre. This electronic structure is compared to the tris-dithiolene and tris-diimine analogues that possess V(IV) and V(II) ions, respectively.

Naphthalene diimides can have electrochromic applications due to their highly stable dark reduced state along with a transparent colourless neutral state. We show here that the colouration and reversibility of water-dispersible amino acid appended NDIs are directly influenced by the aggregated state present at different pH using spectroelectrochemistry, small angle neutron scattering (SANS) and cyclic voltammetry (CV). We find the aggregation itself is influenced by both pH and the amino acid or dipeptide in the structure, with each NDI having a preferred morphology giving rise to a more intensely coloured state.

The use of a sodium in sodium chloride dispersion is systematically evaluated for the synthesis of nickel(0) and nickel(I) complexes from readily-prepared nickel(II) precursors. A variety of complexes with phosphine and bipyridine-type ligands were accessed, although some reactions were found to produce mixtures of nickel(0) and nickel(I), and yields were highly variable. Several new nickel(I) complexes were obtained, and these were characterised using techniques including NMR spectroscopy, EPR spectroscopy, and single crystal X-ray diffraction analysis.

Understanding magnetic anisotropy and specifically how to tailor it is crucial in the search for high-temperature single-ion magnets. Herein, we investigate the magnetic anisotropy in a six-coordinated cobalt(II) compound that has a complex geometry and distinct triaxial magnetic anisotropy from the perspective of the electronic structure, using electronic spectra, ab initio calculations, and an experimental charge density, of which the latter two provides insight into the d-orbital splitting. The analysis showed that the d-orbital splitting satisfactorily predicted the complex triaxial magnetic anisotropy exhibited by the compound. Furthermore, a novel method to directly compare the ab initio results and the d-orbital populations obtained from the experimental charge density was developed, while a topological analysis of the density provided insights into the metal-ligand bonding. This work thus further establishes the validity of using d-orbitals for predicting magnetic anisotropy in transition metal compounds while also pointing out the need for a more frequent usage of the term triaxial anisotropy in the field of single-molecule magnetism.

The mechanism of the reactions between dppf-Ni0 complexes and alkyl halides has been investigated using kinetic and mechanistic experiments and DFT calculations. The active species is [Ni(κ2-dppf)(κ1-dppf)], which undergoes a halide abstraction reaction with alkyl halides and rapidly captures the alkyl radical that is formed. The rates of the reactions of [Ni(COD)(dppf)] with alkyl halides and the yields of prototypical nickel-catalyzed Kumada cross-coupling reactions of alkyl halides are shown to be significantly improved by the addition of free dppf ligand.

The reaction of [(Ph2C2S2)2M] (M = Ni2+, Pd2+, Pt2+) with 2 equiv of RN≡C (R = Me (a), Bn (b), Cy (c), tBu (d), 1-Ad (e), Ph (f)) yields [(Ph2C2S2)M(C≡NR)2] (M = Ni2+, 4a–f; M = Pd2+, 5a–f; M = Pt2+, 6a–f), which are air-stable and amenable to chromatographic purification. All members have been characterized crystallographically. Structurally, progressively greater planarity tends to be manifested as M varies from Ni to Pt, and a modest decrease in the C≡N bond length of coordinated C≡NR appears in moving from Ni toward Pt. Vibrational spectroscopy (CH2Cl2 solution) reveals νC≡N frequencies for [(Ph2C2S2)M(C≡NR)2] that are substantially higher than those for free C≡NR and increase as M ranges from Ni to Pt. This trend is interpreted as arising from an increasingly positive charge at M that stabilizes the linear, charge-separated resonance form of the ligand over the bent form with lowered C–N bond order. UV–vis spectra reveal lowest energy transitions that are assigned as HOMO (dithiolene π) → LUMO (M–L σ*) excitations. One-electron oxidations of [(Ph2C2S2)M(C≡NR)2] are observed at ∼+0.5 V due to Ph2C2S22– → Ph2C2S–S• + e–. Chemical oxidation of [(Ph2C2S2)Pt(C≡NtBu)2] with [(Br-p-C6H4)3N][SbCl6] yields [(Ph2C2S–S•)Pt(C≡NtBu)2]+, identified spectroscopically, but in the crystalline state [[(Ph2C2S–S•)Pt(C≡NtBu)2]2]2+ prevails, which forms via axial Pt···S interactions and pyramidalization at the metal. Complete substitution of MeNC from [(Ph2C2S2)Ni(C≡NMe)2] by 2,6-Me2py under forcing conditions yields [(2,6-Me2py)Ni(μ2-η1,η1-S′,η1-S″-S2C2Ph2)]2 (8), which features a folded Ni2S2 core. In most cases, isocyanide substitution from [(Ph2C2S2)M(C≡NMe)2] with monodentate ligands (L = phosphine, CN–, carbene) leads to [(Ph2C2S2)M(L)(C≡NMe)]n (n = 0, 1−), wherein νC≡N varies according to the relative σ-donating power of L (9–21). The use of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) provides [(Ph2C2S2)M(IPr)(C≡NMe)] for M = Ni (18), Pd (19), but for Pt, attack by IPr at the isocyanide carbon occurs to yield the unusual η1,κC-ketenimine complex [(Ph2C2S2)Pt(C(NMe)(IPr))(C≡NMe)] (20).

The ground state electronic structures of [FeIIIX(LISQ)2]0 where X is a halide (F−, Cl−, Br−, I−) or pseudo‐halide (N3−, NCS−) and (LISQ)1− is the o ‐iminobenzosemiquinonato π‐radical ligand, have been calculated using DFT at the B3LYP* level of theory. The modified functional with 15% Hartree‐Fock exchange is required to successfully reproduce the spin ground state of the complex as either S =3/2 for X=F−, Cl− and NCS−, or S =1/2 for X=Br−, I− and N3−. The difference in ground state stems from an S Fe=5/2→S Fe=3/2 spin transition at the iron ion, prompted by the donor properties of the apical ligand. The computational methodology was validated through accurate calculation of the Mössbauer parameters. The redox chemistry of the o ‐aminophenolate ligand was examined for the putative five‐membered electron transfer series for [FeIIIF(LISQ)2]z and [FeIIII(LISQ)2]z (z =2+1+, 0, 1−, 2−). The redox chemistry is entirely ligand‐centered with retention of the ferric ion, where only the strong ligand field provided by a fully reduced o ‐anilinophenolate(2−) ligand in conjunction with a soft apical donor will support an intermediate‐spin Fe(III) central ion.

The chiral dicobalt(ii) complex [CoII2(μ2-L)2] (1) (H2L = N2,N6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide) and its tert-butyl analogue [CoII2(μ2-LBu)2] (2) were synthesized and structurally characterized. Addition of one equivalent of AgSbF6 to the dichloromethane solution of 1 and 2 resulted in the isolation of the mixed-valent dicobalt(iii,ii) species [CoIIICoII(μ2-L)2]SbF6 (3) and [CoIIICoII(μ2-LBu)2]SbF6 (4). Homovalent 1 and 2 exhibited catalytic activity towards proton reduction in the presence of acetic acid (AcOH) as the substrate. The complexes are stable in solution while their catalytic turnover frequency is estimated at 10 and 34.6 h-1 molcat-1 for 1 and 2, respectively. Calculations reveal one-electron reduction of 1 is ligand-based, preserving the dicobalt(ii) core and activating the ligand toward protonation at the quinoline group. This creates a vacant coordination site that is subsequently protonated to generate the catalytically ubiquitous Co(iii) hydride. The dinuclear structure persists throughout where the distal Co(ii) ion modulates the reactivity of the adjacent metal site by promoting ligand redox activity through spin state switching.

Previously, we reported the synthesis of Ti[N(o-(NCH2P(iPr)2)C6H4)3] and the Fe–Ti complex, FeTi[N(o-(NCH2P(iPr)2)C6H4)3], abbreviated as TiL (1), and FeTiL (2), respectively. Herein, we describe the synthesis and characterization of the complete redox families of the monometallic Ti and Fe–Ti compounds. Cyclic voltammetry studies on FeTiL reveal both reduction and oxidation processes at −2.16 and −1.36 V (versus Fc/Fc+), respectively. Two isostructural redox members, [FeTiL]+ and [FeTiL]− (2ox and 2red, respectively) were synthesized and characterized, along with BrFeTiL (2-Br) and the monometallic [TiL]+ complex (1ox). The solid-state structures of the [FeTiL]+/0/– series feature short metal–metal bonds, ranging from 1.94–2.38 Å, which are all shorter than the sum of the Ti and Fe single-bond metallic radii (cf. 2.49 Å). To elucidate the bonding and electronic structures, the complexes were characterized with a host of spectroscopic methods, including NMR, EPR, and 57Fe Mössbauer, as well as Ti and Fe K-edge X-ray absorption spectroscopy (XAS). These studies, along with hybrid density functional theory (DFT) and time-dependent DFT calculations, suggest that the redox processes in the isostructural [FeTiL]+,0,– series are primarily Fe-based and that the polarized Fe–Ti π-bonds play a role in delocalizing some of the additional electron density from Fe to Ti (net 13%)., An isostructural redox series of Fe≡Ti complexes was investigated using a combination of spectroscopic methods and density functional theory to elucidate their electronic structures and to understand their polarized metal−metal bonding. Overall, the results support that the redox changes occur primarily at the Fe site though some electron density is delocalized to Ti. Hence, the Ti plays an important role in enhancing the redox flexibility of the single Fe site.

A series of six-coordinate [Cu(L)L1][BF4]2 (L1 = 2,6-bis{1-oxyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-2-yl}pyridine) complexes are reported. Ferromagnetic coupling between the Cu and L1 ligand spins is enhanced by an L coligand with distal methyl substituents, which is attributed to a sterically induced suppression of its Jahn–Teller distortion.

The mechanism of the reactions between dppf-Ni0 complexes and alkyl halides has been investigated using kinetic and mechanistic experiments and DFT calculations. The active species is [Ni(dppf)2], which undergoes a halide abstraction reaction with alkyl halides and rapidly captures the alkyl radical that is formed. The yields in prototypical nickel-catalysed Kumada cross-coupling reactions are shown to be improved by the addition of free phosphine ligands

Optical properties of low-temperature pulsed DC-sputter deposited ( ≤ 70 ° C ) hydrogenated carbon are presented. Increasing hydrogen incorporation into the sputter deposited carbon significantly decreases infrared optical absorption due to a decrease in deep absorptive states associated with dangling bonds. Hydrogen flow is optimized (hydrogen flow 3 sccm), achieving the best compromise between increased infrared transmittance and hardness for durable coating performance. Optical, environmental, and durability performance of pulsed DC-sputtered carbon incorporated in multilayer (a-C:H/Ge) infrared antireflective coatings indicates suitability as a durable infrared optical coating for commonly used infrared substrates, including temperature sensitive chalcogenide glass.

The introduction of (N2)3–• radicals into multinuclear lanthanide molecular magnets raised hysteresis temperatures by stimulating strong exchange coupling between spin centers. Radical ligands with larger donor atoms could promote more efficient magnetic coupling between lanthanides to provide superior magnetic properties. Here, we show that heavy chalcogens (S, Se, Te) are primed to fulfill these criteria. The moderately reducing Sm(II) complex, [Sm(N††)2], where N†† is the bulky bis(triisopropylsilyl)amide ligand, can be oxidized (i) by diphenyldichalcogenides E2Ph2 (E = S, Se, Te) to form the mononuclear series [Sm(N††)2(EPh)] (E = S, 1-S; Se, 1-Se, Te, 1-Te); (ii) S8 or Se8 to give dinuclear [{Sm(N††)2}2(μ-η2:η2-E2)] (E = S, 2-S2; Se, 2-Se2); or (iii) with Te=PEt3 to yield [{Sm(N††)2}(μ-Te)] (3). These complexes have been characterized by single crystal X-ray diffraction, multinuclear NMR, FTIR, and electronic spectroscopy; the steric bulk of N†† dictates the formation of mononuclear complexes with chalcogenate ligands and dinuclear species with the chalcogenides. The Lα1 fluorescence-detected X-ray absorption spectra at the Sm L3-edge yielded resolved pre-edge and white-line peaks for 1-S and 2-E2, which served to calibrate our computational protocol in the successful reproduction of the spectral features. This method was employed to elucidate the ground state electronic structures for proposed oxidized and reduced variants of 2-E2. Reactivity is ligand-based, forming species with bridging superchalcogenide (E2)−• and subchalcogenide (E2)3–• radical ligands. The extraordinarily large exchange couplings provided by these dichalcogenide radicals reveal their suitability as potential successors to the benchmark (N2)3–• complexes in molecular magnets., A spectroscopically verified computational study reveals the potential for giant exchange couplings using bridging dichalcogenide σ- and π-radicals as the ideal successors to dinitrogen radicals in lanthanide molecular magnets.

We present a series of monometallic ([Cu(Mabiq)OTf] (1) and [Cu(Mabiq)] (2)) and bimetallic copper-Mabiq complexes ([Cu2(Mabiq)(PPh3)2(OTf)2] (3) and [Cu2(Mabiq)(PPh3)2]PF6 (4)). The latter compounds contain an additional CuI center that binds in a tetrahedral fashion to the external bipyrimidine nitrogens of the macrocyclic ligand. Compounds 3 and 4 represent the first examples of bimetallic transition metal Mabiq complexes, stable both in solution and in the solid state. The structural and electronic properties of compounds 1-4 were analyzed by means of X-ray crystallography, cyclic voltammetry, and spectroscopic methods. One-electron reduced 2 and 4 consist of a CuII ion coordinated by a Mabiq ligand radical, [CuII(Mabiq•)]. Thus, both bimetallic compounds are mixed-valent with respect to the copper oxidation states. Complexes 2 and 4 can be generated photochemically, upon irradiation of 1 or 3 with visible light in the presence of a sacrificial electron donor.

Two dinuclear copper(II) complexes, [Cu2(L)2(μ1,1-NCO)2] (1) and [Cu2(L)2(μ1,3-NCS)2]·H2O·DMF (2), have been synthesized using a tridentate N2O donor Schiff base ligand (HL), [1((2-(ethylamino)ethylimino)methyl)naphthalen-2-ol], and characterized by elemental analysis, spectral study and X-ray crystallography. Both complexes are centrosymmetric dimers in which square pyramidal copper(II) centres are connected by pseudo-halides: end-on cyanate in 1 and end-to-end (EE) thiocyanate in 2. Variable temperature (2–300 K) magnetic susceptibility measurements indicate the presence of ferromagnetic exchange coupling between copper(II) centres in complex 1 (J = 0.97 cm−1), and antiferromagnetic exchange coupling in 2 (J = −0.6 cm−1).

Reduction of 1,10-phenanthroline-5,6-dione (pd) with CoCpR2 resulted in the first molecular compounds of the pd˙- semi-quinone radical anion, [CoCpR2]+[pd]˙- (R = H, (1); R = Me4, (2)). Furthermore compounds 1 and 2 were reacted with [Y(hfac)3(thf)2] (hfac = 1,1,1-5,5,5-hexafluoroacetylacetonate) to synthesise the rare earth-transition metal heterometallic compounds, [CoCpR2]+[Y(hfac)3(N,N'-pd)]˙- (R = H, (3); R = Me4, (4)).

Three elongated (4+1) square pyramidal copper(II) complexes, [Cu2(L)2(μ1,1-N3)2]·H2O (1), [Cu2(L)2(μ1,1-NCO)2] (2) and [Cu(L)(μ1,5-dca)]n (3) [HL = 1((2-(methylamino)ethylimino)methyl)naphthalen-2-ol and dca = dicyanamide], have been synthesized using a tridentate N2O donor Schiff base ligand (HL) and characterized. Complexes 1 and 2 are centrosymmetric dimers in which copper(II) centres are connected by asymmetric double end on pseudohalide bridges. Complex 3 features a 1D zigzag chain in which copper(II) centres are connected by end to end dca bridges. Variable temperature (2–300 K) magnetic susceptibility measurements indicate the presence of antiferromagnetic exchange coupling between copper(II) centres in complexes 1 (J = −2.313 cm−1) and 3 (J = −0.344 cm−1), whereas complex 2 shows ferromagnetic exchange coupling between copper(II) centres (J = 0.513 cm−1). DFT calculations also corroborate the data. The fluid solution EPR spectra recorded at 293 K are typical of copper(II) species. Significant supramolecular interactions are explored using high level DFT calculations (BP86-D3/def2-TZVP) and characterized by Bader’s theory of “atoms-in-molecules”.

Bimetallic complexes of the transition metals containing mixed diimine and dithiolate ligands are of fundamental interest on account of their intriguing electronic properties. Almost always, such complexes are isolated as species in which both the metal centers are in identical coordination environments - this means that the two metals often have identical redox properties. In contrast, mixed-diimine/dithiolate bimetallic complexes of the first row transition metals where the two metals are in dissimilar coordination environments are exceedingly rare, and are only known for nickel. Herein, we report the first ever example of a mixed-diimine/dithiolate dicobalt complex where the two cobalt centers are in different coordination environments. The synthesis of this compound is straightforward, and produces a complex in which the two cobalt centers display very different redox properties.

The scope of direct substitution of the dithiolene ligand from [M(S2C2Ph2)2] [M = Ni2+ (1), Pd2+ (2), Pt2+ (3)] to produce heteroleptic species [M(S2C2Ph2)2Ln] (n = 1, 2) has been broadened to include isonitriles and dithiooxamides in addition to phosphines and diimines. Collective observations regarding ligands that cleanly produce [M(S2C2Ph2)Ln], do not react at all, or lead to ill-defined decomposition identify soft σ donors as the ligand type capable of dithiolene substitution. Substitution of MeNC from [Ni(S2C2Ph2)(CNMe)2] by L provides access to a variety of heteroleptic dithiolene complexes not accessible from 1. Substitution of a dithiolene ligand from 1 involves net redox disproportionation of the ligands from radical monoanions, –S•SC2Ph2, to enedithiolate and dithione, the latter of which is an enhanced leaving group that is subject to further irreversible reactions.

The synthesis, metalation, and redox properties of an acyclic bis(iminothienyl)methene L− are presented. This π-conjugated anion displays pronounced redox activity, undergoing facile one-electron oxidation to the acyclic, metal-free, neutral radical L* on reaction with FeBr2. In contrast, reaction of L− with CuI forms the unique, neutral Cu2I2(L*) complex of a ligand-centered radical, whereas reaction with the stronger oxidant AgBF4 forms the metal-free radical dication L*2+.

Resumen del trabajo presentado a la X International School on Organometallic Chemistry “Marcial Moreno Mañas”, celebrada en Ciudad Real (España) del 5 al 7 de julio de 2017., The interest in nickel complexes which are able to achieve cross-coupling reactions is increasing in recent years due to their potential as an alternative to more expensive palladium catalysts. In spite of this, there are relatively few mechanistic studies of Ni based precatalysts, and it is often assumed that the reactivity of nickel systems is similar to that of their palladium analogues. This fact makes improvements in the design of new systems more challenging. In this context, we have explored the rates at which a relevant Ni0 complex ((dppf)Ni(cod) (cod = 1,5-cyclooctadiene; dppf = 1,1´-bis (diphenylphosphino)ferrocene) undergoes oxidative addition with different electrophiles, and the selectivity of these oxidative addition reactions. In addition, we have studied the interaction of this nickel fragment with several functional groups that are present in synthetic chemistry targets. Together, this is allowing us to build a quantitative picture of the processes that take place in nickelcatalysed reactions.

We present a formally zero-valent compound, [Co(Mabiq)Na(OEt2)]2 (1). The complex was characterized by crystallographic, spectroscopic and DFT computational methods. The electronic structure is described as a CoII–(ligand-biradical). Compound 1 is reactive toward proton sources; CoI or CoII products result, depending on the source of protons used. The redox non-innocence of the Mabiq ligand, which accepts both protons and electrons, has important ramifications for reactivity.

An alternative synthetic route for the design of N,N′-diquaternised-3,3′-biquinoxalinium “biquinoxen” dications is reported, involving oxidative radical coupling of dithionite reduced quinoxaline quaternary salts. Although the reaction is not regioselective, leading to relatively modest yields (up to 32%), the advantages of this new synthetic protocol lie in a simple potentially gram scale synthesis using inexpensive easily accessible reagents with no metal catalysts and no purification steps. Thus whereas the method reported previously to access the N,N′-dimethyl-3,3′-biquinoxalinium, “methylbiquinoxen” precursor gave higher yield than the new method reported here, this new method avoids the limitation of using scarce oxonium reagents. Overall, the new protocol is a robust synthetic strategy which offers new design possibilities.

The catecholate groups in [{Pt(L)} 3 (μ 3 -tctq)] (H 6 tctq = 2,3,6,7,10,11-hexahydroxy-4b,8b,12b,12d-tetramethyltribenzotriquinacene; L = a diphosphine chelate) undergo sequential oxidation to their semiquinonate forms by voltammetry, with ΔE 1/2 = 160-170 mV. The monoradical [{Pt(dppb)} 3 (μ 3 -tctq)] + is valence-localised, with no evidence for intervalence charge transfer in its near-IR spectrum. This contrasts with previously reported [{Pt(dppb)} 3 (μ 3 -ctc)] + (H 6 ctc = cyclotricatechylene), based on the same macrocyclic tris-dioxolene scaffold, which exhibits partly delocalised (class II) mixed valency.

Reaction of the cyclic ligand (2Z,6Z)-piperidine-2,6-dione dioxime with TiCl4 and KOH yielded the hexanuclear cluster K6[TiIV6(μ3-O)2(μ2-O)3(CH3O)6(μ2-η1,η1,η2-Hpidiox-O,N,O')4(μ2-η1,η1,η2-pidiox-O,N,O')2]·7.5CH3OH possessing a new {Ti6O5} structural motif. The cluster core {Ti6O5} is wrapped by external tripodal imide dioxime ligands, showing good solubility and stability and thus, allowing its solution to be studied by means of electrospray ionization mass spectrometry, electrochemistry and 2D NMR, c. w. EPR and UV-vis spectroscopies. Density Functional Theory (DFT) calculations reveal that the cyclo-Ti3 metallic cores exhibit metallaromaticity which is expected to contribute to the stabilization of this system.

An organic radical attached to gold represents an electrically addressable prototype electron spin qubit with an impressively long coherence lifetime., A bis(dithiolene)gold complex is presented as a model for an organic molecular electron spin qubit attached to a metallic surface that acts as a conduit to electrically address the qubit. A two-membered electron transfer series is developed of the formula [AuIII(adt)2]1–/0, where adt is a redox-active dithiolene ligand that is sequentially oxidized as the series is traversed while the central metal ion remains AuIII and steadfastly square planar. One-electron oxidation of diamagnetic [AuIII(adt)2]1– (1) produces an S = 1/2 charge-neutral complex, [AuIII(adt23–˙)] (2) which is spectroscopically and theoretically characterized with a near negligible Au contribution to the ground state. A phase memory time (TM) of 21 μs is recorded in 4 : 1 CS2/CCl4 at 10 K, which is the longest ever reported for a coordination complex possessing a third-row transition metal ion. With increasing temperature, TM dramatically decreases becoming unmeasurable above 80 K as a consequence of the diminishing spin-lattice (T1) relaxation time fueled by spin–orbit coupling. These relaxation times are 1–2 orders of magnitude shorter for the solid dilution of 2 in isoelectronic [Ni(adt)2] because this material is a molecular semiconductor. Although the conducting properties of this material provide efficient pathways to dissipate the energy through the lattice, it can also be used to electrically address the paramagnetic dopant by tapping into the mild reduction potential to switch magnetism “on” and “off” in the gold complex without compromising the integrity of its structure. These results serve to highlight the need to consider all components of these spintronic assemblies.

Phase control in the self-assembly of metal-organic frameworks (MOFs) – materials wherein organic ligands connect metal ions or clusters into network solids with potential porosity – is often a case of trial and error. Judicious control over a number of synthetic variables is required to select for the desired topology and control features such as interpenetration and defectivity, which have significant impact on physical properties and application. Herein, we present a comprehensive investigation of self-assembly in the Fe-biphenyl-4,4'-dicarboxylate system, demonstrating that coordination modulation, the addition of competing ligands into solvothermal syntheses, can reliably tune between the kinetic product, non-interpenetrated MIL-88D(Fe), and the thermodynamic product, two-fold interpenetrated MIL-126(Fe). DFT simulations reveal that correlated disorder of the terminal anions on the metal clusters in the interpentrated phase results in H-bonding between adjacent nets and is the thermodynamic driving force for its formation. Coordination modulation slows self-assembly and therefore selects the thermodynamic product MIL-126(Fe), while offering fine control over defectivity, inducing mesoporosity, but electron microscopy shows the MIL-88D(Fe) phase persists in many samples despite not being evident in diffraction experiments, suggesting its presence accounts for the lower than predicted surface areas reported for samples to date. Interpenetration control is also demonstrated by utilizing the 2,2'-bipyridine-5,5'-dicarboxylate linker; DFT simulations show that it is energetically prohibitive for it to adopt the twisted conformation required to form the interpenetrated phase, and are confirmed by experimental data, although multiple alternative phases are identified due to additional coordination of the Fe cations to the N-donors of the ligand. Finally, we introduce oxidation modulation – the concept of using metal precursors in a different oxidation state to that found in the final MOF – as a further protocol to kinetically control self-assembly. Combining coordination and oxidation modulation allows the synthesis of pristine MIL-126(Fe) with BET surface areas close to the predicted maximum capacity for the first time, suggesting that combining the two may be a powerful methodology for the controlled self-assembly of high-valent MOFs.

Complexes of Co(III) containing mixed chelating diimine and o-quinone ligand sets are of fundamental interest on account of their fascinating magnetic and electronic properties. Whilst complexes of this type containing one diimine and two o-quinone ligands have been studied extensively, those with the reverse stoichiometry (two diimines and one o-quinone) are much rarer. Herein, we describe a ready route to the synthesis of the complex [CoIII(o-catecholate) (2,2′-bipyridine)2]+ (1), and also report the synthesis of [CoIII(o-catecholate)(5,5′-dimethyl-2,2′-bipyridine)2]+ (2) and [CoIII(o-benezenedithiolate)(5,5′-dimethyl-2,2′-bipyridine)2]+ (3) for the first time. Spectroscopic studies show that complex 2 displays intriguing solvatochromic behaviour as a function of solvent hydrogen bond donation ability, a property of this type of complex which has hitherto not been reported. Time-dependent density function theory (TD-DFT) shows that this effect arises as a result of hydrogen bonding between the solvent and the oxygen atoms of the catecholate ligand. In contrast, the sulfur atoms in the benzenedithiolate analogue 3 are much weaker acceptors of hydrogen bonds from the solvent, meaning that complex 3 is only very weakly solvatochromic. Finally, we show that complex 2 has some potential as a molecular probe that can report on the composition of mixed solvent systems as a function of its absorbance spectrum.

It is shown that control of the degree of coking can lead to the observation of hyperfine structures in the carbonaceous residues deposited from methanol over mordenite (H-MOR) at temperatures relevant to the conversion of methanol to hydrocarbons. EPR measurements of the catalyst samples at various times on stream have been recorded, with a rich hyperfine splitting pattern observed in the early stages of the reaction. Interpretation of the EPR data with the aid of density functional theoretical calculations has afforded the first definitive assignment of the radical cations formed in high temperature coke. The results detail a shortlist of six species: 2,3/2,6/2,7-dimethylnaphthalenium, 2,3,6-trimethylnaphthalenium, 2,3,6,7-tetramethylnaphthalenium, and anthracenium radical cations whose proton hyperfine splitting profiles match the experimental spectra; 2,3,6,7-tetramethylnaphthalenium showed the best agreement. The observation of these particular isomers of polymethylnaphthalene suggest the formation of more highly branched polyaromatic species is less likely within the confines of the H-MOR 12-membered ring channel. These radicals formed when the catalyst is active may constitute key intermediates in the conversion of methanol to light olefins.

The intrinsic redox activity of the dithiolene ligand is presented here as the novel spin host in the design of a prototype molecular electron spin qubit, where the traditional roles of the metal and ligand components in coordination complexes are inverted. A series of paramagnetic bis(dithiolene) complexes with group 10 metals—nickel, palladium, platinum—provides a backdrop to investigate the spin dynamics of the organic ligand radical using pulsed EPR spectroscopy. The temperature dependence of the phase memory time (TM) is shown to be dependent on the identity of the diamagnetic metal ion, with the short times recorded for platinum a consequence of a diminishing spin‐lattice (T1) relaxation time driven by spin‐orbit coupling. The utility of the radical ligand spin center is confirmed when it delivers one of the longest phase memory times ever recorded for a molecular two‐qubit prototype.

Smart windows in which the transmittance can be controlled on demand are a promising solution for the reduction of energy use in buildings. Windows are often the most energy inefficient part of a building, and so controlling the transmittance has the potential to significantly improve heating costs. Whilst numerous approaches exist, many suitable materials are costly to manufacture and process and so new materials could have a significant impact. Here we describe a gel-based device which is both photo- and electrochromic. The gel matrix is formed by the self-assembly of a naphthalene diimide. The radical anion of the naphthalene diimide can be formed photo or electrochemically, and leads to a desirable transition from transparent to black. The speed of response, low potential needed to generate the radical anion, cyclability of the system, temperature stability and low cost mean these devices may be suitable for applications in smart windows.

A recent Communication in this journal reported the stabilization of low-valent iron(I) in a fully oxidized polyoxovanadate. With no ligand-field argument to support such an assignment, a re-evaluation of the data accompanied by detailed computational analysis reveals the redox chemistry is localized to the polyoxovanadate, and when reduced, instigates a spin transition at iron.

The addition of various oxidants to the near-linear Sm(ii) complex [Sm(N††)2] (1), where N†† is the bulky bis(triisopropylsilyl)amide ligand {N(SiiPr3)2}, afforded a family of heteroleptic three-coordinate Sm(iii) halide complexes, [Sm(N††)2(X)] (X = F, 2-F; Cl, 2-Cl; Br, 2-Br; I, 2-I). In addition, the trinuclear cluster [{Sm(N††)}3(μ2-I)3(μ3-I)2] (3), which formally contains one Sm(ii) and two Sm(iii) centres, was isolated during the synthesis of 2-I. Complexes 2-X are remarkably stable towards ligand redistribution, which is often a facile process for heteroleptic complexes of smaller monodentate ligands in lanthanide chemistry, including the related bis(trimethylsilyl)amide {N(SiMe3)2} (N''). Complexes 2-X and 3 have been characterised by single crystal X-ray diffraction, elemental analysis, multinuclear NMR, FTIR and electronic spectroscopy. The Lα1 fluorescence-detected X-ray absorption spectra recorded at the Sm L3-edge for 2-X exhibited a resolved pre-edge peak defined as an envelope of quadrupole-allowed 2p → 4f transitions. The X-ray absorption spectral features were successfully reproduced using time-dependent density functional theoretical (TD-DFT) calculations that synergistically support the experimental observations as well as the theoretical model upon which the electronic structure and bonding in these lanthanide complexes is derived.

Noncovalent interactions of organic moieties with Lewis acidic alkali cations can greatly affect structure and reactivity. Herein, we describe the effects of interactions with alkali-metal cations within a series of reduced iron complexes bearing a redox-active formazanate ligand, in terms of structures, magnetism, spectroscopy, and reaction rates. In the absence of a crown ether to sequester the alkali cation, dimeric complexes are isolated wherein the formazanate has rearranged to form a five-membered metallacycle. The dissociation of these dimers is dependent on the binding mode and size of the alkali cation. In the dimers, the formazanate ligands are radical dianions, as shown by X-ray absorption spectroscopy, Mossbauer spectroscopy, and analysis of metrical parameters. These experimental measures are complemented by density functional theory calculations that show the spin density on the bridging ligands.

Furan and thiophene diarylmethenes are potential redox-active ligands for metal centers that could be exploited in the development of nontraditional, stoichiometric, and catalytic redox reactions. As such, we describe here the selective meso-deprotonations of dithiophene, difuran, and diimine-difuran diarylmethanes to form the π-conjugated anions, for which only the diimino-difuryl anion is truly isolable and studied by X-ray crystallography. In all cases, facile one-electron oxidation of these anions occurs, which allows the isolation of the neutral dithienyl and diimino-difuryl radicals. UV-Visible and time-dependent density functional theory studies reveal that the oxidation of the dithienyl anion to its radical is associated with an increase in the highest (singly) occupied molecular orbital-lowest unoccupied molecular orbital gap, evident through a hypsochromic shift of the main absorption band in the electronic spectrum, whereas oxidation of the diimino-difuryl anion causes only minor spectroscopic changes. Electrochemical studies support the stability of the radicals with respect to the anion, showing strongly negative oxidation potentials. The control of the redox activity of these diarylmethene carbanions through variation of the nature of the substituents, donor-atom, and the conjugated π-system and their potential as ligands for redox-inert metal centers makes them intriguing candidates as noninnocent partners for redox reactions.

Coordination of redox-active ligands to metals is a compelling strategy for making reduced complexes more accessible. In this work, we explore the use of redox-active formazanate ligands in low-coordinate iron chemistry. Reduction of an iron(II) precursor occurs at milder potentials than analogous non-redox-active β-diketiminate complexes, and the reduced three-coordinate formazanate-iron compound is characterized in detail. Structural, spectroscopic, and computational analysis show that the formazanate ligand undergoes reversible ligand-centered reduction to form a formazanate radical dianion in the reduced species. The less negative reduction potential of the reduced low-coordinate iron formazanate complex leads to distinctive reactivity with formation of a new N-I bond that is not seen with the β-diketiminate analogue. Thus, the storage of an electron on the supporting ligand changes the redox potential and enhances certain reactivity.

Multicomponent supramolecular gels have great potential for optoelectronics. Ideally, we could control the self-assembly of multiple components across many length scales, from the primary assembled structures to how these are arranged in space. This would allow energy transfer between p-type and n-type fibers to be controlled. Usually, a single network is formed and analyzed. It is not clear how most networks could be modified, and certainly not how these might be differentiated. Here, we address both of these issues. We show how the different components in a multicomponent gel can be differentiated by small-angle neutron scattering using contrast-matching experiments. The rate of self-assembly can be used to vary the networks that are formed, leading directly to changes in the efficiency of electron transfer. The assembly kinetics can therefore be used to prepare different networks from the same primary building blocks and primary self-assembled structures. We expect that these advances will allow multicomponent systems to become effective electronic materials.

We report a robust and modular synthetic route to heterometallic rare earth-transition metal complexes. We have used the redox-active bridging ligand 1,10-phenathroline-5,6-dione (pd), which has selective N,N′ or O,O′ binding sites as the template for this synthetic route. The coordination complexes [Ln(hfac)3(N,N’-pd)] (Ln = Y [1], Gd [2]; hfac = hexafluoroacetylacetonate) were synthesised in high yield. These complexes have been fully characterised using a range of spectroscopic techniques. Solid state molecular structures of 1 and 2 have been determined by X-ray crystallography and display different pd binding modes in coordinating and non-coordinating solvents. Complexes 1 and 2 are unusually highly coloured in coordinating solvents, for example the vis-NIR spectrum of 1 in acetonitrile displays an electronic transition centred at 587 nm with an extinction coefficient consistent with significant charge transfer. The reaction between 1 and 2 and VCp2 or VCpt2 (Cpt = tetramethylcyclopentadienyl) resulted in the isolation of the heterobimetallic complexes, [Ln(hfac)3(N,N′-O,O′-pd)VCp2] (Ln = Y [3], Gd [4]) or [Ln(hfac)3(N,N′-O,O′-pd)VCpt2] (Ln = Y [5], Gd [6]). The solid state molecular structures of 3, 5 and 6 have been determined by X-ray crystallography. The spectroscopic data on 3–6 are consistent with oxidation of V(II) to V(IV) and reduction of pd to pd2− in the heterobimetallic complexes. The spin-Hamiltonian parameters from low temperature X-band EPR spectroscopy of 3 and 5 describe a 2A1 ground state, with a V(IV) centre. DFT calculations on 3 are in good agreement with experimental data and confirm the SOMO as the dx2−y2 orbital localised on vanadium.

The influence of excess Fe3+ in ZnFe2O4 for the catalytic oxidative dehydrogenation of 1-butene to 1, 3-butadiene was investigated to try to clarify inconsistencies in the existing literature. A series of nanoscale zinc ferrite powders were produced with increasing Fe: Zn ratios. The materials were characterized by a range of techniques, which showed the presence of α-Fe2O3 as a distinct phase with an increasing excess of Fe3+ and SEM highlighted the increased presence of surface structures on the ferrites at higher Fe: Zn ratios. Reaction testing showed α-Fe2O3to be virtually inactive for the oxidative dehydrogenation of 1-butene. Results for the ferrite catalysts showed a significant decrease in both conversion and yield with an increasing excess of Fe3+. Therefore an excess of Fe3+ has a negative effect on catalytic activity and selectivity of zinc ferrite for the oxidative dehydrogenation of 1-butene, but acts as a promoter for competing hydrogenation and combustion side reactions.

This work was supported by the EPSRC (Grant No. EP/ K031732/1) and the Royal Society (University Research Fellowship UF150104 to M.D.S.). The data which underpin this work are available at http://dx.doi.org/10.5525/gla. researchdata.590 and are available under a CC-BY licence. The selective and efficient electrocatalytic reduction of nitrite to nitric oxide (NO) is of tremendous importance, both for the development of NO-release systems for biomedical applications and for the removal of nitrogen oxide pollutants from the environment. In nature, this transformation is mediated by (among others) enzymes known as the copper-containing nitrite reductases. The development of synthetic copper complexes that can reduce nitrite to NO has therefore attracted considerable interest. However, there are no studies describing the crucial role of proton-coupled electron transfer during nitrite reduction when such synthetic complexes are used. Herein, we describe the synthesis and characterization of two previously unreported Cu complexes ( 3 and 4 ) for the electrocatalytic reduction of nitrite to NO, in which the role of proton-relaying units in the secondary coordination sphere of the metal can be probed. Complex 4 bears a pendant carboxylate group in close proximity to the copper center, while complex 3 lacks such functionality. Our results suggest that complex 4 is twice as effective an electrocatalyst for nitrite reduction than is complex 3 and that complex 4 is the best copper-based molecular electrocatalyst for this reaction yet discovered. The differences in reactivity between 3 and 4 are probed using a range of electrochemical, spectroscopic, and computational methods, which shed light on the possible catalytic mechanism of 4 and implicate the proton-relaying ability of its pendant carboxylate group in the enhanced reactivity that this complex displays. These results highlight the critical role of proton-coupled electron transfer in the reduction of nitrite to NO and have important implications for the design of biomimetic catalysts for the selective interconversions of the nitrogen oxides. Publisher PDF