Two-electron Oxidation Wave Research Articles

A triradical-containing trinuclear Pd(II) complex: spin-polarized electronic transmission, analog resistive switching and neuromorphic advancements.

Neuromorphic computation has emerged as a potential alternative to subvert the von Neumann bottleneck issue in conventional computing. In this context, the development of resistive switching-based memristor devices mimicking various synaptic functionalities has engendered paramount attention. Here, we report a triradical-containing trinuclear Pd(II) cluster with a cyclohexane-like framework constituted by the Pd-Se coordination motif displaying facile memristor property with neuromorphic functionality as a thin-film device. The metal-ligand complex (complex 1) possessed an St = 1/2 ground state by experiencing a spin-frustrated-type magnetic coupling phenomenon amongst the three ligand-based organic radicals (SR = 1/2), coordinated to the Pd(II) ions. Three reversible one-electron reduction waves countered with a one-electron and one two-electron reversible oxidation waves were noticed in the cyclic voltammogram of the complex, confirming electrons accepting and releasing capacity of the complex at low potentials, i.e., within +0.2 V to -1.1 V. Employing the radical-containing complex 1 as the active thin-film sandwiched between two orthogonal electrodes, resistive switching based memristor property with biological synaptic actions were successfully emulated. Intriguingly, the artificial neural network (ANN) simulated efficient pattern recognition demonstrated using the recorded potentiation and depression curves from the device, which is a step ahead for the hardware realization of neuromorphic computing. The performance of the ANN on MNIST data with reduced image resolution has further been evaluated. Density functional theory (DFT)-based theoretical calculation predicted that the spin-polarized electronic transmission substantiated the memristive property in the neutral complex 1.

Synthesis, Structure and Properties of Donor-acceptor-type [4]Dendralenes

[4]Dendralene and its analogs possessing both strongly electron-donating 1,3-dithiol-2-ylidenes and electron-accepting dicyanomethylidenes (2b–4b) were successfully synthesized. X-ray structure analysis revealed that 2b adopts a nonplanar structure, in which half units of 2b are significantly inclined to each other. Cyclic voltammograms of 2b–4b consisted of one pair of two-electron oxidation waves and one pair of one-electron reduction waves.

Binuclear complexes of Pt(II) with platinated 2-phenylbenzothiazole and bridged derivatives of pyridin- and benzothiazol-2-thiols

Binuclear complexes of Pt(II) cycloplatinated with 2-phenylbenzothiazole and bridging ligands have been shown to contain the Pt-Pt bond. The complexes have been studied by X-ray diffraction, 1H NMR and electronic absorption spectroscopy, and electrochemical methods. The complexes cis-N(bt),S-isomers with antisymmetric positions of the cyclometalated and the bridging ligands have been detected in the crystals as well as in the solutions. The low-wavelength absorption and luminescence of the complexes have been assigned to the metal-metal-ligand charge transfer. The two-electron oxidation and reduction waves in the voltamperograms are associated with the metal- and the ligand-centered processes, respectively.

Apically linked iron(ii) α-dioximate and α-oximehydrazonate bis-clathrochelates: synthesis, structure and electrocatalytic properties

Iron(II) α-oximehydrazonate and α-dioximate bis-clathrochelates with apical hydrocarbon linkers were obtained by template condensation on an iron(II) ion followed by H(+)-catalyzed macrobicyclization of the bis-semiclathrochelate precursor with formaldehyde and triethyl orthoformate, and by transmetallation of the triethylantimony-containing clathrochelate precursor with diboron-containing bifunctional Lewis acids, respectively. The geometry of the para-phenylenediboron-capped iron(II) bis-clathrochelate studied by single-crystal X-ray diffraction is intermediate between a trigonal prism and a trigonal antiprism with a distortion angle of 20.4°; the rigidity of its C6H4 linker results in the presence of the expected three-fold pseudo-rotational B···Fe···B···B···Fe···B axis and a staggered conformation of the cyclohexane-containing chelate moieties. The cyclic voltammograms (CVs) for the oximehydrazonate bis-clathrochelates contain single one-electron (for each metallocentre, and therefore, two electrons per molecule) quasi-reversible reduction waves assigned to the redox-processes of Fe(2+/+), and no interaction is observed between the two encapsulated iron(I)-containing metallocenters; six strong electron-withdrawing ethoxy substituents in the 1,3,5-triazacyclohexane capping fragments substantially affect the potential of this reduction. The corresponding waves for the dioximate complexes are irreversible: due to the structural rigidity of the caging tris-dioximate ligands, their reduced dianionic forms are unstable on the CV time scale. The CV for the hexaethoxy bis-clathrochelate complex contains one two-electron reversible oxidation wave assigned to the metal-centered oxidation of Fe(2+/3+), whereas those for its dioximate analogs are quasi-reversible. The relative lability of the ligand cavity in binuclear oximehydrazonates causes a stabilization of both the oxidized and the reduced forms; the reduced iron(I)-containing species are highly electrocatalytically active in the hydrogen-producing 2H(+)/H2 reaction. Their higher activity as compared with that for dioximate bis-clathrochelates was explained by the higher availability of the catalytically active metallocentres for H(+) ions.

Electrochemistry and Electrogenerated Chemiluminescence of a Novel Donor−Acceptor FPhSPFN Red Fluorophore

We report here the electrogenerated chemiluminescence (ECL) of a red fluorophore diphenylaminospirobifluorenylfumaronitrile (FPhSPFN). FPhSPFN contains two diphenylamino groups as strong electron donors at the ends linked through a nonplanar bulky spirobifluorene linker to a common fumaronitrile group as a strong electron acceptor. The cyclic voltammetry of this compound shows two one-electron transfer reduction waves and one single overall two-electron oxidation wave consisting of closely spaced waves with a peak separation of 63 mV. Chronoamperometry with an ultramicroelectrode (UME) confirmed that each reduction wave involves a 1e transfer and that the oxidation wave contains an overall 2e transfer. The first reduction wave is Nernstian, Eo1,red = −1.09 V versus SCE, and the second reduction wave, Eo2,red = −1.50 V versus SCE, produces a film on the electrode. By comparison to a digital simulation, the oxidation is assigned to two reversible, closely spaced, one-electron processes for oxidation with Eo...

The electrochemical oxidation of catechol and dopamine on platinum in 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 2mim][NTf 2]) and 1-Butyl-3-methylimidazolium tetrafluoroborate ([C 4mim][BF 4]): Adsorption effects in ionic liquid voltammetry

The electrochemical oxidation of catechol and dopamine has been studied at a platinum micro-electrode (10 μ m diameter) in two room temperature ionic liquids (RTILs): 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 2mim][NTf 2]) and 1-Butyl-3-methylimidazolium tetrafluoroborate ([C 4mim][BF 4]). For catechol in [C 2mim][NTf 2], an electrochemically quasi-reversible oxidation peak was observed at 1.1 V vs. Pt with a back peak at 0.4 V vs. Pt. This is assigned to the two-electron oxidation of catechol to doubly protonated o-benzoquinone. Double-step chronoamperometry gave a diffusion coefficient for the catechol and the oxidised species which is 3.8 × 10 - 11 m 2 s - 1 for both. For catechol in [C 4mim][BF 4], a two-electron oxidation wave was observed at 1.0 V vs. Pt with no back peak. Another peak at less positive potential was also observed at 0.6 V vs. Pt in [C 4mim][BF 4] but not in [C 2mim][NTf 2] which is assigned to the adsorption of electrochemically formed neutral o-benzoquinone on the platinum electrode. The oxidised protonated o-benzoquinone is suggested to be deprotonated by the [ BF 4 ] - anion, but not by the [ NTf 2 ] - anion: hence adsorption of the neutral species at the platinum electrode, not the charged species. For dopamine in both RTILs, two chemically irreversible oxidation peaks were observed at 0.75 V and 1.1 V vs. Pt, and assigned to the oxidation of dopamine to the corresponding semi-quinone and the quinone. Potential-step chronoamperometry was carried out on the oxidation waves of dopamine in [C 2mim][NTf 2] and the diffusion coefficient of species in solution was calculated to be 6.85 × 10 - 12 m 2 s - 1 and confirmed that the waves corresponded to one and two electron processes. A third wave was observed at 1.8 V vs. Pt which is attributed to the oxidation of the amine group to a radical cation with likely subsequent follow up chemistry. In [C 4mim][BF 4] a peak at less positive potential was observed for dopamine, similar to catechol which is assigned to the adsorption of the neutral quinone species on the platinum electrode formed by the reaction of the removal of protons from the oxidised dopamine with the [ BF 4 ] - anion.

Theoretical and electrochemical studies on organometallic symmetrical Schiff base complexes of Zn(ii), Cu(ii), Ni(ii) and Co(ii)

The electronic communication between two redox centres through a Schiff base complex has been investigated in a series of ethylenediimine-bis(1-ferrocenyl-1,3-butanedionate) complexes of Zn(II) 1, Cu(II) 2, Ni(II) 3 and Co(II) 4. Cyclic voltammetry experiments of 1 and 2 exhibit a unique two-electron reversible oxidation wave, whereas in the case of 3 and 4 two and three one-electron oxidation processes are, respectively, observed. These results suggest some electronic interaction between the iron atoms of the ferrocenyl groups. DFT calculations carried out on model complexes show that for all the studied compounds the removal of the first two electrons corresponds to the oxidation processes of the iron centres in the weakly coupled ferrocenyl termini. The electronic communication between the two iron centres increases on going from 1 to 4. Finally, a re-indexation of the bands observed in the UV-Visible spectra has been carried out using TDDFT calculations.

Investigation on the electro-oxidation of iodide in the room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate at platinum electrode

The oxidation behavior of iodide has been investigated by linear sweep voltammetry and cyclic voltammetry at a platinum electrode in the room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([C 4mim][BF 4]). The experimental results showed that iodide yielded two oxidation peaks P a1 and P a2 in [C 4mim][BF 4], and both of P a1 and P a2 are diffusion-controlled. P a1 yielded from iodide to triiodide at +0.58 V is a two-electron oxidation wave, and P a2 yielded from triiodide to iodine at +1.00 V is one-electron oxidation wave. Linear relationships between I pa1 and the concentration of iodide can be established from 0.45 to 7.2 mmol L −1 with a detect limit of 0.3 mmol L −1 by linear sweep voltammetry, and from 0.30 to 7.8 mmol L −1 with a detect limit of 0.2 mmol L −1 by differential pulse voltammetry. These methods can be used for simple, rapid determination of iodide in the crude [C 4mim][BF 4].

Extreme Conformational Constraints in π-Extended Tetrathiafulvalenes: Unusual Topologies and Redox Behavior of Doubly and Triply Bridged Cyclophanes

Doubly and triply bridged 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (ex-TTF) derivatives have been synthesized. Key steps are the generation and macrocyclization reactions of ex-TTF-dithiolate reagents. The X-ray crystal structures of the doubly bridged cyclophanes 15 and 16 and the triply bridged system 23 show that the saddle-like conformation of the ex-TTF framework is enhanced by the short bridges between the dithiole rings. Unlike all previous ex-TTF derivatives (which display a single quasi-reversible two-electron oxidation wave, D0 --> D2+), cyclic voltammetry of the cyclophanes reveals two reversible, one-electron oxidation steps (D0 --> D*+ --> D2+), with differences between the half-wave potentials (E2(1/2) - E1(1/2)) of 0.22-0.26 V. The conformational changes and gain in aromaticity which drive the second oxidation process in unrestricted ex-TTF systems (including singly bridged cyclophanes) have been prevented by multiple bridging. The radical cation species gives rise to a very broad, low-energy band (lambdamax = 2175 and 2040 nm for 15 and 21, respectively), assigned to an intramolecular interaction. The steric constraints imposed by multiple bridging have become so extreme that the pi-framework of 15, 16, 21, and 23 exhibits remarkable optical and redox behavior which is not characteristic of ex-TTF systems.

The Interplay of Inverted Redox Potentials and Aromaticity in the Oxidized States of New π‐Electron Donors: 9‐(1,3‐Dithiol‐2‐ylidene)fluorene and 9‐(1,3‐Dithiol‐2‐ylidene)thioxanthene Derivatives

Derivatives of 9-(1,3-dithiol-2-ylidene)fluorene (9) and 9-(1,3-dithiol-2-ylidene)thioxanthene (10) have been synthesised using Horner-Wadsworth-Emmons reactions of (1,3-dithiol-2-yl)phosphonate reagents with fluorenone and thioxanthen-9-one. X-ray crystallography, solution electrochemistry, optical spectroscopy, spectroelectrochemistry and simultaneous electrochemistry and electron paramagnetic resonance (SEEPR), combined with theoretical calculations performed at the B3P86/6-31G** level, elucidate the interplay of the electronic and structural properties in these molecules. These compounds are strong two-electron donors, and the oxidation potentials depend on the electronic structure of the oxidised state. Two, single-electron oxidations (E(1)ox < E(1)ox) were observed for 9-(1,3-dithiol-2-ylidene)fluorene systems (9). In contrast, derivatives of 9-(1,3-dithiol-2-ylidene)thioxanthene (10) display the unusual phenomenon of inverted potentials (E(1)ox > E(1)ox) resulting in a single, two-electron oxidation process. The latter is due to the aromatic structure of the thioxanthenium cation (formed on the loss of a second electron), which stabilises the dication state (10(2+)) compared with the radical cation. This contrasts with the nonaromatic structure of the fluorenium cation of system 9. The two-electron oxidation wave in the thioxanthene derivatives is split into two separate one-electron waves in the corresponding sulfoxide and sulfone derivatives 27-29 owing to destabilisation of the dication state.

Understanding Electrochromic Processes Initiated by Dithienylcyclopentene Cation-Radicals

Simple photochromic dithienylethylenes with either a perfluoro or a perhydro cyclopentene ring, and a variety of substituents (chlorine, iodine, trimethylsilyl, phenylthio, aldehyde, carboxylic acid, and ethynylanisyl), have been prepared and their electrochemical behavior was explored by cyclic voltammetry. All dithienylethylenes present two-electron irreversible oxidation waves in their open form, but the cation-radical of the open isomers can follow two different reaction pathways: dimerization or ring closure, whereas the halogen derivatives follow a dimerization mechanism, the presence of donor groups, such as the phenylthio-substituted compound, promote an efficient oxidative ring closure following an ECE/DISP mechanism. Electrochromic properties are also found in the corresponding ring-closed isomers. Depending on the substituents on the thiophene ring, and the perfluro or perhydro cyclopentene ring, open isomers can be obtained from oxidation (chemical or electrochemical) of the corresponding ring-closed isomers via an EC mechanism. This reaction pathway is favored by the presence of electron-withdrawing groups in the molecule. For all these compounds, closed or open, the oxidation lies between 0.8 and 1.5 V vs SCE, and provokes a permanent modification of the color, even after an oxidation-reduction cycle. This could be qualified as "electrochromism with memory". On the other hand, the ring-closed electron-rich isomers (E degrees < 0.8 V), which show reversible waves at the cation-radical or even dication level, give rise to "true electrochromism", for which no structural changes are observed. The experimental study was completed by theoretical calculations at the DFT level, using B3LYP density functional, which gave information on the total energy, the geometry, and the electronic structures of several representative compounds, either in the neutral form or in the cation-radical state. These results are important for the potential design of photochromic systems, such as three-state conjugated systems and photoelectrical molecular switching devices.

Charge-transfer hybrids containing covalently bonded polyoxometalates and ferrocenyl units.

Two new charge-transfer hybrids with one or two ferrocenyl units covalently attached to a hexamolybdate cluster through an extended pi-conjugated bridge have been prepared using Pd-catalyzed coupling reactions on monoiodo- or diiodo-functionalized cluster substrates in over 60% yields. These hybrids have been characterized by (1)H NMR, FTIR, electrospray ionization mass spectrometry, and X-ray diffraction. The electronic spectra of these hybrids show a broad absorption tail extending beyond 550 nm, indicating the existence of charge-transfer transition from the ferrocenyl donor to the cluster acceptor. The observation of the clear charge-transfer transition indicates the contribution of charge-transfer resonance to the ground state in both 2a and 2b even though the donor-acceptor separation distance of 11.29 A is rather long, signaling a through-bond charge-transfer nature made possible by the organic pi-conjugated bridge. Cyclic voltammetry studies reveal a one-electron oxidation wave and a one-electron reduction wave for the hybrid with one ferrocenyl unit. For the one with two ferrocenyl units, a lower reduction potential and a two-electron oxidation wave are observed, indicating negligible electronic interactions between the two ferrocenyl units.

Synthesis, cyclic voltammetric studies, and electrogenerated chemiluminescence of a new phenylquinoline-biphenothiazine donor-acceptor molecule.

We report the synthesis, electrochemistry, and luminescence of a novel ECL emitting compound containing two electron-accepting hexyl-phenylquinoline groups covalently attached to the 3,3'-positions of the electron-donating 10,10'-dimethylbiphenothiazine group. The optimized geometry as determined from semiempirical MNDO calculations shows that the two quinoline groups are twisted 82.5 degrees from the two phenothiazine rings, indicating a lack of electron delocalization among these groups. This unique geometry allows generation of localized radical cations and radical anions capable of generating ECL upon annihilation. However, the phenothiazine rings are twisted 46.5 degrees relative to each other, suggesting possible interactions between the two moieties. This is evident in the electrochemical behavior in which two closely spaced one-electron oxidations, rather than a single two-electron oxidation wave, were observed. The photophysical properties of BHQ-BPZ show strong resemblances to the parent compound, BPQ-PTZ, which contains a single phenothiazine moiety. In addition, the ECL spectrum produced via radical ion annihilation shows good agreement with the fluorescence emission of the compound.

New strategies and building blocks for functionalised 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene derivatives, including pyrrolo-annelated derivatives and pi-extended systems with intramolecular charge-transfer.

A range of new functionalised 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (TTFAQ) derivatives have been synthesised from the key di(halomethyl) building blocks, 10-[4,5-bis(bromomethyl)-1,3-dithiol-2-ylidene]-anthracene-9(10H)-one 10, 10-[4,5-bis(chloromethyl)-1,3-dithiol-2-ylidene]anthracene-9(10H)-one 11 and 9-[4,5-bis(chloromethyl)-1,3-dithiol-2-ylidene]-10-[4,5-bis(hexylsulfanyl)- 1,3-dithiol-2-ylidene]-9,10-dihydroanthracene 18. A Diels-Alder strategy comprising trapping of the transient exocyclic diene 19, which is derived from 18, with 1,4-naphthoquinone leads to the aromatised TTFAQ anthraquinone system 21. Horner-Wadsworth-Emmons olefination of 21 with the anion generated from reagent 22 gave the fused bis(TTFAQ) structure 23. Pyrrolo-annelated derivatives 30-34 have been obtained in a sequence of reactions from compound 10. Mono-formylation of the pyrrole ring of 32 and 33 under Vilsmeier conditions gave 35 and 36 which upon reaction with 2,4,5,7-tetranitrofluorene gave the donor-pi-acceptor diads 38 and 39. Cyclic voltammetry (CV) in solution for all the TTFAQ derivatives shows the typical quasi-reversible two-electron oxidation wave of the TTFAQ core at potentials which vary slightly depending on the substituents. For example, the value of Eox is raised by the electron withdrawing anthraquinone and tetranitrofluorene units of 21 and 38, respectively. The CV of the conjugated TTFAQ dimer 23 showed two, two-electron oxidation waves corresponding to the sequential formation of 23(2+) and 23(4+) (delta Eox = 130 mV) providing evidence for a significant intramolecular electronic interaction, i.e. the dication 23(2+) acts as a conjugated donor-pi-acceptor diad, thereby raising the oxidation potential of its partner TTFAQ unit. Spectroelectrochemical studies on 23 support this explanation. A strong intramolecular charge transfer band at lambda max 538 nm is seen in the UV-Vis spectra of the TTFAQ-pi-tetranitrofluorene diads 38 and 39. The X-ray crystal structures are reported for compounds 30, 33 and 34. The pyrrolo-TTFAQ moiety adopts a saddle-shape with the central ring of the dihydroanthracene moiety folded along the C(9) ... C(10) vector in each case. Significant intermolecular interactions are observed in the structures.

A (pi-extended tetrathiafulvalene)-fluorene conjugate. Unusual electrochemistry and charge transfer properties: the first observation of a covalent D(2+)-sigma-A(.-) redox state(1).

The synthesis of novel electrochemically amphoteric TTFAQ-sigma-A compounds (TTFAQ = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene, sigma = saturated spacer, A = polynitrofluorene acceptor) is reported. Their solution redox behavior is characterized by three single-electron reduction and one two-electron oxidation waves. Electrochemical quasireversibility of the TTFAQ(2+) state and a low E(ox) - E(red) gap ( approximately 0.25 V) for 3-(9-dicyanomethylene-4,5,7-trinitrofluorene-2-sulfonyl)-propionic acid 2-[10-(4,5-dimethyl-[1,3]dithiol-2-ylidene)-9,10-dihydroanthracen-9-ylidene]-5-methyl-[1,3]dithiol-4-ylmethyl ester (10) has enabled the electrochemical generation of the hitherto unknown transient D(2+)-sigma-A(.-) state as observed in cyclic voltammetry and time-resolved spectroelectrochemistry. The ground state of compound 10 was shown to be ionic in the solid but is essentially neutral in solution (according to electron paramagnetic resonance). The X-ray structure of an intermolecular 1:2 complex between 2-[2,7-bis(2-hydroxyethoxy)-9,10-bis(4,5-dimethyl-[1,3]dithiol-2-ylidene)-9,10-dihydroanthracene and 2,5,7-trinitro-4-bromo-9-dicyanomethylenefluorene, 14.(17)(2), reveals, for the first time, full electron transfer in a fluorene charge-transfer complex.

Synthesis of new highly conjugated bis-(4 H-pyrans) involving electron rich polyene linkage, by Pd° catalytic coupling of γ-methylenepyran Fischer-type carbene complexes

Self dimerisation of methylenepyran carbene complexes affords bis-pyrans containing electron rich polyene linkage. The cyclic voltammograms of these new donors show one two-electron oxidation wave at low potential.

Multistep redox properties of 2,2′-bipyridylboronium substituted ferrocenes

A high-yield synthesis and the X-ray crystal structure analysis of the dinuclear complex [FcB(bipy)OC 6H 4O(bipy)BFc](PF 6) 2, 6(PF 6) 2, which consists of two ferrocenyl moieties, two 2,2′-bipyridylboronium substituents and a hydroquinone linker, is described. The compound is perfectly stable toward air and moisture. 6(PF 6) 2 exhibits a ferrocene-centered two-electron oxidation wave and two separate bipyridylboronium-centered two-electron reduction steps. No oxidation of the hydroquinone spacer takes place in the solvent window. 6(PF 6) 2 is thus able to accept or deliver up to six electrons. Attempts to connect two [FcB(bipy)] fragments using glycol rather than hydroquinone as the bridging element gave the mononuclear complex [FcB(bipy)O(CH 2) 2OH]PF 6 only. A similar reaction scheme that was applied for the generation of [FcB(bipy)O(CH 2) 2OH]PF 6 was employed to synthesize the diol {1,1′-[HO(CH 2) 2OB(bipy)]2fc}(PF 6) 2; fc=[(C 5H 4) 2Fe]. This compound is able to store up to five electrons and may find use as a monomer for the generation of cationic, redox-active polyesters and polyurethanes.

Crown-Annelated 9,10-Bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene Derivatives as Cation Sensors: Synthesis, X-ray Crystal Structures, Voltammetric and Spectroscopic Monitoring of Metal Complexation

The synthesis of O4S2-crown annelated derivatives of 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene using the novel Horner−Wadsworth−Emmons reagent 7 is reported. The bis- and mono-crown systems 9 and 12 function as efficient ligands in the voltammetric and UV/Vis spectroscopic recognition of Na+ and Ag+. Solution electrochemical studies reveal that metal complexation to the crown unit(s) leads to a significant positive shift in the potential of the first, two-electron oxidation wave of 9 and 12 [maximum shift E1ox = 115 mV for 9 in the presence of Ag+ (ca. 10 molar equivalents)]. Considerably smaller shifts (< 30 mV) were observed for complexation of Li+, K+ and Ba2+. UV/Vis spectrophotometric studies of metal binding (Na+ and Ag+) to 9 are consistent with the simultaneous formation of 1:1 and 1:2 complexes. The X-ray crystal structures of compounds 10 and 12·CH2Cl2 are reported. The anthracenediylidene moiety of 12 is U-shaped due to the boat conformation of the central (quinodimethane) ring and folding of both 1,3-dithiole rings, providing an overall saddle conformation. The folding in 10 is reduced as steric crowding is relieved by removal of one of the 1,3-dithiole units.

The transition-metal complexes of the thiamacrocycle containing two ferrocene nuclei in the main chain. Synthesis, properties, and molecular structure of Ag(I), Cu(I), Pd(II), and Pt(II) complexes of 1,5,16,21-tetrathia[5.5]ferrocenophane

1,5,16,21-Tetrathia[5.5]ferrocenophane reacted with (MeCN) 4CuClO 4 and AgBF 4 in THF to give the 1:1 complexes in good yields. The treatment of the ligand with (MeCN) 2MCl 2 (M=Pd and Pt) and two equivalents of AgBF 4 in MeCN gave the 1:1 complexes in good yields. A reversible two-electron redox wave was observed near +0.3 V in the Cu(I) and Ag(I) complexes. The Pd(II) and Pt(II) complexes showed the irreversible two-electron oxidation wave near +0.7 V and that of the Pd(II) complex exhibited a slight peak separation, inferring a small interaction between the two Fe atoms through the central Pd(II) atom. As can be seen by X-ray analysis, the free ligand employed the pseudo-square conformation with regard to the thiamacrocycle in the molecular structure. The Pt(II) complex took the square-planar arrangement around the Pt(II) atom, while the Cu(I) and Ag(I) complexes maintained the tetrahedral configuration around the metal center.

Synthesis, Properties, and Theoretical Characterization of Largely π-Extended Tetrathiafulvalene Derivatives with Quinonoid Structures

A series of highly conjugated tetrathiafulvalene (TTF) analogues with a quinonoid structure has been synthesized, and their structural and electronic properties have been characterized by both experimental techniques and quantum-chemical calculations. Cyclic voltammetry measurements show a two-electron oxidation wave to form the dication, which is mainly located on the dithiole rings. The second irreversible oxidation wave to form the trication-radical corresponds to the oxidation of the polyacenic backbone. The temperature dependence of the reduction peak corresponding to the donor2+ → donor0 process is explained in terms of the low stability of the cation and the high aromaticity of the dication. Charge-transfer complexes are formed with the strong acceptor TCNQF4 showing a 1:2 (D:A) stoichiometry and a semiconducting behavior. The molecular structures of neutral and oxidized compounds are investigated by performing theoretical calculations at the semiempirical, ab initio, and density functional theory levels. The steric hindrance introduced by lateral benzoannulation determines the loss of planarity of the neutral molecules, which adopt butterfly shaped structures. The folded structures are retained in the cations, reducing the gain of aromaticity in the first oxidation step. The dications are by contrast predicted to be fully aromatic and are formed by a planar polyacenic moiety and two orthogonal, singly charged dithiole rings. The destabilization of the cations and the high aromaticity of the dications explain the redox properties observed experimentally. Theoretical calculations also help to rationalize the UV−vis data since they predict the appearance of a low-energy charge-transfer absorption band for the neutral compounds where the laterally fused polyacenic units act as acceptors.