Radical and diradical states of bis(molybdenocene dithiolene) complexes

The synthesis and characterization of two bis(dithiolene) proligands involving heteroatomic linkers such as 1,4-dithiine and dihydro-1,4-disiline between the two protected dithiolene moieties are described. Two bimetallic complexes involving these heteroatomic bridges between two redox active bis(cyclopentadienyl)molybdenum dithiolene moieties have been synthesized and characterized by electrochemistry, spectroelectrochemistry, and their properties rationalized with (TD-)DFT. Cyclic voltammetry experiments show sequential oxidation of the two redox centers with ΔE values between successive one-electron transfers varying according to the nature of the bridge. Depending on the nature of the heteroatomic bridge, the bis-oxidized complexes exhibit either a diradical character with both radicals essentially localized on the metallacycles, or a closed-shell dicationic state.

A bimetallic benzene-1,2,4,5-tetrathiolate (btt) molybdenocene complex Cp2Mo(btt)MoCp2: radical and diradical states

Benzene-1,2,4,5-tetrathiolate (btt) has been used as a bridging ligand to prepare a redox active (molybdenocene dithiolene)-based bimetallic complex Cp2Mo(btt)MoCp2, which exhibits four successive electron transfers up to the tetracation. Spectro-electrochemical investigations together with DFT and TD-DFT calculations evidence that the two electroactive MoS2C2 metallacycles are electronically coupled in the monocationic as in the dicationic state. Two salts of the dication [Cp2Mo(btt)MoCp2]2+ have been structurally characterized with PF6- and HSO4- counterions, showing different chair or boat conformations associated with variable folding angles of the two MoS2C2 metallacycles along the S---S hinge. The bis-oxidized dicationic complex exhibits a diradical character, with both radicals essentially localized on the metallacycles and with antiferromagnetic coupling evidenced from magnetic susceptibility measurements.

Block Copolymer Micelles Encapsulating Au(III) Bis(Dithiolene) Complexes as Promising Nanostructures with Antiplasmodial Activity

Block copolymer micelles (BCMs) can be used to improve the solubility of lipophilic drugs and increase their circulation half-life. Hence, BCMs assembled from MePEG-b-PCL were evaluated as drug delivery systems of gold(III) bis(dithiolene) complexes (herein AuS and AuSe) to be employed as antiplasmodial drugs. These complexes exhibited remarkable antiplasmodial activity against liver stages of the Plasmodiumberghei parasite, and low toxicity in a model of zebrafish embryos. To improve the complexes' solubility, BCMs were loaded with AuS, AuSe, and the reference drug primaquine (PQ). PQ-BCMs (D_h = 50.9 ± 2.8 nm), AuSe-BCMs (D_h = 87.1 ± 9.7 nm), and AuS-BCMs (D_h = 72.8 ± 3.1 nm) were obtained with a loading efficiency of 82.5%, 55.5%, and 77.4%, respectively. HPLC analysis and UV-Vis spectrophotometry showed that the compounds did not suffer degradation after encapsulation in BCMs. In vitro release studies suggest that AuS/AuSe-BCMs present a more controlled release compared with PQ-loaded BCMs. The antiplasmodial hepatic activity of the drugs was assessed in vitro and results indicate that both complexes present higher inhibitory activity than PQ, although encapsulated AuS and AuSe presented lower activity than their non-encapsulated counterparts. Nevertheless, these results suggest that the use of BCMs as delivery vehicles for lipophilic metallodrugs, particularly AuS and AuSe, could enable the controlled release of complexes and improve their biocompatibility, constituting a promising alternative to conventional antimalarial treatments.

Gold(iii) bis(dithiolene) complexes: from molecular conductors to prospective anticancer, antimicrobial and antiplasmodial agents

The anticancer, antimicrobial and antiplasmodial activities of six gold(iii) bis(dithiolene) complexes were studied. Complexes 1-6 showed relevant anticancer properties against A2780/A2780cisR ovarian cancer cells (IC50 values of 0.08-2 μM), also being able to overcome cisplatin resistance in A2780cisR cells. Complex 1 also exhibited significant antimicrobial activity against Staphylococcus aureus (minimum inhibitory concentration (MIC) values of 12.1 ± 3.9 μg mL-1) and both Candida glabrata and Candida albicans (MICs of 9.7 ± 2.7 and 19.9 ± 2.4 μg mL-1, respectively). In addition, all complexes displayed antiplasmodial activity against the Plasmodium berghei parasite liver stages, even exhibiting better results than the ones obtained using primaquine, an anti-malarial drug. Mechanistic studies support the idea that thioredoxin reductase, but not DNA, is a possible target of these complexes. Complex 1 is stable under biological conditions, which would be important if this compound is ever to be considered as a drug. Overall, the results obtained evidenced the promising biological activity of complex 1, which might have potential as a novel anticancer, antimicrobial and antiplasmodial agent to be used as an alternative to current therapeutics.

Diselenolene proligands: reactivity and comparison with their dithiolene congeners

Selenophene and diselenine were synthesized from diselenolene proligands.

Structures and transistor properties of extended and unsymmetrical birhodanines

Extended and unsymmetrical birhodanines, including phenyl and unsubstituted parts, are prepared and show characteristic molecular packing and n-channel transistor properties.

Temperature-dependent characteristics of n-channel transistors based on 5,5′-bithiazolidinylidene-2,4,2′,4′-tetrathiones

Single-crystal transistors of the title compounds show isotropic mobilities exceeding 1 cm² V⁻¹ s⁻¹.

Halogen and chalcogen-bonding interactions in sulphur-rich π-electron acceptors

Sulphur and iodine heteroatoms on the acceptor skeleton induce chalcogen⋯chalcogen and halogen-bonding interactions.

Charge-transfer complexes of sulfur-rich acceptors derived from birhodanines

The title acceptors form charge-transfer complexes with mixed stacks, whose transistors are affected by the S–S interaction between the acceptors.

Impact of bulky phenylalkyl substituents on the air-stable n-channel transistors of birhodanine analogues

By introducing bulky 2-phenylethyl groups into sulfur-rich electron acceptors, 5,5′-bithiazolidinylidene-2,2′-dione-4,4′-dithione and 5,5′-bithiazolidinylidene-2,4,2′,4′-tetrathione, electron transport with the mobility of 0.27 cm² V⁻¹ s⁻¹ with ambient and long-term stability is achieved in thin-film transistors. Bulky groups destroy the intermolecular S–S network, but the long-term transistor stability is maintained. Here, benzyl groups realize one-dimensional stacking structures, whereas 2-phenylethyl groups lead to herringbone structures.

Performance and long-term air stability of birhodanine-based n-channel transistors are improved by introducing phenylethyl moieties.

Chiral 1,2-dithiine as a sulfur rich electron acceptor

Both enantiomers of a 1,2-dithiine containing two 1-phenylethyl groups of the same chirality were selectively synthesized and electrochemically and spectro-electrochemically characterized.

The near infra red (NIR) chiroptical properties of nickel dithiolene complexes

Circular dichroism (CD) thin layer spectro-electrochemical experiments reveal a redox switching of CD-active bands in the NIR region.

Hydrogen-bonding interactions in a single-component molecular conductor: a hydroxyethyl-substituted radical gold dithiolene complex

The anionic hydroxyethyl-substituted gold dithiolene complex [NEt4][Au(EtOH-thiazdt)2] is synthesized and further oxidized to the neutral radical species [Au(EtOH-thiazdt)2](•) through electrocrystallization. Single-crystal X-ray diffraction studies highlight the existence of the two cis and trans isomers for the monoanionic complex, with involvement of the hydroxy group in intermolecular O-H···S hydrogen-bonding interactions. The neutral radical complex, [Au(EtOH-thiazdt)2](•), is isostructural with its known ethyl analogue, namely, [Au(Et-thiazdt)2](•). It exhibits a semiconducting behavior (σRT = 0.05-0.07 S cm(-1)) at room temperature and ambient pressure with an activation energy of 0.14 eV. Comparison of the crystal structures and transport and magnetic properties with those of the prototypical [Au(Et-thiazdt)2](•) single-component conductor shows that the replacement of ethyl by a slightly bulkier hydroxyethyl substituent affects only weakly the overlap interactions, complemented here by added O-H···S hydrogen-bonding interactions.

2D and 3D Polymeric Wells-Dawson polyoxometelates: synthesis, crystal structures, and cyclic voltammetry of [(M(H(2)O)(4))(x)][H(6-2x)P(2)W(18-n)Mo(n)O(62)] (M = Cu(II), Co(II), Ni(II))

The synthesis, X-ray crystal structures, cyclic voltammetry, and IR and (31)P NMR characterizations of five new Wells-Dawson-type polyoxometalates are reported, the formulas of which being [(Cu(H(2)O)(4))(2.5)][HP(2)W(18)O(62)].11.33H(2)O (4), [(Cu(H(2)O)(4))(2.4)][H(1.2)P(2)W(12)Mo(6)O(62)].11.4H(2)O (5), [(Cu(H(2)O)(4))(2.3)][H(1.4)P(2)W(15)Mo(3)O(62)].10.1H(2)O (6), [Co(H(2)O)(4))(2.3)][H(1.4)P(2)W(14)Mo(4)O(62)].18.8H(2)O (7), and [Ni(H(2)O)(4))(1.85)][H(2.3)P(2)W(15)Mo(3)O(62)].20.6H(2)O (8). These compounds are obtained as crystalline materials from the corresponding acids by substitution of a transition metal in aqueous solution. Compounds 4, 5, and 6 are isostructural; their crystal structure consists of 2D polymeric hexagonal layers where each Wells-Dawson anion is connected to six neighbors by [CuO(6)] octahedra. On the other hand, compounds 7 and 8, which are also isostructural, present a 3D structure where the Mo-substituted [P(2)W(14)Mo(4)O(62)] units are connected by [MO(6)] octahedra (M = Co(II), Ni(II)). Different types of substitution modes of Mo ions are observed within polyanions. Cyclic voltammetry shows that Cu(II) derivatives have similar behavior but different from that of the starting compounds. No electrochemical activity has been detected for the Ni-containing compound 8.

First trinuclear paramagnetic transition metal complexes with redox active ligands derived from TTF: Co2M(PhCOO)6(TTF-CHCH-py)2·2CH3CN, M = CoII, MnII

The first paramagnetic homo- and hetero-metallic trinuclear complexes with redox active ligands derived from TTF are synthesized, the central metal ion has an octahedral coordination sphere while the outer Co(II) ions are in a distorted bipyramidal surrounding, bearing TTF-ligands, the magnetic properties show antiferromagnetic coupling leading to a magnetic ground state.

Co(II)−Co(II) Paddlewheel Complex with a Redox-Active Ligand Derived from TTF

A new trimethyltetrathiafulvalene (Me3TTF) derivative Me3TTF-CH=CH-py bearing a pyridyl was synthesized and coordinated to a cobalt(II) benzoate dimer, having paddlewheel core structure, leading to a complex formulated as Co2(PhCOO)4(Me3TTF-CH=CH-py)2. Single-crystal X-ray diffraction studies of the complex performed at 293 and 100 K evidenced the existence of a weak metal-metal interaction. Magnetic studies revealed an antiferromagnetic behavior, which is explained as the result of the direct exchange between metal centers.