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In the search for high performance n-type organic semiconductors (OSCs) a simple strategy might be substitution of aromatic CH groups for nitrogen heteroatoms. Here, we report the synthesis and characterisation of two novel N-heteroacene compounds, namely, 1,5,12-triazatetracene (TrAT1) and 2,5,12-triazatetracene (TrAT2). Their potential as n-type materials is evaluated against 5,12-diazatetracene (DAT) by UV/vis and EPR spectroscopy, cyclic voltammetry, DFT, single crystal X-ray diffraction and thin film characterisation. Increasing the number of N-heteroatoms was found to stabilise the HOMO and LUMO leading to electron affinities for TrAT1 and TrAT2 of ca. −4 eV. Both compounds were found to exhibit columns of co-facial π-stacked molecules. For TrAT1, molecules are also linked by hydrogen bonding, while the crystal structure of TrAT2 was found to be inherently disordered. Thin films of DAT, TrAT1 and TrAT2 were grown by organic molecular beam deposition (OMBD) and found to form discontinuous films, where TrAT1 exhibited a preferential orientation.

Single crystal X-ray diffraction, magnetic and 57Fe Mossbauer spectroscopic studies of a new iron(II)-based spin transition complex – [Fe(3-bpp)2](CF3COO)2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine) are reported. The complex exhibits an incomplete thermal high spin (HS) low spin (LS) transition at ∼226 K which is not associated with any crystallographic transition. Only one of the two crystallographic iron(II) sites undergoes the spin transition, while the other HS site remains invariant of temperature down to 10 K. The origin of the incomplete spin transition is understood by analysing the nature of crystal packing below and above the transition temperature with special attention to the degree of distortion. The present study shows the role of the degree of distortion associated with the cations in the [Fe(3-bpp)2]2+ spin transition complexes.

We report the first example of a chiral BDH-TTP radical-cation salt. Chirality is induced in the structure via the use of a chiral spiroboronate anion where three stereocentres are present, one on each chiral ligand and one on the boron centre. Despite starting from a labile racemic mixture of BS and BR enantiomers, only one enantiomer is present in the crystal lattice. The anions pack in a novel double anion layer which is the thickest anion layer found in a BDH-TTP salt. This material is chiral and shows metallic behaviour down to at least 4.2 K.

The chiral and racemic salts β′′-(BEDT-TTF)2(S- and rac-PROXYL-CONHCH2SO3) (S-2 and rac-2) are almost isomorphous apart from a deviation in the C–H bond direction at the chiral centre. Both salts are metallic at room temperature, with similar broad metal-insulator transitions. Band structure calculations of the chiral and racemic salts indicate that both electronic structures are quite similar. However, at 30 K, S-2 has a resistivity that is nearly three orders of magnitude higher than that of rac-2. The results suggest a significant effect of the broken inversion symmetry, due to the positional change of only one atom.

Materials exhibiting both chirality and conductivity do not exist in nature and very few examples have been synthesised. We report here the synthesis of a chiral molecular metal which remains metallic down to at least 4.2 K. This material also exhibits room-temperature switching capabilities with a transition upon cooling below 10 °C.

We report the first examples of radical-cation salts of BEDT-TTF with spiroborate anions [B(mandelate)2]− and [B(2-chloromandelate)2]−, synthesized from either enantiopure or racemic bidentate mandelate or chloromandelate ligands. In the salts prepared using enantiopure ligands only one of two diastereoisomers of the spiroborate anion is incorporated, with the boron centre having the same stereochemistry as the enantiopure ligand. For the racemic salts one racemic pair of spiroborate anions containing an R and an S mandelate ligand is incorporated. In certain solvents helical crystals were obtained when using spiroborate anions with enantiopure ligands. Electrical and magnetic properties, and band structure calculations are reported.

The chiral TTF-based donor molecule bis(2′-hydroxylpropylthio)(ethylenedithio)tetrathiafulvalene (BHPT-EDT-TTF) has produced enantiopure R,R and S,S radical-cation salts with polyiodide anions I3− and I82−. Enantiomorphic 6 : 6 donor : I3 phases grown from either the R,R or S,S donor are semiconducting with similar activation energies of 0.24–0.30 eV and 0.22–0.23 eV, respectively, and contain three unique face-to-face donor pairs whose relative orientation is determined by side chain conformations and hydrogen bonding. Racemic material under the same conditions gave an insulating centrosymmetric phase with R,R and S,S donor cations in a face-to-face pair partnered with an octaiodide dianion, and with a ca. 3 : 1 disorder between the enantiomers. Enantiopure BHPT-EDT-TTF yielded two further insulating crystalline phases of composition 2 : 2 with triiodide and 2 : 1 with octaiodide.

Crystallisation from chiral electrolyte (R)-(−)-carvone has produced three new chiral semiconducting salts of BEDT-TTF from racemic anion tris(oxalato)chromate(III).

The new chiral TTF-based donor molecule bis(2-hydroxypropylthio)ethylenedithiotetrathiafulvalene has produced enantiopure R,R and S,S radical cation salts with the tetrafluoroborate anion as well as the nearly isostructural meso/racemate mixture. The enantiopure R,R or S,S salts are both 1:1 semiconducting salts with activation energies of 0.19–0.24 eV, both crystallising in the orthorhombic space group C2221. The semiconducting salt containing both meso and racemic donor cations has a very similar crystal structure but crystallising in the monoclinic space group C2/c (β = 91.39°) with similar S⋯S interactions but a smaller activation energy of 0.15–0.17 eV. This is in contrast to previous families of this type where the disordered racemate has a larger activation energy than its enantiopure salts.

The first chiral BEDT-TTF-tris(oxalato)metallate(III) salt has been crystallised from a solution containing the racemic anion in the chiral solvent (R)-(−)-carvone.

Several photo-responsive norbornadiene as well as spiropyran derivatives with TEMPO radical substituents were prepared and their light-induced structural changes to the corresponding quadricyclanes or merocyanine dyes and reverse reactions to the starting materials were investigated. While the intermolecular magnetic interactions tend to be preserved in norbornadiene–quadricyclane systems in spite of the differences of their Weiss temperatures, a switching of the intermolecular magnetic interactions was observed in the spiropyran–merocyanine systems.

SQUID magnetometry and transport measurements combined with crystal structure refinement have been used to examine the variation in superconducting properties (Tc and Meissner fraction) in the molecular superconductor β″-(BEDT-TTF)4[(H3O)Fe(C2O4)3]·C6H5CN on replacing the C6H5CN guest molecule with pyridine (C5H5N). Up to approximately 65% pyridine substitution there is only a small decrease in Tc and Meissner fraction but above that the superconductivity is suppressed.

The structure and properties of a new semiconducting BEDT-TTF-based charge-transfer salt containing the ferrocenesulfonate (Fc-SO3(-)) anion, α-(BEDT-TTF)2Fc-SO3·2.5H2O, are described. The structure and magnetic properties of a zwitterion of ferrocenesulfonate, Fc(+)-SO3(-), are also reported.

Three ferrocene derivatives carrying different kinds of nitroxide radicals (1–3) were prepared as dual redox compounds. All of them have distorted molecular conformations between a Cp unit of a ferrocene group and a nitroxide group and the largest dihedral angle between the units is observed in the PO derivative 3. A unique magnetic behavior with a spin gap is disclosed in the derivative 3, reflecting two-dimensional interactions between the paired spins. Each derivative has two oxidation potentials based on both ferrocene and nitroxide groups and multi-step charge–discharge processes are found for all derivatives with the first discharge capacity over 200 A h kg−1.

The preparation, crystal structure and physical properties of beta-(BDA-TTP)2GaCl4 has been investigated; the salt exhibits superconductivity at 3.1 K (onset) under a hydrostatic pressure of 7.6 kbar.

The synthesis and electrochemical properties of the DHDA-TTP donor, a hybrid of 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP) and 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP), has been investigated, and its ability to form metallic cation-radical salts is elucidated.

Two polymorphs of a chiral conductor formulated (BEDT-TTF)3NaCr(C2O4)3·CH3NO2 have been crystallised from a solution containing the racemic anion tris(oxalato)chromate(III). In the presence of (R)-(−)-carvone the electrocrystallisation of Na3Cr(C2O4)3 with BEDT-TTF and nitromethane yields two products: hexagons crystallising in the space group P212121 (I) and needles in the space group P21 (II). Single crystal electrical transport measurements show semiconducting behavior for both salts.

We have prepared a novel organic molecule, 2-sulfo-3,5,6-trichloro-1,4-benzoquinone (1), that has both an electron acceptor part (chloranil) and an anionic part (sulfonate). The reduction potential of the PPh4 salt is −0.34 V (vs.SCE in PhCN) which indicates it is a weaker acceptor than chloranil (−0.18 V). The anionic acceptor provided one TTF (tetrathiafulvalene) and two BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) salts, the structures and physical properties of which are reported.

We have prepared an organic magnetic anion, PROXYL-4-CONHCH2SO3− (1). The electrocrystallisation of BEDT-TTF with PPh41 gave the first purely organic paramagnetic metal, β″-(BEDT-TTF)2(1). The salt shows a broad metal–insulator transition at approximately 210 K.

The synthesis, columnar behaviour and magnetic properties of the first examples of radical discotics are reported. These organic molecular systems with spin sources have been accomplished by covalently linking triphenylene with molecular radicals. The columnar mesomorphism of these new radicals has been established unambiguously using several complementary techniques. Magnetic susceptibility measurements in the fluid columnar, frozen columnar and solid states reveal the antiferromagnetic intermolecular interactions of Curie–Weiss behaviour.

Metallic charge-transfer salts of BEDT-TTF containing both racemic (R/S)- and chiral (S)-sec-phenethyl alcohol as guest molecules have been crystallised and their structures and physical properties are compared.

The pressure-induced electrical conductivity properties of beta-(BDA-TTP)2I3 have been investigated; the salt exhibits a dramatic change in the conductivity behaviour above ca. 10 kbar and undergoes a superconducting transition with an onset near 10 K.

A new BEDT-TTF-based organic salt with a ferrocene-containing dianion has been prepared: β″-(BEDT-TTF)4(Fe(Cp-CONHCH2SO3)2)·2H2O. The salt shows metallic behaviour from 300 to 70 K, followed by a sharp metal–insulator transition. The transition is suppressed by applying a static pressure of 9.5 kbar.

Three conducting BEDT-TTF charge-transfer salts with tris(oxalato)metallate anions have unit cells containing both[small alpha] and [small beta][double prime] donor packing motifs.