Semiconductive 2D arrays of pancake-bonded oligomers of partially charged TCNQ radicals

Multicentre two-electron (mc/2e or 'pancake bonding') bonding between 7,7,8,8-tetra-cyano-quinodi-methane (TCNQ) radical anions was studied on its 14 novel salts with planar organic cations. The formal charges of the TCNQ^δ- moieties are -1/2 and -2/3, and they form mc/2e bonded dimers, trimers and tetramers which are further stacked into extended arrays. Multicentre bonding within these oligomers is characterized by short interplanar separations of 2.9-3.2 Å; distances between the oligomers are larger, typically >3.3 Å. The stacks are laterally connected by C-H⋯N hydrogen bonding, forming 2D arrays. The nature of mc/2e bonding is characterized by structural, magnetic and electrical data. The compounds are found to be semiconductors, and high conductivity [10^-2 (Ω cm)^-1] correlates with short interplanar distances between pancake-bonded oligomers.

Pyridinium modification of a hexaazaphenalene skeleton: structure and spectroelectrochemical analysis

N-Alkylation of tris(4-pyridyl) hexaazaphenalene (TPHAP) anions afforded corresponding pyridinium derivatives.

Control of anisotropy of a redox-active molecule-based film leads to non-volatile resistive switching memory

Control of the π-π interaction direction in a redox-active π-molecule based film led to the formation of new mechanistic nonvolatile resistive switching memory: a redox-active organic molecule, 2,5,8-tri(4-pyridyl)1,3-diazaphenalene, showed non-volatile bistable resistance states with a high on-off ratio, retention, and endurance only when the molecular orientation was anisotropic. Control experiments using redox-active/redox-inert organic molecules with isotropic/anisotropic molecular orientations implied that the formation of conductive oxidized π-π stacking layers from non-conductive neutral π-π stacking layers is responsible for resistive switching phenomena, indicating new mechanisms such as ReRAM. Our findings will give a comprehensive understanding of electron transport in organic solid materials based on the effects of redox-activity and molecular arrangement, leading to fabrication of a new class of ReRAM based on organic molecules.

Solid-Gas Phase Synthesis of Coordination Networks by Using Redox-Active Ligands and Elucidation of Their Oxidation Reaction

Formation of coordination networks is a complex process affected by a multitude of factors. Many synthetic strategies have been developed that attempt to control these factors and direct the structure of the final product. Coordination bond formation and structural assembly processes, however, typically take place either in the solution or solid states. In comparison, gas-phase network synthesis remains largely unexplored. Herein, two new two-dimensional coordination networks are obtained from the solid-gas phase reaction between ZnX₂ (X=I, Br) and the redox-active 2,5,8-tri(4-pyridyl)1,3-diazaphenalene (HTPDAP) ligand. Their structures were solved by ab initio powder X-ray diffraction analysis and feature a novel Zn halide trimeric cluster. This strategy is contrasted with a conventional solvothermal synthesis, which led to a one-dimensional coordination polymer instead. The intrinsic electroactive properties of these materials were probed by solid-state cyclic voltammetry measurements, which revealed the presence of HTPDAP and halide-based processes. Chemical oxidation of the two-dimensional networks by using NOPF₆ agent, unexpectedly, led to the formation of a nitrated analog of HTPDAP, the PF₆ ^- salt of diprotonated 4,6,7,9-tetranitro-2,5,8-tris(4-pyridyl)diazaphenalene cation (denoted N-TPDAP), which was isolated and characterized. These results provide deeper insights into the oxidation process of HTPDAP-containing networks and uncover unique redox-induced chemical transformations.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

Bidirectional non-innocence of the β-diketonato ligand 9-oxidophenalenone (L-) in [Ru([9]aneS3)(L)(dmso)]n, [9]aneS3 = 1,4,7-trithiacyclononane

The new compound [Ru(II)([9]aneS3)(L)(dmso)]ClO4 ([]ClO4) ([9]aneS3 = 1,4,7-trithiacyclononane, HL = 9-hydroxyphenalenone, dmso = dimethylsulfoxide) has been structurally characterised to reveal almost equal C-O bond distances of coordinated L(-), suggesting a delocalised bonding situation of the β-diketonato ligand. The dmso ligand is coordinated via the sulfur atom in the native (1+) and reduced states (1 and 1-) as has been revealed by X-ray crystallography and by DFT calculations. Cyclic voltammetry of 1+ exhibits two close-lying one-electron oxidation waves at 0.77 V and 0.94 V, and two similarly close one-electron reduction processes at -1.43 V and -1.56 V versus SCE in CH2Cl2. The electronic structures of 1n in the accessible redox states have been analysed via experiments (EPR and UV-vis-NIR spectroelectrochemistry) and by DFT/TD-DFT calculations, revealing the potential for bidirectional non-innocent behaviour of coordinated L(˙/-/˙2-). Specifically, the studies establish significant involvement of L based frontier orbitals in both the oxidation and reduction processes: [([9]aneS3)(dmso)Ru(III)-L˙](3+) (1(3+)) ⇌ [([9]aneS3)(dmso)Ru(III)-L(-)](2+)/[([9]aneS3)(dmso)Ru(II)-L˙](2+) (1(2+)) ⇌ [([9]aneS3)(dmso)Ru(II)-L(-)](+) (1(+)) ⇌ [([9]aneS3)(dmso)Ru(II)-L(˙2-)] (1) ⇌ [([9]aneS3)(dmso)Ru(II)-L(3-)](-)/[([9]aneS3)(dmso)Ru(I)-L(˙2-)](-) (1-).

Naphthalene-1,8-di-amine-2-(pyrimidin-2-yl)-1H-perimidine (2/1)

In the title adduct, C15H10N4·2C10H10N2, the pyrimidine ring is nearly co-planar with the heteroatomic perimidine ring, as indicated dihedral angle between their mean planes of 3.21 (11)°. The di-aminona-phthalene mol-ecules are slightly twisted [dihedral angles = 4.2 (2) and 3.0 (2)°] because of the steric encumbrance of NH2 groups. The perimidine and di-aminona-phthalene mol-ecules are linked by N-H⋯N hydrogen bonds, forming an R (4) 4(12) graph-set motif across an inversion center. In the crystal, alternating layers of the perimidine and di-aminona-phthalene mol-ecules are formed along [100]. In the perimidine layer, mol-ecules are π-π stacked along the c-axis direction with an inter-plane separation of approximately 3.4 Å.

Synthesis and characterization of acetylene-linked bisphenalenyl and metallic-like behavior in its charge-transfer complex

We prepared and isolated a phenalenyl-based neutral hydrocarbon (1 b) with a biradical index of 14%, as well as its charge-transfer (CT) complex 1 b-F(4)-TCNQ. The crystal structure and the small HOMO-LUMO gap assessed by electrochemical and optical methods support the singlet-biradical contribution to the ground state of the neutral 1 b. This biradical character suggests that 1 b has the electronic structure of phenalenyl radicals coupled weakly through an acetylene linker, that is, some independence of the two phenalenyl moieties. The monocationic species 1 b*+ was obtained by reaction with the organic electron acceptor F4-TCNQ. The cationic species has a small disproportionation energy deltaE for the reaction 2 x 1 b*+ <==> 1 b + 1 b2+, which presumably originates from the independence of the phenalenyl moieties. The small deltaE led to a small on-site Coulombic repulsion U(eff) = 0.61 eV in the CT complex. Moreover, a very effective orbital overlap of the phenalenyl rings between molecules afforded a relatively large transfer integral t = 0.09 eV. The small U(eff)/4t ratio (= 1.7) resulted in a metallic-like conductive behavior at around room temperature. Below 280 K, the CT complex showed a transition into a semiconductive state as a result of bond formation between phenalenyl and F4-TCNQ carbon atoms.