A three-dimensional synthetic metallic crystal composed of single-component molecules

Colloidal solutions of organic conductive nanoparticles

Although molecular metals have been known for decades, their insolubility, low vapor pressure, and synthesis routes have prevented them from being integrated into electronic devices. We have prepared stable colloidal solutions of the organic metal TTF-TCNQ that overcome such difficulties. The solutions contain well-dispersed nanoparticles stabilized by long alkyl chain amines. They afford soluble powders by evaporation and homogeneous thin films by drop-casting. Powders and films show room temperature conductivities in the 0.01-0.1 S cm(-1) range.

Electronic excitation spectra of radical anions of cyanoethylenes and cyanobenzenes: symmetry adapted cluster-configuration interaction study

Electronic excitation spectra of the radical anions of cyanoethylenes (trans-dicyanoethylene and tetracyanoethylene) and cyanobenzenes (1,2-dicyanobenzene: o-DCNB, 1,3-dicyanobenzene: m-DCNB, and 1,4-dicyanobenzene: p-DCNB) were studied by the symmetry adapted cluster-configuration interaction (SAC-CI) method. Theoretical calculations predicted positive electron affinities for all the molecules in good agreement with the experimental observations. Electronic excitation spectra of open-shell radicals is a topic that has not been studied as much as such spectra of closed-shell molecules, but this can be easily addressed using SAC-CI theory. The present paper systematically describes the calculation procedures for radical anions by investigating several basis sets, including anion diffuse and Rydberg functions. The calculated excitation energies were in good agreement with the experimental UV∕NIR (near infrared region) spectra, which had been observed by one of the present authors in 2-methyltetrahydrofuran matrix frozen to transparent glassy solids at 77 K. For p-DCNB, the SAC-CI theoretical spectrum agreed particularly well with the experimental spectrum. An extremely weak π*(SOMO) - π* excitation at 1.41 eV predicted in the present work, but had been overlooked in the previous experimental spectrum published in 1988, was confirmed to be real by a careful re-examination of the old spectrum.

Ab initio derivation of multi-orbital extended Hubbard model for molecular crystals

From configuration interaction (CI) ab initio calculations, we derive an effective two-orbital extended Hubbard model based on the gerade (g) and ungerade (u) molecular orbitals (MOs) of the charge-transfer molecular conductor (TTM-TTP)I(3) and the single-component molecular conductor [Au(tmdt)(2)]. First, by focusing on the isolated molecule, we determine the parameters for the model Hamiltonian so as to reproduce the CI Hamiltonian matrix. Next, we extend the analysis to two neighboring molecule pairs in the crystal and we perform similar calculations to evaluate the inter-molecular interactions. From the resulting tight-binding parameters, we analyze the band structure to confirm that two bands overlap and mix in together, supporting the multi-band feature. Furthermore, using a fragment decomposition, we derive the effective model based on the fragment MOs and show that the staking TTM-TTP molecules can be described by the zig-zag two-leg ladder with the inter-molecular transfer integral being larger than the intra-fragment transfer integral within the molecule. The inter-site interactions between the fragments follow a Coulomb law, supporting the fragment decomposition strategy.

Bis(tetra-n-butyl-ammonium) bis-(5,6-dicyano-pyrazine-2,3-dithiol-ato-κS,S')palladium(II)

In the title complex, (C(16)H(36)N)(2)[Pd(C(6)N(4)S(2))(2)], the centrosymmetric dianion is planar, with an r.m.s. deviation of 0.034 (8) Å. The Pd(II) atom, lying on an inversion center, has a square-planar coordination geometry, with Pd-S bond lengths of 2.276 (3) and 2.294 (3) Å.

Study of molybdenum(4+) quinoxalyldithiolenes as models for the noninnocent pyranopterin in the molybdenum cofactor

A model system for the molybdenum cofactor has been developed that illustrates the noninnocent behavior of an N-heterocycle appended to a dithiolene chelate on molybdenum. The pyranopterin of the molybdenum cofactor is modeled by a quinoxalyldithiolene ligand (S(2)BMOQO) formed from the reaction of molybdenum tetrasulfide and quinoxalylalkyne. The resulting complexes TEA[Tp*MoX(S(2)BMOQO)] [1, X = S; 3, X = O; TEA = tetraethylammonium; Tp* = hydrotris(3,5-dimethylpyrazolyl)borate] undergo a dehydration-driven intramolecular cyclization within quinoxalyldithiolene, forming Tp*MoX(pyrrolo-S(2)BMOQO) (2, X = S; 4, X = O). 4 can be oxidized by one electron to produce the molybdenum(5+) complex 5. In a preliminary report of this work, evidence from X-ray crystallography, electronic absorption and resonance Raman spectroscopies, and density functional theory (DFT) bonding calculations revealed that 4 possesses an unusual asymmetric dithiolene chelate with significant thione-thiolate character. The results described here provide a detailed description of the reaction conditions that lead to the formation of 4. Data from cyclic voltammetry, additional DFT calculations, and several spectroscopic methods (IR, electronic absorption, resonance Raman, and electron paramagnetic resonance) have been used to characterize the properties of members in this suite of five Mo(S(2)BMOQO) complexes and further substantiate the highly electron-withdrawing character of the pyrrolo-S(2)BMOQO ligand in 2, 4, and 5. This study of the unique noninnocent ligand S(2)BMOQO provides examples of the roles that the N-heterocycle pterin can play as an essential part of the molybdenum cofactor. The versatile nature of a dithiolene appended by heterocycles may aid in modulating the redox processes of the molybdenum center during the course of enzyme catalysis.

Frontiers of organic conductors and superconductors

We review the development of conductive organic molecular assemblies including organic metals, superconductors, single component conductors, conductive films, conductors with a switching function, and new spin state (quantum spin liquid state). We emphasize the importance of the ionicity phase diagram for a variety of charge transfer systems to provide a strategy for the development of functional organic solids (Mott insulator, semiconductor, superconductor, metal, complex isomer, neutral-ionic system, alignment of chemical potentials, etc.). For organic (super)conductors, the electronic dimensionality of the solids is a key parameter and can be designed based on the self-aggregation ability of a molecule. We present characteristic structural and physical properties of organic superconductors.

Synthesis, characterization, spectroscopy, electronic and redox properties of a new nickel dithiolene system

A new dithiolene ligand with 3,5-dibromo substituted phenyl groups was designed and synthesized. The protected form of the ligand was reacted with a nickel salt providing neutral Ni(S(2)C(2)(3,5-C(6)H(3)Br(2))(2))(2) and anionic [Ni(S(2)C(2)(3,5-C(6)H(3)Br(2))(2))(2)](-) isolated as a Bu(4)N(+) salt. Both were characterized by UV-visible and IR spectroscopy and compared with the similar known molecular systems. They exhibit intense low-energy transitions that are characteristic of such systems. The electrochemical behavior of these molecules was investigated by cyclic voltammetry.