Dicyanomethylene Group Research Articles

Effects of Acceptor Modification on Charge Transfer in Crystals of Donor‐Acceptor Systems of TTF

AbstractThe degree of charge transfer has been determined in six TTF‐fluorene derivative charge transfer complexes, using IR and Raman vibrational spectroscopies. It has been found that changes of the intermolecular electronic distribution is strongly influenced by the presence of the dicyanomethylene group, by the increase of the nitro groups, as well as by the symmetry of the acceptor.

Synthesis and characterization of metal tris-dithiocroconate complexes and dicyanomethylene-substituted analogues. Crystal and molecular structure of [Ph 4P] 3[Co(dtcroc) 3]·)0.6acetone

Metaltris-dithiolene compounds with the composition [Ph 4P] 3[M(dtcroc) 3]·solvent (M s= Cr, solvent s= EtOH; M s= Fe, solvent s= DMF; M s= Co, solvent s= acetone; dtcroc =3,4,5-trioxocyclopent-1-ene-1,2-dithiolato-) have been prepared and characterized. The magnetic properties of the paramagnetic Fe and Cr salts are consistent with strong-field octahedral coordination of the metal ion. The crystal structure of [Ph 4P] 3[Co(dtcroc) 3]·0.6acetone confirms that the cobalt ion is octahedrally coordinated by the sulfur atoms of three chelating dithiocroconate ligands. Each [M(dtcroc) 3] 3− (M s= Cr, Fe, Co) ion undergoes reversible or quasi-reversible one-electron oxidation in acetonitrile solution at 25°C; the measured E 1/2(−2/−3) values are ca 300 mV more anodic than those of any previously reported metal tris-dithiolene analogues. The Fe(dtcroc) 3] 3− ion also exhibits a quasi-reversible one-electron reduction. Reaction of [M(dtcroc) 3] 3− ions with excess malononitrile in DMF solution yields dicyanomethylene-substituted analogues with the formula [M(dcmdtcroc) 3] 3− (M s= Cr, Fe, Co; dcmdtcroc s= 4-dicyanomethylene-3,5-dioxocyclopent-1-ene-1,2-dithiolato). Replacement of the central oxo-group of each dithiocroconate ligand with the more electronegative dicyanomethylene group causes significant shifts in both the visible absorption bands and redox potentials of the complexes; however, the similar stabilities and magnetic properties of analogous [M(dcmdtcroc) 3] 3− and [M(dtcroc) 3] 3− complexes indicate that dicyanomethylene substitution on the ligand periphery does not dramatically alter the character of the metal-ligand interaction.

Theoretical studies on the electronic structure and nonlinear properties of dicyanomethylene substituted squaramides, croconamides and rhodizonamides

The structure and dipole moments of squaramides, croconamides and rhodizonamides, and their derivatives containing the dicyanomethylene group, have been calculated using the AM1 and ab initio 3-21G methods. The molecular hyperpolarisabilities and dipole moments of these structures calculated using a semi-empirical sum-over-states method are predicted to increase with increasing ring size and increasing substitution by the dicyanomethylene group. 1,2,3-Tris(dicyanomethylene)croconamide has a calculated frequency dependent hyperpolarisability and dipole moment which exceed the values obtained for typical donor-acceptor azobenzenes, and shows potential as a new material for electro-optic modulation.

A theoretical study of the molecular and electronic structure of benzoannulated tetracyanoquinodimethanes

The molecular and electronic structure of a series of TCNQ derivatives with laterally extended π-systems is investigated using quantum-chemical methods. The steric hindrance introduced by lateral benzoannulation determines the loss of planarity of the molecular system which adopts a butterfly-type structure with the TCNQ ring folded in a boat conformation. PM3-optimized geometries are in good agreement with experimental X-ray data and show that the structural identity of the polyacenic units laterally fused to TCNQ is preserved. The evolution of the acceptor properties is rationalized with the help of VEH calculations. For the more extended TCNQs, these calculations show that the lateral naphthalene or anthracene units act as donors and determine the appearance of low-energy charge-transfer absorption bands. The geometries of negatively charged TCNQs up to the trianion are optimized at the PM3 level. The anions are calculated to be non-planar, thus explaining their low stability. For the dianions, the polycyclic skeleton is planar and the dicyanomethylene groups are rotated out of the molecular plane. While the first two extra electrons are mostly incorporated into the dicyanomethylene groups, the third electron added to form the trianion is shown to enter the central polycyclic unit. This result explains the formation of relatively stable trianions and tetra-anions for π-extended TCNQs.

Cyano‐substituted polyester, polyurethanes, and epoxy resin derived from 2,6‐bis(4‐hydroxybenzylidene)‐1‐dicyanomethylene–cyclohexane

AbstractThe condensation of cyclohexanone with 4‐hydroxybenzaldehyde utilizing dry HCI as the catalyst afforded 2,6‐bis(4‐hydroxybenzylidene)cyclohexanone. The latter was condensed with malononitrile to yield 2,6‐bis(4‐hydroxybenzylidene)‐1‐dicyanomethylene–cyclohexane, which was used as the starting material for the preparation of a novel class of polyesters, polyurethanes, and epoxy resins. In addition, a model diester and diurethane were synthesized and their spectroscopic data were correlated with those of the corresponding polymers. It was shown that the introduction of the dicyanomethylene groups in the polymer backbone remarkably improved the polymer solubility as well as its thermal stability. The crosslinked polymers obtained upon curing the polyester and polyurethanes at 300°C for 40 h were stable up to 365–407°C in N2 or air and afforded anaerobic char yields of 64–70% at 800°C. © 1994 John Wiley & Sons, Inc.

Novel Electron Acceptors Bearing a Heteroquinonoid System. 4. Syntheses, Properties, and Charge-Transfer Complexes of 2,7-Bis(dicyanomethylene)-2,7-dihydrobenzo[2,1-b:3,4-b']dithiophene, 2,7-Bis(dicyanomethylene)-2,7-dihydrobenzo[1,2-b:4,3-b']dithiophene, and 2,6-Bis(dicyanomethylene)-2,6-dihydrobenzo[1,2-b:4,5-b']dithiophene

The three title compounds were prepared as novel hetero-TCNQ electron acceptors comprising the quinonoid skeletons of different benzodithiophene types between two dicyanomethylene groups. On the basis of cyclic voltammetry, they have electron affinities comparable to or stronger than that of TCNQ. In addition, the extensive building blocks serve to induce the effective reduction of on-site coulombic repulsion. They thus behaved as superior electron acceptors for forming electrically conductive charge-transfer complexes. In particular, 2,7-bis(dicyanomethylene)-2,7-dihydrobenzo[2,1-b:3,4-b']dithiophene was the most tractable in terms of stability and solubility, giving a variety of conductive complexes with typical electron donors of TTT, TTF, and TPBP types. Most of these complexes showed a characteristic broad electronic transition in the infrared region of 2.9-4.0 kcm -1 , supporting the idea that their crystal structures assume a stacking form of segregated donor and acceptor columns with mixed valence states

Novel low bandgap polymers: polydicyanomethylene-cyclopentadithiophene and -dipyrrole

Results of quantum-chemical calculations are reported on the geometric and electronic structure of polydicyanomethylene-cyclopenta-dithiophene and its nitrogen analogue, polydicyanomethylene-cyclopenta-dipyrrole. Geometry optimizations are carried out by means of the semiempirical Austin Model 1 (AM1) technique. The introduction of the electron-withdrawing dicyanomethylene group between the thiophene or pyrrole rings of the unit cell induces major geometry modifications within each ring, resulting in the appearance of a geometric structure which can be viewed as a combination of aromatic and quinoid geometries. Based on the analysis of the bonding-antibonding electronic patterns appearing on the HOMO and LUMO levels of those polymers, as obtained from VEH band-structure calculations, it is shown that the small calculated bandgaps (0.59 and 0.37 eV for the thiophene and pyrrole derivatives, respectively) arise from HOMO and LUMO levels that are located between those of aromatic and quinoid polythiophene or polypyrrole chains.

Vicarious nucleophilic substitution of pyridines via their dicyanomethylide derivatives.

Vicarious nucleophilic substitution of pyridinium 1-dicyanomethylides with 1-chloromethyl phenyl sulfone gave corresponding 4-substituted derivatives. The dicyanomethylene group was readily eliminated via radical reaction to afford 4-phenylsulfonylmethylpyridines.

Studies on π-acceptor molecules containing the dicyanomethylene group. X-Ray crystal structure of the charge-transfer complex of tetramethyltetrathiafulvalene and 2,3-dicyano-1,4-naphthoquinone: (TMTTF)3–(DCNQ)2

The reaction of tetramethyltetrathiafulvalene (TMTTF, 7) with 2-dicyanomethyleneindane-1,3-dione (DCID, 1) leads to isomerisation of DCID to 2,3-dicyanonaphthoquinone (DCNQ, 3) to yield the charge-transfer complex [(TMTTF)3]2˙+–(DCNQ˙–)28. The X-ray crystal structure of complexe 8 reveals stacks of TMTTF molecules along the xdirection in the sequence A ‥ B ‥ A ‥ A ‥ B ‥ A ‥etc.. The A ‥ A and A ‥ B interplanar separation distances are 3.51 Å and 3.44 Å, respectively. The DCNQ radical anions form dinners, with a remarkably short interplanar separation of 3.02 Å, which are orthogonal to the TMTTF stacks. The complex is diamagnetic. Other π-acceptor molecules containing the dicyanomethylene group, viz. compounds 2 and 10–12, have been prepared and their redox properties studied by cyclic voltammetry. Compound 2 rearranges to compound 4 on complexation with TTF 6. DCID derivatives 1and 2 react with a range of amines, by displacement of one cyano group, to yield enamines 15–19; the amphiphilic compound 18 forms Langmuir–Blodgett films which exhibit weak second harmonic generation.

Vicarious Nucleophilic Substitution of 1,2,3-Triazines

Vicarious nucleophilic substitution of 1,2,3-triazinium 2-dicyano- methylides with 1-chloromethyl phenyl sulfone proceeded to give corresponding 5- substituted derivatives. Dicyanomethylene group was readily eliminated by radical reaction to afford 5-phenylsulfonylmethyl-1,2,3-triazines

An Isomeric Series of Thiophene-Fused Tetracyanoquinodimethanes. II. The Crystal and Molecular Structures

Abstract The crystal structures of three isomeric thiophene-fused TCNQs, 4,8-bis(dicyanomethylene)-4,8-dihydrobenzo[1,2-b : 4,5-b′]dithiophene (1), [1,2-b : 5,4-b′] isomer (2), and [1,2-b : 4,5-c′] isomer (3) have been determined by the X-ray method. The crystals of 1, 2, and 3 are an isostructure of the monoclinic system with the space group of P21/n. For 1, a = 16.588(3), b = 7.222(5), c = 11.353(3) Å, β = 89.88(2)°, V = 1360.1(10) Å3, Z = 4, Dx = 1.545 Mg m−3. For 2a = 16.594(4), b = 7.232(2), c = 11.433(2) Å, β = 91.05(2)°, V = 1371.8(5) Å3, Dx = 1.532 Mg m−3. For 3a = 16.738(2), b = 7.342(3), c = 10.922(3) Å, β = 92.98(2)°, V = 1340.4(7) Å3, Dx = 1.568 Mg m−3. These crystals show an orientational disorder with an approximate molecular symmetry of mm. The occupancy factors are 0.834 : 0.166, 0.709 : 0.291, and 0.5 : 0.1 : 0.15 : 0.25 for 1, 2, and 3, respectively. The final R values are 0.065, 0.070, and 0.096 for 2308, 2410, and 1566 observed reflections for 1, 2, and 3, respectively. In the crystals molecules form a sheet-like network perpendicular to the b axis, with short intermolecular S···N distances (3.047 and 3.086 Å for 1 and 3.076 Å for 2). The internetwork distances between S atoms are significantly shorter than the van der Waals contact: 3.451 and 3.461 Å for 1 and 2, respectively. Each molecule has a butterfly shape. Two dicyanomethylene groups are bent from the quinonoid ring to the same side and two thiophene rings are bent to the opposite side of the dicyanomethylene groups.

Photo-Oxidation of Substituted 2-Dicyanomethylene-1,2-dihydropyridines

Abstract About the conversion of dicyanomethylene group to alkylcarboxylate on the photo-oxidation of 2-dicyanomethylene-1,2-dihydropyridines.

Design of Novel Chalcogen-Containing Organic Metals: Extensively Conjugated Electron Donors and Acceptors With Reduced On-Site Coulomb Repulsion

Abstract This review describes the design of extensively conjugated electron donors and acceptors based on structural modifications of tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ), respectively. These molecules have the advantage of reduced on-site Coulomb repulsion which is one of the prerequisites for components of organic metals. The construction of such large compounds is currently accomplished by insertion of an extensively π-conjugated system between two 1,3-dithiolylidene or dicyanomethylene groups. The usefulness of a heteroquinoid system as such a building block is demonstrated by examples of heteroatom-incorporating TCNQ acceptors (hetero-TCNQs), which form a variety of highly conductive charge-transfer complexes. In addition, recent advances concerning quino-2,2′-bis(1,3-dithioles) and TTF vinylogs as novel electron donors are introduced.

Electron acceptor molecules: new, expedient synthesis of substituted 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) derivatives and the X-ray crystal structure of 2,5-dibromo-TCNQ

A range of TCNQ derivatives,viz. 2,5-dichloro-, 2,5-dibromo-, 2,5-dimethoxy-, 2-methoxycarbonyl- and benzo-TCNQ, and 11,11,12,12-tetracyanonaphtho-2,6-quinodimethane (TNAP), have been efficiently synthesised using 2-chlorcbenzyl thiocyanate as the source of electrophilic cyanide in reactions with the corresponding di(cyanomethyl)benzene or di(cyanomethyl)naphthalcne derivatives. The X-ray crystal structure of 2,5-dibrorno-TCNQ has been determined: the molecule is essentially planar with the dicyanomethylene groups bent away from the adjacent bromine atoms. There are close intermolecular Br ⋯ N contacts in the structure.

Electrochemical Oxidation of Croconate Salts; Evidence of the Chemical Equivalence of the Carbonyl Oxygen Atom and the Dicyanomethylene Group

Electrochemical Oxidation of Croconate Salts; Evidence of the Chemical Equivalence of the Carbonyl Oxygen Atom and the Dicyanomethylene Group

Zur Kenntnis organischerLewis-S�uren, 36.Cis?trans-Gleichgewichte und Konformationen von 2,(x)-Dialkyl-1-dicyanomethylencyclohexanen. Wahlweise einfache Darstellung dercis- odertrans-Formen

Knoevenagel condensation of malononitrile withcis- andtrans-2,5-dimethylcyclohexanone (1 c and1 t, respectively) leads to2 c and2 t, respectively, and withtrans-1-decalone to4 t. The equilibria2 c⇌2 t and4 c⇌4 t have been determined as well as, by means of 270-MHz-1H-NMR, the conformations of these four compounds. The dicyanomethylene group is found to induce axial positions of neighbouring alkyl residues on the cyclohexane ring (or when this is impossible, as in the case of4 t, the twist form of the cyclohexane ring). This results in a strong predominance of thecis isomers in the equilibria2 c⇌2 t and4 c⇌4 t whereas thetrans isomers strongly predominate in the equilibria among the starting ketones. This situation allows the optional preparation of2 c or2 t, and of4 c or4 t, from the more stable starting ketone (or ketone mixture). The free conformational energy of the distorted twist form of4 t amounts to 17 kJ/mol.

Synthesis of 4,4′-bis(dicyanomethylene)bicyclohexylidine

4,4′-Bis(dicyanomethylene)bicyclohexylidine and its dihydro derivative, 4,4′-bis(dicyanomethylene)bicyclohexyl were prepared from the condensation of malononitrile with the corresponding diketone. Bicyclohexylidene-4,4′-dione was synthesized from the monoketal of cyclohexanedione via the symmetric azosulfide.The uv spectra of the 4,4′-bis(dicyanomethylene)bicyclohexylidine and related model compounds indicate the presence of a long range interaction between the dicyanomethylene groups of the title compound.

The crystal structure of 10-dicyanomethyleneanthrone, an overcrowded aromatic compound

The crystal structure of 10-dicyanomethyleneanthrone has been determined by three-dimensional X-ray analysis to an accuracy of 0·01 A in the orthogonal atomic co-ordinates. The structure is orthorhombic, space group Pnam, with four molecules in a cell of dimensions a= 7·52, b= 8·84, c= 18·02 A. A clearance of 2·84 A between overcrowded carbon atoms is achieved by means of angular adjustments and by deformations out-of-plane. The configuration, which closely resembles that in bianthronylidene, involves a bend of 28° in the anthracene skeleton, a dihedral angle of 144° between the planar dicyanomethylene group and the anthracene framework, and a twist or non-parallelism of 5° out-of-plane between the direction defined by the 9,10 carbon atoms and corresponding directions in the outer rings.

ESR of Substituted Cyclobutane Anions

Paramagnetic anions of dicyanomethylene-2,2,4,4-tetramethylcyclobutanone (I) and bis-(dicyanomethylene)-2,2,4,4-tetramethylcyclobutane (II) were produced by electrolytic and chemical reduction. The ESR spectrum of II— indicates fast electron transfer between the two dicyanomethylene groups. 1,3-π-interaction and hyperconjugation are considered to be the predominant means of effecting the electron transfer.