Search

New iron and cobalt bis(dithiolene) complexes [M(3cbdt)2] (3cbdt = 3-cyanobenzene-1,2-dithiolate) were prepared as tetraphenylphosphonium (Ph4P+) salts for Fe in the monoanionic state and for Co in both the dianionic and monoanionic states: (Ph4P)2[Fe(III)(3cbdt)2]2 (1); (Ph4P)2[Co(III)(3cbdt)2]2 (2); (Ph4P)2[Co(II)(3cbdt)2] (3). These compounds were characterized by single-crystal X-ray diffraction, cyclic voltammetry, EPR, and static magnetic susceptibility. Their properties are discussed in comparison with the corresponding complexes based on the isomer ligand 4-cyanobenzene-1,2-dithiolate (4cbdt) and 4,5-cyanobenzene-1,2-dithiolate (dcbdt), previously described by us. The Fe(III) and the Co(III) compounds (1 and 2) are isostructural, crystallizing in the triclinic P 1 ¯ space group, with cis [M(III)(3cbdt)2] complexes dimerized in a trans fashion, and the transition metal (M = Fe, Co) has a distorted 4+1 square pyramidal coordination geometry. The Co(II) compound (3) crystallizes in the triclinic P 1 ¯ space group, with the unit cell containing one cis and three trans inequivalent [Co(II)(3cbdt)2] complexes with the transition metal (Co) and having a square planar coordination geometry. The Fe(III) complex (1) is EPR-silent, and the static magnetic susceptibility shows a temperature dependence typical of dimers of antiferromagnetically coupled S = 3/2 spins with −J/kB = 233.6 K and g = 1.8. Static magnetic susceptibility measurements of compound (3) show that this Co(II) complex is paramagnetic, corresponding to an S = ½ state with g = 2, in agreement with EPR spectra showing in solid state a hyperfine structure typical of the I(59Co) = 7/2. Static susceptibility measurements of Co(III) complex (2) showed an increase in the paramagnetic susceptibility upon warming above 100 K, which is consistent with strong AFM coupling between dimerized S = 1 units with a constant −J/kB ~1286 K. [ABSTRACT FROM AUTHOR]

The importance of C–H⋯N≡C interactions in the crystal engineering of conducting materials was recently evidenced by a new type of two-dimensional conducting material with the composition of (5-CNB-EDT-TTF)4A with a variety of anions A, where CNB-EDT-TTF denotes the electron donor cyanobenzene-ethylenedithio-tetrathiafulvalene, which has been described in the last few years, presenting a new type of bilayer structure. The unique bilayer donor structure of these compounds is due to the network of C–H⋯N≡C interactions, which although generally considered weak, are effective in the self-assembly of the crystal structure. The role of these weak interactions is made clear by a comparison of the salts of this donor and the related isomer 4-CNB-EDT-TTF, where no bilayer structure is obtained but a variety of related interactions are observed instead. This comparison allows different patterns of weak C–H⋯N≡C interactions to be identified in these compounds, which can be described as combinations of several different synthons of type R 22 (10), R 22 (24), R 22 (26), R 23 (10), R 24 (8), R 24 (10), R 48 (20), and R 34 (30) or C(5) and C(6) infinite chains. The different patterns of interactions are comparable with those observed in other cyano compounds, as well as the magnitude of the interaction enthalpy associated with the different synthons, as estimated by means of density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

The family of recently described salts based on the electron donor CNB-EDT-TTF (5-cyanobenzene-ethylenedithio-tetrathiafulvalene) and different anions A, with general formula (CNB-EDT-TTF)4A, constitutes an unprecedented type of molecular conductor based on a bilayer structure of the donors. The crystal structures of the bilayer conductors (CNB-EDT-TTF)4A with small discrete anions are reviewed and analyzed considering previously reported compounds with different anions (A = I3−, ClO4−, BF4−, ReO4−, PF6− and SbF6−), as well as three new members of this family described here with AsF6−, AuI2−and I2Br−. A common structural feature of this family of compounds is the head-to-head arrangement of the donors, induced by a network of weak C≡N⋯H–C interactions, which can be described as an effective combination of R 22 (10) and R 24 (10) synthons, forming donor bilayers alternating with anionic layers. The magnitude of the interactions associated with R 22 (10) and R 24 (10) synthons is estimated to be 4.7 and 10.0 kcal mol−1, respectively. In spite of the common donor bilayer arrangement, a rich diversity of structural variations and polymorphs is observed. These structures are related to different types of donor or anion arrangements, which are analyzed. For all anions a β′′-type packing pattern of the donor molecules arranged in virtually identical bilayers is observed. However, for (CNB-EDT-TTF)4I3, so far a unique exception in this family of compounds, a distinct κ-type packing of the donors, is also obtained as a metastable phase as shown also by DFT calculations that predict the κ-phase above the β′′-phase. Another type of polymorphism is observed in β′′-(CNB-EDT-TTF)4A, compounds with tetrahedral anions, related to the tilting of the donor molecules (either alternating or uniform) in successive bilayers, leading to monoclinic or triclinic unit cells, with doubling of one cell parameter corresponding to the thickness of one bilayer (∼25 Å). Finally, the anions, which often appear with fractional site occupation factors, can be ordered in the anionic plane, with different degrees of correlation between successive anion planes as shown in the AsF6.compound. The implications of these structural features in the electronic properties of these compounds are also discussed. [ABSTRACT FROM AUTHOR]

Four salts of the dissymmetric TTF-derivative 4-cyanobenzene-ethylenedithio-tetrathiafulvalene (4-CNB-EDT-TTF) with different anions, namely (4-CNB-EDT-TTF)A with A = ClO4 (1), BF4 (2) and (4-CNB-EDT-TTF)2[M(mnt)2] with M = Ni (3) and Au (4), were obtained by electrocrystallization and characterized by single-crystal X-ray diffraction, magnetic susceptibility and electrical conductivity measurements in comparison with the analogues based on the donor 5-CNB-EDT-TTF. All the compounds present dimerization of the donor units. Compounds 1 and 2 are isomorphous with a crystal structure characterized by slipped head to tail donor dimer stacks segregated from anion columns. Compounds 3 and 4 are isostructural with a crystal structure characterized by alternated stacks of head to tail donor dimers and acceptors. In spite of the different structural types and stoichiometries, all of these compounds have C≡N⋯H pairing interactions associated with R 22 (8), R 24 (8), R 22 (10), and R 24 (10) synthons between donors in nearby dimers. 3 and 4 are semiconductors, and their magnetic susceptibility exhibits a behaviour typical of antiferromagnetically coupled spin chains with magnetic exchange values J/k = −149.9 and −60.1 K, respectively, and in the case of 3, a Curie–Weiss contribution from the paramagnetic anions [Ni(mnt)2]−. [ABSTRACT FROM AUTHOR]

α-Methyldithiophene-tetrathiafulvalene (α-mDT-TTF), the first alkyl-substituted thiophene-tetrathiafulvalene electronic donor, and some of its charge-transfer salts were explored. The crystal structure of α-mDT-TTF is composed of molecular stacks aligned parallel to each other. Its cyclic voltammetry shows higher electron-donor ability than the unsubstituted analogue. This material was employed as a semiconductor in an organic field-effect transistor and showed a mobility of 4 × 10-4 cm2 V-1 s-1. Two charge-transfer salts of this donor with [M(mnt)2]- anions (mnt = maleonitriledithiolate), M = Co and Au, were obtained by electrocrystallization; they present unusual stoichiometries: (α-mDT-TTF)[Co(mnt)2] and (α-mDT-TTF)3[Au(mnt)2]2. In the cobalt compound, the donor molecules are fully oxidized and the Co complex is dimerized; it presents semiconducting behavior (7 × 10-3 S cm-1). The gold compound is composed of alternating stacks of donor trimers and pairs of anions. [ABSTRACT FROM AUTHOR]

Transition metal complexes based on the new ligand 5-methylthiophene-2,3-dithiolate (α-mtpdt) and Au, Ni, Fe, Co, Cu Pt and Pd were prepared as tetraalkylammonium and tetraarylphosphonium salts and characterised by cyclic voltammetry, X-ray diffraction, electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements. Except for the Cu complex, which forms a four-metal cluster [Cu4(α-mtpdt)3]2-, the metals form complexes of the general formula [M(α-mtpdt)2]. With Au, Ni and Fe, the complexes are directly obtained from the synthesis as monoanionic salts, and the isostructural crystal structures of [ nBu4N][Ni(α-mtpdt)2] and [ nBu4N][Au(α-mtpdt)2] were solved by single-crystal X-ray diffraction. For M = Co, Pt and Pd, both monoanionic and dianionic salts were obtained, and the crystal structures of [Ph4As]2[Co(α-mtpdt)2] and [Ph4As]2[Pd(α-mtpdt)2] were determined by single-crystal X-ray diffraction. The Co compound presents a rare tetrahedral coordination geometry. The oxidation of the monoanionic Ni and Au complexes with iodine leads to stable neutral complexes, which are fairly soluble in common organic solvents such as acetonitrile and dichloromethane. The crystal structure of [Ni(α-mtpdt)2] was solved by single-crystal X-ray diffraction. The electrical conductivities of the neutral Ni and Au complexes as polycrystalline compressed pellets are typical of a semiconductor; the room-temperature conductivities are 5.2 × 10-7 and 8.7 × 10-5 S cm-1, and the activation energies are 325 and 287 meV, respectively. [ABSTRACT FROM AUTHOR]

The electronic donor α-DT-TTF (α-dithiophene-tetrathiafulvalene), which among the thiophenic TTF derivatives has remained essentially unexplored, and some of its charge transfer salts are described in detail in this paper. This donor was efficiently prepared by the homocoupling of 5,6-thieno[2,3- d]-1,3-dithiol-2-one, and its redox properties are intermediate between those of DT-TTF (dithiophene-tetrathiafulvalene) and BET-TTF [bis(ethylenethio)tetrathiafulvalene]. The crystal structure of α-DT-TTF shows a molecular packing composed of trios of donor chains with alternating orientation. This pattern is clearly distinct from those previously found in all other thiophenic TTF donors. Used as an active material in a field-effect transistor, α-DT-TTF presents a mobility μFE = 5 × 10-5 cm2/V s. The possibility to convert this new donor to conducting charge-transfer salts with suitable anions was demonstrated by preparing its PF6- salts. Two salts with different crystal structures and stoichiometries were identified by X-ray diffraction studies: (α-DT-TTF)(PF6)0.6 and (α-DT-TTF)2(PF6). The electrical conductivities of these salts, measured in the single crystal, range from 9 to 50 S/cm at room temperature. In all cases, the salts show a semiconducting behaviour and properties that are comparable to those of the analogous nonaromatic BET-TTF salts. [ABSTRACT FROM AUTHOR]

Abstract: Pyrazinedicyanoethylthiotetrathiafulvalene, (pzdc-TTF) (1a), an extended TTF fused with a pyrazine moiety and also a dithiolene ligand precursor, was synthesized through a cross-coupling with triethyl phosphite between pyrazine-1,3-dithiole-2-thione (I) and 4,5-bis(2-cyanoethylthio)-1,3-dithiole-2-one (III). This reaction also yields to dipyrazine TTF derivative (1b) and 2,3,6,7-Tetrakis(2-cyanoethylthio)TTF (1c), resulting from the self-coupling reactions of the thione (I) and ketone (III). The crystal structure of 1a is composed by pairs of head to head donor stacks of pzdc-TTF molecules along b in opposite orientations. Single crystals of 1b revealed a new polymorph with a face-to-face π-stacking motif. The electrochemical properties of 1a studied by cyclic voltammetry (CV) in DMF, shows two single electron oxidation processes typical of TTF-based donors; one pair of asymmetric redox waves centered at 627mV versus Ag/Ag+ is ascribed to the couple [pzdc-TTF]+/[pzdc-TTF]2+, and one pair of quasi-reversible redox waves centered at 430mV is ascribed to the couple [pzdc-TTF]0/[pzdc-TTF]+. [Copyright &y& Elsevier]

We report the synthesis of the iron(III) complex of the hexadentate Schiff base ligand nsal2trien obtained from the condensation of triethylenetetramine and 2 equiv. of 2-hydroxy-l-naphthaldehyde. The study of the salt [Fe(nsal2trien)]SCN (l) by magnetic susceptibility measurements and Mossbauer spectroscopy reveals a rather unique behavior that displays thermally induced spin crossover (SCO) with two well-separated steps at 250 (gradual transition) and 142 K (steep transition). Single crystal X-ray structures were obtained at 294, 150, and 50 K, for the high spin (HS), intermediate (Int), and low spin (LS) phases. The HS and LS phases are isostructural, and based on a single FeIII site (either HS or LS) an unusual symmetry break occurs in the transition to the Int ordered phase, where the unit cell includes two distinct Felu sites and is based on a repetition of the [HS--LS] motif. The two-step SCO behavior of 1 must result from the existence of structural constraints preventing the full conversion HS ↔ LS in a single step. [ABSTRACT FROM AUTHOR]

The synthesis of the [Fe(5-Cl-qsal) 2 ][Ni(dmit) 2 ]·2CH 3 CN ( 1 ) is reported in the present work. The crystal structures of 1 , solved at 150, 245, 255 and 294 K, revealed the presence of low spin (LS) and high spin (HS) Fe III centers at 150 and 294 K, respectively, and mixed HS/LS states ∼50:50 and 75:25 at 245 and 255 K. The crystal structure is based on alternating cationic and anionic layers, where each layer is composed of an arrangement of chains of cations or anions. The anionic chains consist on the stacking of face-to-face pairs of [Ni(dmit) 2 ] − anions. Extended ππ contacts, involving the 5-Cl-qsal ligands, were observed in the cationic chains. The contribution of the anions to the magnetization correlates well with an alternating chain, dominated by antiferromagnetic interactions. A spin crossover (SCO) process, assigned to the [Fe(5-Cl-qsal) 2 ] + cationic network was observed at high temperatures ( T ∼ 240 K). The thermal dependence of the magnetization suggests the existence of an abrupt change at ∼233 K from the LS state to a mixed 50:50 HS/LS state, followed by a gradual transformation at ∼256 K to the HS state. A structural transformation consisting of the doubling of the unit cell was observed to be associated with the SCO process. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of (α-DT-TTF)2[Au(mnt)2] is reported. The magnetic properties of this new salt show that it is still a rare example of an organic spin-ladder. (α-DT-TTF)2[Au(mnt)2] shares the same ladder structure of the DT-TTF and ETT-TTF analogues, and its room temperature conductivity is ~2 S/cm. Despite the observed donor orientation disorder associated with the thiophenic sulfur atoms, the intermolecular interactions between donor units, calculated using the extended Hückel approximation and a double-ζ basis set, show that the interaction values do not depend on the configuration of the sulfur atom on the thiophenic ring. The insensitivity of the spin-ladder magnetic properties to the donor molecular disorder in (α-DT-TTF)2[Au(mnt)2] is a direct consequence of the negligible contribution of the disordered thiophenic sulfur atom to the HOMO. In the related donor ETT-TTF, this contribution is significant and destroys the magnetic interactions, and no spin-ladder is observed. This compound not only enlarges the number of organic spin-ladder systems in diis series of closely related compounds but also provides an interesting example of weakly disordered molecular spin-ladder system. [ABSTRACT FROM AUTHOR]

Abstract: The Ni and Au bis(dithiolene) complexes based on the 1-(pyridine-4-yl)-ethylene-1,2-dithiolate ligand were prepared in their neutral state and characterized namely by single-crystal X-ray diffraction, electronic UV–Vis–NIR spectroscopy, EPR and magnetic susceptibility measurements. The crystal structure of the neutral complex [Ni(4-pedt)2]0 lacks a regular and multidimensional extended network of short contacts and as a consequence electrical conductivity measurements in single crystals show a semiconducting behavior with room temperature values of the order of 10−6 S/cm, while the magnetic measurements of the gold compounds indicate a reduced effective magnetic moment due to strong antiferromagnetic interactions between radical neutral complex units. The nitrogen coordination ability of theses complexes was demonstrated by the coordination of pyridine to a sodium ion observed in the [Au(4-pedt)2]2NaPF6 complex which was also characterized by single-crystal X-ray diffraction and magnetization. In this compound the Na ions in half occupied positions are coordinated by anion fluorine atoms and nitrogen and carbon atoms from the neutral [Au(4-pedt)2] complexes. [Copyright &y& Elsevier]

Abstract: The monoanionic Ni, Au and Cu bisdithiolene complexes based on the 1-(pyridin-4-yl)-ethylene-1,2-dithiolate were prepared and isolated as [PPh4]+, [n-Bu4N]+ and [Na(18C6)]+ salts which were characterised by single-crystal X-ray diffraction, cyclic voltammetry, EPR and magnetic susceptibility measurements. All the complexes adopt a square planar coordination geometry with a trans arrangement of the substituent pyridine rings whose planes are rotated from 13° to 33° relatively to the central MS4 core. The C–C and C–S bond lengths are consistent with ene-1,2-dithiolate form of the ligand and MIII oxidation state. The Ni complexes are paramagnetic with an effective magnetic moment of ∼1.7BM. [Copyright &y& Elsevier]

We report on the straightforward synthesis, characterization and photovoltaic and light-emission applications of two series of BODIPY molecules with aryloxy or alkoxy groups bonded to the boron centre. The crystal structures of two of these new dyes are also presented. The BODIPYs have absorption features similar to those of the analogous boron-fluorinated BODIPYs used as starting materials. However, the fluorescence properties vary significantly with the nature of the aryloxy/alkoxy group. The photovoltaic performance in bulk heterojunction solar cells of the newly synthesized compounds does not, however, outperform that of the parent boron-fluorinated BODIPYs. The maximum power conversion efficiency was obtained with two non-fluorescent BODIPYs, reaching 0.9%, compared with 2.79% obtained for the cells based on the corresponding boron-fluorinated precursor. The fluorine replacement by aryloxy/alkoxy groups had instead a positive effect on the light-emitting properties of the compounds of one of the series, leading to higher maximum luminance (114 cd/m2) and efficiency (0.057 cd/A), compared to devices based on the corresponding boron-fluorinated dye (35 cd/m2 and 0.015 cd/A, respectively). • Straightforward synthesis and characterization of a new O-BODIPY dyes series. • Crystal structure of two O-BODIPY dyes. • Performance evaluation of the BODIPY dyes as electron-donors in bulk heterojunction photovoltaic cells. • Application as emissive materials in light-emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]