Structure of thiocarbamide-containing cobalt(III) dioximates with [BeF4]2− and [BF4]− anions

The crystal structure of the complexes [Co(DH)₂(Tu)₂]₂[BeF₄]·C₂H₅OH (I) and [Co(DfH)₂(Tu)₂][BF₄] 0.5H₂ (II) (where DH^? is the dimethylglyoxime monoanion, DfH^? is the α-benzyldioxime monoanion, and Tu is thiourea) has been determined by X-ray diffraction analysis. The coordination polyhedron of the Co³⁺ atom is an N₄S₂ octahedron formed by four nitrogen atoms of the dioxime molecule and two sulfur atoms of the fragments of thiourea (Tu); the latter have parallel and perpendicular orientations relative to the dioxime residue. The deviation of the cobalt atom from the four-angle plane (formed by the nitrogen atoms of the dimethylglyoxime residues) does not exceed 0.019 Å. The Co-N and Co-S distances vary from 1.877(3) Å to 1.901(3) Å and from 2.280(1) Å to 2.307(1) Å, respectively. The statistically disordered cations [BeF₄]^2? and [BF₄]^? play an important role in crystal formation — they form a complex system of hydrogen bonds.     

Synthesis,crystal structure,and biological properties of the complex [Co(DmgH)<Subscript>2</Subscript>(Seu)<Subscript>1.4</Subscript>(Se-Seu)<Subscript>0.5</Subscript>(Se<Subscript>2</Subscript>)<Subscript>0.1</Subscript>][BF<Subscript>4</Subscript>]

A new Co(III) dioxime complex with selenocarbamide was obtained by the reaction of Co(BF₄)₂ ? 6H₂O, DmgH₂, and Seu (DmgH2 = dimethylglyoxime, Seu = selenocarbamide). According to X-ray diffraction (CIF file CCDC no. 1485732), the product was an ionic coordination compound with unusual composition, [Co(DmgH)₂(Seu)_1.4(Se-Seu)_0.5(Se₂)_0.1][BF₄] (I). Apart from two monodeprotonated DmgH￣ molecules, the central atom coordinates neutral Seu, Se-Seu, and Se₂ molecules. Thus, the crystal contains the complex cations [Co(DmgH)₂(Seu)₂]⁺, [Co(DmgH)₂(Seu)(Se-Seu)]⁺, and [Co(DmgH)₂(Seu)(Se₂)]⁺. Each [BF₄]￣ anion is linked to the cations not only by electrostatic forces but also by intermolecular N–H···F hydrogen bonds (H-bonds). The complex cations are combined by intermolecular N–H···O H-bonds. The new coordination compound was found to possess biological activity. Treatment of the garlic (Allium sativum L.) foliage with an aqueous solution of I optimizes the content of selenium in the leaves and cloves and enhances the growth and plant productivity. The organs of treated plants are characterized by enhanced antioxidant protection owing to increasing activity of antioxidant enzymes and contents of proline and assimilation pigments, and decreasing lipid peroxidation.     

Cobalt(III) dimethylglyoximates containing selenourea and an unusual diselenourea ligand: Synthesis and structures

The complexes [Co(DH)₂(Seu) _y (Se-Seu) _z ]₂X · mSolv (DH is the dimethylglyoxime monoanion, Seu is selenourea, and X is [TiF₆]²⁻, [ZrF₆]²⁻) were obtained from the system CoX · 6H₂O-DH₂-Seu in DMF-MeOH or MeOH-H₂O and examined by UV, IR, and NMR spectroscopy and X-ray diffraction. Unexpectedly, the ligand Se-Seu (the oxidized form of selenourea) was detected on the axial coordinate, partially replacing selenourea. The complexes were formulated as [Co(DH)₂(Seu)_1.75(Se-Seu)_0.25]₂[TiF₆] · H₂O (I) and [Co(DH)₂(Seu)(Se-Seu)]₂[ZrF₆] · 3H₂O (II). The complex cations in I and II have trans-octahedral structures. Their crystal structures are made up of the complex Co³⁺ cations and the outer-sphere MF₆²⁻ anions (M = Ti(IV) (I) and Zr(IV) (II)) held together by electrostatic interactions and hydrogen bonds; water of crystallization is also involved in hydrogen bonding.     

Prediction of remarkable ambipolar charge-transport characteristics in organic mixed-stack charge-transfer crystals

We have used density functional theory calculations and mixed quantum/classical dynamics simulations to study the electronic structure and charge-transport properties of three representative mixed-stack charge-transfer crystals, DBTTF-TCNQ, DMQtT-F(4)TCNQ, and STB-F(4)TCNQ. The compounds are characterized by very small effective masses and modest electron-phonon couplings for both holes and electrons. The hole and electron transport characteristics are found to be very similar along the stacking directions; for example, in the DMQtT-F(4)TCNQ crystal, the hole and electron effective masses are as small as 0.20 and 0.26 m(0), respectively. This similarity arises from the fact that the electronic couplings of both hole and electron are controlled by the same superexchange mechanism. Remarkable ambipolar charge-transport properties are predicted for all three crystals. Our calculations thus provide strong indications that mixed-stack donor-acceptor materials represent a class of systems with high potential in organic electronics.     

The vibrational reorganization energy in pentacene: molecular influences on charge transport

The reorganization energy in pentacene is reported on the basis of a joint experimental and theoretical study of pentacene ionization using high-resolution gas-phase photoelectron spectroscopy, semiempirical intermediate neglect of differential overlap calculations, and first-principles correlated quantum-mechanical calculations at MP2 and density functional theory levels. The reorganization energy upon positive ionization of pentacene is determined both experimentally and theoretically to be remarkably low. This is one key element that allows one to rationalize the extremely high hole mobilities recently measured in pentacene single crystals.     

The role of vibronic interactions on intramolecular and intermolecular electron transfer in π-conjugated oligomers

The importance of electron-vibrational coupling for intermolecular and intramolecular electron-transfer processes is discussed on the basis of first-principles correlated quantum-mechanical calculations and of a dynamic vibronic approach. The methodology is illustrated for examples selected from some of our recent work. In all instances, the theoretical results are thoroughly compared to experimental data.     

Synthesis,Crystal and Molecular Structures of [Co(MH)2(Thio)2][BF4] · H2O and [Co(DH)2(NH3)2][BF4]

Crystal structures of [Co(MH)₂(Thio)₂][BF₄] · H₂O (I) and [Co(DH)₂(NH₃)₂][BF₄] (II), where MH^– is H₃C–C(NOH)–C(NO^–)–H and DH^– is H₃C–C(NOH)–C(NO^–)–CH₃, were determined by X-ray diffraction. The crystals are monoclinic, space group C2/c, unit cell parameters (for I and II, respectively): a = 22.018(2) Å, b = 7.943(1) Å, c = 11.681(1) Å, = 92.68(1)° and a = 21.436(2) Å, b = 6.400(2) Å, c = 12.389(2) Å, = 113.13(1)°. In both cases, the Co(III) coordination polyhedron is a centrosymmetrical trans-octahedron, N₄S₂ for I and N₆ for II. In the crystals of I and II, the complex cations and the outer-sphere [BF₄]^– anions (and the crystal water molecules in I) form elaborate hydrogen bonding system.     

Electronic couplings in organic mixed-valence compounds: the contribution of photoelectron spectroscopy

We show that the electronic coupling in strongly coupled organic mixed-valence systems can be effectively probed by means of gas-phase ultraviolet photoelectron spectroscopy (UPS). Taking six diamines as examples, the UPS estimates for the electronic couplings H(ab) are compared with the corresponding values determined from the intervalence charge-transfer absorption bands and from electronic structure calculations. Similar trends are observed for the H(ab) values estimated from UPS and optical spectra; this provides support for the applicability of Hush theory to strongly coupled organic mixed-valence systems. The UPS electronic couplings are found to be somewhat smaller than those from optical spectroscopy, which is attributed to the role of vibronic coupling to symmetrical modes; when corrected for this vibronic coupling, the UPS H(ab) estimates confirm that triarylamine-based mixed-valence systems are close to the class-II/class-III borderline.     

Synthesis and characterization of inner-sphere substitution products in azide-containing сobalt(III) dioximates

New compounds of Co(III) dimethylglyoximate with the sulfanilamide derivative [Co(N₃)(DmgH)₂(SAM)] (DmgH^– is the dimethylglyoxime monoanion, and SAM is–NH₂–C₆H₄–SO₂–NH–R) are synthesized using the structural block [Co(N₃)(DmgH)₂(Н₂О)] as the initial one. The reaction products of various [Co(N₃)(DmgH)₂(SAM)] with ligand L (L is pyridine (Py), thiourea (Thio), triphenylphosphine (PPh₃), nicotinamide (Nia), iso-nicotinamide (INia), isonicotinic acid (НINА), 4-pyridinaldoxime (4-PaoH), 4,4’-bipyridine (Bipy), and NH₄NCS) are synthesized. The compounds are studied by IR and NMR spectroscopy and X-ray diffraction analysis (CIF files CCDC 1414767–1414775 (I, V–XII)). The following facts are established. First, only the coordinated water molecule in [Co(N₃)(DmgH)₂(Н₂О)] is replaced by SAM. Second, SAM from different similar compounds also undergoes substitution by the aforementioned organic ligands. The exception is the compound obtained by the reaction of [Co(N₃)(DmgH)₂(SAM)] with NH₄NCS, due to which the NCS^– anion replaces both SAM and inorganic anion N ₃ ^- . The X-ray diffraction analysis shows that the substitution reactions give both mononuclear compounds [Со(N₃)(DmgH)₂(Py)], [Со(N₃)(DmgH)₂(PPh₃)], [Со(N₃)(DmgH)₂(Thio)], [Со(N₃)(DmgH)₂(Nia)] [Со(N₃)(DmgH)₂(INia)], [Со(N₃)(DmgH)₂(HINА)] ? H₂O, [Со(N₃)(DmgH)₂(4-PaoH)] ? DMF, and [Со(N₃)(DmgH)₂(Bipy)] and binuclear molecular complexes [(Со(N₃)(DmgH)₂)₂(Bipy)] ? 0.5H₂O and [(Со(N₃)(DmgH)₂)₂(Bipy)] ? H₂O, as well as ionic complex (NH₄)[Co(SCN)₂(DmgH)₂] ? 3H₂O. The obtained compounds supplement a series of complexes that make it possible to evaluate the trans effect of the N ₃ ^- anion on the bond lengths along the axial coordinate and on the Со–N bonds in the equatorial plane of the octahedron.     

Stabilisation of a heptamethine cyanine dye by rotaxane encapsulation

The crystal structure of a cyanine dye rotaxane shows that the cyclodextrin is tightly threaded round the polymethine bridge of the dye; encapsulation dramatically increases the kinetic chemical stability of the radicals formed on oxidation and reduction of the dye, making it possible to observe the rotaxane radical dication by ESR and UV-vis-NIR spectroscopy.