Vol 67, No 7 (2018)

The paper presents a review of the state of the art and prospects for the development of rotary molecular switches based on transition metal bis(dicarbollide) complexes.

The review addresses synthetic approaches to composite materials based on graphene oxide and nano tin dioxide and their electrochemical properties as anodes for lithium- and sodiumion batteries. The introduction of a carbon matrix into the composite material improves the electrochemical characteristics of the anodes. In most methods, the synthesis of graphene oxide–tin dioxide composites is based on the use of tin(II,IV) chlorides as the starting compounds, and the most efficient electrode materials were obtained by the hydrothermal or solvothermal routes. Thermal processing is much more economic than the gas phase deposition protocols but requires heating of a large volume of dilute tin oxide dispersions in an autoclave. Mechanochemistry (ball milling) is also economically unfavorable for the synthesis of composite materials. In addition, large volumes of acidic wastes that should be neutralized and safely discarded are formed when tin chlorides are used. An alternative environmentally friendly technique based on the use of aqueous peroxide solutions can be applied for the production of efficient anode materials based on graphene oxide and tin dioxide. This process does not involve acidic wastes, uses hydrogen peroxide and ethanol as reagents, and accomplishes film deposition (coating) at room temperature. Final thermal treatment is required only for the active material, which minimizes energy expenses and equipment costs.

The quantum chemical simulation of exchange interaction according to the broken symmetry approach was performed for a series of binuclear Cu^II complexes containing the asymmetric exchange moiety based on bis-hydrazones of 2,6-diformylphenol. The calculated values were compared between themselves and with the experimental values of the exchange parameter 2J for the binuclear copper(II) complexes with bis-hydrazones based on 2,6-diformylphenol in order to reveal the influence pattern of the nature of nonbridging donor atoms X (O, N, S, and Se) onto the exchange interaction. The strength of exchange interaction of the antiferromagnetic type depends significantly on the nature of nonbridging donor atoms, increasing in the series of X = O, NH, S, and Se.

Mono- and dinuclear adducts of cobalt diketonates with tetradentate 4,7-phenanthroline- 5,6-dione were modeled within the framework of DFT UB3LYP*/6-311++G(d,p) approximation. A competitive coordination of the metal ion to different donor centers of the redox-active ligand was studied. Variation of substituents in the diketone moieties allowed one to reveal compounds than can undergo thermally initiated one- and two-step valence tautomeric rearrangements. The calculated energy and magnetic characteristics of the dinuclear complexes give reasons to consider them as potential basis of molecular electronics and spintronics devices.

The Pd-PEPPSI complexes widely used to catalyze numerous reactions eliminate the pyridine ligand on treatment with protic acids to give binuclear complexes [Pd(NHC)X₂]₂ with the Pd–X–Pd (X = Cl, Br, I) bridging bonds. The reaction proceeds with high yields (78–98%) and can be regarded as a preparative approach to binuclear complexes. A prolonged heat treatment of either Pd-PEPPSI complexes or binuclear [Pd(NHC)X₂]₂ complexes in the presence of strong protic acids results in the Pd–NHC bond cleavage to give azolium salts (proligands) and palladium salts.

A series of new N,O-hybrid ligands was synthesized by oxidation of pyridyl-substituted phospholanes. These ligands were employed in the first synthesis of water-soluble mononuclear nickel(II) complexes [NiL₂(H₂O)₂](BF₄)₂ and [NiL₂(MeCN)₂](BF₄)₂. Physicochemical properties and crystalline structures of the synthesized compounds were thoroughly studied.

Controllable self-assembly and properties of nanocomposites based on CdSe/ZnS semiconductor quantum dots (QDs) and tetrapyridylporphyrin molecules (H₂P) as well as the dynamics of relaxation processes in these systems were studied for solutions and single nanoobjects in the temperature range of 77–295 K. It was proved that the formation of surface states of different nature is crucial to nonradiative relaxation of exciton excitation in QDs. The efficiency of QD→Н₂Р energy transfer was shown to be at most 10–15%. Regularities of photoluminescence (PL) quenching for QDs in nanocomposites in solutions of different polarity correlate with the dependences of PL blinking for single QDs. A scheme was proposed of excited states and main relaxation channels of exciton excitation energy in semiconductor QDs and QD–Н₂Р nanocomposites.

It is revealed by FTIR and electron absorption spectroscopy that the reactions of dimethyl sulfoxide with the nitro complexes of Co-porphyrins both in the solid phase and an inert solvent afford six-coordinate complexes with the general formula (DMSO)Со(Por)(NO₂) (Por is meso-tetraphenyl- and meso-tetra-p-tolylporphyrinato dianions). These compounds are stable in the solid state, whereas they partially decompose in an inert solvent to form five- and six-coordinate complexes. The ambident nitrite and dimethyl sulfoxide ligands are coordinated to the metal atom through the N and O atoms, respectively, which was confirmed by the application of isotope-containing compounds ¹⁵NO₂ and DMSO-d₆.

The complex salt {[CuL₂][Cu₄I₆]•MeCN}_n (1) and the compound [Cu₄L₃I₄]•3 MeCN (2) (L is a chiral ligand bearing a natural monoterpene (+)-3-carene moiety) were synthesized. The crystal structures of compounds 1 and 2 were determined by X-ray diffraction. The structure of compound 1 consists of complex cations [CuL₂]²⁺ (N₃O₂ polyhedron is a trigonal bipyramid) and Cu^I coordination polymers (CuI₄ polyhedron is a tetrahedron) as anions. The experimental magnetic moment μ_eff at 300 K is 1.90 μ_B, which is consistent with the X-ray diffraction data and the assumption that compound 1 is mixed-valence. The structure of compound 2 comprises a tetranuclear Cu^I complex, in which three Cu atoms are coordinated by two N atoms of the ligand L and two I atoms, and the fourth Cu atom is coordinated by four I atoms (coordination polyhedra are distorted tetrahedra). Compounds L and 2 were found to influence the viability of human laryngeal carcinoma cells (Hep2). The IC₅₀ value for complex 2 (13.0±1.7 μM) is substantially smaller than IC₅₀ for compound L (30.5±0.5 μM).

The inclusion compound of zinc lactate terephthalate with R-butan-2-ol, [Zn₂(R-Bu^sOH) (bdc)(S-lac)]•(R-Bu^sOH) (Bu^sOH is butan-2-ol, H₂bdc is terephthalic acid, S-H₂lac is lactic acid), was prepared by soaking crystals of [Zn₂(dmf)(bdc)(S-lac)]•DMF in pure R-butan-2-ol. The positions of chiral alcohol molecules in voids of the chiral framework and the host–guest contacts were determined by X-ray diffraction. These data provide an explanation for the origin of chiral discrimination of zinc lactate terephthalate toward the R-isomer of butan-2-ol.

The surface activity, micelle formation, and solubilization ability towards hydrophobic compounds were estimated for the series of new cationic surfactants belonging to the type of 1-alkyl-1-(2-hydroxyethyl)pyrrolidinium bromides. The presence of 2-hydroxyethyl group in these surfactants leads to the twofold increase in their micelle-forming ability as compared to unsubstituted analogs. The critical micelle concentration for the investigated series of pyrrolidinium surfactants is lower at the same hydrophobicity than that for the analogs belonging to the alkylpyridinium, alkylimidazolium, and alkylmorpholinium types. The data acquired for the studied surfactants on their solubilization ability, antimicrobial activity, and hemolytic efficiency indicate their prospective applications to encapsulate hydrophobic biologically active molecules and as the promising bactericidal agents.

Pentacoordinated monofluorosilanes R¹SO₂NHCHR₂C(O)N(Me)CH₂SiMe₂F containing moieties of N′-methyl-N-(organosulfonyl)-2-amino acid amides of glycine, alanine, and leucine as C,O-chelating ligands were synthesized via the reaction of corresponding disiloxanes with BF₃•Et₂O. The structures of obtained compounds were investigated by single-crystal X-ray diffraction analysis.

The interaction of calf thymus DNA (CT DNA) with trans-[PtCl₂L₂] and trans-[PdCl₂L₂] complexes (L–5-methyl-1H-tetrazol-1-ylacetic acid and its ethyl, butyl, and isobutyl esters; ethyl esters of 2-R-2H-tetrazol-5-ylacetic acids, R = Bu^t, CH₂CH₂OH) have been quantitatively studied by a spectrophotometric method. The binding constants (K_b) of the tetrazolecontaining coordination compounds with CT DNA at pH 7.2 and 298 K are in the range of (3.67–5.93)•10⁵ mol L^–1 for the Pd^II complexes and (7.82–13.30)•10⁵ mol L^–1 for and the Pt^II complexes, respectively. The K_b values, as well as negative values of ΔG_b (–(31.7–34.9) kJ mol^–1) indicate the effective binding between the studied complexes and CT DNA.

Published data on the electronic structure of boron chelates are summarized for the first time. Ultraviolet photoelectron spectra of vapors, X-ray photoelectron spectra of molecular crystals, and results of modeling within the framework of the density functional theory are analyzed. Data on the effect of substituents on the electronic structure of complexes are systematized.

New composite materials of collagen with electrical conductivity up to 6.1•10^–4 S cm^–1 were obtained using colloidal dispersions of polyvinylpyrrolidone-stabilized graphene.