S. V. Kolotilov

Electrochemical and Electrocatalytic Characteristics of Coordination Polymers Based on Trinuclear Pivalates and Heterocyclic Bridging Ligands

It was shown by cyclic voltammetry that the coordination polymers [Fe2NiO(Piv)6(L)x]n, where L is a ligand containing a 1,2,4,5-tetrazine or thiazolothiazole fragment, Piv– is pivalate, and x = 1 or 1.5, possess redox activity in the solid form when deposited on an inert electrode, and the redox potentials of the transitions correlate with the corresponding redox potentials of the ligands in solutions. The coordination polymer containing bis(4-pyridyl)thiazolothiazole catalyzes the electrochemical dehalogenation of CF3CHClBr with the formation of CF2=CHCl and CF3CH2Cl.

Electrochemically Active Coordination Polymers: A Review

The dependence of the electrochemical properties of coordination polymers (CPs) on their structure was analyzed. It is shown on the basis of published data that the potential of an electrochemical reaction in CPs is close to the potential of this reaction of a compound with similar molecular structure containing the corresponding redox-active fragment in solution. Electrochemical reactions involving CPs proceed not only on the surface of particles supported on the electrode but also in the bulk. The introduction of counter-ions from the electrolyte into the CP particle has a significant effect on the electrochemical reaction in this system.

Influence of morphology and defects in crystals of porous coordination polymers on the sorption characteristics

Porous coordination polymers [Fe2MO(Piv)6(L)x]n (L is tris(4-pyridyl)pyridine, M = Ni (I) and Co (II); L is tris(4-pyridyl)triazine, M = Ni (III) and Co (IV); x varies from 0.7 to 1.17) are obtained. The structure of polymer I is determined by X-ray diffraction analysis. The choice of the solvent (chloroform or dimethylformamide (DMF)) for the preparation of polycrystalline samples affects the morphology of the crystals. It is found for the studied samples that an increase in the average crystal size (from 1 to 20 μm) and the enhancement of the crystallinity of the samples increase the sorption capacity with respect to hydrogen from 0.7 to 0.9% (78 K, 1 atm).

Structures and magnetic properties of new trinuclear CoII, NiII, and CuII complexes with trimethylacetate and 1,1-cyclohexanediacetate

The reactions of transition metal trimethylacetates [Cu2(Piv)4(HPiv)2], [Ni9(OH)6(Piv)12(HPiv)4], [Co(Piv)2]n (Piv− = −O2CBut) with 1,1-cyclohexanediacetic acid (H2Chda) neutralized by tetrabutylammonium hydroxide in the presence of 2,2-bipyridine (2,2′-bpy) afford linear trinuclear homometallic complexes [(2,2′-bpy)2Cu3(Chda)2(Piv)2]··2EtOH (1) and [(2,2′-bpy)2M3(Chda)2(Piv)2(EtOH)2] (M = NiII (2) or CoII (3)). In molecules of these compounds, anions of both mono- and dicarboxylic acids act as bridges between the transition metal atoms. Compounds 1–3 were characterized by X-ray diffraction, and their magnetic properties were studied. Spin-spin ferromagnetic interactions dominate in complexes 1–3 with CuII (S = 1/2) (1) and CoII (S = 3/2) (3) ions.

Formation of hierarchically-ordered nanoporous silver foam and its electrocatalytic properties in reductive dehalogenation of organic compounds

Nanoporous silver foam on a glassy carbon electrode (AgNF/GC) was formed by cathodic deposition of silver from an acidic solution of AgBF4 at high current density. The material can be described (based on results of optical microscopy, SEM, TEM and XRD investigation) as hierarchically (micro/nano) porous matter with ca. 40 nm silver crystals assembled in irregular ca. 70–300 nm thick filaments arranged in a foam-like structure with ca. 20 μm cavities and ca. 7 μm walls. The AgNF surface area was estimated by pseudocapacitance measurement as ca. 12 times higher than the geometrical area. Reduction of bromobenzene and other aryl bromides containing redox-inactive (F-, CH3-, CH3O-) or redox-active (–NO2, –CN and CH3CO-) substituents, as well as alkyl bromides (CF3CHClBr, CF2Br2) on AgNF/GC was studied. The peak potentials of the processes assigned to debromination of the organic halides were less negative (up to +345 mV) than on smooth silver, indicating superior electrocatalytic properties of the nanoporous silver foam. Comparison of the CV peak currents of the processes on AgNF/GC and smooth silver, as well as their changes in cycling in different regimes allowed formation of a few kinds of electrocatalytically active sites on the AgNF surface to be suggested. Electrolysis of 1-bromo-4-fluorobenzene on the AgNF electrode led to fluorobenzene, and less than 1 mg of AgNF revealed performance comparable to 500 mg of smooth silver wire. The results can be utilized for creation of electrochemical sensors as well as for preparative detoxification of halogen-containing persistent organic pollutants.

New Approaches to Creation of Micro- and Mesoporous Functional Materials

New approaches to the creation of porous materials for various functional purposes based on coordination polymers, zeolites and extra-large pore zeolites, carbon materials, silicon carbide and carbon nitride are considered. The effect of the structure of such materials on their common and distinctive properties and differences is demonstrated, and possible directions of their use as sorbents and catalysts of organic reactions are presented.

Chromatographic Separation of Racemates of Alcohols Using Porous Coordination Compounds of Zinc and Vanadium(IV) with Lactate and β-Cyclodextrin

It was shown that the efficiency of chromatographic separation of the racemates of 2-butanol, 2-hexanol, 3-hexanol, and 1-phenylethanol on columns with coordination compounds [Zn2(bdc)(S-Lact)(DMF)]n (bdc2– = 1,4-benzenedicarboxylate, S-Lact– = (S)-lactate) and Na7{(VO)7Na7(H2O)7(β-CD)2} (β-CD = β-cyclodextrin) does not depend on the size of the alcohol molecule. It was found that in the case of the 1-phenylethanol racemate separation with [Zn2(bdc)(S-Lact)(DMF)]n the enantiomeric excess of the alcohol varies inversely with the viscosity of the solvent.

Influence of the Synthesis Conditions and the Presence of Guest Molecules on the Structures of Coordination Polymers [Fe 2 MO(Piv) 6 (L) x ] n (L = 4,4′-Bipyridine, Bis(4-Pyridyl)ethane) with the Labile Crystal Lattice

Coordination polymers [Fe2MO(Piv)6(L1)x]n · nSolv (L1 = 1,2-bis(4-pyridyl)ethane, M = Ni (I), Co (II), x = 1.5; M = Cо (III), x = 2) are synthesized. Depending on the synthesis conditions, compounds II (cross diffusion of reactants) or III (fast mixing of reactant solutions) of different compositions are formed. It is shown by X-ray diffraction analysis (CIF files CCDC 1550804 (I) and 1550805 (III)) that compound I is a porous coordination polymer built of parallel 2D layers and compound III is a 1D coordination polymer. The crystals of complexes I and II are isostructural. The mutual arrangement of the 2D layers in compound II depends on the solvent in which this coordination polymer is formed. The desolvation of polymers I and II leads to the collapse of the crystal lattice. Unlike the complexes with L1, [Fe2NiO(Piv)6(L2)1.5]n · nSolv (IV · nSolv) is formed in the case of 4,4-bipyridine (L2), regardless of the solvent nature, and its crystal lattice is formed by interpenetrating 2D layers. The mutual arrangement of the 2D layers in the crystal lattice of compound IV varies with the solvent used for the synthesis of this coordination polymer or for the resolvation of a sample of polymer IV. It is found that the parameters of the 57Fe Mössbauer spectra for compounds IV and IV · nDEF (DEF is N,N-diethylformamide) differ, which can be explained by a decrease in the symmetry of the coordination environment of the Fe3+ ions when the pores are filled with DEF molecules.

Structure and Electrochemical Properties of Copper(Ii) Coordination Polymers with Ligands Containing Naphthyl and Anthracyl Fragments

The potentials for the electrochemical reduction of glassy carbon electrodes with deposited copper(II) coordination polymers (CP) containing polypyridine ligands with naphthyl and anthracyl substituents are similar to the potentials of the redox transformations of the corresponding ligands. The difference between the reduction potential of the CP-modified electrode and the potential for the redox transformation of the ligands in solution is greater when the lowest unoccupied molecular orbital of the ligand is predominantly located not on the carbocyclic but rather heterocyclic fragment.

Special Features of the Template Effect in the Formation of Porous Coordination Polymers

It was shown that the influence of guest molecules on the structure of porous coordination polymers (PCP) can be considered as the manifestation of a template effect. The presence of such molecules and their nature affect the composition of the PCP and the topology of the polymer framework and can also determine the chirality of the crystal lattice. The criteria that can be used to reach conclusions about the special features of the template effect during the formation of PCPs are analyzed.