Template Condensation Research Articles

Pharmacologically significant tetraaza macrocyclic metal complexes derived from isatin and 3,4-diaminobenzophenone: Synthesis, spectral studies and comparative in vitro biological assessment

The 12-membered Schiff base macrocyclic complexes, [Dichloro [5,6;11,12-dibenzophenone-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene-2,3,8,9-diindole] metal(II) [M = Co(II), 1; Ni(II), 2; Cu(II), 3 and Zn(II), 4] were synthesized via template condensation of isatin and 3,4-diaminobenzophenone. These four complexes were characterized employing the analytical, spectral viz., FTIR, NMR, Mass, UV-Vis, EPR, TGA/DTA and SEM. The formation of metal complexes has been confirmed on account of the characteristic band positions in FTIR spectra and resonance signals in NMR spectra while the absorption bands in UV-Vis spectra and magnetic moment analysis signify the geometry of the complexes. However, the EPR study inferred distorted octahedral geometry in Cu(II) complex. The binding profile of the metal complexes (1–4) with CT-DNA was monitored by fluorescence and circular dichroism (CD) spectroscopy coupled with molecular docking studies. The binding constants were found to be highest for complex 3. Further, the hypothesis of preferential binding in the minor groove of double-stranded DNA is supported by CD and docking results. The antioxidative properties showed substantial radical scavenging potency of the complex 3. The comparative in vitro antibacterial study of the metal complexes against different pathogenic microbes (S. aureus, E. coli and C. albicans) revealed enhanced activity for complex 3 which is further certified by its efficacy to resist biofilm formation as investigated by XTT reduction assay. SYNOPSIS 12-membered Schiff base macrocyclic complexes (1–4) were synthesized via template condensation of isatin and 3,4-diaminobenzophenone and the binding mode of complexes with CT-DNA was divulged through the fluorescence and circular dichroism studies. Molecular docking studies are reported for complexes 3 and 4. In addition, the pharmacological efficacy of the newly synthesized complexes was explored by examining their antioxidant, antimicrobial, antibiofilm activities.

Synthesis, X-ray structure and reactivity of the vinyl-terminated iron(II) clathrochelate precursors and their cage derivatives with non-equivalent capping groups

A novel vinyl-terminated boron, antimony-capped iron(II) tris-dimethylglyoximate with labile triethylantimony cross-linking group was prepared using two-step synthetic procedure including template condensation of dimethylglyoxime and triethylantimony(V) dibromide on an iron(II) ion as a matrix followed by transmetallation with 4-vinylphenyl boronic acid. This labile clathrochelate precursor and its bis-methoxyboron-capped analog underwent the same capping group exchange (transmetallation) reactions with more strong Lewis acids, such as trigonal boron compounds or hafnium(IV) phthalocyaninate (HfPc), giving the macrobicyclic iron(II) tris-dimethylglyoximates with non-equivalent capping groups and a binuclear HfPc-capped phthalocyaninoclathrochelate, respectively. The complexes obtained were characterized using elemental analysis, 1H and 13C{1H} NMR, MALDI-TOF MS, IR and UV–vis data as well as by single crystal X-ray diffraction. The number, positions and multiplicity of the signals in the solution 1H and 13C{1H} NMR spectra of these clathrochelates as well as the ratios of their integral intensities in 1H NMR spectra confirmed the composition and symmetry of the macrobicyclic molecules, suggesting the presence of their molecular C3 symmetry pseudoaxis. In the 1H NMR spectrum of a hybrid phthalocyanine-capped cage complex, the π-electron current in its apical macroheterocyclic fragment caused the substantial high-field shifts of the signals of protons of the ribbed methyl substituents because their nuclei are located in its shielding region. Single crystal X-ray diffraction data for the monovinyl-terminated mixed Sb, B- and Hf, B-capped iron(II) cage complexes suggest that their FeN6-coordination polyhedra possess the geometry of a rotationally distorted truncated trigonal pyramid that is close to intermediate between a trigonal prism and a trigonal antiprism with slightly expanded trigonal bases, which are connected with a heavy (Sb or Hf) atom. The encapsulated iron(II) ion is slightly shifted from the center of these polyhedra in the direction of such capping atom.

Control of chitin nanofiber production by the lipid-producing diatom Cyclotella Sp. through fed-batch addition of dissolved silicon and nitrate in a bubble-column photobioreactor.

Diatoms are single-celled algae that make cell walls of nanopatterned biogenic silica called frustules through metabolic uptake of dissolved silicon and its templated condensation into biosilica. The centric marine diatom Cyclotella sp. also produces intracellular lipids and the valued coproduct chitin, an N-acetyl glucosamine biopolymer that is extruded from selected frustule pores as pure nanofibers. The goal of this study was to develop a nutrient feeding strategy to control the production of chitin nanofibers from Cyclotella with the coproduction of biofuel lipids. A two-stage phototrophic cultivation process was developed where Stage I set the cell suspension to a silicon-starved state under batch operation, and Stage II continuously added silicon and nitrate to the silicon-starved cells to enable one more cell doubling to 4 × 106 cellsmL-1 . The silicon delivery rate was set to enable a silicon-limited cell division rate under cumulative delivery of 0.8 mM Si and 1.2 mM nitrate (1.5:1 mol N/mol Si) over a 4- to 14-day addition period. In Stage II, both cell number and chitin production were linear with time. Cell number and the specific chitin production rate increased linearly with increasing silicon delivery rate to achieve cumulative product yields of 13 ± 1 mg chitin/109 cells and 33 ± 3 mg lipid/109 cells. Therefore, chitin production is controlled through cell division, which is externally controlled through silicon delivery. Lipid production was not linearly correlated to silicon delivery and occurred primarily during Stage I, just after the complete co-consumption of both dissolved silicon and nitrate. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:407-415, 2017.

Antioxidant, DNA interaction, molecular docking and cytotoxicity studies of aminoethylpiperazine‐containing macrocyclic binuclear copper(II) complexes

A series of new macrocyclic binuclear copper(II) complexes of the type [Cu2L1–5(ClO4)](ClO4) (1–5) were synthesized by template condensation between precursor compounds 2,6‐bis(4‐aminoethylpiperazin‐1‐ylmethyl)‐4‐substituted phenols and 2,6‐diformyl‐4‐substituted phenols. The synthesized precursors and complexes were characterized using regular physicochemical techniques. The rate constant values obtained for the hydrolysis of 4‐nitrophenylphosphate were in the range 1.83 × 10−2–4.19 × 10−2 min−1. Antioxidant studies against 2,2′‐diphenyl‐1‐picrylhydrazyl revealed the antioxidant potency of the synthesized complexes. Binding studies of the complexes with calf thymus DNA were conducted using electronic, viscometric and voltammetric techniques, and the obtained results suggested a non‐covalent groove mode of binding. The oxidative cleavage of pBR322 DNA in the presence of co‐reactant H2O2 and radical scavengers showed single strand scission and involvement of H2O2 radical in the cleavage process. Molecular docking studies were performed to insert complexes into the crystal structures of 1BNA and VEGFR kinase at active sites to determine the possible binding mode and predominant binding interactions. In vitro cytotoxicity of the complexes was tested against human epidermoid carcinoma cells (A431) by MTT assay, which revealed the effective anticancer activity of the complexes. Live cell and fluorescent imaging of A431 cells showed that the complexes induce cell death through apoptosis.

Synthesis of nickil (ii) complex of taazatricyclotetracosane (octc) macrocyclic complexes from the contaminated soil

Consumer demand for better quality produce is now on an increasing surge. In particular, some metals are not desirable in agriculture as they may harm the environment or humans. Because of this, the concentrations of metals in soils and foods should be regularly monitored. This paper extensively addresses our concerns about these undesired metals in the farm soil and farm produce and how to manage the situation so that it does not become a menace. This paper deals with the synthesis and characterization of macro cyclic ligand and its complex compound. Template condensation of chlorocarbons such as 1,1,2,2-tetrachloroethane with 1,3-diaminopropane in presence of nickel (II)) yielded the corresponding metal complexes such as 3,7,10,14,15,19,20,24- octaazatricyclotetracosane (OCTC). The macrocyclic ligands and their complexes have been characterized by elemental analysis, molecular weight determination, conductance, IR and NMR spectral studies. The magnetic moments, along with electronic spectral data suggested hexa coordinated state for Nickel, its geometry is outer orbit octahedral .Conductivity data suggests that they behave as electrolytes. The formulation of the complexes has been established on the basis of chemical composition. The significant ligand and their complexes have now widely being used as a catalyst in many industries.

OXOVANADIUM(IV)-CONTAINING N2O2 CHELATE COMPLEX ; CRYSTAL STRUCTURE DETERMINATION AND DFT

A stable oxovanadium(IV) complex was obtained by template condensation of 2-hydroxynaphthaldehyde S-methylthiosemicarbazone and salicylaldehyde in the presence of VOSO 4 . The structure of VO(II) centered metal complex was confirmed by elemental analysis and was characterized by single crystal X-ray diffraction technique and density functional theory (DFT/B3LYP) LANL2DZ compared with experimental data. The complex crystal is in the form of dark green-colored small sticks. The experimental data of the monoclinic crystalline structure which belonging P1 21/n1 space group was compared to those obtained with DFT-B3LYP-LANDL2DZ. It was seen that experimental and theoretical values are in a good agreement.

Template synthesis and X-ray structure of the tris-glyoximate iron(II) clathrochelates with terminal reactive groups

One-pot template condensation of glyoxime with the corresponding functionalized phenylboronic acids on an iron(II) ion as a matrix afforded 3- and 4-substituted phenylboron-capped tris-glyoximate iron(II) clathrochelates with terminal amine, formyl (acetal) and vinyl groups; those with acetal groups were converted into the formyl-terminated cage complexes using H+-catalyzed hydrolysis. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–Vis, 1H and 13C NMR spectroscopies, and by single crystal X-ray diffraction (for three of these clathrochelates). Their molecules possess a geometry intermediate between a trigonal prism (TP) and a trigonal antiprism (TAP) and the bite angles α remain almost constant being in the range 77–79°, whereas the heights h of FeN6-coordination polyhedra depend on the distortion angle φ values (from 12.2 to 20.7°) thus being in the range 2.36–2.37Å. An encapsulated iron(II) ion is situated almost in the centre of cage frameworks and the average chelate CC bonds in these tris-glyoximate frameworks are substantially shorter than those for their aliphatic and aromatic analogs. The crystal packings are governed by weak supramolecular hydrophobic interactions and an absence of the steric hindrances between the ribbed substituents (hydrogen atoms) allowed to form intermolecular π…π interactions.As follows from single crystal X-ray diffraction data, the synthesized macrobicyclic tris-glyoximates with reactive terminal groups, which the macrobicyclic molecules contain no bulky ribbed substituents, have large ligand aspect ratio and, therefore, they seem to be promising syntones and building blocks for preparation of covalent (including imine and amine) and coordination metallomacrocycles, MOFs and cages (capsules) with big voids and cavities as hosts, suitable for inclusion of various organic and inorganic guests.

New rhenium(III) semiclathrochelates with biorelevant apical substituents: Synthesis, X-ray structure and reactivity

One-pot reduction–condensation of K2ReCl6, dimethylglyoxime and phenylboronic acid anhydride in the presence of metallic silver gave the mixture of the boron-capped tris-dioximate rhenium(III) semiclathrochelate with its reduced diimine-iminoximate derivatives, resulted from the side ligand-centered domino-reaction; one of them was characterized by single crystal X-ray diffraction. Its rhenium(III) cation coordinates two boron-bridged iminooximate moieties and one non-bridged imine chelate ligand. Third oxygen atom of the boron-containing bridging fragment is also coordinated to this ion, thus giving a capped trigonal-prismatic (TP) ReN6O‐ coordination polyhedron in which the Re–O distance is substantially smaller than the Re–N ones {1.966(8) and 2.029(11)–2.099(11)Å, respectively}. Template condensation of ReCl3((C6H5)3P)2(CH3CN) with cyclohexane-1,2-dione dioxime (nioxime) and 3-formylphenylboronic acid afforded a formyl-terminated rhenium(III) tris-nioximate, undergoing a further H+-catalyzed condensation with isoniazid to give the semiclathrochelate hydrazone with apical functionalizing vector substituent. As follows from single crystal X-ray diffraction data, the ReN6Cl‐ coordination polyhedron of the former formyl-terminated complex possesses a geometry of a capped TP with the distortion angle φ equal to 5.0° and with the Re–Cl distance (2.4040(9)Å) that is substantially greater than the Re–N ones (2.046(3)–2.127(3)Å). The attempted capping of this formylphenylboron rhenium(III) complex with IGe(CF3)3 resulted in its transmetallation, leading to the germanium-capped semiclathrochelate. The analogous boron-capped semiclathrochelates with apical hexadecyl and cholesteryl groups were prepared using the direct template condensation of nioxime and hexadecylboronic acid on a rhenium(III) ion as a matrix, and by capping of the non-macrocyclic rhenium(III) tris-nioximate with cholesterylboronic acid, respectively.

Synthesis, Crystal Structure, and Spectroscopic Properties of Cu(II) Complex with 14-Membered Hexaazamacrocyclic Ligands

[CuL(ClO4)2] complex of 14-membered hexaazamacrocyclic ligand (L = 6,13-dimethyl-3,10-dioctyl-1,3,5,8,10,12-hexaazacyclotetradecane) was synthesized by template condensation reaction of 1,2-diaminopropane, octylamine, and formaldehyde in ethanol. The product was characterized by elemental analysis, Fourier-transformed infrared spectroscopy (FT-IR), ultraviolet–visible spectroscopy (UV–vis), diffused reflectance spectroscopy (DRS), liquid chromatography-mass spectrometry (LC–MS), and X-ray crystallographic technique. Thermal behavior of this complex was studied by thermogravimetric analysis (TGA). The IR and other spectral properties were consistent with the result from X-ray diffraction. The electronic absorption spectra of [CuL(ClO4)2] complex showed one band at 500 nm corresponding to 2B1g → 2B2g transition. The complex crystallized in the triclinic space group of Pī with a = 8.1307(6) A, b = 9.3579(7) A, c = 13.3930(10) A, α = 95.932(2)°, β = 98.579(2)°, and γ = 114.478(2)°. The copper(II) ion of the macrocyclic cation displayed a tetragonally distorted octahedral geometry with four nitrogen atoms in the equatorial plane and two oxygen atoms from the perchlorate ions weakly coordinated to the copper(II) ion in the axial positions. The complex exhibited only weak luminescent property. A new macrocyclic complex that can be easily obtained from the one-pot synthesis.

ChemInform Abstract: Coordination Complexes of 15‐Membered Pentadentate Aza, Oxoaza and Thiaaza Schiff Base Macrocycles “Old Complexes Offer New Attractions”

AbstractReview: 141 refs.

Synthesis, structure and reactivity of iron(II) clathrochelates with terminal formyl (acetal) groups

3- and 4-Formylphenylboron-capped aliphatic iron(II) clathrochelates were obtained by direct template condensation of the corresponding α-dioxime with 3- and 4-formylphenylboronic acids on an iron(II) ion as a matrix under mild reaction conditions in methanol or acetonitrile media; with methanol as a solvent, such one-pot reactions gave also their acetals. The latters were converted to the formyl-terminated iron(II) clathrochelates by H+-catalyzed hydrolysis. The reactive formyl-terminated cage complexes obtained underwent their further H+-catalyzed condensation with isoniazid as a hydrazone component giving the hydrazonate cage complexes with vector apical substituents of this type. The formyl-terminated iron(II) hexachloroclathrochelate was synthesized by template reaction of dichloroglyoxime on an iron(II) ion with 3-formylphenylboronic acid. Nucleophilic substitution of its reactive chlorine atoms with thiolate ions generated in situ from para-mercaptobenzoic acid afforded hexasulfide iron(II) cage complex with six ribbed para-mercaptobenzoic substituents and formyl groups in its apical substituents. The iron(II) complexes synthesized were characterized using elemental analysis, MALDI–TOF mass spectrometry, IR, UV–Vis, 1H and 13C{1H} NMR spectroscopies and by X-ray crystallography (for three aliphatic macrobicyclic acetals).

Synthesis, characterization and crystal structure determination of a new Zn(II) Schiff base complex derived from condensation of a new asymmetrical tripodal amine, 3-((4-aminobutyl)(pyridin-2-ylmethyl)amino)propan-1-ol and 2-hydroxy-3-methoxybenzaldehyde

A new tripodal amine, 3-((4-aminobutyl)(pyridin-2-ylmethyl)amino)propan-1-ol (HL) has been prepared. This has been used to synthesize a new Schiff base complex by template condensation with 2-hydroxy-3-methoxybenzaldehyde in the presence of Zn(II) metal ion in methanol. The complex has been characterized using spectroscopic methods and the crystal structure of [ZnL]BF4, L:3-((4-aminobutyl)(pyridin-2-ylmethyl)amino)propan-1-ol was confirmed by single crystal X-ray diffraction studies. Single crystal X-ray structure analysis showed that in the mononuclear Zn(II) complex, [ZnL]BF4 the Zn(II) ion is in a distorted square pyramidal environment.

Template synthesis, and X-ray crystal structures of copper(II) and nickel(II) complexes of new unsymmetrical tetradentate Schiff base ligands. Electrochemistry, antibacterial properties, and metal ion effect on hydrolysis–recondensation of the ligand

Two metal complexes, [CuII(naphsal)] (1), and [NiII(salnaph)] (2), of two new unsymmetrical tetradentate Schiff base ligands, H2naphsal {H2naphsal=N-naphthylidene-N′-salicylidene-2-aminobenzylamine} and H2salnaph {H2salnaph=N-salicylidene-N′-naphthylidene-2-aminobenzylamine} have been synthesized by metal template reaction of a tridentate Schiff base, Hnaphtabza {Hnaphtabza=N-(naphthylidene)-2-aminobenzylamine} and salicylaldehyde in the presence of the corresponding metal acetate. The dianionic naphsal2− ligand, produced in the presence of Cu(II), is a simple template condensation product, while the dianionic salnaph2− ligand, produced in the presence of Ni(II), is the hydrolytically rearranged isomer of naphsal2−. The copper(II) and nickel(II) complexes have been fully characterized and their crystal structures have been determined by single crystal X-ray diffraction. Both copper(II) and nickel(II) ions adopt a distorted square planar geometry. The cyclic voltammetric studies of 1 and 2 in acetonitrile solution showed that the CuII/CuI and NiII/NiI reduction processes are electrochemically reversible. The metal complexes were also screened for their in vitro antimicrobial activity.

Synthesis and Characterization of Some Macrocylic Complexes Incorporating Indole and 2,2'-Bipyridine or 1,10-Phenanthroline

Complexes of anionic pentadentate macrocyclic ligands by the template condensation of bis(hydrazino)2,2'-bipyridine or 1,10-phenanthroline with an indoledialdehyde have been synthesized. The new Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) macrocyclic complexes have been characterized by analytical and spectroscopic techniques and by conductivity and magnetic susceptibility measurements.

Template Synthesis, Characterization, Electrochemical Behavior, Antimicrobial, Nematicidal and Pesticidal Activities of Palladium(II) Macrocyclic Complexes

A new class of unsymmetrical palladium(II) macrocyclic complexes have been synthesized by template condensation reaction of the precursor, 2-[4-fluro-2-(2-oxo-1,2-diphenyl-ethylideneamino)-phenylimino]-1,2-diphenyl-ethanone (ML1) with appropriate diamines 1,2- diaminoethane, 1,3- diaminopropane, 1,4- diaminobutane, 1,5- diaminopentane and 1,6- diaminohexane, respectively in the presence of PdCl2.The reactions were carried out in 1:1:1 molar ratio. The precursor and its complexes have been characterized on the basis of elemental analyses, molecular weight determinations, conductance and magnetic susceptibility measurements and spectral studies including IR, 1H-NMR,electronic,mass, spectra and X-ray powder diffraction studies.Based on analytical and spectral data, a four coordinated square planar geometry has been assigned for Pd(II) macrocyclic complexes. The redox properties of the complexes were extensively investigated by electrochemical method using cyclic voltammetry (CV). The in vitro antimicrobial activity of Pd(II) macrocyclic complexes was studied and compared with that of free ligand. These complexes were also screened for their nematicidal and pesticidal activities.

Synthesis and Temperature-Induced Structural Phase and Spin Transitions in Hexadecylboron-Capped Cobalt(II) Hexachloroclathrochelate and Its Diamagnetic Iron(II)-Encapsulating Analogue.

Template condensation of dichloroglyoxime with n-hexadecylboronic acid on the corresponding metal ion as a matrix under vigorous reaction conditions afforded n-hexadecylboron-capped iron and cobalt(II) hexachloroclathrochelates. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-vis, (1)H and (13)C{(1)H} NMR, (57)Fe Mössbauer spectroscopies, SQUID magnetometry, electron paramagnetic resonance, and cyclic voltammetry (CV) and by X-ray crystallography. The multitemperature single-crystal X-ray diffraction, SQUID magnetometry, and differential scanning calorimetry experiments were performed to study the temperature-induced spin-crossover [for the paramagnetic cobalt(II) complex] and the crystal-to-crystal phase transitions (for both of these clathrochelates) in the solid state. Analysis of their crystal packing using the molecular Voronoi polyhedra and the Hirshfeld surfaces reveals the structural rearrangements of the apical long-chain alkyl substituents resulting from such phase transitions being more pronounced for a macrobicyclic cobalt(II) complex. Its fine-crystalline sample undergoes the gradual and fully reversible spin transition centered at approximately 225 K. The density functional theory calculated parameters for an isolated molecule of this cobalt(II) hexachloroclathrochelate in its low- and high-spin states were found to be in excellent agreement with the experimental data and allowed to localize the spin density within a macrobicyclic framework. CV of the cobalt(II) complex in the cathodic range contains one reversible wave assigned to the Co(2+/+) redox couple with the reduced anionic cobalt(I)-containing species stabilized by the electronic effect of six strong electron-withdrawing chlorine substituents. The quasireversible character of the Fe(2+/+) wave suggests that the anionic iron(I)-containing macrobicyclic species undergo substantial structural changes and side chemical reactions after such metal-centered reduction.

Metal-Ion Directed Synthesis of 18-Membered Tetrathia Macrocyclic Complexes of Co(II), Ni(II), Cu(II), and Zn(II), Their Physicochemical Studies and DNA Binding Study of Copper Complex

18-membered tetrathia macrocyclic complexes of the type [MLX2], [M = Co(II), Ni(II), Cu(II), and Zn(II), X = Cl or NO3] have been synthesized by template condensation of α,α′-dibromo-o-xylene and 1,3-propanedithiol. The complexes have been characterized by elemental, ESI-mass, spectral (IR and NMR), molar conductance and magnetic susceptibility analysis. XRD has been used to deduce the morphology of the complex. The Absorption and fluorescence studies of Cu(II) complex show a significant binding to calf-thymus DNA. Among all composition, Cu(II) complex has showed crystalline behavior and significant binding with calf thymus DNA.

Supramolecular polymer of Schiff base gadolinium complex: Synthesis, crystal structure and spectroscopic properties

The new gadolinium(III) nitrate complex [Gd(H2L)2(NO3)3(EtOH)]MeOH where H2L is N,N′-bis(5-methylsalicylidene)-4-methyl-1,3-phenylenediamine was obtained in template condensation reaction of 5-methylsalicylaldehyde with 4-methyl-1,3-phenylenediamine in presence of gadolinium(III) nitrate hexahydrate. The structure of the complex was determined by single-crystal X-ray diffraction analysis and by physicochemical methods. The central cation is nine-coordinated, and the coordination resembles distorted tricapped trigonal prism and only oxygen atoms are involved in coordination. In the crystal structure there is uncoordinated solvent – methanol molecule. The methanol molecule plays an important role in the crystal packing by hydrogen bonding and it connects the complex molecules into infinite chains. Electron paramagnetic resonance studies confirmed complex formation of gadolinium ion because internal coordination sphere of gadolinium was changed. The absorption and fluorescence properties of [Gd(H2L)2(NO3)3(EtOH)]MeOH were studied in different solvents: ethyl acetate, 1-propanol, methanol, ethanol and acetonitrile. Fluorescence quantum yields (ΦF) were calculated for the complex in all solvents and the values, of ΦF are rather low, the exact values depend on solvent, being between 0.0005 (in acetonitrile and ethyl acetate) and 0.0014 (in 1-propanol).

First iron and cobalt(ii) hexabromoclathrochelates: structural, magnetic, redox, and electrocatalytic behavior

Template condensation of dibromoglyoxime with n-butylboronic acid on the corresponding metal ion as a matrix under vigorous reaction conditions afforded iron and cobalt(ii) hexabromoclathrochelates. The paramagnetic cobalt clathrochelate was found to be a low-spin complex at temperatures below 100 K, with a gradual increase in the effective magnetic moment at higher temperatures due to the temperature 1/2↔3/2 spin crossover and a gap caused by the structure phase transition. The multitemperature X-ray and DSC studies of this complex and its iron(ii)-containing analog also showed temperature structural transitions. The variation of an encapsulated metal ion's radius, electronic structure and spin state caused substantial differences in the geometry of its coordination polyhedron; these differences increase with the decrease in temperature due to Jahn-Teller distortion of the encapsulated cobalt(ii) ion with an electronic configuration d(7). As follows from CV and GC data, these cage iron and cobalt complexes undergo both oxidation and reduction quasireversibly, and showed an electrocatalytic activity for hydrogen production in different producing systems.

Molecular design of cage iron(II) and cobalt(II,III) complexes with a second fluorine-enriched superhydrophobic shell.

Pentafluorophenylboron-capped iron and cobalt(II) hexachloroclathrochelate precursors were obtained by the one-pot template condensation of dichloroglyoxime with pentafluorophenylboronic acid on iron and cobalt(II) ions under vigorous reaction conditions in trifluoroacetic acid media. These reactive precursors easily undergo nucleophilic substitution with (per)fluoroarylthiolate anions, giving (per)fluoroarylsulfide macrobicyclic complexes with encapsulated iron and cobalt(II) ions; nucleophilic substitution of the cobalt(II) hexachloroclathrochelate precursor with a pentafluorophenylsulfide anion gave the target hexasulfide monoclathrochelate and the mixed-valence Co(III)Co(II)Co(III) bis-clathrochelate as a side product. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-Vis, (57)Fe Mössbauer (for the X-rayed iron complexes), (1)H, (11)B, (13)C and (19)F NMR spectroscopies and by X-ray diffraction; their redox and electrocatalytic behaviors were studied using cyclic voltammetry and gas chromatography. As can be seen from the single-crystal X-ray diffraction data, the second superhydrophobic shell of such caged metal ions is formed by fluorine atoms of both the apical and ribbed (per)fluoroaryl peripheral groups. The main bond distances and chelate N=C-C=N angles in their molecules are similar, but rotational elongation (contraction) along the molecular C3-pseudoaxes, accompanied by changes in the geometry of the corresponding MN6-coordination polyhedra from a trigonal prism to a trigonal antiprism, allowed encapsulating Fe(2+), Co(2+) and Co(3+) ions. The nature of an encapsulated metal ion and its oxidation state affect the M-N bond lengths, and, for cobalt(ii) clathrochelate with an electronic configuration d(7) the Jahn-Teller structural effect is observed as an alternation of the Co-N distances. Pentafluorophenylboron-capped hexachloroclathrochelate precursors, giving stable catalytically active metal(I)-containing intermediates due to the electron-withdrawing effect of their six ribbed chlorine substituents, were found to show moderate electrocatalytic activity in a 2H(+)/H2 hydrogen-forming reaction. In the case of their ribbed-functionalized sulfide derivatives, the strong electron-withdrawing (per)fluoroaryl groups do not stabilize the reduced electrocatalytically active metal(i)-containing species as their mesomeric effect is absent or substantially decreased by steric hindrances between them.