Oleg A. Varzatskii

A Trigonal Prismatic Mononuclear Cobalt(II) Complex Showing Single-Molecule Magnet Behavior.

Single-molecule magnets (SMMs) with one transition-metal ion often rely on unusual geometry as a source of magnetically anisotropic ground state. Here we report a cobalt(II) cage complex with a trigonal prism geometry showing single ion magnet behavior with very high Orbach relaxation barrier of 152 cm(-1). This, to our knowledge, is the largest reported relaxation barrier for a cobalt-based mononuclear SMM. The trigonal prismatic coordination provided by the macrocyclic ligand gives intrinsically more stable molecular species than previously reported SMMs, thus making this type of cage complexes more amendable to possible functionalization that will boost their magnetic anisotropy even further.

Template synthesis, structure and unusual series of phase transitions in clathrochelate iron(II) α-dioximates and oximehydrazonates formed by capping with functionalized boron-containing agents

Abstract A series of clathrochelate α-dioximates and oximehydrazonates with apical long-chain paraffin and allyl substituents has been synthesized and characterized by X-ray analysis. For the hexadecylboronic FeNx3(BHd)2 complex (where Nx2− is the cyclohexanedion-1,2-dioxime dianion) in the temperature range 100–305 K, two structural phase transitions have been detected by X-ray diffractometry and 57Fe Mossbauer spectroscopy.

Size matters, so does shape: Inhibition of transcription of T7 RNA polymerase by iron(II) clathrochelates.

Coordination and organoelement compounds are rarely proposed as the drug candidates despite their vast potential in the area owing to their strictly controlled geometry and rather extensive surface. This is the first example of the inhibition of transcription in the system of T7 RNA polymerase by cage metal complexes. Their IC50 values reach as low as the nanomolar range, placing them among the most potent metal-based transcription inhibitors.

Interaction of dichloride iron(II) clathrochelate with dimercaptomaleodinitrile: synthesis of the precursor monoribbed-functionalized phthalocyaninoclathrochelates and the unexpected formation of a new thiophene-containing heterocyclic system in the ribbed chelate fragment of the clathrochelate framework.

Clathrochelate iron(II) FeBd 2(S2C2(CN)2Gm)(BF)2 tris-dioximate with a ribbed vic-dinitrile fragment was synthesized as a precursor of the monoribbed-functionalized hybrid phthalocyaninoclathrochelates by nucleophilic substitution of the vic-dichloride FeBd2(Cl2Gm)(BF)2 clathrochelate (1) with the potassium salt of dimercaptomaleodinitrile. Reaction of nitromethane with this salt was followed by the condensation of the reaction products with 1 to yield the clathrochelate with an annulated previously unknown thiazinothiophene heterocyclic system in the ribbed fragment. Both complexes were characterized on the basis of elemental analysis; MALDI-TOF mass spectrometry; IR, UV-vis, (57)Fe Mössbauer, and NMR spectroscopies; and X-ray crystallography.

First trigonal-antiprismatic tris-dichloroglyoximate iron(II) clathrochelate and its reactivity in nucleophilic substitution reactions

Tris-dichloroglyoximate clathrochelate [Fe(Cl2Gm)3(SnCl3)2]2− dianion has been synthesized by a procedure differing from those described earlier for boron-capped analogs. The co-ordinately saturated SnCl62− dianion is now used as the capping agent instead of boron-containing Lewis acids. The tris-dichloroglyoximate tin-capped product obtained is far less reactive than its boron-capped analogs, and only in the case of a thiophenolate anion was the “regular” hexafunctionalized clathrochelate obtained. The complexes synthesized have been characterized by elemental analysis, PD and MALDI-TOF mass, IR, UV-vis and 1H, 13C and 119Sn NMR spectra, cyclic voltammetry, and X-ray crystallography for the clathrochelate [Fe(Cl2Gm)3(SnCl3)2]2− dianion. The geometry of the functionalized complex (the distortion angle φ and main bond lengths in the clathrochelate framework) has been deduced from the quadrupole splitting value in the 57Fe Mossbauer spectrum and EXAFS data, respectively.

Cage complexes of transition metals in biochemistry and medicine

The review presents the following main trends and the perspectives of application of the transition metal clathrochelates in medicine and biochemistry: encapsulation of radioactive metal ion for diagnostics and therapy; imaging agents for MRI; antidotes and prolonged pharmaceuticals; pharmaceuticals for boron neutron capture therapy; antihelminthic and antiparasitic detergents; antioxidants; membrane transport of the metal ions; interaction of the cage metal complexes with nucleic acids and the potential of their self-assembling reactions in immunology and molecular biology (recognition of antibodies, antigens and DNA sites); design of HIV inhibitors for the therapy.

Insight into the electronic structure, optical properties, and redox behavior of the hybrid phthalocyaninoclathrochelates from experimental and density functional theory approaches.

An insight into the electronic structure of several hafnium(IV), zirconium(IV), and lutetium(III) phthalocyaninoclathrochelates has been discussed on the basis of experimental UV-vis, MCD, electro- and spectroelectrochemical data as well as density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. On the basis of UV-vis and MCD spectroscopy as well as theoretical predictions, it was concluded that the electronic structure of the phthalocyninoclathrochelates can be described in the first approximation as a superposition of the weakly interacting phthalocyanine and clathrochelate substituents. Spectroelectrochemical data and DFT calculations clearly confirm that the highest occupied molecular orbital (HOMO) in all tested complexes is localized on the phthalocyanine ligand. X-ray crystallography on zirconium(IV) and earlier reported hafnium(IV) phthalocyaninoclathrochelate complexes revealed a slightly distorted phthalocyanine conformation with seven-coordinated metal center positioned ∼1 Å above macrocyclic cavity. The geometry of the encapsulated iron(II) ion in the clathrochelate fragment was found to be between trigonal-prismatic and trigonal-antiprismatic.

THE SYNTHESIS AND STRUCTURE OF A MACROBICYCLIC HEXAHALOGENIDE TRISDIOXIMATE AS A PROMISING PRECURSOR OF FUNCTIONALIZED CLATHROCHELATES

The reactive hexachloride precursor of functionalized α-dioximate clathrochelates and the product of their reaction with thiophenol have been prepared and structurally characterized by single-crystal X-ray diffraction.

Reactions of chloride iron(II) clathrochelates with aliphatic amines: an unexpected influence of the nature of the amine and solvent on the reaction products

The interaction of the reactive di- and hexachloride clathrochelate iron(II) precursors with primary and secondary aliphatic amines of different nature in a wide range of donor and acceptor solvents has been studied. The partially functionalized aminic clathrochelates obtained have been characterized using elemental analysis, PD mass, IR, UV–Vis, 57Fe Mossbauer and 1H, 13C NMR spectra and crystallographically (Fe((C6H11NH)2Gm)(Cl2Gm)(BC6H5)2 · n-C5H12 and Fe((n-C4H9NH)ClGm)(Cl2Gm)2(BC6H5)2 complexes). The causes of an unexpected influence both amine and solvent nature on the product of reaction with chloride clathrochelate precursors have been discussed.

Interaction of the iron(II) cage complexes with proteins: protein fluorescence quenching study.

Interaction of the iron(II) mono- and bis-clathrochelates with bovine serum albumin (BSA), β-lactoglobulin, lysozyme and insulin was studied by the steady-state and time-resolved fluorescent spectroscopies. These cage complexes do not make significant impact on fluorescent properties of β-lactoglobulin, lysozyme and insulin. At the same time, the monoclathrochelates strongly quench a fluorescence intensity of BSA and substantially decrease its excited state lifetime due to their binding to this protein. This occurs due to the excitation energy transfer from a tryptophan residue to a cage molecule or/and to the change of the tryptophan nearest environment caused by either clathrochelate binding or an alteration of the BSA conformation. The effect of the iron(II) bis-clathrochelate on BSA fluorescence is much weaker as compared to its monomacrobicyclic analogs as a result of an increase in its size.