Zdirad Zák

Comenius University in Bratislava, Presburg, Bratislavský, Slovakia

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Publications (4)14.56 Total impact

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    ABSTRACT: Two novel heterometallic complexes [Cd(NH3)6][{VO(O2)2(OH)}2{μ-Cd(NH3)4}] (2) and [{VO(O2)2(Im)}2{μ-Cu(Im)4}] (3) (Im = imidazole) containing peroxidovanadium complexes as metalloligands were prepared and characterized by spectral methods. X-ray single-crystal analysis revealed the presence of unique trinuclear complexes in the crystal structures of 2 and 3. The structure of 2 contains an anionic complex, whose two {VO(O2)2(OH)}(2-) ions are interconnected by a {μ-Cd(NH3)4}(2+) group. Compound 3 is a trinuclear neutral complex comprising two {VO(O2)2(Im)}(-) ions and a single bridging {μ-Cu(Im)4}(2+) group. The bonding via an equatorial OH(-) ligand in 2 and via a doubly bonded apical oxygen atom in 3 represents coordination modes previously unobserved for diperoxidovanadium complexes. Compared with complex 2, density functional theory studies reported decreased Cu-μ-O bond orders and increased μ-O-V bond orders in 3, in accordance with the expected Jahn-Teller distortion of the latter complex.
    Inorganic Chemistry 05/2014; · 4.59 Impact Factor
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    ABSTRACT: The first dinuclear nonperoxido tartrato complexes of vanadium(V), (NMe(4))(2)[V(2)O(4)((2R,3R)-H(2)tart)(2)] x 6 H(2)O (1), (NMe(4))(2)[V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)] (2), (NEt(4))(2)[V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)] (3) (tart = tartrato(4-) = C(4)H(2)O(6)(4-)) have been prepared from water-ethanol medium and characterized by X-ray structure analysis and spectral methods. The formation of the complexes has been found to be stereospecific; the composition and structure of anions containing one or both enantiomers of the ligand are profoundly different. The structure of anions in 1-3 also differs significantly from the structure of other dinuclear vanadium(V) alpha-hydroxycarboxylato complexes, but, interestingly, the geometry of the [V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)](2-) ion resembles the structure of the [(VO)(2)((2R,3R)-tart)((2S,3S)-tart)](4-) ion which has a vanadium(IV) center. Using Raman and (51)V NMR spectroscopy the solvent dependent mutual transformations of [V(4)O(8)((2R,3R)-tart)(2)](4-) (V(4)L(2)-RR), [V(4)O(8)((2S,3S)-tart)(2)](4-) (V(4)L(2)-SS), [V(2)O(4)((2R,3R)-H(2)tart)(2)](2-) (V(2)L(2)-RR), [V(2)O(4)((2S,3S)-H(2)tart)(2)](2-) (V(2)L(2)-SS), and [V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)](2-) (V(2)L(2)-rac) have been established. In aqueous solution the following reactions take place; 2 V(2)L(2)-rac --> V(2)L(2)-RR + V(2)L(2)-SS followed by partial decomposition, V(2)L(2)-RR --> V(4)L(2)-RR + 2 L (V(2)L(2)-SS --> V(4)L(2)-SS + 2 L). On the other hand V(2)L(2)-rac is stable in CH(3)CN solution while V(2)L(2)-RR (V(2)L(2)-SS) decomposes into several species.
    Inorganic Chemistry 09/2009; 48(17):8423-30. · 4.59 Impact Factor
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    ABSTRACT: The structure of the title compound, (C(6)H(7)N(2)O)(6)[V(10)O(28)].2H2O, at 120 (2) K has monoclinic (C2/c) symmetry. The asymmetric unit consists of one half-decavanadate anion of Ci symmetry, three cations and one water molecule. Each water molecule is hydrogen bonded to two decavanadate anions, thus forming a one-dimensional chain of anions. The three-dimensional supramolecular structure is formed by a network of N-H...O, O-H...O and C-H...O hydrogen bonds, in which the cations, anions and water molecules are involved, and by nonparallel-displaced pi-stacking interactions between pyridine rings. As a result of hydrogen bonding, the carboxamide groups of the cations are somewhat twisted from the pyridine ring plane.
    Acta Crystallographica Section C Crystal Structure Communications 10/2007; 63(Pt 9):m419-22. · 0.78 Impact Factor
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    ABSTRACT: A study of the aqueous H3O+(OH-)/H2VO4-/(2R,3R)-tartrate system has been performed at 273 K in a 1.0 mol/L Na+(Cl-) ionic medium using 51V NMR spectroscopy. In this relatively complicated system, more than 12 different species were observed. Ligand concentration, vanadate concentration, and pH variation studies were carried out, particularly for the range of pH 5.8-8.0 and for pH 2.4. Chemical shifts, vanadium-ligand stoichiometry, and also composition and formation constants for some, but not all, species are given. Despite some reduction of vanadium(V) to vanadium(IV) in an acidic medium at pH approximately 2.4, the stoichiometries of the principal species in solution at this pH were determined. Electrospray ionization mass spectra for some solutions were obtained and were in accordance with the conclusions drawn from the speciation studies. A series of crystalline vanadium(V) tartrato complexes M4[V4O8(tart)2].aq were also prepared and characterized. X-ray diffraction studies of Na4[V4O8(rac-tart)2].12H2O (1) and (NEt4)4[V4O8((R,R)-tart)2].6H2O (2) revealed unique tetranuclear [V4O8(tart)2]4- ions for which the {V4O4} rings have boat conformations.
    Inorganic Chemistry 06/2007; 46(10):3971-83. · 4.59 Impact Factor