Gordana Vuckovic

SYNTHESIS, CHARACTERIZATION, STRUCTURE AND POSSIBLE CATALYTIC PROPERTIES OF CIS-OXALATO(1,4,8,11-TETRAAZACYCLOTETRADECANE)COBALT(III) NITRATE

Abstract A new complex of cobalt(III) with 1,4,8,11-tetraazacyclotetradecane (cyclam) and oxalato ion as a bidentate ligand was prepared and characterized by elemental analysis, IR, electronic and 1H NMR spectroscopy and cyclic voltammetry. X-Ray analysis has shown that this compound crystallizes in the orthorhombic system, space group Pccn, with a = 8.583(1), b = 12.854(2), c = 14.944(1)A, V = 1649.3(4) A3, Z = 4, R = 0.512, Rw = 0.545, and has a crystallographic two-fold rotation axis. The complex was identified as cis-oxalato(1,4,8,11-tetraazacyclotetradecane)cobalt(III) nitrate, [Co(ox)cyclam]NO3 (oxH2 = oxalic acid), and it can be described in terms of a cis octahedral geometry with a folded cyclam configuration around the cobalt atom with the oxalato ion occupying the remaining two sites. Cyclic voltammetric data suggest a large stability for this compound, as well as its possible catalytic effect on electrochemical CO2 reduction.

MIXED-LIGAND COMPLEXES OF COBALT(III) WITH DITHIOCARBAMATES AND A CYCLIC TETRADENTATE SECONDARY AMINE

Abstract 4-Morpholine-, piperidine-, 4-piperazine- and N-methyl- piperazine-dithiocarbamate complexes of Cobalt (III) with 1, 4, 8, 11-tetraazacyclotetradecane, of general formula [Co(Rdtc)cyclam] (C104)2, have been prepared and have been characterized. The complexes adopt cis-octahedral geometry with folded macrocyclic ligand and with the dithiocarbamate bound as a bidentate. trans-influence of the dithiocarbamate ligands was studied by NMR spectroscopy and established the order piperidine-dtc > 4-morpholine-dtc > N-methyl-piperazine-dtc.

Synthesis, Crystal Structure, Magnetic Properties and Cyclic Voltammetry of the Unsymmetric (μt-Oxalato)-[N, N′, N″, N″′-Tetrakis-(2-Pyrii)Ylmethyl)-1, 4, 8, 11-Tetraazacyclotetfw-Decane]Dicobalt(II) Pekchlokate Trihydkate

Abstract A new dinuclear cobalt(II) complex, [Co2(ox)tpmc](ClO4)2 3H2O, (tpmc = N, N′, N″, N″′-tetrakis(2-pyridylmethyl)-1, 4, 8, 11-tetraazacyclotetradecane, ox2 -oxalate ion), has been synthesized and its crystal structure solved by single crystal X-ray diffraction studies. It crystallizes in the monoclinic system, space group P21, with a = 97558(8) A, b = 21.455(2) A, c - 21.241(2) A, β=100.069(8)°, V=4391.0(8) A3, Z =4,R = 0.083, Rw = 0.086. Its structure consists of two dinuclear, crystallographically unique molecules in which the oxalate ion bridges two cobalt(II) ions unsymmetrically. E:ach cobalt is hexa-coordinated with four macrocyclic nitrogens and two oxygens in an octahedral arrangement of an “em” coordination of a macrocyclic ligand. The third oxygen is simultaneously bonded to both cobalt ions and the last one remains uncoordinated, which is the unique way of oxalato ion coordination. Intramolecular antiferromagnetic coupling between the two cobalt(II) ions is observed and yielded J = -9.3 ...

Preparation, characterization and redox properties of o,o′‐geometrical isomers of μ‐α and μ‐β‐aminoisobuty‐rato co(ii) complexes with n,n′,n′,n‴‐tetrakis(2‐pyridylmethyl)‐1,4,8,11‐tetraazacyclotetradecane

Abstract Two new dinuclear cobalt(II) complexes which, besides macrocyclic ligand N′,N′,N″,N‴-tetrakis (2-pyridylmethyl)-l,4,8,11-tetraazacyclotetradecane (tpmc) contain α- or β-aminoisobutyrato ions (α-aibu − and β-aibu −, respectively) were synthesized. The complexes having general formula [Co2(aibu)tpmc](CIO4)3 were characterized by elemental analysis, electronic and 1R spectroscopy, magnetic measurements and cyclic voltammetry. It was assumed that in both complexes an exo coordination of the macrocyclic ligand is achieved. Cobalt(II) ions are bridged with O,O′-aminoisobutyrato ligand. Both complexes are stable against air oxidation, whereas the oxidation of the complex containing the α-aibu− ion by hydrogen-peroxide gave the coresponding mixed-valence Co11/Co111 complex. The complexes are also electrochemically stable in the potential range from-0,6V to 0,4V vs SCE.

Salting-out thin-layer chromatography of transition metal complexes. III: Investigation of the behaviour of mixed aminocarboxylato cobalt(III) complexes on cellulose

SummarySalting-out thin-layer chromatography of fourteen mixed aminocarboxylato cobalt(III) complexes (three homologous series) on cellulose has been investigated with eight aqueous ammonium sulphate solutions. A pronounced salting-out effect, with reversed-phase order, was observed with bis(aminocarboxylato) complexes, whereas with mono(aminocarboxylato) complexes such a behaviour was noticeable only at higher salt concentrations. In both cases a positive linear dependence between the RM values of the complexes and mol % of the salt in the solvent system, and between the RM values and the number of carbon atoms in the hydrocarbon part of the complexes belonging to the same homologous series, were found. These phenomena were explained by the mechanism of non-specific hydrophobic interactions.

Salting-out thin layer chromatography of transition metal complexes : a comparative study of the effect of increased number of CH2 groups in chelate rings

SummaryThe regularities previously established in salting-out thin-layer chromatography on silica gel of Co(III) complexes, in which the side chains of a specific chelate ring were successively increased in length, were also found to be valid for two series of Co(III) complexes of the EDTA type, in which different chelate rings were enlarged by one CH2 group. It was found that in the case of complexes of the EDTA type the salting-out efficiencies were practically the same for all members of a series, while the values of the separation factors were paractically independent of the ammonium sulphate concentration in the solvent system used. The results obtained were consistent with the mechanism of nonspecific hydrophobic interactions. The method used can be applied to the separation of the members of the series of complexes that we investigated.

SYNTHESIS AND X-RAY CRYSTAL ANALYSIS OF [Cu2(HCOO)tpmc]-[Cu2(CH3COO)tpmc](ClO4)6·6H2O(tpmc = N,N′,N″,N‴-TETRAKIS-(2-PYRIDYLMETHYL)-1,4,8,11-TETRAAZACYCLOTETRADECANE). PREPARATION AND CHARACTERIZATION OF [Cu2(HCOO)tpmc](ClO4)3·H2O

The new structure of [Cu2(HCOO)tpmc][Cu2(CH3COO)tpmc](ClO4)6·6H2O (tpmc = N,N′,N″,N‴-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetra-decane), consists of [Cu2(HCOO)tpmc]3+ and [Cu2(CH3COO)tpmc]3+ cations, perchlorate anions and water of crystallization. Two different binuclear transition metal complexes with the tpmc ligand form the same crystal lattice giving the monocrystals. The crystal structure of this compound has been solved by single crystal X-ray diffraction studies. It crystallizes in the triclinic system, space group with a = 14.176(3), Å, b = 16.864(4) Å, c = 20.681(3), Å, α = 100.68(3)○, β = 101.00(3)○, γ = 101.37(3)○, V = 4628.6(16), Å3, R = 0.0729. Each copper atom is penta-coordinated in a distorted square-pyramidal arrangement. In addition, [Cu2(HCOO)tpmc](ClO4)3·H2O was prepared and its properties were compared with the previously described μ-acetato analogue.

Crystal structure, thermal behavior, and microbiological activity of a thiosemicarbazide-type ligand and its cobalt complexes

The synthesis of a potentially bioactive mixed-valence CoIII/CoII complex with 2-acetylpyridine S-methylisothiosemicarbazone (HL) ligand is described. The crystal and molecular structure of the formed [CoIIIL2][CoIICl3py]·Me2CO (I) compound (py stands for pyridine) is determined by single-crystal X-ray crystallography. It’s thermal decomposition along with the decomposition of the ligand and six structurally related complexes with formulas [CoL2]NO3·MeOH (1), [CoL2]Br·MeOH (2), [CoL2]HSO4·MeOH (3), [CoL2]2[CoII(NCS)4] (4), [Co(HL)(L)]I2·2MeOH (5), and [Co(HL)(L)][CoIICl4]·MeOH (6) was determined by simultaneous TG/DSC measurements. The decomposition pattern is evaluated using TG/DTA-MS data. The results were related to the solvent/moisture content and the decomposition mechanism of the compounds. The antimicrobial activity of the ligand and of all the complexes was tested in vitro for selected gram-negative and gram-positive bacteria and fungi. The activity of the ligand against all tested bacteria is comparable with those obtained for standard antibiotics, while it is less active against fungi. Surprisingly, the activity of the complexes is very low. The low antimicrobial activity of the complexes may be in connection with their high thermodynamic and kinetic inertness in solution. The results are also supported by the relatively high thermal stability of the complexes.

Linear interdependence ofRM pair values of substances in salting-out planar chromatography

SummaryIt has been established that in salting-out planar chromatography there is a linear dependence between the pair ofRM values of substances obtained on one or two sorbents using the same series of aqueous ammonium sulphate solutions (RM pair linearity rule). In addition, the proportionality between the distance of the individual points on the regression straight line and the difference in mol% of the salt in the corresponding solvents has been established (proportionality rule).

Separation Mechanisms of Co(III) Complexes with EDTA-Type Ligands during Salting-Out TLC on Impregnated and Non-Impregnated Silica Gel

A separation mechanism of eight Co(III) complexes with ethylenediaminetetraacetate-type ligands belonging to two series during salting-out thin-layer chromatography on silica gel is investigated. The sorbent is impregnated with five poly(ethylene glycol)s with different molecular masses, and ammonium sulphate solutions are used as mobile phase. Additionally, on non-impregnated sorbent, mobile phases containing one of eight salts with ions of different lyotropic properties are used: kosmotropic Mg(2+) accompanied with SO(4)(2-) (kosmotrope), Cl(-) (border), NO(3)(-) (chaotrope), ClO(4)(-)(chaotrope), Cl(-) of Li(+) (kosmotrope), Na(+) (border), K(+) (chaotrope) and NH(4)(+) (chaotrope). Salting-out and salting-in effects were observed depending on salt nature. The combined retention mechanism of specific H-bonding and nonspecific hydrophobic interactions is proposed.