Katarina Andjelkovic

Synthesis and structure of aqua-2′,‴-(2,6-pyridindiyldiethylidene) dioxamohydrazide-copper(II) hydrate

Abstract In a template synthesis from copper(II) acetate, 2,6-diacetylpyridine, and semioxamazide (NH2CO CONHNH2), two copper(II) complexes, [Cu(dapsox)(H2O)]·H2O and [Cu(Hdapsox)](H2O)]ClO4, (where H2dapsox = 2′,2‴-(2,6-pyridindiyldiethylidene)dioxamohydrazide) were obtained and characterized. The structure of the former complex was determined by a single-crystal X-ray analysis. CuII is located in a square pyramidal environment. The polydentate ligand, dapsox2− is coordinated in dianionic form, as an unsymmetrical quadridentate planar system forming one-membered and two-five-membered metal-chelate rings. The fifth coordination site is occupied by a water molecule.

Thermal Analysis in Structural Characterization of Hydrazone Ligands and Their Complexes

Results of our research on synthesis and characterization of complexes with acylhydrazone derivatives are described in this review paper. Structural characterization of newly synthesized complexes by thermal analysis (TG, DTA, DSC) is particularly emphasized in this paper. Thermal analysis enabled us to study not only structural changes of substances during thermal treatment, but also the mode of coordination and degree of deprotonation of acylhydrazones, as well as geometry of the coordination sphere of complexes, the structure of which had not been determined by X-ray analysis. Topics in this paper are as follows: complexes of dioxomolybdenum(VI) with tridentate hydrazones, usnic acid derivatives and their Cu(II) complexes, as well as transition metal complexes with 2,6-diacetylpyridine bis(hydrazones).

An Fe(III) Complex with the Dianionic form of 2,6-Diacetylpyridine Bis(Acylhydrazone). The Crystal Structure of [Diaqua-2′,2′′′-(2,6-PyridinediyldiEthylidyne)Dioxamohydrazide]Iron(III) Perchlorate Trihydrate, [Fe(dapsox)(H2O)2]ClO4·3H2O

The title compound was prepared by a template synthesis from 2,6-diacetylpyridine, dioxamohydrazide and Fe(ClO4)3·6H2O(mol ratio 1:2:1) in MeOH/H2O(3:1) solution and its structure determined by single-crystal X-ray diffraction; triclinic, space group P1, a = 7.5186(7), b = 10.9730(9), c = 14.6110(10) Å, α = 95.866(1), β = 100.252(1), γ = 92.895(1), z = 2. The polydentate ligand is coordinated as a dianionic pentadentate while water molecules occupy apical positions in the structure. This is the first example of a monomeric, pentagonal bipyramidal structure of an Fe(III) complex with a dianionic bis(acylhydrazone) derivative of 2,6-diacetylpyridine.

Synthesis and structural characterization of copper(II) complexes with the 2′-[1-(2-pyridinyl)ethylidene]oxalohydrazide ligand

The octahedral copper(II) complex with two 2′-[1-(2-pyridinyl)ethylidene]oxalohydrazide molecules was synthesized from bis(acetylacetonato)copper(II) and 2′-[1-(2-pyridinyl)ethylidene]oxamohydrazide (Hapsox). The complex is unstable when not in solution. X-ray analysis confirmed the tridentate coordination of the ligands in the monoanionic form. In addition, the stable tetrahedral copper(II) complex with one ligand molecule coordinated as a tridentate in the dianionic form was prepared by direct synthesis from Cu(NO3)2·3H2O and Hapsox, and characterized by elemental analysis, magnetic measurements and by i.r. and u.v./vis. spectrophotometry.

Synthesis and Structural Characterization of the Co(III) Complex with 2'-[1-(2-Pyridinyl)-Ethylidene]-Oxamohydrazide (Hapsox): The Crystal Structure of Bis-{2'-[1-(2-Pyridinyl)-Ethylidene]-Oxamohydrazido} Cobalt(III) Perchlorate, [Co(apsox)2]ClO4

The synthesis of a novel ligand 2′-[1-(2-pyridinyl)-ethylidene]-oxamohydrazide (Hapsox), from a series of 2-acetylpyridine acylhydrazones, and its complex with Co(III), which is the first in this series of complexes are described. Both the ligand and the complex were characterized by elemental analysis, IR, 1H-NMR, and 13C-NMR spectra, and the structure of the complex [Co(apsox)2]ClO4 was determined by X-ray structural analysis. It was established that [Co(apsox)2]ClO4 has an octahedral geometry with two tridentate apsox ligands in monoanionic form. Structural characteristics, lengths of the bonds, and angles between the bonds were typical for Co(III) complexes of distorted octahedral geometry. Both direct and template synthesis afforded the same geometrical isomer of the complex with two apsox ligands meridionally bound to the central metal ion, even in the case when equimolar quantities of Co(ClO4)2 and Hapsox were applied.

PENTAGONAL BIPYRAMIDAL COMPLEXES OF Co(II) WITH SINGLY- AND DOUBLY-DEPROTONATED2′,2″-(2,6-PYRIDINDIYLDI-ETHYLIDENE)DIOXAMOHYDRAZIDE The Crystal Structure of [Diaqua-2′,2″-(2,6-Pyridindiyldiethylidene) Dioxamohydrazidecobalt(II)] Hexahydrate

Abstract This paper reports the first Co(II) complexes with a singly- and doubly-deprotonated H2L ligand (H2L = 2′,2″-(2,6-pyridindiyldiethylidene)dioxamohydrazide belonging to the planar pentadentate class. The complexes were characterized by elemental analysis, thermal analysis, IR spectroscopy, molar conductivity and magnetic susceptibility measurements. The crystal structure of [Co(L)(H2O)2] 6H2O complex has been determined. The pentagonal bipyramidal geometry present in the previously synthesized complex [Co(H2L)(H2O)(MeOH)](ClO4)2, wherein the ligand is present in a neutral form, has been preserved around Co(II).

Ni(II) complexes with neutral and dianionic form of 2,6-diacetylpyridine bis(acylhydrazones). Crystal structure of bis[dioxo-2,6-pyridinediylbis(ethylidyne-1-hydrazinyl-2-ylidene)diacetic acid]nickel(II) perchlorate

Abstract The octahedral Ni(II) complex with dioxo-2,6-pyridinediylbis(ethylidyne-1-hydrazinyl-2-ylidene)diacetic acid (H2dapoamh) was synthesized and X-ray analysis confirmed the tridentate coordination for the neutral ligand. Besides, the square planar Ni(II) complex with dianion 2′,2‴-(2,6-pyridinediyldiethylidyne)dioxamohydrazide (H2dapsox) was synthesized and characterized.

Role of spin state and ligand charge in coordination patterns in complexes of 2,6-diacetylpyridinebis(semioxamazide) with 3d-block metal ions: A density functional theory study

We report here a systematic computational study on the effect of the spin state and ligand charge on coordination preferences for a number of 3d-block metal complexes with the 2,6-diacetylpyridinebis(semioxamazide) ligand and its mono- and dianionic analogues. Our calculations show excellent agreement for the geometries compared with the available X-ray structures and clarify some intriguing experimental observations. The absence of a nickel complex in seven-coordination is confirmed here, which is easily explained by inspection of the molecular orbitals that involve the central metal ion. Moreover, we find here that changes in the spin state lead to completely different coordination modes, in contrast to the usual situation that different spin states mainly result in changes in the metal-ligand bond lengths. Both effects result from different occupations of a combination of π- and σ-antibonding and nonbonding orbitals.

Synthesis, Characterization and Biological Activity Evaluation of Novel Pd(II) and Pt(II) Complexes with Heterocyclic Hydrazone Ligands

New complexes of Pt(II) with condensation derivatives of ethyl hydrazinoacetate and either 2-acetylpyridine or 2-quinolinecarboxaldehyde, and of Pd(II) with the condensation derivative of ethyl hydrazinoacetate and 2-quinolinecarboxaldehyde were synthesized and characterized by elemental analysis, IR, 1H- and 13C-NMR spectroscopy, and molar conductivity measurements. The complexes have a square planar geometry, ligands binding as bidentates in the neutral form, and the remaining two coordination sites being occupied by chloride ions. Biological activity of new complexes, and of previously synthesized Pd(II), Cd(II), Co(III) and Zn(II) complexes with this ligand type was evaluated by the brine shrimp test. All the complexes showed a moderate activity.

PENTAGONAL-BIPYRAMIDAL Mn(II) AND Zn(II) COMPLEXES WITH 2′,2′″-(2,6-PYRIDINDIYLDI-ETHYLIDENE)DIOXAMOHYDRAZIDE

ABSTRACT [Mn(H2dapsox)Cl(H2O)]ClċH2O (1) and Zn(H2dapsox)-(H2O)2]Cl2ċH2O (2) were synthesized from 2,6-diacetylpyridine (dap), oxamic acid hydrazide (sox) and MnCl2ċ4H2O or ZnCl2ċ2H2O in 1:2:1 molar ratio, employing a template approach. Based on elemental analyses, molar conductivity and magnetic susceptibility data, IR, 1H and 13C NMR and EA spectra, as well as thermal analyses (DSC and TG), a pentagonal-bipyramidal (PBP) geometry for the complexes was determined. Symmetrically coordinated 2′,2′″-(2,6-pyridindiyldiethylidene)dioxamohydrazide (H2dapsox) is located as a pentadentate ligand in the equatorial plane. The stability of the 3d metal complexes having the PBP geometry is discussed. It was found that Co(II) and Mn(II) produce the most stable complexes of this type, while the Zn(II) complex of the same geometry is much less stable.