Birgül Erk

Synthesis, Physico‐Chemical Characterization, and Stability Constants of Metal Complexes of Pyridine‐2‐carbaldehyde Thiosemicarbazone

The synthesis, physico‐chemical properties and complexes with transition element cations of pyridine‐2‐carbaldehyde thiosemicarbazone (L) are reported. The synthesis and structural analysis of L, its complexes with MCl2 (M = Mn(II), Zn(II), Cd(II)) and MıCl3 (Mı = Cr(III), Co(III)) salts are reported. Their general formulas are [M(L)3]Cl3 · 3H2O [M = Cr(III) and Co(III)], [M(L)(H2O)Cl]Cl [M = Zn(II) and Mn(II)] and [Cd(L)Cl2)] · H2O. Mn(II), Zn(II), Cd(II) complexes with a metal‐ligand ratio 1:1 and Cr(III), Co(III) complexes with a metal‐ligand ratio 1:3 have been prepared. Molecular structures of these complexes were identified using elemental analyses, FT‐IR UV‐Vis, thermogravimetric (TGA) and conductivity techniques. The structure, along with other physico‐chemical studies, establishes that the complexes of L, except for the cobalt complex, are low‐spin. Spectroscopic analysis shows that the transition metal complexes have octahedral or tetrahedral geometry. For the Cr(III) and Co(III) complexes octahedral geometry is proposed, and the Zn(II), Cd(II) and Mn(II) complexes are proposed to be of tetrahedral geometry. The stability constants of the Zn(II) and Mn(II) complexes were determined by the Job method. The stability constants of the Zn(II) and Mn(II) complexes were found to be 8.77 × 104 M–1 and 6.40 × 105 M–1, respectively. The increase in stability constants follows the order of Zn(II) > Mn(II) and this increase is in agreement with the Irving‐Williams series.

The preparation and characterization of some uranium(VI) complexes of N,N′-bis(o-hydroxyaryl) aldimino Schiff bases

Abstract Some of the stable chelate complexes of uranium(VI) were prepared with alkyl or aryl (R) bridged o,o′-dihydroxyaryl Schiff bases of HOC6H4CHNRNCHC6H4OH and HOC10H6CHNRNCHC10H6OH (R: (CH2)n; (C2H4NH)n(C2H4); (C6H4CH2C6H4; o, m, p-C6H4). Their structures were determined by UV, IR and elemental analyses. It is evident that strong ligand-ion interaction usually caused the polymeric structure. This is supported by the high decomposition point and low solubilities of the complexes.

Copper(II) and zinc(II) complexes of thiophene/furan carboxamides: Synthesis, structure and properties

Cu(II) and Zn(II) complexes were synthesized from equimolar amounts of carboxamides; 1,8-bis(2-thiophenecarboxamido)-p-menthane (tkdam) and 1,8-bis(2-furancarboxamido)-p-menthane (furdam). The structure of the carboxamides were determined by elemental analysis; 1H NMR, 13C NMR, FT-IR and LC-MS spectra. The relative energies and the electronic properties (LUMO, HOMO, LUMO-HOMO gap) of the ligands were investigated theoretically by performing Semi-empirical molecular orbital theory PM3 method in Hyperchem 7 (Release). Carboxamide complexes having general formula as; monomeric, [ML]Cl2 and dimeric [Cu(tkdam)Cl]2Cl2 · 5H2O were synthesized and characterized by using element analysis; FT-IR, LC-MS spectra; magnetic susceptibility, molar conductivity and thermal (TGA/DTA curve) studies. It was found that the coordination number of the monomeric complexes is four whereas dimeric’s is six. The changes in the selected vibration bands in FT-IR indicate that, carboxamides behave as tetradentate ligands and coordinate to metal ions from acyl ring (through S/O) and amide carbonyl (C=O). Molar conductivity measurements indicate the 1: 2 ionic nature of the carboxamide complexes.

Kinetics of Formation of Some Uranium(VI) Complexes of Schiff Bases and Their pKa Values

Abstract The kinetics of the complex formation reaction of the UO2+ 2 ion with a series of O and N donor ligands of Schiff bases were studied in methanol. The rate constants for the formation of UO2+ 2 Schiff base complexes are sensitive to the structure of the Schiff base. The specific rates increase if the ligands are multidentate. Schiff bases have their donor atoms fixed in cis position and, therefore, should generally react faster than unidentate ligands. Activation parameters and pKa values of the complexes are reported.

Preparation, Characterization and Kinetics of Formation of Some Schiff Base Chelates of Sn(II) and UO2(V1)

Abstract The synthesis, characterization and formation kinetics of Sn(II) and UO2(VI) complexes of the nitrogen and oxygen donor ligands m-chlorophenylsalicylaldimine (Heps), m-nitrophenylsalicylaldimine (Hmps), m-methoxvphenylsalicylaldimine (Hmps) and m-methyl-phenylsalicylaldimine (Hmsa) are reported. The structures of the free ligands and their Sn(II) and UO2(VI) complexes were determined by NMR, elemental analyses, IR and UV-Vis studies and magnetic susceptibility measurements. Under pseudo-first order conditions, having an excess of the Schiff base present, the kinetics of complex formation of Sn(II) and UO2(VI) with a series of Schiff bases was studied spectrophotometrically using the stopped-flow technique in methanol as solvent. The activation parameters δH# and δS#for the formation reactions of the complexes studied in methanol are almost identical which supports the assumption that the reactions have a common mechanism. The reactions are considered to proceed through an associative mechanism.

SYNTHESIS, CHARACTERIZATION, AND ELECTRICAL PROPERTIES OF METAL COMPLEXES OF 2-PYRIDINECARBALDEHYDE THIOSEMICARBAZONE

ABSTRACT The synthesis, characterization, physico-chemical and electrical properties of complexes of pyridine-2-carbaldehyde thiosemicarbazone (PTSC) with transition element cations are reported. The complexes [Fe(PTSC)2Cl2]Cl and [Ni(PTSC)2-(H2O)2]Cl2 were prepared. Molecular structures of these complexes were identified by using elemental analyses, FT-IR, UV-VIS, thermogravimetric and molar conductivity techniques. The structure, along with other physico-chemical studies, established that the complexes of PTSC were low-spin. The spectroscopic study of the compounds showed that the transition metal complexes had octahedral geometry. A spectrophotometric determination of nickel(II) with pyridine-2-carbaldehde thiosemicarbazone in methyl alcohol solution is proposed and the stability constants of the nickel(II) complex were determined by the Job method. The electrical conductivity of the compounds increases with elevated temperature. Their conductivities follows the order Ni>Fe. The calculated values of the activation energy of mobility, Eμ, suggests that conduction in the studied complexes takes place by a hopping mechanism, where one electron hops from one molecule to another.

Studies on the interaction of iron(III) with tetraaza macrocycles

Tetraaza macrocycles and their Fe3+ complexes have been prepared and characterized by elemental analysis, i.r., n.m.r., and e.s.–m.s. spectroscopic techniques. The solution behaviour of the macrocycles and their complexes was studied by potentiometric titrations.