Laila El-Sayed's research while affiliated with Alexandria University and other places

Four new nickel(II) complexes, [{Ni(L)}2], [NiL · HPyr], [NiL · HIm] and [Ni(HL)2] · H2O, derived from diacetylmonoxime-S-benzyldithiocarbazonate (H2L) have been synthesized and characterized by elemental analyses, field desorption and electrospray ionization mass spectra, UV–Vis, infrared absorption spectra, as well as 1H NMR spectra. X-ray molecular structures showed that the Ni(II) in both [NiL · HPyr] and [NiL · HIm] are in a distorted square planar environment and is coordinated to the dianionic NNS tridentate hydrazoneoxime ligand via deprotonated oximate nitrogen, hydrazone imine nitrogen, and thiolate sulphur. The fourth coordination sites are occupied, respectively, by the pyrazole and imidazole nitrogens. The oximate O1 of [NiL · HPyr] is involved in intramolecular hydrogen bond with the pyrazole NH proton as well as intermolecular hydrogen bond pyrazole C6H proton, forming a helical chain propagating along the b-axis. The structure is stabilized by a set of π⋯π and CH⋯π interactions. The molecular units in [NiL · HIm] are linked together by hydrogen bond formation between the oximate oxygen and imidazole NH proton, giving rise to an infinite zigzag chain extended along the a-axis. The chains are interconnected by π⋯π and CH⋯O interactions. In [Ni(HL)2] · H2O, the Ni(II) is in a distorted octahedral environment. The two mononegative hydrazoneoxime ligands are coordinated in the meridional configuration where the two thiol sulphur atoms and the two oxime nitrogen atoms are cis to each other, while the imine nitrogen atoms are trans. The oxime proton O2H is involved in a reciprocal bifurcated hydrogen bond formation with both N2 and S3 of the adjacent molecule giving rise to hydrogen bonded dimer. This dimeric structure is further stabilized by a pair of reciprocal CH⋯O interactions. A one dimensional chain of alternating dimeric unit and water molecule propagating along the c-axis is formed via hydrogen bond formation between the oxime O1 oxygen and the bridged water molecule proton.

Five binuclear nickel(II) complexes [{Ni(L-R)}2] derived from diacetylmonooxime aroylhydrazones (H2L-R) have been prepared and characterized. In these complexes the oximate group functions as a bridge between the two nickel(II) ions. The corresponding octahedral bisligand complexes [Ni(HL-R)2] have been also prepared and characterized. Reaction of [{Ni(L-R)}2] with excess pyrazole (HPyr) afforded square planar [Ni(L-R)HPyr] complexes. The structure of [Ni(L-H)HPyr] (11), [Ni(L-CH3O)HPyr] (13) and [Ni(L-Cl)HPyr] (14) have been determined by single-crystal X-ray diffraction. In these complexes, the Ni(II) is coordinated to the oximate nitrogen, hydrazone nitrogen and enolimine oxygen of the aroylhydrazoneoxime ligand, the fourth coordination site is occupied by pyrazole nitrogen. In 11 and 13 the molecular units are linked together by intramolecular NH⋯O hydrogen bonds forming a helical chain propagating along a and b axis respectively. The helical structure is stabilized by CH⋯O, CH⋯π and π⋯π noncovalent interactions. The structure of 14 consists of two independently crystallographic molecular units. The Ni1 molecular units are assembled together by CH⋯O and CH⋯Cl1 interactions forming a two dimensional sheet, while the Ni2 units are jointed together by CH⋯O and CH⋯C interactions forming a chain extending along b-axis which are enclosed between sheets of Ni1 units.

Two series of dicopper(II) complexes derived from bis(N-salicylidine)dicarboxylic acid dihydrazides (H4L) of general formula [Cu2(L)·xH2O]·yH2O and [Cu2(H2L)Cl2·xH2O]·yH2O have been synthesized and characterized, where n refers to the number of carbon atoms in the aliphatic spacer between the two N-salicylideneacylhydrazine units. Magnetic susceptibility measurements for neutral dicopper(II) complexes [Cu2(L)·xH2O]·yH2O indicate significant antiferromagnetic coupling between copper(II) centers. The −2J values obtained from the Bleany–Bowers equation are within the range 121–223 cm, suggesting association of the coordinated copper(II) units Cu(ONO) via phenoxy bridges. This leads to a polynuclear structure in which the dimeric units are connected with the aliphatic spacer. From the best-fit values of the mole fraction of paramagnetic uncoupled copper(II) centers (ρ), the degree of association in these polynuclear copper(II) complexes has been estimated. The chloro dicopper(II) complexes [Cu2(H2L)Cl2·xH2O]·yH2O with n = 0, 2 and 3 also show strong antiferromagnetic exchange coupling (−2J = 215–423 cm), suggesting a polynuclear structure in which the copper(II) is in a distorted square-pyramidal environment, bound in the equatorial plane with a monoanionic ONO tridentate acylhydrazone unit and the μ-phenoxy oxygen and the axial site occupied by a chloride. The dicopper(II) complexes with n = 1 and 4 show weak antiferromagnetic exchange coupling (−2J = 16–20 cm). In these complexes the chloride ion may occupy the fourth equatorial site while the μ-phenoxy is in the apical position.

Three types of copper(II) complexes, [Cu(HL)Cl·H2O]·xH2O, [{Cu(HL)Cl}2] and [{Cu(L)}2], derived from N-Salicylidene-n-alkanoylhydrazines (H2L) have been synthesized and characterized by elemental analyses, infrared spectra and field desorption mass spectra as well as variable temperature magnetic susceptibility measurements. The X-ray molecular structure of bis[monochloro(μ-N-salicylidene myristoylhydrazine)ONO′(−1)]dicopper(II) showed that this complex is a centrosymmetric dimer in which each copper(II) is in a distorted square pyramidal environment and coordinated in the equatorial plane to the ONO mononegative tridentate acylhydrazone ligand. The fourth coordination site is occupied by the symmetry related phenoxy oxygen of the other monomeric unit. The chloride ion occupies the fifth axial coordination site. Magnetic susceptibility measurements at different temperatures (5–298 K) showed that the hydrated chloro complexes [Cu(HL)Cl·H2O]·xH2O are monomeric and no spin–spin interaction was detected, while the anhydrous chloro complexes [{Cu(HL)Cl}2] are dimeric and exhibit strong antiferromagnetic coupling with −2J values the range 466–477 cm−1. The neutral complexes [{Cu(L)}2] also show antiferromagetic behaviour with −2J varying from 170 to 243 cm−1.

The synthesis and spectroscopic and EPR characterization of a vanadyl complex with acetone Schiff base, bis(S-methyl-3-isopropylidenehydrazinecarbodithioato)oxovanadium(IV), are described. The magnetic moment of 1.75 μB at room temperature is close to the spin only magnetic moment (1.73 μB). The experimental values of g∥ = 1.960 and g⊥ = 1.988 and the normal occurence of v( V=O) vibration suggest a monomeric five-coordinate square pyramical structure of the complex. A correlation was found between g∥ and A∥ of the title compound when compared with other model compounds of the vanadyl complexes in which possible combinations of four ligands may include all nitrogen (N4) and all sulfur (S4). This information could be useful in characterizing aqueous pyridine cuts of asphaltenes with molecular weights less than 400 found in some heavy crude oils.

A variety of α-dicarbonylbis(aroylhydrazone) H2L (1) ligands were synthesized and used to synthesize complexes formulated as NiL·nH2O, Zn2L2·nH2O, CuL, CoL·nH2O and Na[CoL(NO2)2], where L refers to the dinegative anion of α-dicarbonylbis(aroylhydrazone) ligand. These complexes were investigated by elemental analyses, IR and UV-vis spectra and, for zinc(II), Na[CoL(NO2)2] and the anhydrous NiL complexes, 1H NMR spectra were measured in order to elucidate their structures. Other octahedral complexes such as Ni(H2L)2(OAc)2 and Co(HL)3·nH2O were isolated and characterized. Different modes of coordination were assigned to the ligand 1 and its anions in the isolated complexes; dinegative tetradentate, monenegative bidentate and neutral bidentate.

Kinetics and mechanism of the reaction of the title complex (I) with heterocyclic amines (Py and methyl derivatives), sec. aliphatic amines (e.g.

In a spectrophotometric study of the substitution reactions of the title complexes (I) with the amines (II) two successive steps (III) and (IV) are observed.

The substitution reactions of 1,2-diphenylethane- diylidene bis(S-methylhydrazinecarbodithioate)NN′-SS′(−2) nickel(II) and palladium(II) complexes with piperidine and morpholine were followed spectrophotometrically in benzene. Two successive steps were observed, the substitution of the first SMe group deactivating the second SMe group. The first substitution step shows third order kinetics, first order in the substrate and second order in the nucleophile. The third order rate constants increase with the greater basicity of piperidine relative to morpholine, and it was noted that the nickel(II) complex is more susceptible to nucleophile catalysis than the palladium(II) complex. The values of activation parameters show that the higher rate of substitution of the palladium(II) complex is due to entropy effects. It was deduced that the initial attachment of the nucleophile on the SMe carbon to give a dipolar intermediate is followed by the rate determining nucleophile catalyzed formation of the monosubstituted product.

The reactions of the title chelates (I) with piperidine or morpholine (II) are studied.