Metal complexes as ligands—IV [1,2,3]

Three series of heterometallic NiII–LnIII Schiff base complexes: synthesis, crystal structures and magnetic characterization

Three series of Ni^II–Ln^III complexes were synthesized using compartmental Schiff base ligands in conjunction with auxiliary ligands. Their magnetic properties have been well studied.

Synthesis, Ion Recognition Ability, and Metal-Assisted Aggregation Behavior of Dinuclear Metallohosts Having a Bis(Saloph) Macrocyclic Ligand

Macrocyclic molecule 1 that has two saloph coordination sites was designed and synthesized. The macrocycle 1 was easily converted into the corresponding metallohosts 2 and 3 by the reaction with nickel(II) and palladium(II), respectively. As expected from the molecular structure of these metallohosts having an 18-crown-6-like cavity, the nickel(II) metallohost 2 showed excellent binding affinity toward Na(+), Ca(2+), and Sr(2+) to give 1:1 host-guest complexes. Preorganization effect due to the extremely rigid metal-containing macrocycle was suggested to be a major factor for the strong binding. Larger cations such as K(+), Rb(+), Cs(+), and Ba(2+) gave higher aggregated host-guest complexes such as 22M, 23M2, and 24M3. Density functional theory calculations revealed that smaller metal ions do not occupy the center of each macrocycle in the sandwich structures 22M, while larger Cs(+) simultaneously interacts with all the 12 oxygen donor atoms. On the basis of the interaction energy calculations, the preference for 2·Na over 22Na can be explained by destabilization of 22Na due to the elongated Na-O bonds and repulsive three-body interactions. When the ionic radius of the guest ion increases (K(+), Rb(+), Cs(+)), this destabilization becomes less significant and the formation of sandwich complexes 22M is favored. Such aggregation would significantly affect the physical and chemical properties of the metal complexes due to the interplane interactions between the metal centers.

Synthesis of a new family of ionophores based on aluminum–dipyrrin complexes (ALDIPYs) and their strong recognition of alkaline earth ions

Mononuclear and dinuclear aluminum–dipyrrin complexes (ALDIPYs) recognize alkaline earth ions via multipoint interactions with the oxygen atoms.

Design, characterization, teratogenicity testing, antibacterial, antifungal and DNA interaction of few high spin Fe(II) Schiff base amino acid complexes

In this study, new Fe(II) Schiff base amino acid chelates derived from the condensation of o-hydroxynaphthaldehyde with L-alanine, L-phenylalanine, L-aspartic acid, L-histidine and L-arginine were synthesized and characterized via elemental, thermogravimetric analysis, molar conductance, IR, electronic, mass spectra and magnetic moment measurements. The stoichiometry and the stability constants of the complexes were determined spectrophotometrically. Correlation of all spectroscopic data suggested that Schiff bases ligands exhibited tridentate with ONO sites coordinating to the metal ions via protonated phenolic-OH, azomethine-N and carboxylate-O with the general formulae [Fe(HL)2]·nH2O. But in case of L-histidine, the ligand acts as tetradentate via deprotonated phenolic-OH, azomethine-N, carboxylate-O and N-imidazole ring ([FeL(H2O)2]·2H2O), where HL=mono anion and L=dianion of the ligand. The structure of the prepared complexes is suggested to be octahedral. The prepared complexes were tested for their teratogenicity on chick embryos and found to be safe until a concentration of 100 μg/egg with full embryos formation. Moreover, the interaction between CT-DNA and the investigated complexes were followed by spectrophotometric and viscosity measurements. It was found that, the prepared complexes bind to DNA via classical intercalative mode and showed a different DNA activity with the sequence: nhi>nari>nali>nasi>nphali. Furthermore, the free ligands and their complexes are screened for their in vitro antibacterial and antifungal activity against three types of bacteria, Escherichia coli, Pseudomonas aeruginosa and Bacillus cereus and three types of anti fungal cultures, Penicillium purpurogenium, Aspergillus flavus and Trichotheium rosium in order to assess their antimicrobial potential. The results show that the metal complexes are more reactive with respect to their corresponding Schiff base amino acid ligands.

Polyfluorinated Pd(II)-3,5-di-tert-butylsalicylaldimenes complexes: synthesis, structure, spectroscopy, redox behaviors and catalytic activity

A series of new polyfluorinated palladium(II) complexes (7-12) of N-polyfluorophenyl-3,5-di-tert-butylsalicylaldimines (1-6) have been synthesized. They were characterized by analytical, spectroscopic (UV/Vis, IR, (1)H NMR, and ESR), electrochemical methods and their chemical oxidation and hydrogenation catalytic activity were studied. The X-ray crystal structure analysis of bis[N-(3,5-di-tert-butylsalicylidene)-F5Ph]Pd(II) (12) revealed a slightly distorted square-planar trans-PdN2O2 geometry around the palladium center. The UV/Vis and EPR results indicate that chemical oxidation of 7-10 by Ce(IV) in CHCl3 generates relatively stable Pd(II)-phenoxyl radical complexes (g=2.0044-2.0062). The results of chemical and electrochemical oxidation of 1-12, as well as the catalytic activity of 7-10 complexes in the hydrogenation of PhNO2 were presented.

Synthesis, spectroscopy, magnetic and redox behaviors of copper(II) complexes with tert-butylated salen type ligands bearing bis(4-aminophenyl)ethane and bis(4-aminophenyl)amide backbones

New salen type ligands, N,N'-bis(X-3-tert-butylsalicylidene)-4,4'-ethylenedianiline [(X=H (1), 5-tert-butyl (2)] and N,N'-bis(X-3-tert-butylsalicylidene)-4,4'-amidedianiline [X=H (3), 5-tert (4)] and their copper(II) complexes 5-8, have been synthesized. Their spectroscopic (IR, (1)H NMR, UV/vis, ESR) properties, as well as magnetic and redox-reactivity behavior are reported. IR spectra of 7 and 8 indicate the coordination of amide oxygen atoms of 3 and 4 ligands to Cu(II). The solid state ESR spectra of 5-8 exhibits less informative exchange narrowed isotropic or anisotropic signals with weak unresolved low field patterns. The magnetic moments of 5 (2.92 μ(B) per Cu(II)) and 6 (2.79 μ(B) per Cu(II)) are unusual for copper(II) complexes and considerably higher than those for complexes 7 and 8. Cryogenic measurements (300-10 K) show weak antiferromagnetic exchange interactions between the copper(II) centers in complexes 6 and 8. The results of electrochemical and chemical redox-reactivity studies are discussed.

Cooperative formation and functions of multimetal supramolecular systems

Multimetal complexes provide a variety of interesting structures, unique properties, and functions. Such sophisticated functions are often produced by synergistic and cooperative interactions among the metal ions accumulated in the restricted small area of the multimetal systems. We describe novel three strategies (i.e., macrocyclic, C-shape, and multimetal template) for the preparation of the multimetal supramolecular systems by the cooperative metal binding of a multi-Schiff-base and multi-oxime ligands, and their characteristic structures and functions. The three approaches are versatile and effective because the employed coordination reactions smoothly and quickly proceeded under mild conditions to quantitatively form the desired coordination structures. The multimetal supramolecular systems obtained here exhibit the synergistic and cooperative functions for ion recognition, magnetic properties, helicity control, and modulation of reaction selectivity. These types of multimetal complexes could be developed for a cascade functional supramolecular system that shows highly synergistic properties, integrated multifunctions, and function amplification.

Synthesis, Characterization of La(III), Nd(III), and Er(III) Complexes with Schiff Bases Derived from Benzopyran-4-one and Thier Fluorescence Study

The Schiff bases, L1, L2, and L3, are synthesized from the condensation of 5,7-dihydroxy-6-formyl-2-methylbenzopyran-4-one (L) with 2-aminopyridine (1), p-phenylenediamine (2), and o-phenylenediamine (3). The prepared Schiff bases react with lanthanum (III), neodymium (III), and erbium (III) nitrate to give complexes with stoichiometric ratio (1 : 1) (ligand : metal). The binuclear complexes of Er(III) with L3 and the three metal ions with L2 are separated. The complexes have been characterized by elemental analysis, molar conductance, electronic absorption, and infrared, 1H-NMR spectral studies. The presence of hydrated and coordinated water molecules is inferred from thermogravimetric analysis. Thermal degradation studies show that the final product is the metal oxide. The luminescence properties of the Nd(III) and Er(III) complexes in dimethylformamide (DMF) solutions were investigated.

Synthesis, spectroscopic characterization and reactivity studies of oxovanadium(IV) complexes with bulky N,N'-polymethylenebis(3,5-(t)Bu(2)salicylaldimine) ligands

A series of new sterically hindered N,N'-polymethylenebis(3,5-(t)Bu(2)salicylaldimine) ligands (H(2)L(x)) VO(IV) complexes, [VO{(2-O-3,5-(t)Bu(2)C(6)H(2))CHN-R-NCH-(3,5-(t)Bu(2)-C(6)H(2)O-2)] (X), where R=-(CH(2))(3)- (3), -(CH(2))(4)- (4), -(CH(2))(5)- (5), -(CH(2))(6)- (6) and -CH(2)C(CH(3))(2)CH(2)- (7) and early reported -(CH(2))(2)- (1) and -CH(2)CH(CH(3))- (2), has been synthesized and characterized by spectroscopic (IR, UV/vis, (1)H NMR, EPR), electrochemical and magnetic susceptibility measurements. Complexes 1-7 are described a trigonal distorted pyramids. All seven compounds give nearly the same parallel hyperfine coupling constant (A(z)) regardless that the geometry of VO(IV) changes from square pyramidal to trigonal distorted pyramids. Chemical oxidation of 1-7 by one equiv Ce(IV) leads to the formation of stable [VO(V)L(x)](+) complexes. Cyclic voltammograms of 2-6 in DMSO along with a quasi-reversible VO(IV)/VO(V) redox couple also showed irreversible phenolate/phenoxyl responses. Each 1 and 7 shows only one reversible VO(IV) centered oxidation waves. Chemical oxidation of H(2)L(x) forms the stable [H(2)L(x)](+) radical species.

Spectroscopic and electron-transfer reactivity studies of bulky bis(N-cycloalkyl-3,5-tBu2-salicylaldiminato)copper(II) complexes: generation of uncoordinated and coordinated phenoxyl radicals

This work summarizes the results of our studies on the spectral, magnetic, electrochemical and chemical redox properties of N-cycloalkyl-3,5-(t)Bu(2)-salicylaldimine ligands [cycloalkyl=cyclo-C(5)H(9)(HL(1)), cyclo-C(6)H(11) (HL(2)), cyclo-C(7)H(13) (HL(3)), cyclo-C(8)H(15) (HL(4)), 1-adamantyl (HL(5)), 2-adamantyl (HL(6))] and their copper(II) complexes (1-6). The compounds have been characterized by IR, (1)H NMR, UV-vis, EPR spectroscopy, electrochemical and magnetic susceptibility measurements. The geometry of 1-6, according to their EPR (g(II) and g(II)/A(II)) and visible spectral data, exhibit a significant amount distortion from slightly distorted square-planar to pseudo-tetrahedral. The cyclic voltammetric studies of 1-6 reveal that as the extent of the tetrahedral distortion of Cu(II) center increases on going from 1 to 5, the values of Cu(II)/Cu(I) potentials became more negative. The compounds have been oxidized electrochemically and chemically and the generated relatively stable uncoordinated phenoxyl [HL(x)](*+) and coordinated Cu(II)-phenoxyl radical [1-6](*+) species have been characterized by UV/vis and EPR spectroscopy.

Synthesis, spectroscopic characterization and magnetic properties of homo- and heterodinuclear complexes of transition and non-transition metal ions with a new Schiff base ligand

Four homodinuclear complexes of Ni(II)-Ni(II), Cu(II)-Cu(II), Co(II)-Co(II) and Co(III)-Co(II) and five heterodinuclear complexes of Co(III)-Zn(II), Co(III)-Cu(II), Co(III)-Ni(II), Cu(II)-Zn(II) and Zn(II)-Cu(II) with the octadentate Schiff base compartmental ligand 1,8-N-bis(3-carboxy)disalicylidene-3,6-diazaoctane-1,8-diamine (H4fsatrien) have been synthesized. The complexes have been characterized with the help of elemental analyses, molecular weights, molar conductances, magnetic susceptibilities and spectroscopic (UV-vis, IR, ESR) data. Cryomagnetic data also helped to elucidate the structural features of the Cu(II) complexes.