Showing papers on "Schiff base published in 1979"

Schiff base complexes of rhenium(IV) and rhenium(V)

Abstract: The interaction of various Schiff bases, LH2, with trichloro-oxobits (triphenylphosphine) rhenium(V), tetrachlorobis(triphenylphosphine) ruthenium(IV), and other rhenium complexes has given rise to complexes of the following types: (a) ReV2O3L2 that have a linear ORe–O–ReO system which quadridentate ligands on each rhenium; (b) ReVOCIL that appear to be octahedral with trans ORe–Cl groups; (c) ReIVCl2L that are octahedral with trans chlorines; (d) complexes that have neutral Schiff bases, LH2 bound to the metal.

Infrared and raman studies on some imines and their picrates. relation to the problem of protonation in visual pigments

Abstract: — Picrates of conjugated Schiff bases have C=N stretching frequencies similar to those of the respective free bases. This raises the question if the frequency of this vibration can provide proof for the protonation of the retinylidene Schiff base occurring in visual pigments.

New dioxouranium(VI) complexes with tridentate dibasic Schiff bases containing ONO donor sets

Abstract: Several new dioxouranium(VI) complexes with the tridentate dibasic Schiff bases derived from salicylaldehyde, 5-chloro-, 5-bromo-, 5-nitro-, 3,5-dichloro-, 4-methoxy-, 5-methoxy- and 3-ethoxysalicylaldehyde and 2-hydroxy-1-naphthaldehyde ando-aminobenzyl alcohol, have been synthesized from uranyl acetate dihydrate and the Schiff base in methanol The complexes are of the type UO2(AAA) MeOH (where AAAH2 = a tridentate dibasic Schiff base) The complexes have been characterized by elemental analyses, ir and electronic spectra, conductance, magnetic susceptibility and molecular weight measurements Thev (U=O) stretching frequency of the complexes occurs atca 900 cm−1 and the U-O distance is 174A The complexes are monomers, diamagnetic and octahedral

Schiff base derivatives of lanthanons-synthesis of La(III), Pr(III) and Nd(III) derivatives of β-ketoimines derived from 2,4-pentanedione

Abstract: Reactions of the isopropoxides of some of the lighter lanthanons with bidentate β-ketoimines, such asAAH-n-C4H9 andAAH-C6H5 (donor system: N,OH) and tridentate β-ketoimines such asAA(CH2CH2)H2 andAA(CH2CHCH3)H2 (donor system: HO,N.OH) have led to products of the typesLn(O-i-C3H7)3n (AA-R) n ,Ln(Oi-C3H7) (AAR') andLn 2(AAR')3 [Ln=La(III), Pr(III) or Nd(III);n=1 or 2;R=-n-C4H9 or-C6H5 andR'=-CH2CH2-or-CH2CHCH3-]. Some undergo exchange reactions with an excess oftert-butanol, leading to the corresponding complexesLn(O-tert-C4H9)3n (AA-n-C4H9) n andLn(O-tert-C4H9) (AA-CH2CH2). All these have been characterised by elemental analysis, molecular weight determinations and their ir spectra. A thermogravimetric analysis of the diisopropoxy derivatives has also been carried out.

Calcium, strontium, and barium complexes of pyridyl-containing macrocyclic Schiff bases

Abstract: Reaction of 2,6-diacetylpyridine, or pyridine-2,6-dicarbaldehyde, with 3,6,9-trioxaundecane-1,11-diamine, 1,5-bis(2-aminophenoxy)-3-oxapentane, or 4,7-diazadecane-1,10-diamine in ethanol in the presence of M[NCS]2 or M[ClO4]2(M = Ca, Sr, or Ba) gives complexes of the type [M(NCS)2L] or [M(ClO4)2L] where L is the corresponding macrocyclic Schiff base. In the absence of the metal salt the macrocycles are formed in very small yield or not at all. Alkali-metal salts are ineffective in promoting the synthesis of the macrocycles, and magnesium only promotes the formation of a macrocycle derived from the tetra-amine.

Studies on Some Azomethine Derivatives of Titanium(IV)

Abstract: Synthesis and characterization of some new titanium(IV) complexes of Schiff bases have been described. These have been obtained by the reactions of titanium isopropoxide with dibasic tridentate Schiff bases derived by the condensation of 2,4-pentanedione, o-hydroxyacetophenone, salicylaldehyde and 2-hydroxy-1-naphthaldehyde with 3-hydroxy-1-propyl and 1-hydroxy-2-butylamines in 1:1 and 1:2 stcichiometry in the medium of anhydrous benzene. The isopropoxy groups of the diisopropoxy titanium Schiff base derivatives have been found to undergo replacement reactions with 2-methylpentane-2,4-diol and the resulting complexes are hydrolytically stable. Suitable structures based on IR, UV, PMR and mass spectral studies have been indicated for these new derivatives.

Coordination compounds of hydrazine derivatives with transition metals, part XVIII. Cobalt(II) and cobalt(III) chelates with schiff bases derived from hydrazine-S-methyldithiocarboxylate and thiosemicarbazide

Abstract: The reactions of aldehydic and ketonic Schiff bases derived from hydrazine-S-methyl dithiocarboxylate and thiosemicar-bazide with cobalt(II) acetate were investigated. Octahedral tris ligand cobalt(III) chelates were formed with aldehydic Schiff bases whereas tetrahedral bis ligand cobalt (II) chelates were isolated with ketonic Schiff bases.N-isopropylidene hydrazine-S-methyldithiocarboxylate, however, gave both octahedral tris cobalt(III) and tetrahedral bis cobalt(II) chelates. These results are interpreted in terms of the steric requirements of the Schiff base used.

Synthesis of Some Ketimine Derivatives of Silicon(IV)

Abstract: Synthese einiger Ketiminderivate des vierwertigen Siliciums A brief survey of the literature revealed that so far very few silicon Schiff base complexes have been reported [1, 2]. Although, the reactions of metal alkoxides of a number of metals of III, IV, V and VI groups of the periodic table with Schiff bases have been found to be facile and straight forward, the reactions of alkoxy silanes with azomethines as well as other nitrogen donor ligands have been reported to be quite slow [3]. However, silicon tetraacetate has been found to be a suitable starting material for such reactions and this has been used in the present studies as well. In previous communications from these laboratories, the reactions with bifunctional tridentate or tetradentate Schiff bases have been reported [4, 5]. The present paper describes the synthesis and properties of silicon complexes with monofunctional bidentate Schiff bases of the type 1.

Spectroscopy of polyenes–iii. absorption and emission spectral investigation of polyene schiff bases and protonated schiff bases related to visual pigments

Abstract: — A number of n-butylamine Schiff bases of polyenals related to retinals as homologues and analogues, and their protonated forms, have been studied for absorption and emission spectral properties. The polyene Schiff bases exhibit the same general features in their absorption spectra as those of the parallel polyenals except that the lBu1Ag and π*n singlet transitions are at substantially higher energy in the Schiff bases (the shift being larger for the π* n transition). The Schiff bases with short polyene chainlength (n= 2, 3 where n is the number of double bonds including C=N) do not fluoresce or phosphoresce in 3-methylpentane in the temperature range 298–77 K. The Schiff bases with intermediate chainlength (n= 4, 5) show fluorescence at 77 K with intensity strongly dependent on the nature of solvent. The Schiff bases with relatively long chainlength (n= 5–7) show strong or moderately strong fluorescence at 77 K and very weak fluorescence at 298 K (n = 7) with intrinsic radiative lifetimes much longer than those estimated from the oscillator strength of the low-energy, strong absorption band (1Bu1Ag). A discussion on the possible state order and nature of the fluorescing state of the various polyene Schiff base systems is presented.

Synthesis of Some Novel Germanium(IV)-Schiff Base Complexes

Abstract: Non-electrolytes and hexacoordinated germanium complexes of the type Ge(SB)2 (where SBH2 is the bifunctional tridentate Schiff base having the donor system, HO-N-OH) have been synthesized by the reaction between germanium tetraethoxide and the Schiff base in benzene medium. The Schiff bases used in these reactions are of the general types o-HOC6H4C(CH3):NROH and 2-HOC10H6CH:NR′OH (where R = R′ = stoichiometry are exclusively obtained in whatever molar ratio the reactants are mixed. The infrared, mass and proton magnetic resonance spectra of these complexes show the coordination of azomethine nitrogen and phenolic and alcoholic oxygens to the central germanium atom. The integral procedual decomposition temperature (IPDT) of germanium bis[2-hydroxy-1-naphthylidene-2-hydroxyethylamine] and germanium bis[2-hydroxyacetophenone-2-hydroxyethylimine] complexes has been calculated and this shows the higher thermal stability of the latter as compared to the former.

Implications of modelling the chromophore of rhodopsin and bacteriorhodopsin with resonance Raman spectra of retinal Schiff bases

Abstract: Resonance Raman spectra of protonated and unprotonated Schiff bases of all-trans retinal with propylamine, hexylamine, butylamine, deuterated butylamine (d9), methylamine and N15 methylamine have been obtained. The spectra of methylated and deuterated butylamine Schiff bases of retinal have also been recorded. It was found that the carbon–nitrogen stretching vibration associated with the Schiff base is insensitive to changes in the mass and/or length of the saturated hydrocarbon group attached to the Schiff base except for the case of methylamine. The fingerprint region, on the other hand, is sensitive to alterations in the Schiff base substituent. Deuterating the Schiff base has a larger effect on the carbon–nitrogen stretching frequency than replacing the Schiff base nitrogen N14 with N15. Furthermore, the data on deuterated Schiff bases indicate that the CCH bending vibrational mode is altered by deuteration. Implications concerning use of these compounds for modelling visual pigments and bacteriorhodopsin are discussed.

Mononuclear iron, cobalt, and nickel complexes of a 30-membered macrocyclic ligand

Abstract: The preparation of a series of mononuclear complexes [ML2]Xn{M = FeII, CoIII, CoII, or NiII; L2= a 30-membered, potentially decadentate, macrocyclic Schiff base ligand; X =[ClO4]–, [BPh4]–, or [Co(NCS)4]2–, n= 1, 2, or 3} from the binuclear complex [Pb2L2(SCN)4] is described. Unlike the reactant lead(II) complex, in which the macrocycle uses all ten donor atoms in bonding to the metal ions, only the six nitrogen atoms are co-ordinated in the new complexes. A distorted octahedral (approximate D2d symmetry) structure is assigned to all the complexes on the evidence of i.r., electronic, and Mossbauer spectra, magnetic data, and of the properties of corresponding complexes of two open-chain Schiff-base ligands. The d6 and d7 complexes have spin-singlet and spin-doublet ground states, respectively. The electrochemical behaviour of the iron and cobalt complexes is reported and correlated with other properties.