Solution chemistry and Mössbauer study of iron(II) and iron(III) complexes from gallocyanine

The iron solution chemistry of the FeCl₃-gallocyanine system has been investigated by pH titration, UV visible spectroscopy and Mössbauer spectroscopy. Iron reduction was found in the pH range 2–5 and photo-reduction of the iron(III) present was also noted. Due to the instability of the species present in solution, the use of gallocyanine as a spectrophotometric indicator in iron systems is not encouraged. The iron-gallocyanine system was proposed as a potential model of the photosensitive anti-cancer drug, Bleomycin.     

Copper(II) halide complexes of 2-aminobenzophenone. Crystal and molecular structure of bis(2-aminobenzophenone)dichlorocopper(II)

The complexes CuX₂L₂ (X = Cl, Br; L = 2-aminobenzophenone) were prepared and characterized by means of magnetic and spectroscopic measurements. For the Cl compound the crystal structure was also determined. Crystals are triclinic, space group P$\text{1}$, with a = 13.397(3), b = 10.752(2), c = 9.205(2) Å, α = 72.26(1)°, β = 91.58(1)°, γ = 106.86(1)°, and Z = 2. The structure was solved by the heavy-atom method and refined by least-squares calculations to R = 0.034 for 2581 counter data. It consists of discrete CuX₂L₂ monomers showing distorted trigonal bipyramidal coordination geometry about the copper ion. The amino nitrogens are axial ligands, with the equatorial positions occupied by two chlorine atoms and a carbonyl oxygen from one L molecule acting as a bidentate ligand. Infrared and ligand field spectroscopies and magnetic measurements, interpreted on the basis of the known crystal structure, also suggest a similar structure for the related Br compound.     

Synthesis and characterization of tertiary phosphine Pd(0) complexes

The synthesis of PdL_n complexes (L = tertiary phosphine; n = 2,3,4) is reported. The coordination number results to be a function of the steric hindrance of the phosphine. Two-coordinate, 14-electron complexes, have been isolated with bulky phosphines (PPrⁱ₃, P (cyclohexyl)₃, PBu^t₂Ph). The behaviour in solution of the PdL_n complexes has been studied by ¹³C NMR spectroscopy.     

Spectroscopic investigation of europium(III) nitrato complexes in anhydrous and aqueous acetonitrile

Electronic absorption and emission spectra, along with lifetime measurements and vibrational spectra, are used to investigate the interaction between nitrate and trivalent europium ions in dilute solutions in anhydrous and aqueous acetonitrile. Upon addition of increasing quantities of nitrate, the complexes [Eu(NO₃)_n]^(3?n)+, with n = 1–5, form quantitatively in anhydrous acetonitrile. In solution, the pentanitrato species is not further solvated and its spectroscopic properties are similar to those of solid samples, indicating a similar structure with five bidentate nitrates bonded to the 10-coordinate Eu(III) ion. The lifetimes of the ⁵D₀ level are 1.35(5) and 1.25(5) ms for Eu(NO₃)₃ and (Me₄N)₂Eu(NO₃)₅ 0.05 M in CH₃CN. The quantum yield of Eu(NO₃)₃ in CH₃CN is 27.4%.The addition of small quantities of water to Eu(NO₃)₃ solutions does not result in the dissociation of the nitrate ions, provided R_w = [H₂O]_t/[Eu³⁺]_t is smaller than 8; the apparent equilibrium rations for [Eu(NO₃)₃(H₂O)_n] are K₃ = 40 ± 15 M^?1 and K₄ = 9 ± 3 M^?1; K₁ and K₂ are too large to be determined. The formation of nitrato complexes is studied in mixtures containing increasing amounts of water and nitrate. Deconvolution of the different components of the ⁵D₀ → ⁷F₀ transition allows a semi-quantitative estimate of the relative concentration of the nitrato complexes. The total number of coordinated nitrate ions per europium ion can be determined on the basis of fluorescence lifetime measurements. The apparent equilibrium ratios for the formation of the mono- and dinitrato species amount to K₁ = 23 ± 3, 15 ± 5 and 5 ± 1 for R_w = 44, 94 and 304, respectively, and to K₂ = 17 ± 8 for R_w = 44 and 94.     

Five-coordinated rhodium(I) carbonyl compounds

The title compounds were synthesised by the replacement of chlorine in Rh(CO)(PPh₃)₂Cl with monobasic bidentate chelating ligands such as salicylaldehyde, acetylacetone, benzoylacetone, dibenzoylmethane, 8-hydroxyquinoline, benzoylphenyl hydroxylamine, 2-hydroxyacetophenone and 2-hydroxybenzophenone. IR spectral evidence points out that these compounds have a trigonal bipyramidal geometry around rhodium in the solid state. However, in benzene solutions, except for the 8-hydroxyquinoline and 2-hydroxybenzophenone derivatives they all take a square planar structure, as seen from their electronic spectra.     

Unusual Cu(III)—Schiff's base complexes

A new series of CU(III) complexes of the type [Cu(SB)]ClO₄, where SB is a dibasic tetradentate Schiff's base, were synthesized and characterized by elemental analysis, IR and electronic spectra. The prepared complexes are compared with Cu(II) complexes of the same ligands. The room temperature magnetic susceptibility and the x-band EPR spectra of the two types of complexes showed different behaviour. Cu(II) complexes were non conducting whereas Cu(III) complexes gave a conductance corresponding to 1:1 electrolyte. In fact this is the first report on the Cu(III) complexes with the tetradentate Schiff base ligands.     

Circularly polarized luminescence studies of the adducts formed with Eu(III) β-diketone complexes and (—)-sparteine

The optical activity resulting from the complexation of (—)-sparteine by a series of Eu(III) β-diketone compounds has been studied by means of circularly polarized luminescence spectroscopy. It was found that the presence of at least one perfluoro group was necessary for the formation of an adduct complex. With Eu(III) complexes containing achiral β-diketone ligands, it was found that the observed chirality could be considered to result from a combination of vicinal and conformational effects. With Eu(III) complexes containing chiral β-diketone ligands, the optical activity was found to be dominated by confïgurational effects.     

Photostability and emission characteristics of In(III)octaethylporphyrin - and in(III)tetraphenylporphyrin-chloride

The absorption, emission and excitation spectra of indium(III) tetraphenylporphyrinchloride (In(III)TPPCl) and indium(III)octaethylporphyrinchloride (In(III)OEPCl) methanolic solutions have been studied and compared with their metal-free bases. The study reveals a strong interaction between indium ion and the porphyrin π-systems.The photolability of the above-mentioned compounds has been studied in deoxygenated methalonic solutions using sunlight and/or UV-light in excitation. A fragmentation mechanism is proposed to account for the consumption of the porphyrin systems.     

Synthesis and reactivities of binuclear iron(III) complexes with ligands composed of two tridentate chelating groups

Several new binuclear iron(III) complexes were prepared using the binucleating ligands in which two molecules of N,N-bis(2-benzimidazolymethyl)amine are linked by a polyatomic chain, such as-(CH₂)₄(L-4), -(CH₂)₆- (L-6), and -CH₂CH(OH)CH₂H(L-3), etc., and were characterized in terms of the magnetic measurements and cyclic voltammetry. The complexes, Fe₂(L-3′0(NO₃)₅ showed subnormal magnetic moments, 4.10 BM at 299 K and 2.22 BM at 87 K, respectively, suggesting the presence of an alkoxo-bridge structure. This complex showed much higher catalytic activity for the O₂ oxidation of N, N, N′,N′-tetramethyl-1-1,4-diaminobenzene than those of the relevant mononuclear complexes and other binuclear complexes studied here which have no alkoxo-bridge. The complex reacts with catechol and hydrogen peroxide to form 1:1 adducts.     

The crystal and molecular structures of tris(O-ethylxanthato)-gallium(III) and indium(III)

The crystal structures of the title compounds, Ga(S₂COEt)₃ (1) and In(S₂COEt)₃ (2) have been determined by three dimensional X-ray diffraction methods. Both compounds crystallize in the trigonal space group R with Z = 6. Cell dimensions for (1) are a_hex 15.065(1) and c_hex 13.421(1) Å and for (2) 15.319(3) and 13.522(4) Å. Final R. and R_w values 0.044 and 0.049 for (1) and 0.040 and 0.037 for (2) for 668 and 1153 statistically significant reflections respectively.The complexes are isostructural. The metal centres are in a distorted octahedral environment, the distortion arising from the restricted bite distance of the xanthate ligands. For each compound, each xanthate moiety chelates the metal atom with similar M-S bonds.     

Chromium(III) complexes and their relationship to the glucose tolerance factor. Part II. Structure and biological activity of amino acid complexes

A number of octahedral chromium complexes with amino acids are ligands have been prepared and their structures assigned on the basis of their chromatographic and spectral properties. These include complexes with the general structure Cr(AA)₂(H₂O)₂ where the amino acids glycine, glutamic acid and glutamine act as bidentate ligands. The analogous compound with cysteine as ligand is stable at low pH, but at high pH a terdentate cysteine complex, Cr(cysteine)₂^?, is formed. These complexes, as well as a solution of monodentate glycine aquo complexes, and Cr-nicotinic acid-glycine and Cr-nicotinic acid-cysteine complexes of undetermined structure, have been assayed for glucose tolerance factor activity using a yeast assay. Only Cr(glutamine)₂- (H₂O)₂⁺, Cr-nicotinic acid-glycine and the mixture of complexes Cr(glycine)_n(H₂O)_6-n⁺³ showed significant activity. It is proposed that a trans arrangement of the non-coordinated nitrogen atoms in the ligands of these complexes can mimic the structural features of the glucose tolerance factor which are essential for biological activity.     

Amidino-complexes of iron(II) and (III)

Lithioamidines {R′N(Li)C(R)NR′, I; R = CH₃, R′ = C₆H₅, p-CH₃,C₆H₄} react with iron(III) chloride

in monoglyme to produce navy-blue, high spin Fe{R′NC(R)NR′}₃ complexes which are extremely air and moisture sensitive. The corresponding reaction when R = R′ = C₆H₅ produces a soluble red complex and an air-stable green complex, whereas when R = H, R′ = C₆H₅ and R = R′ = C₆H₅ and the reaction is started at ca. ?20°, red and green complexes respectively are formed. Though all the complexes are formulated Fe{R′NC(R)NR′}₃, their properties reflect association through bridging amidino-groups. Iron(II) chloride reacts with I(R = CH₃, R′ = p-CH₃C₆H₄) to form two complexes, one crimson and soluble in organic solvents, and one brown and insoluble, which are fomulated [Fe{R′NC(R)NR′}₂]_n. The iron(III) complexes failed to react with, or were decomposed by, a variety of reducing, electrophilic and nucleophilic reagents, though blue Fe{p-CH₃C₆H₄NC(CH₃)N-p-CH₃C₆H₄}₃ reacts readily with nitric oxide to form a purple addition complex from which the N-nitroso-compound p-CH₃C₆H₄NC(CH₃)N(NO)-p-CH₃C₆H₄ was obtained in high yield. Treatment of the corresponding brown iron(II) complex with nitric oxide gave no reaction.     

Synthesis and characterization of a series of new mixed ligand complexes of manganese(III), iron(III), nickel(II), copper(II) and zinc(II) with schiff bases of N,N-diethylamino-dithiocarbamate as ligands

Twenty new bioactive complexes of Mn(III), Fe(III), Ni(II), Cu(II) and Zn(II) have been prepared containing Schiff bases of N,N-diethylaminodithio- carbamate as ligands. These complexes have been characterized by elemental analyses, IR and UV-Vis spectroscopy as well as by magnetic susceptibility measurements. The spectra of the complexes suggest that the ligands are coordinated to the metal ions via the sulfur atoms of the dithiocarbamato group.     

Coordination chemistry of higher oxidation states. Part 15. Cobalt(III) complexes of bi- and multi-dentate phenylphosphines

Six-coordinate cobalt(III) complex trans-[Co{o-C₆H₄(PPh₂)₂}₂X₂]ClO₄, fac-[Co{PhP(CH₂CH₂PPh₂)₂}X₃],cis-[Co{P(CH₂CH₂PPh₂)₃}X₂]ClO₄ and cis-β-[Co{-CH₂P(Ph)CH₂CH₂PPh₂}₂X₂]PF₆ (X = Cl, Br) have been prepared by halogen oxidation of the Co(II) analogues, and characterised by IR, electronic and ³¹P NMR spectroscopy. The failure to obtain complexes with X = I, and with some related ligands is discussed, and the rather low stability of the above complexes is rationalised in terms of steric crowding at the metal centre.