Synthesis and characterization of a new family of bi-, tri-, tetra-, and pentanuclear ferric complexes

Nine members of a new family of polynuclear ferric complexes have been synthesized and characterized. The reaction of Fe(O(2)CMe)(2) with polydentate Schiff base proligands (H(2)L) derived from salicylidene-2-ethanolamine, followed in some cases by reaction with carboxylic acids, has afforded new complexes of general formulas [Fe(2)(pic)(2)(L)(2)] (where pic(-) is the anion of 2-picolinic acid), [Fe(3)(O(2)CMe)(3)(L)(3)], [Fe(4)(OR)(2)(O(2)CMe)(2)(L)(4)], and [Fe(5)O(OH)(O(2)CR)(4)(L)(4)]. The tri-, tetra-, and pentanuclear complexes all possess unusual structures and novel core topologies. M?ssbauer spectroscopy confirms the presence of high-spin ferric centers in the tri- and pentanuclear complexes. Variable-temperature magnetic measurements suggest spin ground states of S = 0, 1/2, 0, and 5/2 for the bi-, tri-, tetra-, and pentanuclear complexes, respectively. Fits of the magnetic susceptibility data have provided the magnitude of the exclusively antiferromagnetic exchange interactions. In addition, an easy-axis-type magnetic anisotropy has been observed for the pentanuclear complexes, with D values of approximately -0.4 cm(-)(1) determined from modeling the low-temperature magnetization data. A low-temperature micro-SQUID study of one of the pentanuclear complexes reveals magnetization hysteresis at nonzero field. This is attributed to an anisotropy-induced energy barrier to magnetization reversal that is of molecular origin. Finally, an inelastic neutron scattering study of one of the trinuclear complexes has revealed that the magnetic behavior arises from two distinct species.     

Zinc(II) binding ability of tri-, tetra- and penta-peptides containing two or three histidyl residues

Macroscopic and microscopic protonation processes and zinc(II) complexes of a series of multihistidine peptides (Ac-HGH-OH, Ac-HGH-NHMe, Ac-HHGH-OH, Ac-HHGH-NHMe, Ac-HVGDH-NH(2), Ac-HHVGD-NH(2), Ac-HVHAH-NH(2), Ac-HAHVH-NH(2), Ac-HPHAH-NH(2) and Ac-HAHPH-NH(2)) were studied by potentiometric, NMR and ESI-MS spectroscopic techniques. Protonations of histidyl imidazole-N donor functions were not much affected by the number and location of histidyl residues, but the presence of C-terminal carboxylate groups had a significant impact on the basicities of the neighbouring histidyl sites. The formation of 2N(im) and 3N(im) macrochelates with the stoichiometry of [ZnL] was the major process in the complexation reactions of all peptides followed by the formation of hydroxo or amide bonded species. Thermodynamic stabilities of the zinc(II) complexes were primarily determined by the number of histidyl residues, but the presence of C-terminal carboxylate functions has also a significant contribution to metal binding. The stabilizing effect of the aspartyl beta-carboxylate group was also observed, but its extent is much weaker than that of the C-terminal carboxylate with a neighbouring histidyl residue. Zinc(II) promoted peptide amide deprotonation and co-ordination was observed only in the zinc(II)-Ac-HHVGD-NH(2) system above pH 8.     

A practical synthesis of novel hydroxyl-substituted macrocyclic tri-,tetra- and hexa-amines

Macrocyclic tri- and tetra-amines containing a hydroxyl group in the ring have been prepared in moderate yields by a 1:1 cyclocondensation of l,3-dichloro-2-propanol with the disodium salt of N-tosylated diethylenetriamine and triethylenetetraamine.In the case of condensation of 1,3-dichloro-2-propanol with the disodium salt of N-tosylated diethylenetriamine,the 2:2 cyclocondensation product,dihydroxyl macrocyclic hexaamine,was also isolated.     

A comparative study on textural characterization: cation-exchange and sorption properties of crystalline alpha-zirconium(IV), tin(IV), and titanium(IV) phosphates

Tetravalent metal phosphates (M=Zr, Ti, and Sn) were prepared and characterized by XRD, surface properties, and TG-DTA. The cation exchange and sorption behavior of these metal phosphates toward transition metal ions such as Cu(2+), Co(2+), and Ni(2+) have been studied comparatively as a function of temperature and concentration. The adsorption process was found to increases with increase in temperature and concentration. The selectivity order for alpha-titanium and alpha-tin phosphates is Cu(2+)>Co(2+)>Ni(2+), whereas for alpha-zirconium phosphate it is Cu(2+)>Ni(2+)>Co(2+). The ion exchange capacity of alpha-titanium phosphate is greater than those of other phosphates, which is explained on the basis of the surface behavior, disorderness of the system, degree of hydrolysis of incoming guest adsorbate metal ions, and structural steric hindrance of the exchangers during adsorption and sorption. The distribution coefficient, Gibbs free energy, enthalpy, and entropy values indicate that the ion-exchange processes are spontaneous.     

A practical synthesis of novel hydroxyl-substituted macrocyclic tri-, tetra- and hexa-mines

Macrocyclic tri- and tetra-amines containing a hydroxyl group in the ring have been preparad in moderate yields by a 1:l cyclocondensation of 1,3-dichloro-2-propanol with the disodium salt of N-tosylated diethylenetriamine and triethylenetetraamine. In the case of condensation of 1,3-dichloro-2-propanol with the disodium salt of N-tosylated diethylenetriamine, the 2:2 cyclocondensation product, dihydroxyl macrocyclic hexaamine, was also isolated.     

Mixed ligand titanium(IV) complexes. Chlorobis(dithiocarbamato)bis(methylsalicylato)titanium(IV) andbis(dithiocarbamato)bis(methylsalicylato)titanium(IV)

Summary Dichlorobis(methylsalicylato)titanium(IV) reacts with potassium or amine salts of dialkyl or diaryl dithiocarbamates in 11 and 12 molar ratios in anhydrous benzene (room temperature) or in boiling CH₂Cl₂ to yield mixed ligand complexes: (AcOC₆H₄O)₂ Ti(S₂CNR₂)Cl (1) and (AcOC₆H₄O)₂ Ti(S₂CNR₂)₂ (2), R=Et, n-Pr, n-Bu, cyclo-C₄H₈ and cyclo-C₅H₁₀. These compounds are moisture sensitive and highly soluble in polar solvents. Molecular weight measurement in conjunction with i.r.,¹H and¹³C n.m.r. spectral studies suggest coordination number 7 and 8 around titanium(IV) in (1) and (2) respectively.     

Schiff base derivatives of titanium(IV) and zirconium(IV)

The reactions of a few bifunctional and tridentate Schiff bases with titanium-(IV) and zirconium(IV) isopropoxides in equimolar and bimolar ratios are described. The resulting compounds have been obtained in almost quantitative yields and are of the general formulae M(SB)_x(OPrⁱ)_4?2X (where M = Ti or Zr; SB- = anion of the Schiff base SBH₂ and x = 1 or 2). Their molecular weights have been determined ebullioscopically and IR spectra recorded.     

Intramolecular charge resonance in dimer radical anions of di-, tri-, tetra-, and pentaphenylalkanes

Intramolecular dimer radical anions of di-, tri-, tetra-, and pentaphenylalkanes were investigated on the basis of absorption spectral measurements during γ-radiolysis in 2-methyltetrahydrofuran (MTHF) glassy matrix at 77 K and theoretical calculations. The absorption spectrum of 1,1,2,2-tetraphenylethane (1,1,2,2-Ph(4)E) radical anion showed two bands in the near-infrared (NIR) region (900-2600 nm). One band observed at shorter wavelength than 2000 nm is assigned to the intramolecular charge resonance (CR) band between two phenyl groups of the 1,1-diphenylmethyl chromophore (1,1-dimer radical anion). The intramolecular CR band of the 1,1-dimer radical anion was observed for various alkanes having 1,1-diphenylmethyl chromophore such as 1,1,1-triphenylmethane (1,1,1-Ph(3)M), 1,1,1,1-tetraphenylmethane (1,1,1,1-Ph(4)M), and so on. The other intramolecular CR band observed at longer wavelength than 2200 nm is assigned to intramolecular dimer radical anion between two phenyl groups of the 1,2-diphenylethyl chromophore (1,2-dimer radical anion). The intramolecular CR band of the 1,2-dimer radical anion was observed for various alkanes having a 1,2-diphenylethyl chromophore, such as 1,1,2-triphenylethane (1,1,2-Ph(3)E), 1,1,2,2-Ph(4)E, and 1,1,1,2,2-pentaphenylethane (1,1,1,2,2-Ph(5)E) and so on. No dimer radical anion was observed for 1,n-diphenylalkanes (n > 2) without 1,1-diphenylmethyl chromophore. The relationship between the structure and negative charge delocalization over two phenyl groups connected by an sp(3) carbon is discussed.     

Reductions by titanium(II) as catalyzed by titanium(IV)

The cobalt(III) complexes, [(NH3)5CoBr]2+ and [(NH3)5CoI]2+ are reduced by Ti(II) solutions containing Ti(IV), generating nearly linear (zero-order) profiles that become curved only during the last few percent of reaction. Other Co(III)-Ti(II) systems exhibit the usual exponential traces with rates proportional to [Co(III)]. Observed kinetics of the biphasic catalyzed Ti(II)-Co(III)Br and Ti(II)-Co(III)I reactions support the reaction sequence: [Ti(II)(H20)n]2+ + [Ti(IV)F5]- (k1)<==>(k -1) [Ti(II)(H2O)(n-1)]2+ + [(H2O)Ti(IV)F5]-, [Ti(II)(H2O)(n-1)]2+ + Co(III) (k2)--> Ti(III) + Co(II) with rates determined mainly by the slow Ti(IV)-Ti(II) ligand exchange (k1 = 9 x 10(-3) M(-1) s(-1) at 22 degrees C). Computer simulations of the catalyzed Ti(II)-Co(III) reaction in perchlorate-triflate media yield relative rates for reduction by the proposed active [Ti(II)(H2O)(n-1)]2+ intermediate; k(Br)/k(I) = 8.     

Monocyclopentadienyl titanium(IV) dithiocarbamate complexes

Preparation of titanium(IV) complexes of the type CpTi(dtc)Cl₂, CpTi(dtc)₂Cl and CpTi(dtc)₃ has been carried out by reacting CpTiCl₃ and respective sodium dithiocarbamate viz. N-(ethyl, m-tolyl), N-cyclopentyl and N-cycloheptyl dithiocarbamates in the desired metal to ligand ratio in refluxing dichlomethane. Studies of the physical properties reveal monomeric and nonelectrolytic nature of these complexes, where dithiocarbamate behaves as bidentate ligand. Therefore, 5, 6 and 7 coordinate structure can be assigned to CpTi(dtc)Cl₂, CpTi(dtc)₂Cl and CpTi(dtc)₃, respectively.     

Phospha(III)guanidinate complexes of titanium(IV) and zirconium(IV) amides

Two procedures for the synthesis of group 4 phosphaguanidine compounds M(R₂PC{NR′}₂)(NR″₂)₃ (M = Ti, Zr; R = Ph, Cy; R′ = ⁱPr, Cy; R″ = Me, Et) are described. Spectroscopic characterization indicated symmetrical bonding of the phosphaguanidinate ligand in solution for the P-diphenyl derivatives whereas the P-dicyclohexyl analogs adopt a more rigid geometry with inequivalent N_amidine substituents within the phosphaguanidinate ligand. X-ray diffraction studies show exclusively monomeric tbp metal centers for a series of derivatives, with a chelating phosphaguanidinate ligand that spans an axial and an equatorial position. Two different conformers have been identified in the solid-state that differ in the relative orientation of the phosphorus R₂P–C substituents with respect to the equatorial plane of the tbp metal. The synthetic protocol was extended to the bimetallic complex, [PhP(C{NⁱPr}₂Ti{NMe₂}₃)CH₂–]₂, which was characterized by crystallography as the meso-form.     

Pyridine based zirconium(IV) and tin(IV) phosphates as new and novel intercalated ion exchangers

Pyridine based zirconium(IV) phosphate (PyZrP) and tin(IV) phosphate (PySnP) have been synthesized as new and novel intercalated ion exchangers. These materials have been characterized using X-ray, IR spectra, TG, DTG and DTA studies in addition to their ion exchange capacity, elution, pH titration, concentration and distribution behaviour. The distribution studies towards several metal ions in different media/concentrations have suggested that PyZrP and PySnP are selective for Hg(II) and Pb(II), respectively. As a consequence some binary separations of metal ions involving Hg(II) and Pb(II) ions have been performed on a column of these materials, demonstrating their analytical and environmental potential.     

Synthesis, structure, and catalytic activity of titanium(IV) and zirconium(IV) amides with chiral biphenyldiamine-based ligands

A new series of titanium(IV) and zirconium(IV) amides have been prepared from the reaction between M(NMe₂)₄ (M = Ti, Zr) and C₂-symmetric ligands, (R)-2,2′-bis(pyridin-2-ylmethylamino)-6,6′-dimethyl-1,1′-biphenyl (2H₂), (R)-2,2′-bis(pyrrol-2-ylmethyleneamino)-6,6′-dimethyl-1,1′-biphenyl (3H₂), (R)-2,2′-bis(diphenylphosphinoylamino)-6,6′-dimethyl-1,1′-biphenyl (4H₂), (R)-2,2′-bis(methanesulphonylamino)-6,6′-dimethyl-1,1′-biphenyl (5H₂), (R)-2,2′-bis(p-toluenesulphonylamino)-6,6′-dimethyl-1,1′-biphenyl (6H₂), and C₁-symmetric ligands, (R)-2-(diphenylthiophosphoramino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (7H) and (R)-2-(pyridin-2-ylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (8H), which are derived from (R)-2,2′-diamino-6,6′-dimethyl-1,1′-biphenyl. Treatment of M(NMe₂)₄ with 1 equiv. of N₄-ligand, 2H₂ or 3H₂ gives, after recrystallization from an n-hexane solution, the chiral zirconium amides (2)Zr(NMe₂)₂ (9), (3)Zr(NMe₂)₂ (11), and titanium amide (3)Ti(NMe₂)₂ (10), respectively, in good yields. Reaction of Zr(NMe₂)₄ with 1 equiv of diphenylphosphoramide 4H₂ affords the chiral zirconium amide (4)Zr(NMe₂)₂ (12) in 85% yield. Under similar reaction conditions, treatment of Ti(NMe₂)₄ with 1 equiv. of sulphonylamide ligand, 5H₂ or 6H₂ gives, after recrystallization from a toluene solution, the chiral titanium amides (5)Ti(NMe₂)₂·0.5C₇H₈ (13·0.5C₇H₈) and (6)Ti(NMe₂)₂ (15), respectively, in good yields, while reaction of Zr(NMe₂)₄ with 1 equiv. of 5H₂ or 6H₂ gives the bis-ligated complexes, (5)₂Zr (14) and (6)₂Zr (16). Treatment of M(NMe₂)₄ with 2 equiv. of diphenylthiophosphoramide ligand 7H or N₃-ligand 8H gives, after recrystallization from a benzene solution, the bis-ligated chiral zirconium amides (7)₂Zr(NMe₂)₂ (17) and (8)₂Zr(NMe₂)₂ (19), and bis-ligated chiral titanium amide (8)₂Ti(NMe₂)₂ (18), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 10, 12, 13, and 17-19 have further been confirmed by X-ray diffraction analyses. The zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in good to excellent yields with moderate ee values, while the titanium amides are not.     

Bis(indenyl)titanium(IV) and zirconium(IV) complexes of monofunctional bidentate salicylidimines

Dichlorobis(indenyl)-titanium(IV) and -zirconium(IV), (C₉H₇)₂TiCl₂ and (C₉H₇)₂ZrCl₂, react with bidentate Schiff bases such as salicylidene aniline, salicylidene-o-toluidine, salicylidene-m-toluidine and salicylidene-p-toluidine in a 1:1 molar ratio in refluxing tetrahydrofuran in the presence of triethylamine to yield complexes of the type (C₉H₇)₂Ti(SB)Cl and (C₉H₇)₂Zr(SB)Cl, respectively where SB is the anion of the corresponding Schiff base, SBH. The new derivatives have been characterised on the basis of their elemental analyses, conductance measurements and spectral (IR, ¹H NMR and electronic) studies.     

A pyrazine-bridged linear pentanuclear copper(II) complex and related tri- and dinuclear complexes showing various coordination structures and magnetic couplings

Sterically bulky pyrazines have been successfully utilized for the preparation of discrete oligo-nuclear TBP (trigonal bipyramidal), SqP (square pyramidal), and Oh (octahedral) copper(II) complexes. We have synthesized a unique linear pentanuclear complex [{Cu(hfac)₂}₅(μ-2-butyl-3-methylpyrazine)₄]. The two terminal copper(II) ions have a SqP structure while the three inner ions have an Oh one. The solvent molecule was incorporated in the clearance of the lattice. From another reaction under harsh conditions, we separated [{Cu(hfac)₂}₃(μ-2-butyl-3-methylpyrazine)₂], which can be regarded as the central moiety of the pentanuclear one. We also prepared a dinuclear complex [{Cu(hfac)₂}₂(μ-tetramethylpyrazine)], in which the pyrazine nitrogen atoms were located at TBP equatorial positions. Single-crystal EPR measurements supported its compressed TBP structure. The exchange coupling was antiferromagnetic with J_TBP–TBP/k_B = −3.6 K. The linear trinuclear [{Cu(hfac)₂}₃(μ-2,3,5-trimethylpyrazine)₂], having two TBP Cu ions with an intervening Oh Cu ion, showed very weak antiferromagnetic coupling. DFT calculations on these compounds indicated that the σ-type orbital overlap between the Cu and N atoms is essential for superexchange interactions.