Formation Of Mononuclear Complexes Research Articles

Diagrams for complete representation of binary mononuclear complex systems

Solution equilibria are calculated from the system of equations expressing the mass balance and the law of mass action. The solution of these equations usually requires the use of complicated iterative procedures. It is shown in the present paper, that for mononuclear complex formation, the whole system can be represented by a single diagram exhibiting all of the important chemical information, including solubility equilibria. The data necessary for the construction of the diagrams can be calculated directly without iterative procedures.

Tetrazoles as ligands. Part IV. Iron(II) complexes of monofunctional tetrazole ligands, showing high-spin ( p5T 2g) ⇋ low-spin transitions

1-Alkyl substituted tetrazoles and iron(III) tetrafluoroborate lead to the formation of hexacoordinated iron(II) complexes, viz.: [FeL 6](BF 4) 2 with L = 1-methyltetrazole (MTZ), 1-ethyltetrazole (ETZ), 1-propyltetrazole (PTZ) and 1-isopropyltetrazole (IPTZ). The complexes were identified and characterized by elemental analyses, IR and ligand field spectra and magnetic susceptibility measurements. The iron(II) ions are octahedrally surrounded by monodentate ligands and a mononuclear complex formation is obvious. At temperatures varying from 140–80 K the complexes show high-spin ( 5T 2g) ⇋ low-spin ( 1A 1g) transitions, recognizable by a colour change from white to purple. The transitions were followed by magnetic measurements.

Physical and chemical characterization of soil and poultry litter humic and fulvic metal complexes

Humic and fulvic-zinc complexes obtained from soil and poultry litter were characterized by I.R. spectroscopy, determination of stability constant and the free energy change associated with their formation. Infrared spectroscopy confirmed that both electrovalent, coordinate-covalent bonds of Zn2+ with the carboxylate, phenolic hydroxyl and amine groups lead to the formation of their stable complexes. This is evident from the changes in absorption bands at 1700 cm−1, 1725 cm−1, 1625 cm−1 and 1400 cm−1 of their infrared spectra. The stability constants of complexes are pH-dependent. Interaction of Zn with humic and fulvic acid involved the formation of mononuclear complexes. The values of stability constants of these complexes are lower than those reported earlier. The calculation of the free-energy change associated with salts and complex formation indicates the spontaneity of both reactions, although a higher probability of complex reaction than that of salt formation is evident. The implications of the complexation of metal ions by these naturally occurring polydisperse plyaanions in regulating the movement of metal ions from the ambient soil matrix to plant roots and biological system in terresterial and aquatic environments are indicated.

The synthesis and characterization of mono- and dinuclear cobaloxime selenocyanate and thiocyanate complexes containing phosphines, arsines and stibines

Complexes of the type trans-[Co(DH) 2(L)X] and trans-[(L)Co(DH) 2-X-Co(DH) 2-X] have been synthesized by the reaction between trans-[Co(DH) 2(L)Y] and X in a variety of solvents (DH = monoanion of dimethylglyoxime; L = triphenylstibine, triphenylarsine, triphenylphosphine, tri- n-butylstibine; X = SeCN −, SCN −; Y = Cl −, Br −). The formation of mononuclear complexes resulted in solvents of high dielectric, while dinuclear complexes usually resulted in solvents of low dielectric. All of the terminal SeCN − groups exhibit coordination via the selenium atom, regardless of the nature of L. Several of the terminal SCN − groups in the mononuclear complexes were N-bound. Little or none of the dinuclear complexes could be produced from N-bound complexes, regardless of solvent dielectric. These results are in accord with the dissociative mechanism proposed for the formation of the dinuclear complexes, i.e., dissociation of the neutral L ligands would be expected to be facilitated by solvents of low dielectric and retarded by the lower trans-effect of the N-bound thiocyanate. The bonding modes adopted by the NCS − and NCSe − ions in these complexes are discussed in the context of competing anti-symbiotic and symbiotic effects, respectively.

Evidence of complex formation in concentrated solutions by x-ray diffraction technique

For several years remarkable contributions to the knowledge of the coordination of metal ions in solutions have been provided by X-ray diffraction studies. The description of the structure of the solutions is usually confined to the first coordination shell of the ions in terms of distances, geometries and coordination numbers. Recently, attempts have been to describe interactions arising from the second coordination shell of the cations [1]. Further complex formation has been found to be successfully examined by this technique. The structure of complexes in solution, in fact, can often be obtained in a unique way if the scattering measurements are carried out for solutions of different concentration and/or composition and the results are combined with equilibrium analysis and crystal structure determination. X-ray analysis can be performed in several ways. When dealing with solutions of heavy atoms information on the dominant intramolecular interactions can be easily obtained from the high-angle part of a scattering curve by means of a least square procedure which yields the bond lengths and the frequency of the distances, while the low-angle part can be used to obtain information on the packing of solvent molecules around the complex. With light atom solutions the scattered intensities from the cations are levelled of to the other contribution in solution: a complete model is needed to perform a least square procedure, and for its formulation, the greatest amount of information must be drawn from the experimental radial curves. The use of difference curves between radial functions of solutions of different concentration and/or composition is often revealing as far as the structuring of complexes in different chemical conditions is concerned. Transition metal ions, such as Fe(III), Cr(III), Th(IV), have been investigated at different concentration in acidic, neutral and hydrolysed solutions in different chemical conditions [1]. As an exemplification of the method mononuclear complex formation between Fe(III) and typical inorganic anions (sulphate [2] and chloride [3]) will be examined. Polynuclear complex formation will be illustrated by Th(IV) hydrolysed solutions where structural units containing from few up to several tenths of atoms have been found to occur in these solutions [4].

Polynuclear and mononuclear complex formation between indium(III) and sulfhydryl-containing bidentate ligands.

The various physico-chemical studies were made on the complex-formation equilibria between In (III) and sulfhydryl-containing bidentate ligands, such as 2-aminoethanethiol (2-mercaptoethylamine, MEA), 3-mercaptopropionic acid (MPA), and mercaptoacetic acid (thioglycolic acid, TGA). The insoluble and stable complex, InL3, was formed during the titration of the MEA-In (III) solution. The complex formation of In (III) with MPA and TGA was investigated by potentiometric titration over a wide range of the metal concentration. Calculation of the titration data of the MPA-In (III) system indicated that MPA formed the In2L3, In3L4, and In3 (OH) L4 species together with the mononuclear species. In the higher concentration, non-charged species, In3 (OH) L4, was precipitated. In the alkaline solution, the carboxyl group was eliminated from the coordination sphere and the InL4 species was formed. These observations in the MPA-In (III) system were similar to those of the cysteine case. Since TGA forms the stable complex with fivemembered chelate ring, the InL4 or hydrolyzed species were not formed even in the alkaline solution. Calculation indicated the formation of the InL3, In2L3, and In3L5 species in the TGA system.

Stereoselectivity in the formation of mononuclear complexes of histidine and some bivalent metal ions

The formation constants of complexes of Co2+, Ni2+, Cu2+, Zn2+, Pb2+, and [VO]2+ with D- and L-histidine have been measured at 25.0 °C and I= 0.10 mol dm–3(K[NO3]). The importance of protonated complexes in all the systems studied has been demonstrated and the structures of the various species are discussed. Thermodynamic stereoselectivity has been confirmed in the bis(histidinato)-complexes of Co2+, Ni2+, and Zn2+, and has been also found in the monoprotonated bis(histidine) complexes of Co2+, Ni2+, Cu2+, and Zn2+. Stereoselectivity as exhibited in the enthalpy change (ΔH) accompanying formation of bis(histidinato)cobalt(II) has been measured calorimetrically; ΔH for formation of the meso-bis complex is more favourable by 2.4 ± 0.2 kJ mol–1.

Contribution a l'etude des complexes du cation cadmium (II) avec l'acide laćtique et l'acide malonique en milieu Na +(ClO −4)3M A 25°C

The potentiometric study of neutralisation at 25°C, in Na + (ClO − 4)3M medium, with NaOH as titrant, of solutions: Cd 2+ cation-lactic acid (between neutralisation rate values 0 to 1); and of Cd 2+ cation-malonic acid (between neutralisation rate values 1–2), allows consideration of the formation of mononuclear complexes with lactic acid, and mononuclear and polynuclear complexes with malonic acid. The interpretation of experimental data ph = f( x) R induces one to suppose the existence of the following species: lactic acid: Cd(Lact) +, Cd(Lact) 2; malonic acid; Cd(Mal); Cd(Mal) 2− 2; Cd(Mal) 4− 3; Cd 2(Mal) 2; Cd 2(Mal) 2− 3. The constants of formation of those complexes have been determined by non-linear regression.

Complex formation of iron(III) with diglycolic and iminodiacetic acids

complex formation in aqueous solution between iron(III) and diglycolic (H 2Dig) and iminodiacetic acid (H 2Im) has been studied at 25°C in a medium of constant ionic strength 0,5 M NaClO 4, by a spectrophotometric method. At −log [H +] values less than 2 and with excess of ligand ( C L C M up to 500) the formation of mononuclear complexes with metal-ligand molar ratio of 1 : 1 has been observed. The formation constants and the related equilibria are: Fe 3+ + Dig 2− ⇌ FeDig + log β 1 = 5·04 Fe 3+ + Im 2− ⇌ FeIm + log β 1 = 10·72.

Carbonyl complexes of rhodium(I) with aliphatic and aromatic bifunctional ligands

1. Binuclear complexes of rhodium in oxidation state I were obtained with bifunctional ligands: hexamethylenediamine, decamethylenediamine, 2,2′-diaminodiphenyl, o-phenanthroline, and 8,8′-dihydroxy-5,5′-diquinolyl. 2. Mononuclear complexes of rhodium with 2,2′-diaminodiphenyl and o-phenanthroline were obtained. 3. The formation of mononuclear complexes passes through the stage of binuclear complex formation, followed by rupture of the rhodium-nitrogen bond in the presence of excess ligand. It was proposed that one of the factors causing the formation of mononuclear complexes is the trans-effect of the carbonyl group.

Acetato complexes of organolead (IV) in aqueous solution

The complexity of solutions of organolead(IV) and acetate ions has been investigated in a constant ionic medium (1 M ClO 4 − by means of emf measurements of [H +]. Only a mononuclear complex formation occurs. The order of the determined stability constants is correlated with the nature of the organo groups bound to the lead.