Shin-ichi Ishiguro

Formation of chloro complexes of manganese(II), cobalt(II), nickel(II) and zinc(II) in dimethyl sulphoxide

The formation of chloro complexes of MnII, CoII, NiII and ZnII in dimethyl sulphoxide (DMSO) has been studied by calorimetry and spectrophotometry at 25°C. The formation constants, enthalpies and entropies for [MCln](2–n)+(n= 1–4; M = Mn, Co, Ni, Zn) were determined and electronic spectra for the individual CoII and NiII complexes were extracted. It is revealed that the coordination structure of [CoCl]+, [NiCl]+ and [NiCl2] is octahedral and that of [CoCl2], [CoCl3]–, [CoCl4]2–, [NiCl3]– and [NiCl4]2– is tetrahedral. Thus, an octahedral to tetrahedral geometry change occurs at the second step for CoII and at the third step for NiII. The log K1 values for the formation of [MCl]+ vary in the order Mn > Co > Ni Zn, which is different from the Irving–Williams series. The overall log β4 values follow the sequence Mn Ni < Cu < Zn. Complexation entropies of these metal systems are appreciably smaller in DMSO than in N,N-dimethylformamide (DMF), which is ascribed to stronger solvent–solvent interactions in DMSO.

Calorimetric and spectrophotometric studies of chloro complexes of manganese(II) and cobalt(II) ions in N,N-dimethylformamide

The formation of chloro complexes of manganese(II) and cobalt(II) ions has been calorimetrically and spectrophotometrically studied in N,N-dimethyl-formamide (DMF) containing 0.4 mol dm–3(C2H5)4NClO4 as a constant ionic medium at 25 °C. Calorimetric data obtained in each system are explained in terms of the formation of [MCln](2–n)+(n= 1–4 and M = Mn or Co) and their formation constants, enthalpies and entropies were determined. In the cobalt(II) chloro system electronic spectra of individual complexes were also determined. The thermodynamic parameters of formation of the chloro complexes of these metal(II) ions are compared with those of nickel(II), copper(II) and zinc(II) ions.

Thermodynamic and structural studies of metal complexes in various solvents

Abstract Complexation of various metal-ligand systems has been discussed from the view-point of solute-solvent and solvent-solvent interactions in pure solvents and their mixtures on the basis of thermodynamic and structural measurements. In water and dioxane-water mixtures, it was suggested that the solvation structure in the secondary shell of ionic species significantly changes by adding dioxane to water due to the formation dioxane-water associates in the bulk. It was found that 1,10-phenanthroline formed its stacked species, such as [H(phen)2]+ and (phen)2, in water, but the species hydrophobically associated disappeared in dioxane-water mixtures due to breaking of the hydrogen-bonded structure of water. Complexation of Zn(II), Cd(II) and Hg(II) ions with SCN− ions in water was discussed in relation to the structures of the complexes determined by X-ray diffraction, and NMR and Raman spectral measurements. The solvent effect on the complexation of Cu(II) with chloride ions in acetonitrile, N,N-dimeth...

Intramolecular and liquid structure of 2,2,2-trifluoroethanol by X-ray diffraction

Intramolecular and liquid structure of 2,2,2-trifluoroethanol (TFE) have been investigated by x-ray diffraction at 25°C. The structural parameters for the skeleton of the molecules in the liquid phase are similar to those in the gas phase. The conformers of TFE molecules in the liquid phase are discussed. The O...O distance at about 284 pm and additional F...O one at about 302 pm were found to be characteristic for the first neighbor interactions. Various models (dimers and trimers) have been examined for analyzing the first neighbor structure. The liquid structure was explained in terms of small clusters consisting of two to three molecules rather than of a more extended polymeric network.

Unusual affinities of monovalent anions to dicopper(II) complexes with N,N′,N″,N‴-tetrakis(2-aminoethyl)-tetra-azacycloalkanes

Abstract The equilibrium constants for [Cu 2 L] 4+ + X − = [CuXL] 3+ were determined spectrophotometrically in aqueous solution at 25 °C, where L represents the title ligands and X denotes Cl, Br, I and CH 3 COO. The formation constants of [Cu 2 XL] 3+ thus obtained were unusually large compared to those of common copper(II) complexes with CuX bonds, and decrease in the order Cl − > Br − > I − > CH 3 COO − for a given L, and taec > taep > taeh for a given X − . The origin of the surprisingly high stabilities was discussed.

Thermodynamics of complexation of zinc(II) with chloride, bromide and iodide ions in hexamethylphosphoric triamide

The complexation of zinc(II) with chloride, bromide and iodide ions has been studied by calorimetry in hexamethylphosphoric triamide (HMPA) containing 0.1 mol-dm−3 (n-C4H9)4NClO4 as a constant ionic medium at 25°C. The formation of [ZnXn](2−n)+ (n=1,2,3,4 for X=Cl; n=1,2 for X=Br, I) is revealed, and their formation constants, enthalpies and entropies were determined. It is proposed that the zinc(II) ion is fourcoordinated in HMPA and the coordinating HMPA molecules are stepwise replaced with halide ions to form [ZnXn(hmpa)4−n](2−n)+ (n=1−4), as is the case for the cobalt(II) ion. Furthermore, the formation of [ZnClI], [ZnBrI], [ZnBrCl] and [ZnBrCl2]− is revealed in the relevant ternary systems. It is found that the affinity of a given halide ion X− to [ZnCl]+, [ZnBr]+ and [Znl]+ is practically the same.

A calorimetric study ofN,N-dimethylformamide complexes of copper(II) in acetonitrile

Complex formation of copper(II) with N,N-dimethylformamide(DMF) has been investigated calorimetrically in acetonitrile at 25°C. Calorimetric titration curves obtained are explained in terms of formation of [Cu(dmf)n]2+ (n=1–4, 6) and their formation constants, enthalpies and entropies were determined. Formation of [Cu(dmf)5]2+ is uncertain. The stepwise enthalpies ΔS30 and entropies ΔSn0 at each consecutive step are all negative except for ΔS30. The overall enthalpies of formation of [Cu(dmf)6]2+ is −(77.8±5.4) kJ-mol−1, which is compared with the enthalpy of transfer of copper(II) ion, ΔHto=−79.7 kJ-mol−1, from acetonitrile to DMF.

Thermodynamics of formation of binary and ternary complexes of zinc(II) with halide and thiocyanate ions and 2,2′-bipyridine in dimethylformamide

The formation of binary and ternary complexes of zinc(II) with bromide, iodide, and thiocyanate ions and 2,2′-bipyridine (bipy) has been studied by calorimetry in dimethylformamide (dmf) at 25 °C. The formation of the ternary complexes [ZnXm(bipy)n](2 –m)+(denoted as [1mn]), such as [111], [112], and [121] for X = Br and I and [111], [112], [121], and [122] for X = SCN is revealed, along with the binary complexes [ZnXn](2–n)+(n= 1–3 for X = Br, n= 2 or 3 for X = I, and n= 1, 3, or 4 for X = SCN) and [Zn(bipy)n]2+(n= 1–3), and their formation constants, reaction enthalpies, and entropies were obtained. The thermodynamic parameters are discussed together with those for the (2,2′-bipyridine)chlorozinc(II) complexes previously determined. A four-co-ordinate structure is suggested for [ZnX2(dmf)2](X = Br or I), [ZnX3(dmf)]–(X = Br, I, or SCN), and [Zn(NCS)4]2–, and thus the six-co-ordinate, octahedral structure of [Zn(dmf)6]2+ changes upon complexation. The complexes [Zn(NCS)(dmf)5]+ and [Zn(bipy)n]2+(n= 1–3) remain octahedral. The extent of formation of the [111] complex is weak in all halide systems. The [121 ] complex is dominant in the chloride system, significant in the bromide, but very weak in the iodide system, and the reaction enthalpies and entropies suggest that an octahedral–tetrahedral equilibrium, [ZnX2(bipy)(dmf)2](Oh⇌[ZnX2(bipy)](Td)+ 2dmf (X = Cl or Br), is established in solution. On the other hand, the [112] complex, which is not found in the chloride system, becomes dominant in the bromide and especially so in the iodide system. The formation of the [ZnI (bipy)2]+ complex, [Zn(bipy)2]2++ I–→[Znl(bipy)2]+, is accompanied by unusual ΔH⊖ and ΔS⊖ values, implying that a specific interaction operates between iodide ion and 2,2′-bipyridine molecules in the vicinity of the zinc(II) ion.

Thermodynamics of adduct formation of [Ni(dtp)2] (dtp = (C2H5O)2PS2) with some nitrogen-donor bases in benzene

Abstract The adduct formation of [Ni(dtp) 2 ] (dtp = (C 2 H 5 O) 2 PS 2 ) with pyridine (py), 4-cyanopyridine (4-cyp), 2-aminopyridine (2-amp), piperidine (pip) and benzylamine (ba) has been studied by spectrophotometry and calorimetry in benzene at 25 °C. With L = 2-amp, the formation of [Ni(dtp) 2 L] only is concluded. For other bases, the formation of [Ni(dtp) 2 L] and [Ni(dtp) 2L 2 ] is established, and their formation constants, reaction enthalpies and entropies were determined. All the [Ni(dtp) 2 L] complexes exhibit virtually the same electronic spectra arising from the five-coordinate NiNS 4 chromophore. On the other hand, the [Ni(dtp) 2 L 2 ] (L = py, 4-cyp, ba) complexes are octahedral with a triplet Ni II center. However, the [Ni(dtp) 2 (pip) 2 ] complex is not, and its spectrum suggests five-coordination with an NiN 2 S 3 chromophore. Unusual thermodynamic behavior is also observed for the formation of the latter complex.

A thermodynamic study on hydrolytic reactions of divalent metal ions in aquaeous and dioxane-water mixed solvents

We have studied hydrolytic reactions of various divalent metal ions such as beryllium, copper, nickel cadmium and lead in aqueous and dioxane—water mixed solvents containing 3 mol dm−3 LiClO4 as a constant ionic medium at 25 °C [1–4]. It has generally been found that the composition of the hydrolytic species and the formation constant *βpq for the reaction qMz+ + pH2O = Mq(OH)p(qz−p)+ + pH+ were little affected by the solvent composition up to 0.5 mole fraction (ca. 88% w/w) of dioxane in the medium. Free energy changes of transfer, ΔGtpq = −RT[ln{βpq(mix)/βpq(aq)}] fot the reaction: qMz+ + pOH− = Mq(OH)pqz−p+ (βpq = [Mq(OH)pqz−p+]/[M+]q[OH−]p = *βpq/Kpi; Ki denotes the autoprotolysis constant of the solvent) were strongly dependent on the composition and charges of the complexes. However, the values (1/p)ΔGtpq were approximately independent of the complexes examined at a given concentration of dioxane. Since the free energy change of transfer can be expressed as (1/p)ΔGtpq = (/p)(q)Δgpq − ΔgM) − ΔgOH (Δgi stands for the partial molar free energy change of transfer of species i) and the contribution of ΔgOH to (1/p)ΔGtpq is the same in all the cases, the results obtained indicated that the values, (1/q)Δgpq − ΔgM′ depend only on p/q (= z − z′ where z′ represents the formal charge per metal ion of the complex). Enthalpy changes for the hydrolytic reactions of some divalent metal ions and the autoprotolysis reaction of the solvents were determined by use of a fully automatic on-line-controlled system developed in our laboratory [5] and the enthalpy and entropy changes of transfer of the reaction, ΔHtpq and ΔStpq, respectively, were evaluated. The value, (1/p)ΔHtpq = (q/p)((1/p)Δhpq − ΔhM) − ΔhOH, strongly depended on metals, where Δhi denotes the partial molar enthalpy change of transfer of species i. For a given metal ion, (1/p)tpq became more negative (or less positive) with an increase in z′ the value was practically independent of the composition of the complexes. The results obtained indicated that the value of (1/q)Δhpq − Δhm depends on both p/q and ΔhM. For a strongly solvated metal ion (i.e., (1/p)ΔHtpq may be largely negative for such a ion), the ion may have a large ordering effect for the solvent molecules even in the secondary solvation shell of the ion, and thus, (1/p)ΔStpq may become less positive. Therefore, the effect due to (1/p)ΔHtpq on ((1/p)ΔGtpq may be compensated by the effect due to (1/p)ΔStpq and thus the ((1/p)ΔGtpq value becomes practically independent of metal ions.