Kazuhiko Ozutsumi

Strong and weak solvation steric effects on lanthanoid(III) ions in N,N-dimethylformamide–N,N-dimethylacetamide mixtures

Structural parameters of solvated neodymium(III), gadolinium(III), thulium(III) and ytterbium(III) ions in N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA) and their mixtures have been obtained by an extended X-ray absorption fine structure (EXAFS) method. It revealed that the metal–oxygen bond length is shortened and the coordination number is thus decreased with increasing DMA content in the mixture. Interestingly, the decrease in the coordination number takes place evidently at a lower DMA content for the thulium(III) ion than the neodymium(III) ion, i.e., the geometry change is more favorable for the metal ion with a smaller ionic radius. 89Y NMR chemical shifts also demonstrate that the coordination number decreases with increasing DMA content in the mixture, and the profile of varying coordination number is similar to that for the thulium(III) ion. This indicates that the strong solvation steric effect operates with both thulium(III) and yttrium(III) ions in the DMF–DMA mixture. Variations of metal–oxygen bond length for other metal systems in the mixture indicate that, relative to the thulium(III) ion, the gadolinium(III) ion experiences a less strong solvation steric effect, and the neodymium(III) ion even less. Structural parameters have also been determined for a series of lanthanoid(III) ions in both DMF and DMA. The LnIII–O bond length in DMA is generally shorter than that in DMF, and the difference is smallest for the lanthanum(III) ion, and largest for the lutetium(III) ion. The difference is thus larger for a metal ion with a smaller ionic radius, implying that the solvation steric hindrance is enhanced with decreasing ionic radius.

Structure of copper(II)-bpy and -phen complexes : EXAFS and spectrophotometric studies on the structure of copper(II) complexes with 2,2'-bipyridine and 1,10-phenanthroline in aqueous solution

Abstract The structure of copper(II) complexes with 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) in aqueous solution has been studied by EXAFS and spectrophotometric methods. The EXAFS data and electronic spectra for solutions containing [Cu(bpy)]2+, [Cu(bpy)2]2+ and [Cu(bpy)3]2+ complexes as the main species, respectively, showed that the mono(2,2′-bipyridine)copper(II) complex has an axially elongated octahedral structure with four additional water molecules and the tris(2,2′-bipyridine)copper(II) complex also has a distorted octahedral structure. On the other hand, the bis(2,2′-bipyridine)copper(II) complex has a five-coordinate trigonal bipyramidal structure with an additional water molecule. It was also shown that the structure of the mono- and tris(1,10-phenanthroline)copper(II) complexes is axially elongated octahedral similar to the relevant 2,2′-bipyridine complexes. The structure of the bis(1,10-phenanthroline)copper(II) complex was not determinable by the present transmission mode EXAFS experiment because of its very low solubility in water.

Exafs and spectrophotometric studies on the structure of pyridine complexes with copper(II) and copper(I) ions in aqueous solution

Abstract The structure of pyridine (py) complexes with copper(II) and copper(I) ions in aqueous solution has been studied by the EXAFS (extended X-ray absorption fine structure) method. The results of the EXAFS analyses of copper(II) solutions containing the [Cu(py)]2+, [Cu(py)2]2+, [Cu(py)3]2+ and [Cu(py)4]2+ complexes as the main species, respectively, revealed that all copper(II) pyridine complexes have an axially-elongated octahedral structure with additional water molecules. The equatorial Cu—O and Cu—N bond distances within the complexes are found to be slightly lengthened on increasing the number of pyridine molecules bound to the copper(II) ion and the axial Cu—O bond length is lengthened in [Cu(py)4]2+. It was also shown that the tris(pyridine)copper(I) complex is formed in a copper(I) solution containing a large excess of pyridine. No water molecules coordinate to the copper(I) ion and thus the complex has a three-coordinate triangular structure.

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.

A fluorescent EXAFS study on the structure of the solvated cobalt(II) ion and chlorocobalt(II) complexes in hexamethylphosphoric triamide

Abstract The coordination structure of the cobalt(II) ion and its chloro complexes of low concentration (∼20 mmol dm −3 ) in hexamethylphosphoric triamide (HMPA) has been explored by laboratory EXAFS (extended X-ray absorption fine structure) modified for fluorescence detection. The cobalt(II) ion is four-coordinated in HMPA, unlike other oxygen-donor solvents such as water and N,N -dimethylformamide (DMF). The CoO (HMPA) bond lengths within complexes are revealed to be 194(1), 195(1), 194(1) and 202(2) pm for [Co(hmpa) 4 ] 2+ , [CoCl(hmpa) 3 ] + , [CoCl 2 (hmpa) 2 ] and [CoCl 3 (hmpa)] − , respectively. The CoO bond length is significantly shorter than that within six-coordinate [Co(H 2 O) 6 ] 2+ (208 pm) or [Co(dmf) 6 ] 2+ (206 pm), and remains practically unchanged upon formation of mono- and dichloro complexes. On the other hand, the CoCl bond length is 224(1), 227(1) and 229(1) pm within [CoCl(hmpa) 3 ] + , [CoCl 2 (hmpa) 2 ] and [CoCl 3 (hmpa)] − , respectively, all of which are appreciably shorter than that within the six-coordinate [CoCl(H 2 O) 5 ] + (235 pm). The origin of the different thermodynamic behavior of chloro complexation of cobalt(II) in HMPA from that in DMF will be discussed on the basis of these structural data.

Thermodynamics of Solvation of 18-Crown-6 and Its Alkali-Metal Complexes in Various Solvents

Heats of solution of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) in acetonitrile, 1,2-dichloroethane, N,N-dimethylformamide, dimethyl sulfoxide, nitromethane, propylene carbonate, pyridine and water were measured at 25 °C and the enthalpies of the transfer of 18-crown-6 from waterto the aprotic solvents were derived. The thermodynamic quantities, Δ G1°, Δ H1° and TΔ S1°, for the formation of the[M(18-crown-6)]+ (M+ = Na+, K+, Rb+, Cs+, NH4+) complexeswere determined by titration calorimetry in dimethyl sulfoxide containing0.1 mol dm-3 (C2H5)4NClO4 as a constant ionic medium at 25 °C. These thermodynamic quantities suggest that the complexationof 18-crown-6 with the alkali-metal ions mainly reflects the different solvationof 18-crown-6 and also the different degree of solvent structure.

Calorimetric and spectrophotometric studies of complexation of manganese(II), cobalt(II) and nickel(II) with bromide ions in N,N-dimethylformamide

The complexation of manganese(II), cobalt(II) and nickel(II) with bromide ions has been calorimetrically and spectrophotometrically studied in N,N-dimethylformamide (DMF) containing 0.16 mol dm–3(C2H5)4NClO4 as a constant ionic medium at 25 °C. The data obtained are well explained in terms of the formation of [MnBr]+ and [MnBr3]– for MnII, [CoBr]+, [CoBr3]– and [CoBr4]2– for CoII and [NiBr]+ for NiII, and their formation constants, enthalpies and entropies have been determined. The formation of [MBr2] is practically negligible in all the metal systems examined. Electronic spectra of individual complexes have also been extracted for CoII and NiII. The coordination geometry surrounding manganese(II) and cobalt(II) ions changes upon complexation, and the change is strongly correlated to the reaction enthalpies and entropies. The coordination geometry thus postulated is octahedral for [MnBr(DMF)5]+, [CoBr(DMF)5]+ and [NiBr(DMF)5]+, and tetrahedral for [MnBr3(DMF)]–, [CoBr3(DMF)]– and [CoBr4]2–.

The structure of liquid formamide studied by means of X-ray diffraction and NMR at high temperatures and high pressures

Abstract The structure of liquid formamide has been investigated by means of X-ray diffraction and NMR at high temperatures and high pressures (HTHP). The temperatures were fixed at 298 K and 373 K, and the pressures employed were 0.1, 20, and 40 MPa for the X-ray diffraction studies, while the NMR measurements were carried out over the temperature range from 300 K to 395 K at 0.1 MPa and over the pressure range from 0.1 to 200 MPa at 298 K. Formamide has a network structure consisting of a mixed ring and head-and-tail-type linear structures through N-H⋯O hydrogen bonds at 298 K and 0.1 MPa, and the ring structure, which has weaker hydrogen bonds than the linear structure, is broken with increasing temperature to change to the linear-type structure. On the other hand, the linear structure changes to the ring structure, having a more compact molecular arrangement than the linear one, with the increase in pressure.

Thermodynamics of complexation of sodium, potassium, rubidium, caesium and ammonium ions with 18-crown-6 in acetonitrile and propylene carbonate

The complexation of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) with sodium, potassium, rubidium, caesium and ammonium ions has been studied by titration calorimetry in acetonitrile (MeCN) and propylene carbonate (PC) containing 0.05 mol dm–3(C2H5)4NClO4 as a constant ionic medium at 25 °C. The formation of [M(18-crown-6)]+(M = Na+, K+, Rb+, Cs+, NH4+) ions was revealed, and their formation constants, reaction enthalpies and entropies were determined. Consistent with the similar donor and acceptor properties of MeCN and PC, the stability of the 18-crown-6–cation complexes is similar in the two solvents. However, the enthalpic and entropic behaviour are very different. The formation enthalpy of the sodium complex is positive in MeCN, while negative in PC. The reactions for the potassium, rubidium, caesium and ammonium ions are less exothermic in MeCN than in PC. On the other hand, the formation of the sodium complex in MeCN is accompanied by a more positive entropy change than that in PC. The reaction entropies for the potassium, rubidium, caesium and ammonium systems are positive in MeCN, whereas they are negative in PC. Thus, enthalpy–entropy compensation results in a similar stability of [M(18-crown-6)]+(M = Na+, K+, Rb+, Cs+, NH4+) in MeCN and PC.

STRUCTURAL STUDIES ON PREFERENTIAL SOLVATION OF SILVER(I) ION BY ACETONITRILE OVER N, N-DIMETHYLFORMAMIDE IN THEIR MIXTURES

Abstract The solvation structure of the silver(1) ion in neat N,N -dimethylformamide (DMF), neat acetonitrile (AN) and their mixtures has been determined by the X-ray diffraction method at 25 °C. In neat DMF and AN, the silver(1) ion forms the tetrahedral [Ag(dmf) 4 ]+ and [Ag(an) 4 ]+ complexes with the AgO and AgN bond lengths of 233(1) and 226(1) pm, respectively. The tetrahedral [Ag(dmf) 2 (an) 2 ]+ complex is the predominant species in 3:1 and 2:1 DMF:AN molar mixtures.In the 1:2 DMF-AN mixture, the tetrahedral [Ag(dmf)(an) 3 ]+ complex is formed as the main species. The silver(1) ions are present as an equilibrium mixture of [Ag(dmf) 2 (an) 2 ]+ and [Ag(dmf)(an) 3 ]+ (ca. 1:1) in the 1:1 DMF-AN mixture.Thus, a preferential solvation of the silver(1) ion by AN occurs in DMF-AN mixtures, as expected from their solvation energies in each solvent. The AgO bond length in the [Ag(dmf) 2 (an) 2 ]+ and [Ag(dmf)(an)3]+ complexes is 237(3) and 241(3) pm, respectively, and increases with the number of AN molecules within the complexes. On the other hand, the AgN bond length remains practically unchanged by the coordination of DMF molecules; 224(2) pm in [Ag(dmf) 2 (an) 2 ]+ and 324(1) pm in [Ag(dmf)(an) 3 ]+.