Honoh Suzuki

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.

Sterically controlled complexation of manganese(II) and cobalt(II) with chloride ions in N,N-dimethylacetamide

The formation of chloro complexes of manganese(II) and cobalt(II) has been studied in N,N-dimethylacetamide (DMA) by calorimetry and spectrophotometry. Formation constants, enthalpies and entropies of four mononuclear complexes [MIICln](2–n)+(n= 1–4) have been determined for M = Mn and Co at 298 K and for M = Mn at 318 K. In spite of the similar solvent properties of DMA and N,N-dimethylformamide (DMF), overall formation of [MCl4]2– is strongly favoured and less endothermic in DMA than in DMF. Electronic spectra of the CoII complexes obtained at 278, 298 and 318 K indicate an octahedral geometry for [Co(DMA)6]2+ and tetrahedral geometries for [CoCl(DMA)3]+, [CoCl2(DMA)2], [CoCl3(DMA)]– and [CoCl4]2– at each temperature, though an additional solvation equilibrium is observed for the monochloro complex: [CoCl(DMA)5]+⇌[CoCl(DMA)3]++ 2DMA. The relatively large values of ΔH°1 and ΔS°1 suggest that extensive desolvation occurs on formation of the monochloro complex. Thus, the coordination geometry primarily alters at an earlier step (n= 1) in DMA than in DMA (n= 2). For the MnII system, large ΔH°n and ΔS°n values (n= 1, 2) are also diagnostic of an earlier transition from octahedral to tetrahedral geometry in DMA. The results show that the stability and structure of the complexes are strongly controlled by sterically hindered solvation of DMA molecules towards the metal ion, leading to the more favourable, less endothermic complexation and the tendency to form a less-crowded solvation structure. The steric effect of DMA is more pronounced in the order MnII < CoII < NiII.

Photosensitization of nonlinear scattering and photoacoustic emission from single-walled carbon nanotubes

Enhancement of laser-induced nonlinear scattering has been observed from an aqueous suspension of single-walled carbon nanotubes (SWCNTs) doped with near-infrared dye chromophores. The underlying mechanism involves cavitation triggered by optical heating and bubble pulsation, which are further enhanced by the dye adsorbed on SWCNT surfaces, resulting in the scattering enhancement and a modification of the accompanying photoacoustic waveform. These photosensitizing effects suggest potential feasibility of dye-doped nanotubes as optically switchable nanoemitters of ultrasound for biomedical applications such as ultrasonic therapy and imaging.

Complex of cobalt(II) bromide with hexa­methyl­phospho­ric tri­amide

The title compound, dibromobis[tris(dimethylamino)phosphine oxide]cobalt(II), [CoBr2(C6H18N3OP)2], displays tetrahedral coordination about cobalt. The molecule has twofold crystallographic site symmetry. The short P-N bonds and the planarity of the dimethylamino groups indicate the importance of dpi-ppi interactions. One of the NMe2 groups has an irregular conformation about the P-N bond and deviates from planarity. It is ascribed to the steric hindrance induced by coordination at the O atom of hexamethylphosphoric triamide.

Steric solvent effect on small and large cations: calorimetric study of halogeno and thiocyanato complexes of beryllium(II) and cadmium(II) in N,N-dimethylacetamide

Solution equilibria of beryllium(II) and cadmium(II) complexes with halide and thiocyanate ions are studied in N,N-dimethylacetamide (DMA) by calorimetry. Mononuclear BeII complexes, [BeX]+ and [BeX2](X = Cl, SCN), and CdII complexes, [CdX]+, [CdX2], [CdX3]– and [CdX4]2–(X = Cl, Br, I, SCN), are found, and their formation constants, enthalpies and entropies are determined. The BeII systems are also studied in N,N-dimethylformamide (DMF). Each of the BeII complexes has very similar thermodynamic quantities in DMA and in DMF, in sharp contrast to first-row transition metal(II) complexes where a marked solvent effect has been observed. In spite of the very small size of the cation, steric hindrance of DMA is absent in the four-coordinate solvation structure of Be2+. ΔH°n and ΔS°n for the CdII complexes in DMA are largely different from those in DMF, which shows the steric solvent effect of DMA, i.e. steric hindrance does exist in the six-coordinate structure of this fairly large cation. When combined, these results offer clear evidence for the octahedral-specific nature of the steric hindrance in metal–DMA interactions.

Solvation and complexation of copper (II) and chloride ions in 2,2,2-trifluoroethanol–dimethyl sulphoxide mixtures

The formation of copper(II) chloro-complexes has been studied by calorimetry and spectrophotometry in various 2,2,2-trifluoroethanol (TFE)–dimethyl sulphoxide (DMSO) mixtures at 25 °C. It was shown that as the mole fraction of TFE, x, in the mixtures increased, the formation constant of [CuCl]+ gradually decreased to x= 0.8. The result is contrary to that obtained for acetonitrile (AN)–DMSO mixtures. This is ascribed to the decreased entropy of formation of [CuCl]+ in TFE–DMSO mixtures in contrast to the increased entropy in AN–DMSO mixtures with decreasing DMSO content. The corresponding enthalpy of formation of [CuCl]+ remains practically unchanged over the wide range of solvent composition in TFE–DMSO mixtures, as well as in AN–DMSO mixtures. The different variation trend in the entropy of formation of [CuCl]+ in TFE–DMSO and AN–DMSO mixtures may be explained in terms of the different intermolecular interactions between solvent molecules in the bulk.

Localization of laser-induced breakdown in aggregates of silver nanoshells

Abstract Nanoshells are useful in near-infrared (NIR) applications because of the red shift of the Mie resonance into NIR. Silica/gold/silver nanoshells were prepared via gold anchoring and characterized by Mie-theoretical calculations and transmission electron microscopy, which indicated a broad and enhanced NIR absorption and a partially coated, mottled Ag/Au structure on the silica core. The mottled nanoshells were found to spontaneously aggregate in solution to form irregular islands. Their surface roughness was examined by the fractal dimension analysis. When the aggregates were irradiated with 1064-nm laser pulses, highly localized emission due to laser-induced breakdown was observed, which is attributed to the non-uniform metal distribution over the aggregate surface and the localization of the optical field induced by the disordered arrangement of the nanoshells in the aggregate.

Solution equilibria of gallium(III) and indium(III) complexes with halide and thiocyanate ions in N,N-dimethylformamide

Complexation of gallium(III) and indium(III) with halide and thiocyanate ions has been studied by calorimetry in N,N-dimethylformamide (dmf). Four mononuclear halogeno complexes [InX(dmf)5]2+, [InX2(dmf)4]+, [InX3(dmf)3] and [InX4]–(X = Cl, Br, I) are found for lnIII, whereas only two complexes are found for GaIII: [GaX(dmf)5]2+ and [GaX4]–(X = Cl, Br). The absence of GaIII di- and tri-halogeno complexes in solution has been confirmed by 71Ga NMR spectroscopy. The pronounced dominance of [GaX4]– is interpreted by the tendency of GaIII to form a tetrahedron and the steric hindrance of solvent molecules. Both metal ions behave as a hard cation toward halide ligands, i.e. the chloro complexes are the most stable. The indium(III) complexes are by far more stable than the gallium(III) ones. Mixed halogeno complexes were also studied, and three complexes for the Ga—Cl—Br system and six complexes for the In—Cl—Br system were found. Their thermodynamics shows regularity reflecting the primarily ionic character of the metal–halogen coordination. Four mononuclear isothiocyanato complexes are found for AlIII, GaIII and InIII, together with [In(NCS)5]2–.

Synthesis and Structures of Vanadium(III) and -(IV) Complexes with a Tripodal Quadridentate Ligand Containing Alcoholic and Pyridyl or Imidazolyl Functionality

Complexes of vanadium(III) and vanadium(IV) were synthesized with the tripodal quadridentate ligands, N,N- bis(2-pyridylmethyl)-2-aminoethanol (Hbpmae) and N,N-bis(2-imidazolylmethyl)-2-aminoethanol (Hbimae). The chemi- cal structures and geometries were determined by X-ray crystallography or spectral measurements. Vanadium(III) formed structurally similar, oxo-bridged, dinuclear complexes with both ligands and exhibited intense absorption bands in the visible region. Upon exposure to air, the vanadium(III) complexes oxidized spontaneously, yielding the respective vana- dium(IV) complexes. The geometry of the vanadium(IV)-Hbpmae complex was very similar to that of the monomeric unit in the corresponding vanadium(III) dimer. The alkoxo group in all four complexes coordinated to a metal center in a pro- tonated form. The geometrical arrangements of the vanadium(IV)-Hbpmae and -Hbimae complexes were different with each other. The intense absorption bands in the visible region of the oxo-bridged dinuclear vanadium(III) complexes were assigned based on molecular orbital calculation.

trans-Bis(1,4-butane­di­amine)­di­chloro­cobalt(III) chloride monohydrate

The title compound, [CoCl2(C4H12N2)2]Cl·H2O, (I), has an octahedral coordination geometry. The conformations of the seven-membered chelate rings are disordered between the twist-chair and twist-boat forms. The space group of (I) is Cc, although the structure has a pseudo-center of symmetry.