Yasuhiko Yukawa

A Molecular Pair of [GdNi3] Tetrahedra Bridged by Water Molecules

The authors thank the Generalitat de Catalunya for the prize ICREA Academia 2008 (G.A.) and Grant 2009SGR-1459 (E.C. and E.R.) and Spanish MCI through CTQ2009–06959 (G.A., L.B.), MAT2009-13977- C03 (M.E.), and CTQ2008–06670-C02–01 (E.C., ER). The advanced light source (S.J.T.) is supported by the U.S. Department of Energy (DE-AC02–05CH11231).

Structure-dependent spectral behavior of five-coordinate ternary copper(II) complexes containing 2,2′-dipicolylamine. X-ray crystal structures of [Cu(dpa)(pic)]ClO4, and [Cu(dpa)(pic)]PF6·H2O (dpa=2,2′dipicolylamine, pic=picolinate)

Abstract The X-ray crystal structures and the electronic absorption spectra of the two complexes in the title, [Cu(dpa)(pic)]ClO4 (1) and [Cu(dpa)(pic)]PF6·H2O (2) are described. Complex 1 crystallizes in the triclinic space group P 1 , with a=8.592(2), b=17.18(3), c=8.028(2) A, α=102.48(5), β=110.24(2), γ=89.43(5)°, and Z=2. Refinement gave final R and Rw values of 0.072 and 0.108, respectively, for 3147 observed reflections. Complex 2 crystallizes in the orthorhombic space group Pbca, with a=21.949(3), b=14.97(2), c=12.964(6) A, and z=8. Refinement gave final R and Rw values of 0.050 and 0.070, respectively, for 3220 observed reflections. In both complexes, the central copper atom is essentially five-coordinated with a weakly coordinated perchlorate anion or water molecule at the sixth axial position. The terdentate ligand dpa (2,2′-dipicolylamine) coordinates meridionally in the equatorial plane and the bidentate pic (picolinate anion) forms an axial chelate with an apical coordination through its carboxylate group. Intermolecular stackings are observed between the pyridine rings of adjacent complex molecules. The electronic absorption spectra of complexes 1 and 2 varied to a large extent in organic solvents with different coordinating abilities, that is, a solvatochromism was observed for these complexes. Whereas, for a similar five-coordinate complex [Cu(dpa)( l -phe)]ClO4, which has a facially coordinated dpa with an apical coordination of its pyridyl group, such a chromism was not observed. This spectral behavior will be discussed in relation to their complex geometries.

Synthesis, structure, and preliminary magnetic studies of unprecedented hexacopper(II) barrel clusters with spin ground state S= 3

The structure of a discrete hexacopper(II) barrel cluster and that of a coordination polymer formed by a related hexanuclear repeating unit have been determined. The CuII metals of the hexanuclear units are held together by eight chelating L-prolinato type ligands, which in turn provide the eight oxygen donors trapping a sodium ion in the center. The structure of the [Cu6Na] unit in the discrete system and in the infinite cluster-chain are essentially the same and both display intra-unit ferromagnetic superexchange. A preliminary magnetic study shows that, for both compounds, the copper centers within the [Cu6] unit are ferromagnetically coupled, yielding an S = 3 spin ground state.

Study on the boundary structures in a series of lanthanide hexacyanoferrate(III) n-hydrates

The properties of a series of lanthanide hexacyanoferrate(III) n-hydrates were studied by means of thermal analysis, IR spectroscopy, Raman spectroscopy and X-ray crystallography. Thermal analyses showed that there were two kinds of complexes in this series, Ln[Fe(CN)6]·5H2O (Ln=La–Nd) and Ln′[Fe(CN)6]·4H2O (Ln′=Sm–Lu). The boundary complex between them was Nd[Fe(CN)6]·5H2O. The IR spectra of the two kinds of complexes were obviously different. For the pentahydrates, there were two sharp CN stretching bands at 2050 and 2140 cm−1, and one band at 1600 cm−1 assigned to the HOH bending. On the other hand, for the tetrahydrates besides the two CN stretching bands at 2050 and 2140 cm−1, a new band was observed at 1940 cm−1, and the HOH bending band split into three bands around 1600 cm−1. From the X-ray crystal analysis, the structure of the boundary complex Nd[Fe(CN)6]·5H2O was determined. It belonged to hexagonal, P63/m, with a=7.467(2) A, c=13.793(3) A and Z=2 (R=0.082, Rw=0.126). Neodymium was nine-coordinated in the form of the NdN6(H2O)3 group. The three coordinated water molecules of the 5H2O complex with Nd have a large value for the equivalent isotropic thermal parameter. One of the three water molecules was dissociated easily and the 5H2O complex changed into the stable 4H2O complex with Nd. The crystal of the 4H2O complex is orthorhombic, and belongs to the space group Cmcm as well as the other Ln[Fe(CN)6]·4H2O (Ln=Sm–Lu). Therefore, the structure of Nd[Fe(CN)6]·5H2O is regarded as the boundary structure.

A cyclic tetranuclear Ni2Gd2 complex bridged by amino acidato ligands, with an S = 9 ground state, derived from ferromagnetic spin-coupling between nickel(II) and gadolinium(III) ions

Synthesis and structure of a cyclic tetranuclear Ni(2)Gd(2) complex bridged by amino acidato ligands, with an S = 9 spin ground state, derived from ferromagnetic spin-coupling between S(Gd) = 7/2 and S(Ni) = 1 are reported.

Stabilities of five-coordinate ternary copper(II) complexes containing 2,2′-dipicolylamine and α-amino acids and X-ray crystal structure of [Cu(dpa)(l-phe)]ClO4 (dpa=2,2′-dipicolylamine, l-phe=l-phenylalaninate)

Abstract Stabilities of the five-coordinate ternary copper(II) complexes [Cu(dpa)(am)]+ containing 2,2′-dipicolylamine (dpa) and 11 different α-amino acid anions (am) have been studied by potentiometric and spectrophotometric titrations. The effect of the side chains of the amino acid ligand on stability is examined. The ternary complexes containing aromatic amino acids are significantly more stable than the complexes containing alkyl- and hydroxyalkyl-substituted amino acids, indicating the presence of a hydrophobic intramolecular interaction between the hydrophobic moiety of dpa and the aromatic side chains. The X-ray crystal structure of [Cu(dpa)( l -phe)]ClO4, where l -phe is l -phenylalaninate, is also described. The copper ion takes on a slightly distorted square pyramidal geometry with facially-coordinated dpa. There is no intramolecular ring-stacking between the pyridine ring of dpa and the phenyl ring of l -phe, whereas intermolecular stacking is observed between the pyridine rings of adjacent complex molecules.

Synthesis, structure, DNA-binding, and nuclease activity of a 3d–4f mixed metal nitrosyl complex, [Pr(phen)2(MeOH)(H2O)2][Fe(CN)5(NO)] · (Phen)(DMF)(MeOH)(H2O)

A cyano-bridged heterometallic lanthanide-transition metal nitrosyl complex, [Pr(phen)2(MeOH)(H2O)2][Fe(CN)5(NO)] · (Phen)(DMF)(MeOH)(H2O) (Phen = 1,10-phenanthroline and DMF = dimethylformamide), has been synthesized from reaction of PrCl3 · 6H2O with 1,10-phenanthroline in methanol and sodium nitroprusside followed by crystallization from DMF. The crystal structure shows that the complex is a 1-D chain, stabilized by coordination, hydrogen-bonding, and π–π stacking interactions. The complex shows nuclease activity with pUC19 supercoiled DNA in DMF/Tris-HCl buffer in the presence of H2O2.

Studies on the interaction between lanthanide ions and ligands in solid complexes of lanthanide hexacyanometalates. Part I. The thermal dehydration of lanthanide hexacyanocobaltate(III) hydrates, Ln[Co(CN)6]·nH2O (Ln La to Lu; n = 4,5), and yttrium hexacyanocobaltate(III) tetrahydrate

Abstract In the present paper, series complexes of lanthanide hexacyanocobaltates(III), Ln[Co(Cn) 6 ]· n H 2 O, were prepared in the hope of gaining some insight into the relation of the crystal structure and thermal dehydrations of these complexes. The thermal dehydration of the complex was followed by means of TG-DTA, DSC and X-ray powder diffraction analysis. The dehydration mode was discussed by a proper combination of two factors which were contrary to each other, i.e. (1) increasing of the effective charge of Ln 3+ with decreasing of the ionic radius of Ln 3+ , which enhances the interaction of Ln 3+ OH 2 bonds, and (2) decreasing of the ionic radius leading to a narrowing of the coordination sphere and then a mutual repulsion between the ligands, contributing to the instability of Ln 3+ OH 2 bonds. The experimental results suggested a possibility of the occurrence of a metastable phase of tetrahydrate complexes, formed immediately after the dehydration of one water molecule of their pentahydrate complexes.

The comparison of crystal structures of lanthanide complexes with 3,12-bis(carboxymethyl)-6,9-dioxa-3,12-diazatetradecanedioic acid (H4egta)

Abstract Nine lanthanide complexes with 3,12-bis(carboxymethyl)-6,9-dioxa-3,12-diazatetradecanedioic acid (H 4 egta): [M′(H 2 O) n ][M(egta)(H 2 O)] 2 · n H 2 O (M′: Ca, Sr; M: La, Ce, Pr, Dy, Ho, Er) have been prepared and characterized by using their infrared absorption and Raman spectra, magnetic susceptibility and thermal analyses. The results of Raman spectra (600–200 cm −1 ) suggest that these complexes are of two types: the first includes La, Ce, and Pr complexes, and the second Dy, Ho and Er complexes. The crystal and molecular structures of [Ca(H 2 O) 2 ][La(egta)(H 2 O)] 2 ·8H 2 O ( 1 ), [Ca(H 2 O) 2 ][Ce(egta)(H 2 O)] 2 ·6H 2 O ( 2 ), [Sr(H 2 O) 3 ][Dy(egta)(H 2 O)] 2 ·7H 2 O ( 3 ), and [Sr(H 2 O) 3 ][Ho(egta)(H 2 O)] 2 ·7H 2 O ( 4 ) have been determined by a single-crystal X-ray diffraction method. The crystals of complexes ( 1 ) and ( 2 ) are iso-morphous to each other: monoclinic, space group P 2 1 / c , Z =2. The central lanthanide metal atom is 10-coordinated, in a distorted bicapped square antiprism geometry, to two nitrogen and six oxygen atoms of egta 4− , a water molecule, and a carboxyl oxygen atom from an adjacent complex ion. The Ca 2+ is at the center of the octahedral geometry and ligated by four carboxyl oxygen atoms and two water molecules. Complexes ( 3 ) and ( 4 ) are iso-morphous to each other: monoclinic, space group P 2 1 / n , Z =4. The central lanthanide metal atom is nine-coordinated, in a distorted tricapped trigonal prism geometry, to two nitrogen and six oxygen atoms of egta 4− , and to a water molecule which bridges to the Sr 2+ ion. Two carboxyl groups of [M(egta)(H 2 O)] − (M: Dy, Ho) complex ion bridge to the single Sr 2+ ion. In addition, the Sr 2+ is coordinated by three non-bridged water molecules, and then the Sr 2+ is coordinated by nine atoms. A relationship has been found between the average M–N, M–O(ether) and M–O(carboxylate) bond lengths and Shannons metal crystal radii for a series of complexes shown as [M′(H 2 O) n ][M(egta)(H 2 O)] 2 · n H 2 O (M′: Ca, Sr; M: La, Ce, Nd, Dy, Ho, Er).

An Fe(III) wheel with a zwitterionic ligand: the structure and magnetic properties of [Fe(OMe)2(proline)]12[ClO4]12

The structure and magnetic properties of a dodecanuclear iron(III) wheel are reported, featuring a bridging zwitterionic ligand.