Tasuku Murakami

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.

Spectroscopic properties and electronic states of five-coordinate copper(II) complexes with linear pentadentate ligands containing two amide groups

Abstract The geometry and electronic states of five-coordinate copper(II) complexes, [Cu(dgepH −2 )] and [Cu(pcepH −2 ), are discussed on the basis of the absorption and ESR (X- and Q-band) spectra in solid and solution states, where dgepH −2 and pcepH −2 represent the divalent anion of 1,8-di(dimethylglycinoyl)-1,4,8-triazaoctane and 1,8-dipicolinoyl-1,4,8-triazaoctane, respectively. These complexes exhibit the spectral features of the intermediate geometries between square pyramidal(SP) and trigonal bipyramidal(TBP). The magnitude of distortion from TBP to SP was estimated by utilizing the vibronic-coupling treatment of the electronic states.

Stabilities and spectral properties of five-coordinate mixed-ligand copper (II) complexes containing N,N,N′,N″,N″-pentamethyldiethylenetriamine and α-amino acids

Abstract Stabilities of the mixed-ligand copper (II) complexes [Cu (pmdt) (Am)] + containing N , N , N ′, N ″, N ″-pentamethyldiethylenetriamine (pmdt) and 10 different α-amino acid anions (Am − ) and their absorption, CD and ESR spectra are reported. The effect of the C- and N-substituent groups of the amino acid ligand on stability is examined. It was found that the stability depression of the N-substituent is large, while that of the C-substituent is quite small without regard to its bulkiness. The d-d absorption and X- and Q-band ESR spectra suggest that the ternary complexes are of the five-coordinate type with a trigonal bipyramid-based geometry, which causes the distinguishable substituent effect.

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.

Novel trigonal-bipyramidal copper(II) complexes containing one discrete amino acid chelate: crystal structures of [Cu(L-val)(pmdt)]ClO4 and [Cu(aiba) (pmdt)]ClO4·H2O(L-val = L-valinate ion, aiba = α-aminoisobutyrate ion, and pmdt = N,N,N′,N″,N″-pentamethyldiethylenetriamine)

Abstract The title mixed-ligand copper(II) complexes were characterized by X-ray crystallography. These complexes take on a trans (Oamino acid, Ncentral of pmdt) form, and their CuN4O core geometries are approximately regular trigonal bipyramidal, which is novel for copper(II) complexes containing a discrete amino acid chelate ring.

Crystal structures and spectral properties of five-coordinate copper(II) complexes with N,N,N′,N″,N″-pentamethyldiethylenetriamine (pmdt) and α-diamines: Approximately regular trigonal bipyramidal [Cu(en)(pmdt)](ClO4)2 and highly distorted [Cu(SS-chxn(pmdt)](ClO4)2 (en 1,2-diaminoethane and SS-chxn (1S,2S)-1,2-diaminocyclohexane)

Abstract The five-coordinate mixed-chelate copper(II) complexes [Cu(en)(pmdt)](ClO4)2 (1), [ Cu (SS- chxn )( pmdt )]( ClO 4 ) 2 ( 2 ), [ Cu (S- bzen )( pmdt )]( ClO 4 ) 2 ( 3 ) and [ Cu (R- pn )( pmdt )] (NO3)2 (4) have been prepared and characterized [where pmdt = N,N,N′,N″,N″-pentamehyldiethylenetriamine, en = 1,2-diaminoethane, SS-chxn = (1S,2S)-1,2-diaminocyclohexane, S-bzen = (S)-1,2-diamino-3-phenylpropane and R-pn = (R)-1,2-diaminopropane]. The geometry and structures of the complexes were studied by visible electronic, CD and ESR spectra and the structures of 1 and 2 were determined by X-ray single crystal analyses. The geometry around the copper(II) ion of 1 is very close to regular trigonal bipyramidal, whereas that of 2 is intermediate between trigonal bipyramidal (TBP) and square pyramidal (SP). The coordinating geometries of pmdt of 1 and 2 are significantly different from those of some pmdt-containing copper(II) complexes already published. The powder (Nujol mull) and solution (acetonitrile) visible spectra of 1 are identical to each other, showing a main band at 12.5–13 × 103 cm−1 with a shoulder around 15.5 × 103 cm−1, which indicates that the near-regular TBP geometry of 1 is retained also in acetonitrile. The powder Q-band ESR of 3, of which visible spectra are the same as those of 1 in both solid and solution states, shows a dz2-grounded TBP-type spectrum with g⊥ = 2.161 and g‖ = 2.013. On the other hand, the powder visible spectrum of 2, a broad band around 15 × 103 cm−1 with a shoulder at 11.5 × 103 cm−1, is significantly different from those of d1, 3 and 4, which may reflect its highly distorted CuN5 geometry. The powder Q-band ESR of 2 also shows a rhombic-type spectrum with three g values of 2.213, 2.093 and 2.032. However, the solution (methanol and acetonitrile) visible and ESR spectra of 2 are identical to those of the other complexes, which suggests a geometrical transformation of the CuN5 chromophore of 2 to near TBP.

Spectroscopic properties of copper(H) complexes with quadridentate derivatives of L-proline amide and L-proline methyl amide

Abstract The copper(II) complexes with epaH 2 , tpaH 2 , epmaH 2 , and tpmaH 2 , potentially quadridentate derivatives of L-proline amide or methyl amide (see text), have been characterized by absorption, circular dichroism (CD), IR, and ESR spectroscopies. All of the spectral features of the complex with dianionic tpa indicated an ordinary planar geometry, whereas those of the tpma complex suggest an unusual ligand field containing a strong apical coordination. The epa and epma complexes appear to take a distorted geometry on the basis of the splitting of dd bands and the rhombic ESR. The ultraviolet absorption and CD bands associated with the coordinating amide group are also discussed.