Taka-aki Takei

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.

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.

Permanent electric dipole moment and polarizability in Stark modulation spectra of the ICl B–X transition

Because the induced dipole moment due to polarizability in a moderate electric field is thought to be small, the Stark effect due to polarizability has generally been ignored for molecules that have a permanent electric dipole moment. However, by observation of the Stark modulation spectra (SMS), we have confirmed that the effects of polarizability and of the permanent dipole moment are sometimes comparable. Based on this observation, we have sought an estimate of the polarizability. It was also found that the effect of the polarizability on the SMS depends mainly on its isotropic part. Thus, for the B–X electric transition of the ICl molecule, the differences in isotropic polarizabilities were estimated to be Δᾱ=3.4–3.8 A3 at the 3–1 transition, and Δᾱ=3.6–4.3 A3 at the 1–0 transition, assuming that the differences of anisotropic polarizability Δαan are within the range 2–9 A3 for both transitions. Thus, obtained values of Δᾱ were confirmed to be in a reasonable range, in spite of a wide range uncertaint...

The direction of electric dipole moment of ICl A 3Π1 state through the analysis of the Stark modulation spectroscopy

Recently, two works were reported that the permanent electric dipole moment of the ICl A state has the same direction as that of the X state, through the analysis of electric and magnetic pendular spectra and through the direct analysis of the hyperfine structures under the Stark effect, respectively. We determined clearly and sensitively the direction of the dipole moment in the A (v=27) state of I35Cl, through the line shape analysis of the Stark modulation spectra (SMS). While the result was the same as those of previous two works, the analysis of the line shape of the SMS was so useful to determine the relative direction of the dipole moment of the upper electronic state to that in the lower state, whichever of the first-order or the second-order Stark effect the state may show.