@misc{oai:ir.soken.ac.jp:00000216,
 author = {丁, 玉琴 and ディン, ユークン and DING, Yuqin},
 month = {2016-02-17, 2016-02-17},
 note = {Focusing on the charge-transfer complex of transition-metal phthalocyanine MPc(M=CO: d7and Ni: d8), the present thesis intended to clarify the electronic structure of the quasi-one-dimensional (1D) π-d phthalocyanine system.  MPc makes a stable 1D conductor when the molecule is oxidized with a counter anion such as AsF6-.  Phthalocyanine conductors take a characteristic molecular arrangement, in which metal (M) chain and ligand (Pc) chain coexist in the same molecular stack.  CoPc molecule contains unpaired d-electrons which is spacially separated from the highest occupied molecular orbital (HOMO).  Due to this nature in CoPc(AsF6)0.5, the itinerant π-electron coexists with unpaired d-electron.  It has not been investigated in the charge-transfer salt if the unpaired d electron occupies the 3d z2 orbital like in neutral CoPc, and whether the unpaired d electron is localized or forms a 1D band.  To elucidate the electronic structure of this possible two-band system, we prepared the charge-transfer salts of NiPc, CoPc, and their mixed crystals, and characterized them by means of elementary analysis, crystal structural analysis, ESR, Raman spectroscopy, reflection spectroscopy, and magnetic susceptibility.
  The elementary analysis indicated that the organic alloys Co x Ni 1-x Pc(AsF6)0.5 were prepared in a wide range of χ.  The boundary of crystal structure with the tetragonal and orthorhombic system is located between x=O.25 and 0.45 in this alloy system, and the parameter c decreases systematically with the increase of the Co concentration χ.  The angular dependence of g value at 3.2 K clearly showed that the doped CoPc was relevantly substituted in the alloy.  Under the 633 nm excitation, we found new Raman bands at 368 cm-1 and 736 cm-1 which appeared only in the mixed crystals.  These new Raman bands were significantly suppressed under the 515 nm excitation.  In the range of χ<0.45, the reflection spectra polarized parallel to the c-axis are similar to that of NiPc(AsF6)0.5, while the characteristic spectrum of CoPc(AsF6)0.5 is observable in the range of 0.87≦χ≦1.  The reflection spectra polarized perpendicular to c-axis in the visible region also show the systematic change.  The series of evidences described above indicate that the mixed crystals are formed on the molecular level in the whole range of χ.
  Based on the analysis of the well-resolved hyperfine structure in the very dilute alloy, the unpaired d-electron in Co was confirmed to occupy the 3dz2 orbital, which is extended perpendicular to the molecular plane.  As the 3dz2 orbital is doubly occupied in NiPc and singly occupied in CoPc, a repulsive force works between the neighboring Ni atoms in NiPc(AsF6)0.5, whereas an attractive force works between the Co atoms in CoPc(AsF6)0.5.  This result explains the systematic change of the c parameters of the mixed crystal.  The appearance of the new Raman bands is interpreted as a resonance effect, because first the second harmonic band appears, second they show a strong excitation dependence, and third they are highly sensitive to the introduction of CoPc.  This finding indicates that a new excited state is formed in the mixed crystals.  As these new peaks at 368 cm-1 and 736 cm-1 appear only in the (c, c) polarization, the optical transition to this new excited state is polarized along the c-axis.  Therefore the excited state is associated with the infer-molecular charge-transfer state between the 3d orbitals of neighboring CoPc and NiPc.  The Co concentration dependence of the Raman intensity of the new peaks presents an asymmetric tendency with respect to the concentration of Co, and is qualitatively reproduced by the function of χ(1-χ)2.  This implies that the band at 368 cm-1 is assigned to the a1g  mode of NiPc.  According to the molecular orbital calculation, the energy difference between 3dz2 and 3dx2-y2 orbitals is about 2 eV, which is close to the excitation energy of the new optical transition.  Therefore, the new optical transition is assigned to the inter-molecular charge-transfer transition from the 3dz2 orbital of Co to the 3dx2-y2 orbital of Ni.  This means that the introduction of the electron into the 3dx2-y2 orbital induces the geometrical change to the inner macrocycle.
  The reflection spectra in the infrared region provides the information on the bandwidth and anisotropy of a conduction band.  Comparing with the spectrum of NiPc(AsF6)0.5, the reflectivity of CoPc(AsF6)0.5, in the mid-infrared region shows an additional optical transition.  Therefore, we analyzed the reflection and conductivity spectra using Drude and Lorentz models.  The total plasma frequency of the CoPc(AsF6)0.5 is much larger than that of NiPc(AsF6)0.5, which strongly suggests that the 3d orbital also contributes to the optical transition of CoPc(AsF6)0.5 in the mid-infrared region.  The Drude and Lorentz terms are associated with the 3/4-filled π-band and 1/2-filled d-band.  Assuming the 1D tight-binding model for the π-band and 1D Hubbard band model for the d-band, the bandwidth of CoPc(AsF6)0.5 was estimated as 1.8～2.1 eV for the d-band and 0.5～0.6 eV for the d-band.  The low excitation energy of the mid-infrared transition suggests that the 3d-band is located near the Fermi level of the 3/4-filled π-band.
  In a dilute alloy (χ<1), the magnetic moment of Co2+ ion is localized.  The purpose of the ESR properties of dilute Co x Ni 1-x Pc(AsF6)0.5 is to obtain the magnitude of the exchange interaction between the local moment of Co2+ ions and itinerant spins of Pc-ligand.  Using a molecular field approximation, we analyzed the temperature dependence of the g value and linewidth in the high temperature regime, in which the hyperfine signal was replaced by a single Lorentzian line.  The broad single line comes from the coupling between the d- and π-spins through the exchange interaction.  Based on the numerical simulation of the g value and line shape of the ESR signals of Co0.01Ni0.99Pc(AsF6)05, the exchange interaction between d- and π-spins and the density states at Fermi level were obtained as |Jπd|=0.O13±0.002 eV and DF=3.8±0.2 eV-1, respectively.  Using these parameters, the Kondo and RKKY temperatures were estimated as 2x1O-5 K and 7 K.  This result is consistent with the magnetic susceptibility of the alloy system which conforms to the Curie-Weiss law down to 2 K.  This result suggests a small hybridization between the Co 3d z2 orbital and Pc HOMO of the neighbor molecule as well as the small exchange energy between Co 3dz2 and HOMO within the same molecule.  The magnetic susceptibility of Co x Ni 1-x Pc(AsF6)0.5 consists of Curie-Weiss term and nearly temperature independent term.  The Curie constant first increases up to χ=O.1, then decreases in high Co concentration region.  The enhancement of the Co concentration increases the CoPc pair, and then the direct antiferromagnetic interaction between the pairs suppresses the Curie constants.  This feature is consistent with the formation of the half-filled 10 band.
  In conclusion, the formation of the 3dz2 band was verified by the optical spectrum and the magnetic properties of Co x Ni 1-x Pc(AsF6)0.5.  Both results are consistent with each other., application/pdf, 総研大甲第548号},
 title = {Study of Quasi One-Dimensional Organic Alloy Cox Ni1-x Pc(AsF6)0.5},
 year = {}
}