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As one of the strategies to obtain ionic C60 charge transfer complexes, a doping of alkali metals to neutral CT complexes has been attempted under a mild condition. Superconductivity has been detected by magnetic measurements in OMTTF·C60·benzene doped with potassium or rubidium, where OMTTF is octamethylene-tetrathiafulvalene.

The electron-accepting ability of a C 60 molecule in solution was evaluated by the measurements of the charge transfer (CT) absorption energy and the redox potential. It was concluded that C 60 is a weak electron acceptor comparable to 2,5-dibromo- p -xyloquinone, s -tetracyanobenzene or 2,3-dichloro-1,4-naphthoquinone. The adibatic electron affinity of a C 60 molecule was estimated as (2.10–2.21)±0.1 eV. Several black solid CT complexes of C 60 were prepared with mainly TTF derivatives and the ionicity of the ground state was examined by their CT band energies and vibrational spectra. These CT complexes were found to be neutral. A crystal structure of the OMTTF complex from benzene was determined.

The GL coherence lengths were evaluated to be 21±1 and 13±1 A for K3C60 and Rb3C60, respectively, by magnetization measurements based upon the renormalization theory of the fluctuation.

The Ginzburg-Landau coherence lengths were evaluated for C 60 -based superconductors by fitting measured magnetization data with the renormalization theory of the fluctuation. The derived coherence lengths are 21±1 and 13±1 A for K 3 C 60 and Rb 3 C 60 , respectively, which are preliminary results but are apparently smaller than the reported values obtained from H c2 (0) with mean field theory.

Electrical resistivity of the three-dimensional Au mixed-valence compounds Cs2Au2X6 (X=Cl, Br, I) was investigated under hydrostatic pressures up to 7.0 GPa and temperatures between room temperature and 480K. The resistivities and the activation energies of these compounds decrease rapidly with increasing pressure. The activation energies of Cs2Au2Cl6, Cs2Au2Br6 and Cs2Au2I6 are estimated by extrapolation as zero at 4.4 GPa, 7.2 GPa and 7.5 GPa, respectively. In the case of Cs2Au2I6, a sonductor-to-metal transition (P= Gpa, T= room temp.) and a metal-to-metal transition (P=6.5 GPa, T≈330 K) were observed. The metallic phase appeared at P =6.5 GPa and T ⪆ 330 K could be obtained at room temperature and ambient pressure as a metastable phase, whose structure was found to be a cubic perovskite structure from the X-ray diffraction pattern.

The solid-state spectra of two series of [M(mnt)2]–{mnt =[S2C2(CN)2]2–, M = Ni, Pt, or Au} monoanion salts of K– and [NEt4]+ have been recorded. The polarized absorption spectrum of K[Ni(mnt)2]·H2O is characterized by a strong band at 6 700 cm–1 assigned to the intermolecular charge-transfer (c.t.) transition along the stacking direction, which is the first direct evidence of the one-dimensional character of its electronic structure. On the contrary, the polarized reflectance spectra of [Net4][M(mnt)2](M = Ni or Pt) are characterized by reflectance peaks at 7 200 cm–1, corresponding to the intermolecular c.t. transition within the dimer. The magnetic susceptibilities of K[M(mnt)2]·H2O (M = Ni or Pt) are also described. The behaviour of the platinum complex can be explained by the alternating antiferromagnetic S=½ Heisenberg chain model with the alternation parameter α= 0.9 and the exchange parameter 2|J|= 640 cm–1, which is consistent with its weakly dimerized stack structure.

Electrical resistivity of three-dimensional Au mixed-valence compound Cs2Au2I6 was investigated under hydrostatic pressures up to 7.0 GPa and temperatures between room temperature and 480 K, where a semiconductor-to-metal transition (P=4.5 GPa, T=room temperature) and a metal-to-metal transition (P=6.5 GPa, T≈330 K) were observed. The metallic phase appeared at P=6.5 GPa and T⪆ 330 K could be obtained at room temperature and ambient pressure as a metastable phase, whose structure was found to be a cubic perovskite structure from the X-ray diffraction pattern. In connection with these results, the Au valence state of Cs2Au2I6 under high pressures was discussed.

A variety of electron donors including aromatic amines, phenothiazines, phenazines, tetrathiafulvalene (TTF) derivatives, and metallocenes were examined to form charge transfer (CT) complexes with C 60 . Black solid CT complexes were obtained from mainly TTF derivatives and these CT complexes were found to be neutral. Dark brown solid products were prepared by treating decamethylferrocene, cobaltocene, or nickelocene with C 60 . Although these dark brown products with metallocenes have not been completely identified, ferromagnetic behavior was observed in some cases.

A new non-stoichiometric mixed-valence compound CsAu0.6Br2.6 has been prepared, and its powder X-ray diffraction profile, ESR spectra, and electrical conductivity determined. From its empirical formula the average valence of Au is + 2.67. Powder diffraction data indicate that the compound has a cubic perovskite structure [cubic lattice, space group Pm3m, a= 5.462(2)A]. This means that the AuBr6 octahedra are crystallographically equivalent. ESR measurements show the existence of a +II formal oxidation state for Au. The conductivity is four orders of magnitude higher than that of the AuI–AuIII mixed-valence compound Cs2Au2Br6.

The optical absorption spectra of the Mn2+ ion in MnM(edta)·6H2O (M=Zn, Cu, Ni, and Co) were measured at low temperature. Fine structural bands corresponding to the 6A1g→4T2g (D) and 6A1g→4A1g, 4Eg (G) transitions were found. The fine structure corresponding to the 6A1g→4A1g, 4Eg (G) transition in the Zn compound were analyzed with the ligand field theory and the assignment of the absorption peaks was performed. Although the spectra of the Zn, Cu, and Co compounds are similar, those of the Ni compounds show significant broadening, which is possibly due to the energy transfer caused by the overlapping of the absorption bands of the Ni2+ and Mn2+ ions.

A magnon sideband which has an anomalous shape with the cut-offs at the low as well as the high energy sides was observed in the lowest energy region of the absorption spectra 6 A 1g → 4 T 2g ( 4 D ) in (C 2 H 5 NH 3 ) 2 MnCl 4 . This band shape is well fitted by the calculation of the shape of magnon sideband, considering both the inter- and intra-sublattice exciton transfers. The magnitudes of the inter- and intra-sublattice exciton transfers are estimated to be 10.2 cm -1 and 6.8 cm -1 , respectively, from the analysis of the band shape. The behaviour of this magnon sideband in the magnetic field was measured at 4.2 K. From its behaviour, the spin flop field is estimated to be 30±5 kOe, which is confirmed by the measurement of magnetization. The existence of exciton dispersions is supported by the effects of magnetic field and uniaxial stress on this magnon sideband.

The magnetic field dependence of the absorption spectra corresponding to the transition 4 T 1 ( 4 F )→ 2 T 1 ( 2 P ) of Co 2+ in CsCoCl 3 ·2H 2 O was investigated. In this transition region the Davydov splitting of the exciton lines was observed, and the magnitudes of the intersublattice exciton transfers were estimated. As a result, it was found that the exciton shows the two-dimensional migration closely related to the spin structure.

The absorption spectra corresponding to the transitions 6 A 1g → 4 A 1g ( 4 G ), 4 E g ( 4 G ) in (C n H 2 n +1 NH 3 ) 2 MnCl 4 ( n =2, 3) were measured between liquid helium and room temperatures. The temperature dependence of the integrated intensities of these spectra suggests that magnon assisted electric dipole transitions are dominant in these spectra. The temperature dependence of energies of these absorption spectra is very similar to that of the nearest neighbour spin pair correlation function which reflects mainly the energy of short wave-length magnon.The temperature dependence of the integrated intensities and the energies of these absorption spectra shows the two-dimensional magnetic character.

Weak absorption bands below the low-energy absorption edge of the intervalence charge-transfer (IVCT) transition in one-dimensional halogen-bridged mixed-valence complex [Pt(en) 2 ][PtBr 2 (en) 2 ](SO 4 ) 2 .6H 2 O have been investigated at 4.2K for the light polarized parallel to the Pt chain axis. In this complex, we found that three weak absorption bands (A-, B-, C-bands) were observed below the IVCT band. It is the first example of a non-doped halogen-bridged mixed-valence complex having three weak absorption bands. The absorption intensity of the C-band is much weaker than those of the A- and B-bands, but it is remarkably enhanced by the Au-doping. The A-, B- and C-bands have the photo-induced absorption effect, and its effect depends sensitively on the crystal quality and on the condition of the crystal growth, and is enhanced by the Au-doping. The photo-induced absorption decays during several minutes since stopping the irradiating light in the region of the IVCT band. From these behaviors of the A-, B-, and C-bands, we discuss the relation between the origin of these bands and the mismatch of the valence alternation.

The anomalous line shape with a double peak was observed for the magnon sideband in CsCoCl 3 · 2 H 2 O under a magnetic field parallel to the a -axis. This anomalous line shape can be qualitatively explained by a calculation considering an increase of the intrachain exciton transfer.

The XPS study has been carried out for the [Au(mnt)2]− and [Au(mnt)2]2− salts. The AuIII states were confirmed for both monoanion and dianion salts; although the obtained Au4f7/2 peak for the [Au(mnt)2]2− dianion is at 0.8–1.0 eV higher energy than that for the [Auf(mnt)2]− salt, this apparent energy shift is explained as arising from the Madelung potential difference between the two. It is concluded that the oxidation state of the central metal Au does not change with reduction.

The intervalence charge-transfer absorption spectra in the mixed-valence complexes [Pt(en) 2 ][PtI 2 (en) 2 ](SO 4 ) 2 ·6H 2 O and [Au x Pt 1- x I(en) 2 ]SO 4 ·3H 2 O ( x =0.03) have been investigated at 4.2 K. In these complexes, below the charge-transfer absorption edge, a weak absorption band ( A -band) has been observed for the light polarized parallel to the chain axis. When these complexes were irradiated with the light in the region of the charge-transfer transition from Pt II to Pt IV , the absorption coefficient of the A -band increased remarkably, which implies that the A -band is a photo-induced absorption band. The photo-induced effect for the A -band in [Au x Pt 1- x I(en) 2 ]SO 4 ·3H 2 O ( x =0.03) is more intense than that in [Pt(en) 2 ][PtI 2 (en) 2 ](SO 4 ) 2 ·6H 2 O. The A -band suggests the existence of new excitations such as a soliton-like excitation in the electronic state of the platinum chains.

Syntheses and optical properties of some new halogen-bridged mixed-valence platinum complexes analogous to Wolffram’s Red Salt, [Pt(en)2][PtBr2(en)2](HSO4)4 (PBHS), [Pt(en)2][PtI2(en)2](HSO4)4·4H2O (PIHS), and [Pt(en)2][PtX2](en)2](SO4)2·6H2O {X=Br(PBSW), I(PISW)}, are reported. The powder X-ray diffraction pattern shows that PBHS is isomorphous with [Pt(en)2][PtCl2(en)2](HSO4)4 (PCHS), and that PBSW and PISW are isomorphous. The hydrogensulfates PBHS and PIHS crystallize from an aqueous sulfuric acid solution, whereas the sulfates PBSW and PISW crystallize from an aqueous solution. The single crystal absorption spectra of PBHS, PIHS, PBSW, and PISW have been investigated at 4.2 K. The intense optical absorption due to intervalence charge-transfer transition from Pt(II) to Pt(IV) has been observed for the light polarized parallel to the Pt chain axis (E//chain). From the comparison of the energy of the intervalence charge-transfer absorption edges in PBHS, PBSW, and PISW, one can conclude that the influen...

The ligand-field spectra for the cobalt complexes in the single crystals of K3H2[CoIIIW12O40]·16H2O and K4H2[(COII, ZnII)W12O40]·nH2O have been observed at several temperatures above 1.4 K and assigned under D2 site symmetry. In the spectrum of the elongated CoIIIO4 complex, two absorption bands of 8250 and 8953 cm−1 strengthen with increasing temperature by vibronic mechanism. The X-band ESR spectra of both complexes have also been measured at 77 K. The signal from the Co(III) complex is not observed. The signal of the high-spin Co(II) complex of tetrahedral symmetry is unequivocally observed even at relatively high temperature of 77 K. From the analysis of the ESR spectrum, it is concluded that the CoIIO4 tetrahedron of D2 symmetry is flattened and deviated slightly from axial symmetry.

The crystal structure, electrical conductivity and electronic and IR absorption spectra of two metal complexes, K[Ni(mnt)2]·H2O and K[Pt(mnt)2]·H2O (mnt=1,2-dicyano-1,2-ethylenedithiolato, C4N2S22−) were investigated. These two metal complexes belong to orthorhombic system and the lattice constants are a=12.00 A, b=28.85 A, and c=3.90 A for the Ni complex and a=12.11 A, b=29.23 A, and c=7.73 A for the Pt complex. Despite the same stoichiometries and similar crystal structures, the conductivity of Pt complex is 103 times as high as that of the Ni complex. The difference in the conductivity between the Ni and Pt complexes may be explained from the density of the unpaired electron on the central metal. The effects of the central metal on the electrical conduction properties may not be negligible for this type of complexes.

The dependence of the absorption spectra of CsCoCl 3 on temperature and a magnetic field was investigated. It was found that the energy difference between the exciton line and its hot sideband is nearly equal to the soliton energy, and the intensity of the hot band is proportional to the thermal probability of the soliton below T N1 . Therefore, it was concluded that the hot band is ascribed to the exciton creation at the thermally excited soliton.

The low-energy absorption edge due to the intervalence charge-transfer (IVCT) transition from PtII to PtIV has been investigated at 4.2 K and room temperature in single crystals of [Pt(en)2][PtBr2(en)2]Y4 {Y=ClO4(PBC), HSO4(PBHS)}, [Pt(en)2][PtI2(en)2](HSO4)4·4H2O (PIHS) and [Pt(en)2][PtX2(en)2](SO4)2·6H2O {X=Cl(PCSW), Br(PBSW), I(PISW)}. The IVCT absorption edges in PCSW, PBSW, and PISW shifted to the lower-energy side (i.e. red shift), while those in PBC, PBHS, and PIHS shifted to the higher-energy side (i.e. blue shift) with an increase in temperature. We consider that the thermal effect of the valence fluctuation of the Pt mixed-valence state causes a red shift of the IVCT absorption edge and that the thermal effect of the hydrogen bond between the PtII complex ion and the PtIV complex ion causes a blue shift of the IVCT absorption edge. These two effects coexist and compete with each other in one complex. The dominant effect of the two effects determines the direction of the shift of the IVCT absorpt...

A new family of Pt mixed valence complexes : Pt 6 (NH 3 ) 14 Cl 10 X 4 (X=C10 4 , BF 4 and PF 6 ) was synthesized from the Magnus green salt (MGS) by the partial oxidation with an oxidant of H 2 O 2 or by electrochemical method. On partial oxidation, the 1 6 of Cl − ligands in MGS are randomly replaced by NH 3 ligands and simultaneously counter ions X are introduced. These complexes comprise of one-dimensional chains with direct contact between Pt atoms and consequently a quasi-one-dimensional band made up of 5d z 2 orbital of Pt is formed. The average valence of Pt is +2.33 and the distance between Pt atoms along a chain is shorter than or comparable to that of K 2 [Pt(CN) 4 ]Br 0.3 ·xH 2 O (KCP). The electrical conductivity σ and esr spectra of these complexes were presented.

The crystal field absorption spectra in the near infrared to visible regions of CsCoCl 3 ·2H 2 O were investigated. All of the absorption bands were well assiged by taking the crystal field and Racah parameters as D q =720 cm -1 , B =920 cm -1 and C =4320 cm -1 , respectively. In the spin forbidden transition 4 T 1 ( 4 F )→ 2 T 1 ( 2 P ) the exciton line and its magnon sideband were observed. The one-dimensionality of magnetic properties is reflected in the temperature dependence of the peak energy and the integrated intensity of the magnon sideband.

Zeeman effect of the R and B lines in GCrSH was measured. No difference was observed between the Zeeman patterns of the R 1 and R 2 absorption lines. Non-zero g -values of the excited states were obtained from the patterns in a magnetic field perpendicular to the trigonal axis. From these results, it is concluded that these two lines are not attributed to the two transitions 4 A 2 →\bar E ( 2 E ) and 4 A 2 →2\bar A ( 2 E ) of a Cr 3+ ion, but to the transition 4 A 2 →\bar E ( 2 E ) in the two different Cr 3+ sites. Both the B 1 and the B 1 ' lines were assigned to 4 A 2 →\bar E b ( 2 T 2 ) from the Zeeman patterns in a high pulsed magnetic field. New lines were found in the R -line region when GCrSH was diluted by aluminum. They are considered to originate from certain kinds of Cr 3+ sites and to have relation with the ferroelectric character of the crystals. In the B -line region, however, no new lines were observed.

The Zeeman effect of a sharp line in the red region of cesium chromium alum was investigated at low temperatures, using the magnetic fields up to 27 kOe, which were applied parallel to the [100], [111], and [110] axes. The g values and the quantization axis of the excited state of a Cr 3+ ion were determined. Comparing the experimental Zeeman patterns with the theoretical ones on the basis of the ligand field theory, it is concluded that the absorption line corresponds to the magnetic dipole transition from the ground state 4 A 2 to the excited state \bar E ( 2 E ). Although the transition from the ground state 4 A 2 to the excited state 2\bar A ( 2 E ) is not observed, it is suggested that the energy separation between the two states 2\bar A ( 2 E ) and \bar E ( 2 E ) is much larger than 3.5 cm -1 .

The absorption, circular dichroism (CD) and optical rotatory dispersion (ORD) of ZnSeO 4 ·6H 2 O crystals, those doped with Cu 2+ , Ni 2+ and Co 2+ ions, and NiSeO 4 ·6H 2 O crystals are measured in the 200–1500 mµ region at room temperature and 77 K. Several CD bands ascribed to the spin allowed d - d transitions are observed and the concomitant ORD curves are antisymmetric about the center of each CD band. The CD of NiSeO 4 ·6H 2 O-ZnSeO 4 ·6H 2 O mixed crystals depends linearly on the Ni 2+ ion concentration, and the helical arrangement of metal ions is found not to be essential for the optical activity. It is concluded that the optical activity of these crystals is caused by the asymmetric field on the metal ions.

The electrical resistivity of K3Cu8S6 was measured between 290K and 1.5K under hydrostatic pressure up to 1.1GPa. The two phase transitions, which are related to the formation of charge density waves (CDWs), were strongly influenced by pressure; the temperature of the first-order transition (50K under ambient pressure) rose and that of the second-order transition (152K under ambient pressure) fell with increasing pressure. The non-metallic behavior of the resistivity due to the CDWs was almost suppressed by the pressure of 1.1GPa.

Synthesis, transport and magnetic properties of a new ternary system Ce-Ta-S have been investigated. (CeS) 0.6 TaS 2 and (CeS) 1.2 TaS 2 order antiferromagnetically with Neel temperatures of 2.3 K and 2.7 K, respectively. In the former compound, a diverging anomaly in the susceptibility at T N , a small spontaneous magnetization below T N and a magnetic phase transition at 2.5 kOe are observed. From these results, (CeS) 0.6 TaS 2 is supposed to be a quasi-2D antiferromagnet with a weak ferromagnetism composed of ferromagnetic layers. The fractional superconductivity is observed with the magnetic ordering. Ce 4 f electrons are well localized and the correlation between Ce 4 f and conduction electrons is weak in these compounds.

The absorption spectra 6 A 1g → 4 T 2g ( 4 D ) of Mn +2 in the layer type antiferromagnet (C 2 H 5 NH 3 ) 2 MnCl 4 were measured. An absorption band caused by electric dipole was observed, which has an anomalous shape with cut-offs at the low as well as the high energy sides. The temperature dependence of its intensity suggests that it is a magnon sideband. The anomalous shape of this band could be reproduced in calculation as magnon sideband, taking account of the magnon dispersion and the exciton dispersion due to inter- and intra-sublattice transfers. Measurements of the uniaxial stress effect were also undertaken to investigate details of the behaviours of this magnon sideband.

Transport and magnetic properties of Cex TaS2 have been studied. The susceptibility as a function of temperature exhibits a diverging anomaly at 2.3K and the resistivity decreases below this temperature, indicating the appearance of a magnetic ordering with a spontaneous magnetization. The dependence of the magnetization on magnetic field applied parallel to the c-axis shows the meta-magnetic phase transition at 2kOe. Above 45kOe, the magnetization seems to be saturated, but the effective magnetic moment is 0.6µB per Ce atom even at 45kOe which is quite small compared with that of the free Ce3+ ion. It is discussed whether the f-electron in this compound has the localized nature or the itinerant one.

Optical absorption spectra corresponding to the 6A1g→4T2g(D) transition in CSMnCl3⋅2H2O and (CH3)2NH2MnCl3⋅2H2O were investigated under magnetic fields. In these compounds, a sharp exciton line in the lowest energy region of this transition was split by the applied field perpendicular to the spin direction. From the analysis of the spin configuration, it was proved to be a Davydov splitting induced by the field. The field induced Davydov splitting can be explained by the fact that in an external magnetic field perpendicular to the spin direction, spins cant towards the field so as to remove the prohibition of the inter-sublattice exciton transfer. The field dependence of this splitting was explained by the exciton transfer due to the anisotropic exchange interaction.

The absorption spectra corresponding to the transition 4T1 (4F)→2T1(2P) of Co2+ in CSCoCl32H2O were investigated under high magnetic fields up to 230kOe with a hybrid magnet. The anomalous line shapes of the magnon sideband with a double peak were observed under the magnetic fields parallel to the a- and c-axes. The behavior of the magnon sideband under the external magnetic fields is related to the exciton transfer. The intrachain exciton transfer becomes large under the magnetic field that induces the ferromagnetic components of the spins. This change of the exciton dispersion is reflected in the line shape of the magnon sideband. The anomalous behavior of the magnon sideband under the external fields was elucidated by the calculation of the line shape taking into account the field dependence of the exciton transfer.

The absorption spectra in one-dimensional antiferromagnet CsFeCl3⋅2H2O were investigated. From the dependence on uniaxial stress and temperature, the absorption lines observed in the region of 24150 - 24350cm-1 were assigned as exciton lines or magnon sidebands. The one-dimensionality of magnetic properties is reflected in the temperature dependence of exciton lines and magnon sidebands. Under the external magnetic field, the sublattice splitting and the Davydov splitting of the exciton lines were observed.

Magneto-absorption spectra of one dimensional antiferramagnet CsFeCl3⋅2H2O have been measured in the energy region of 24150 - 24350 cm-1 at 4.2 K under the steady magnetic field up to 220 kOe using a hybrid magnet system. The sublattice splitting of the exciton and magnon sideband lines was observed up to 140 kOe, where the metamagnetic transition from antiferramagnetic to ferramagnetic state takes place when the magnetic field is applied parallel to the chain 'along the a-axis. Discontinuous changes of the spectra were found in absorption lines of the exciton and magnon sideband at the transition field.