学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 大越 慎一, 東京大学教授 山内 薫, 東京大学教授 合田 圭介, 東京大学教授 佃 達哉, 東京大学准教授 山野井 慶徳University of Tokyo(東京大学

Umeta Yoshikazu

梅田 喜一

UTokyo Repository

 論文の内容の要旨 
 
論文題目: Synthesis, crystal structure, and first-principles calculations of a cyanide-
bridged copper-molybdate bimetallic assembly 
 
（銅－オクタシアノモリブデン錯体の合成、結晶構造、および第一原理計算） 
 
氏  名   梅  田  喜  一 
 
 
Introduction 
    Molecular magnetism has been studied as an interdisciplinary theme on the border of chemistry, 
materials science, and physics. In this area, control of physical properties by external stimuli is 
aggressively studied as an important target. Photomagnetism, control of magnetic properties by light 
irradiation, is attracting attention due to its potential toward applications in information storage and 
processing. Among photomagnetic materials, bimetallic copper octacyanidomolybdate with the 
general formula of CuII2[Mo
IV(CN)8]･nH2O is known as a classical photo magnet, for which our 
group firstly reported photo-induced reversible magnetization with a Curie temperature of 30 K in 
2001. After the report, various copper octacyanidomolybdate bimetal assemblies have been studied 
as photoresponsive magnetic materials. The mechanism of photomagnetism has been considered as 
the metal to metal charge transfer from MoIV (S = 0) to CuII (S = 1/2). The charge transfer produces 
MoV (S = 1/2) and CuI (S = 0), while the other CuII centers remain due to 2:1 Cu/Mo stoichiometry. 
The ferromagnetic interaction between S = 1/2 spins of CuII and MoV has been considered to be the 
origin of photomagnetism. However, the mechanism of photomagnetism in copper 
octacyanidomolybdate is the issue under discussions due to absence of the precise structural analysis 
for CuII2[Mo
IV(CN)8]･nH2O. There are some efforts to reveal the structure, and it was estimated to 
be the analogous of MII2[Mo
IV(CN)8]･nH2O (MII = MnII , FeII , and CoII) assemblies with tetragonal 
crystal system by wide-angle X-ray analysis and X-ray absorption spectroscopic analysis. As the 
structure is highly symmetrical and simple, it is expected to be a suitable model for calculations to 
examine the mechanism of photomagnetism. However, due to its poor crystallinity, a single crystal 
X-ray analysis was unavailable, and desired for further studies. In this study, the synthesis towards 
the single crystals, crystal structure, and first-principles calculations by a GGA + U method of a 
copper(II) octacyanidomolybdate(IV) bimetallic assembly {[CuII(H2O)]2[Mo
IV(CN)8]}
.2H2O 
(CuMo) are reported. 
 
Result and discussions 
Synthesis and characterization 
A single-crystalline form of the target material was obtained by using a gel method. The gel was 
obtained by mixing a portion of Na2SiO3
.9H2O, acetic acid, and K4[Mo
IV(CN)8]
.2H2O powder. The 
aqueous solution of Cu(NO)3
.3H2O was added on the top of the gel. After the system was kept in dark 
for ca. 6 months, black block crystals were obtained. The elemental analyses by inductively coupled 
plasma mass spectrometer, a standard micro-analytical method, and a thermo-gravimetrical (TG) 
measurement confirmed that the formula is Cu2MoC8H8N8O4. Calcd. Cu: 25.3%; Mo: 19.1%; C: 
19.1%; H: 1.6%; N: 22.3%. Found Cu: 25.3%; Mo: 19.0%; C: 19.2%; H: 1.7%; N: 22.5%. The TG 
measurement shows two steps of weight loss in the range of 30−40 (step 1) and 120−130 oC (step 2). 
The weight loss of both steps are about 7.2%. Steps 1 and 2 correspond to desorption of coordinated 
and non-coordinated water, respectively. The infrared spectrum showed two peaks due to cyanide 
stretching vibration modes at 2185 and 2167 cm−1. 
 
Crystal structure 
    The single crystal X-ray diffraction analysis revealed 
that CuMo has tetragonal I4/mcm space group with the lattice 
constants of a = 11.2833(6) Å, c = 12.8491(8) Å. CuMo 
possesses a three-dimensional network structure, in which 
CuII and MoIV centers are alternately bridged by cyanide 
(Figure 1). The skeleton of the cyanido-bridged network is an 
analogue of other 3d transition metal assemblies, 
{[MII(H2O)2]2[Mo
IV(CN)8]
.nH2O (M
II = MnII, FeII, and CoII). 
CuMo shows a tetragonal crystal system with unit cell 
parameters similar to the analogues. However, CuMo reveals 
higher symmetry and fewer coordinated waters than that of 
the analogues. The independent unit consists of one CuII 
center and one MoIV center. The coordination geometry of MoIV center is 8-coordinated square 
antiprism (D4d), which is the highest symmetry for 8-coordinate centers. The coordination geometry 
of CuII center is 5-coordinated square pyramid. The equatorial positions of the square pyramid are 
occupied by four nitrogen atoms from bridging cyanides, and the axial position is occupied by one 
oxygen atom from coordinated water. The position of the coordinated water is disordered into two 
positions with the occupancy of 50%. The non-coordinated water molecules are located in the 
structural pores along c axis. Coordinated and non-coordinated water molecules are forming hydrogen 
bonding network extending along c axis. The crystal structure of CuMo is stabilized by both the 
hydrogen bonding and cyanide bridging. 
  
 
 
Figure 1. Crystal structure of CuMo 
(the view from a axis). 
First-principles band calculations 
    The first-principles calculations were conducted by using Vienna ab initio simulation package 
(VASP) with a GGA + U method. Structural optimization from the result of the single crystal X-ray 
diffraction analysis as the initial structure was applied. The calculated band structure is shown in 
Figure 2. CuMo reveals a direct optical transition at thepoint with a band gap of 1.2 eV. The 
conduction bands above 1.0 eV are occupied by two MoIV 4d-based bands. Although these bands 
show energy splitting, the charge density of these bands are very similar. This splitting can be 
attributed to a difference in phases of the atomic orbitals for equivalent atoms in the calculated 
primitive unit cell. The valence bands below 1.8 eV are occupied by two CuII 3d-based bands. The 
energy splitting between the same spins is originated from the difference in phase like for the valence  
bands. In addition, the splitting between the different spins 
are caused by the difference of coordination geometry due to 
the disordered coordinated waters. The valence bands in the 
range of −2.0 to −1.0 eV consist of the oxygen 2p-based bands 
from the non-coordinated water. The conduction bands above 
1.8 eV are composed of the carbon and nitrogen atoms of 
cyanide ligands with a slight contribution from MoIV. As a 
result of an absorption spectrum calculation, the optical 
transition between the highest valence band and the lowest 
conduction band are found to be the main contribution to 
absorption in the visible range. The direction dependence of 
absorption strength indicates the strongest absorption along 
[1 1 1] crystallographic direction, where the cyanide ligands 
are aligned in parallel. The charge density map of the highest 
valence band and the lowest conduction band are shown in 
Figure 3. The highest valence band consists of MoIV dz2 orbital 
and nitrogen pz orbital, while the lowest conduction band is 
composed of CuII dx2−y2 orbital, nitrogen spx orbital, and 
carbon spx orbital. Among these bands, orbital overlap  
exists only around the nitrogen center. The transition of pz → spx of nitrogen gives the strong transition 
moment due to the orbital difference in the orbital angular momentum and parity. This result confirms 
the charge transfer from MoIV to CuII is realized through the transition moment on nitrogen atom of 
cyanide ligand, which results also in the anisotropy of the optical transition. 
 
Conclusions 
    In this work, the single crystalline form of a three-dimensional copper(II) octacyanido-
molybdate(IV) was successfully synthesized, and the crystal structure was determined. The crystal 
structure is a tetragonal three-dimensional network structure similar to analogues with other s3d 
transition metals. Using the experimentally determined crystal structure, first principles calculations 
Figure 3. Charge density maps of (a) 
the highest valence band and (b) the 
lowest conduction band. 
Figure 2. Calculated band structure of 
CuMo. 
with a GGA + U method were performed. CuMo shows a direct transition at the  point with a band 
gap of 1.2 eV, and the optical transitions in the visible range were assigned to the charge transfer from 
MoIV to CuII. The absorption strength analysis suggests the anisotropic absorption along [1 1 1] 
crystallographic axis, which is parallel to the arrangement of cyanides. In addition, as the result of 
the charge density analysis, the charge transfer between MoIV and CuII in the visible range was found 
to be facilitated by the optical transition of nitrogen from bridging cyanides, i.e. the changes of the 
parity and the symmetry caused by the pz → spx transition of nitrogen enable the efficient charge 
transfer. The results in this work are expected to give a design criteria for new functional copper 
octacyanidomolybdate-based and other related photomagnetic materials. 


銅－オクタシアノモリブデン錯体の合成、結晶構造、および第一原理計算

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銅－オクタシアノモリブデン錯体の合成、結晶構造、および第一原理計算

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