博 士 （ 地 球環 境 科 学 ）周尉

学位論文題名Sel二IASSenlbledMOnolayerSOfTrirutheni
unlCluSterS：Preparation,Characte
rizatio
na
ndRea
cti
vity（ルテニウム三核クラスターの自己組織化単分子膜の作製、キャラクタリゼーション及び反応性）

学位論文内容の要旨
In this thesis, preparation, characterization and reactivity of self‑assembled monolayers
and multilayers of triruthenium clusters on gold electrode surfaces have been described. The present
results demonstrate that the triruthenium cluster is an eminent building block in the construction offunctional ordered monolayers and multilayers on gold surfaces. Location controlled nanostructuresof the triruthenium clusters provide possibilities to develop nanodevices with novel functions.
In Chapter J, the general background of the present study has been introduced. Top‑downstrategy has approached its limit in nanotechnology. Bottom‑up strategy such as self‑assembly is apromising altemative to the top‑down strategy. Through self‑assembly, various molecular building
blocks can be employed to construct functional nanostructures. Triruthenium clusters are prominent
candidates as building blocks due to their well‑known properties including multistep electrontransfer, ligand‑substitution in solution, fonnation of supramolecular structures. Based on the initial
works on the self‑assembled monolayer (SAM) of the triruthenium cluster, the objectives of thepresent study are given.
In Chapter 2, experimental aspects have been described in detail. Synthesis procedures of
the triruthenium clusters employed in this study and the construction process of the SAM have beengiven. The basic principles of vibrational spectroscopic methods such as infrared reflection
absorption spectroscopy (IRRAS), surface‑enhanced infrared absorption spectroscopy (SEIRAS) andsum‑frequency generation (SFG) as well as their applications in electrochemical systems have beenstated. Combination of electrochemistry with in situ vibrational spectroscopy is an effective probing
technique for the study of SAMs.
In Chapter 3, the structure and the oxidation state of the SAM of the triruthenium clusters
have been characterized by using the techniques introduced in Chapter 2. Based on the assigmnent of
IR absorption peaks in the IRRA spectra of the SAMs, it is concluded that the orientation of theSAMs is perpendicular to the gold surface. The multistep electron transfer behavior has beensuccessfully realized in the SAMs. From the charge estimated in the cyclic voltammogram of the1523

SAMs, the coverage of the SAM on gold surface is estimated to be l.0 x 10'10 lTlol/CIT12, which isrelatively lower than the one of the alkanethiolate with similar length on gold surfaces and isascribed to the large size of the terminal group. In situ IR and SFG measurements provide detailed
structural information about the CO ligand and the acetate bridges in different oxidation states. Thelargest IR peak shift of the CO absorption is observed in the one‑electron oxidation of the Ru moiety
in tlie SAM. This phenomenon confinns the electron localization [RU311"II'III] in the triruthenium
cluster on molecular level. For the first time, the electron localization [RU3II'111'III] is changed toelectron delocalization state such as LRU3111'III'III] and [RU31V'II'''11]in theotheroxidat
ion states asobserved by in situ IR measurement. Absorption bands of the acetate ligands observed from SFG
measurement, which gives absolute vibrational spectra of the acetate Iigands in different oxidation
states, also support the conclusion. A tentative model is suggested to explain the IR absorption bandsof the acetate bridges, which are correlated with the electron localization in the cluster.
In Chapter 4, electrochemically controlled reversibie CO ligand exchange in the SAM of
the triruthenium cluster has been realized for the first time. The oxidation state of the triruthenium
clusters in the SAM is crucial to the stability of the CO ligand. One electron oxidation of the SAM
triggers a CO release process, resulting in a CO free SAM; while one electron reduction of the CO
free SAM triggers a CO re‑introduction process into the SAM at the original site of the CO. Kineticsof both, the CO release and coordination, have been evaluated by the electrochemical and in situ IR
measurements. The reaction rates are significantly affected by the solvent and temperature. The
reaction rate decreases greatly with the decreasing temperature, which is an important factor in thecontrol of the ligand exchange process in the SAM. From the reaction rate constants at varioustemperatures, the reaction activation energies of both processes have been evaluated. Step‑scan IRtechnique has been used to probe the possible intermediates with short life‑time at low temperatureduring the electron transfer process of the Ru cluster moiety in the SAM.
In Chapter 5, immobilization of NO molecule in the monolayer of the triruthe
nium clusters
has been realized under electrochemical control. Different from the CO ligand, NO favors[RU3mj"u'] rather than [RU3n'm'n']. Only was the CO bound SAM oxidized to [RU3'n'n" , can NO
binds to the SAM. NO ligand can also bind to a CO free SAM in the state [RU3m'mnj. The different
binding ability of NO compared to CO is closely related to the one more electron in NO than CO.
Upon one electron reduction of the NO bound SAM, the NO ligand can be replaced by CO orsolvent, resulting in ligand exchanges from NO to CO or solvent molecule. The NO bound SAM issensitive to the visible light irradiation, which leads to the NO ligand release from the SAM. By
employing all the electrochemically controlled ligands exchanges realized in the study, it is possibleto prepare monolayers comprising mixed ligands. The electrochemically controlled reversible CO,
NO and solvent ligand exchange in the SAM has been realized in the present work for the first time.
In Chapter 6, layer‑by‑layer multilayer of the triruthenium cluster has also been
constructed through metal‑ligand coordination on the template of the self‑assembled monolayer of
the triruthenium clusters. The construction process has been characterized by in situ IR spectroscopy.
‑ 1524 ‑InChapter7,generalconclusionsofthethe
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学位論文審査の要旨
主査

助 教授

冨 IJ査

教授

叶深

大澤雅俊

副査

教授

大谷文章

副査

教授

嶋津克明

副査

教授

佐 々 木 陽 一 （ 大 学 院 理 学研 究 科 化学 専 攻 ）学位論文題名Self‑Assembled R/Ionolayers of Triruthenium Clusters:Preparation， Characterization and Reactivity（ルテニウム三核クラスターの・自己組織化単分子膜の作製、キャラクタリゼーション及び反応性）
金属多核 錯体は 、可逆的 多段階多 電子移 動を示す特徴があり、生体内等での電子移動の機構と速度論を調 べるモデ ル化合 物として 研究さ れている 。このような機能性分子を電極表面に固定できれぱ、電子 移動に伴 う反応 過程を分 子レベ ルでより 詳細に解明できるとともに、多電子移動の機能性を持つ新 しい不均 一電極 触媒や機 能性材 料のとし ての利用が期待できる。申請者は、自己組織化法
により、 豊富な酸 化還元 状態をも つルテ ニウム金 属三核クラスターの自己組織化単分子膜くSAM)と多層膜を 金電極表 面に固 定させ、電気化学測定法の他に、その場赤外分光法およぴ和周波発生(SFG)分光法を用 い、機能性 薄膜におけ る分子配向 ・構造と機 能性制御を 詳細に調べた。
申請者は 、オキ ソカルボ キシラト 架橋型 ルテニウ ム錯体 のチオー ル誘導 体を、金電極表面にSAMとして構 築し、ル テニウ ム中心金 属の三 段階四電 子にも及ぶ電子移動反応を電極表面で初めて実現した 。 ル テニ ウ ム 中心 金 属 の多 電 子移動 反応に伴 い、錯体 SAMの 分子構造 と電子 状態の変 化についてその 場赤外分 光法に より明ら かにし た。ルテ ニウム中心金属の電子状態の違いにより、配位子の安定性 と反応正 が大き く異なる ことを 明らかに した。これに基づき、申請者は、電気化学的制御に よ り 、 錯 体 SAMの カ ル ボ ニル (CO)配 位 子 、一 酸 化 窒素 (NO)配 位 子ま た は 溶媒 分 子 を S
AMへ の導入また は脱離を 可逆的 に行うこ とに成 功した。 このような表面反応は溶液中における錯体の反応と比べると、高い反応収率かっ短時間で実現できるメリットがある。また、電気化学的制御により、単分 子 膜とルテ ニウム クラスタ ー間の共 有結合 を通じて ルテニ ウムクラ スター の多層膜 の連続成長に 成 功 した 。 こ れら の 配 位子 交 換 反応 を 利 用す る こ と によ り、将来 、高感 度のCOやNOセ ンサーの開発 が期待で きる。 さらに、 申請者 は分子レ ベルで反応制御の実現を目指し、これらの配位子交換 の 反 応過 程 に つい て 赤 外分 光 法 とSFG分光 法 に よ って そ の場追跡 し、反 応に伴う SAMの分 子
一 1526−構造や配向の変化、電 子状態の局在化の変化および反応速度にっいて定量的に 調べる事が出来た。
こうした申請者の一 連の研究は、機能性有機薄膜の分子構造の解析と機能性 制御に大きく貢献した。こうした成果は今 後、この研究は基礎研究に無論のこと、機能性材料開発 やセンサーへの応用も期待できる。審査員 一同は、これらの成果を高く評価し、また研究者として誠実かっ熱心であり、独特な発想により研究 を推進することや大学院単位取得などを併せ、申請者が博士（地球環境科学）の学位を受けるに十分 な資格を有するものと判定した。

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