Springer Theses Recognizing Outstanding Ph.D. Research Kenta Imoto Multifunctional Molecular Magnets Based on Octacyanidometalates Springer Theses Recognizing Outstanding Ph.D. Research Aims and Scope The series “Springer Theses” brings together a selection of the very best Ph.D. theses from around the world and across the physical sciences. Nominated and endorsed by two recognized specialists, each published volume has been selected foritsscientificexcellenceandthehighimpactofitscontentsforthepertinentfield of research. For greater accessibility to non-specialists, the published versions includeanextendedintroduction,aswellasaforewordbythestudent’ssupervisor explainingthespecialrelevanceoftheworkforthefield.Asawhole,theserieswill provide a valuable resource both for newcomers to the research fields described, and for other scientists seeking detailed background information on special questions. 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More information about this series at http://www.springer.com/series/8790 Kenta Imoto Multifunctional Molecular Magnets Based on Octacyanidometalates Doctoral Thesis accepted by The University of Tokyo, Tokyo, Japan 123 Author Supervisor Dr. Kenta Imoto Prof. Shin-ichi Ohkoshi TheUniversity of Tokyo TheUniversity of Tokyo Tokyo Tokyo Japan Japan ISSN 2190-5053 ISSN 2190-5061 (electronic) SpringerTheses ISBN978-981-10-6134-9 ISBN978-981-10-6135-6 (eBook) DOI 10.1007/978-981-10-6135-6 LibraryofCongressControlNumber:2017947855 ©SpringerNatureSingaporePteLtd.2017 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. 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Theregisteredcompanyaddressis:152BeachRoad,#21-01/04GatewayEast,Singapore189721,Singapore ’ Supervisor s Foreword Multifunctional materials are intensively investigated in the field of chemistry, physics,andmaterialsscienceduetothepossibility oftuningamaterial’sphysical properties by external stimuli. The present thesis by Kenta Imoto deals with the demonstration of multifunctionalities in cyanido-bridged metal assemblies. One system presented in the thesis shows a conversion from the paramagnetic state to theferromagneticallyorderedstatebylightirradiation.Thisbehaviorisachievedby a rational chemical design and alignment of the photoactive spin-crossover sites with strong magnetic interactions.Othernovel contributionsassignedtothisthesis arethedemonstrationofphoto-inducedmagnetizationinatwo-stepspin-crossover material and the realization of the coexistence between metamagnetism and super-ionic conductivity. These multifunctionalities are realized by the incorpora- tion of a spin-crossover moiety or a hydrogen-bonding network to a magnetically coupled cyanido-bridged framework. In particular, in light-induced spin-crossover magnets,amagneticallynon-orderedstatecanbealteredtoamagneticallyordered state by photo-irradiation, which is one of the attractive mechanisms for novel optical switching devices. The results in this work will be appealing to readers related to the field of materials science. ThestudiesinthethesiswereperformedbetweenApril2011andMarch2014at the Department of Chemistry, School of Science, The University of Tokyo, and have led to several publications and presentations at international conferences. Tokyo, Japan Prof. Shin-ichi Ohkoshi December 2016 v Parts of this thesis have been published in the following journal articles: (1) S. Ohkoshi, K. Imoto, Y. Tsunobuchi, S. Takano, H. Tokoro, Nature Chemistry 3, 564 (2011). (2) K. Imoto, K. Nakagawa, H. Miyahara, S. Ohkoshi, Cryst. Growth Des., 13, 4673 (2013). (3) K. Imoto and S. Ohkoshi, Chem. Lett., 45, 359 (2016). vii Acknowledgements This book is based on my doctoral thesis handed in at the University of Tokyo. Firstofall,IwouldliketothankProf.Dr.Shin-ichiOhkoshiforsupervisingthis thesis and supporting my research in numerous ways. He has guided me into this interesting research field and provided valuable feedback on the developing manuscript.Hisbeliefinscience,enthusiasmforexperiments,andlogicalthinking gave me a deep impression. I would like to thank Dr. Hiroko Tokoro for teaching me a lot of experimental techniques. Her attitude and carefulness for experiments taught me about many importantthingsforexperiment.IacknowledgeDr.KojiNakabayashi,Dr.Kosuke Nakagawa, and Dr. Asuka Namai for a lot of useful advice and discussions. I am grateful to Dr. Kimiko Saeki and Dr. Aiko Kamitsubo for the elemental analysisoforganicelementsandMr.ShigeruOtsukaforthemeasurementofSEM images. IamalsogratefultoallthemembersofOhkoshilaboratoryandallex-laboratory members for their help and cooperation. I am indebted to a JSPS Research Fellowship for Young Scientists. Finally, I would like to thank my family for their understanding, support, and encouragement throughout my study. ix Contents 1 Introduction.... .... .... ..... .... .... .... .... .... ..... .... 1 1.1 Molecule-Based Magnet... .... .... .... .... .... ..... .... 1 1.2 Molecular Field Theory ... .... .... .... .... .... ..... .... 2 1.3 Van Vleck Paramagnetism . .... .... .... .... .... ..... .... 9 1.4 Cyanido-Bridged Metal Assemblies and Their Functionalities ... 14 1.5 Octacyanidometalate-Based Magnets . .... .... .... ..... .... 16 1.6 Photo-Induced Magnetization in Cyanido-Bridged Metal Assemblies.... .... ..... .... .... .... .... .... ..... .... 17 1.7 Spin-Crossover Phenomenon ... .... .... .... .... ..... .... 20 1.8 Light-Induced Excited Spin State Trapping (LIESST) ..... .... 21 1.9 Ionic Conductivity .. ..... .... .... .... .... .... ..... .... 22 1.10 Objectives of This Work .. .... .... .... .... .... ..... .... 23 References.. .... .... .... ..... .... .... .... .... .... ..... .... 23 2 Observation of Light-Induced Spin-Crossover Magnetism in a Fe-[Nb(CN) ] Bimetal Assembly. .... .... .... .... ..... .... 29 8 2.1 Introduction ... .... ..... .... .... .... .... .... ..... .... 29 2.2 Experiments ... .... ..... .... .... .... .... .... ..... .... 30 2.2.1 Synthesis.... ..... .... .... .... .... .... ..... .... 30 2.2.2 Characterization.... .... .... .... .... .... ..... .... 31 2.2.3 Photo-Irradiation Measurements ... .... .... ..... .... 31 2.3 Results ... .... .... ..... .... .... .... .... .... ..... .... 31 2.3.1 Elemental Analysis . .... .... .... .... .... ..... .... 31 2.3.2 XRD Patterns and Crystal Structure .... .... ..... .... 32 2.3.3 IR Spectra... ..... .... .... .... .... .... ..... .... 33 2.3.4 Magnetic Properties. .... .... .... .... .... ..... .... 33 2.3.5 UV-Vis Spectra.... .... .... .... .... .... ..... .... 36 2.3.6 57Fe Mössbauer Spectra . .... .... .... .... ..... .... 36 2.3.7 Photomagnetic Measurements. .... .... .... ..... .... 38 2.3.8 UV-Vis Spectra Under the Light Irradiation .. ..... .... 39 xi xii Contents 2.4 Discussion .... .... ..... .... .... .... .... .... ..... .... 41 2.4.1 Electronic States of High-T and Low-T Forms ..... .... 41 2.4.2 XRD Patterns and Crystal Structure .... .... ..... .... 43 2.4.3 Magnetic Properties of Low-T Form.... .... ..... .... 43 2.4.4 Photomagnetic Properties .... .... .... .... ..... .... 44 2.5 Conclusion .... .... ..... .... .... .... .... .... ..... .... 45 References.. .... .... .... ..... .... .... .... .... .... ..... .... 45 3 Two-Step Spin-Crossover and Photo-Induced Spin-Crossover Ferromagnetism in FeII[NbIV(CN) ](4-Methylpyridine) (cid:1) 2H O ........ 47 2 8 8 2 3.1 Introduction ... .... ..... .... .... .... .... .... ..... .... 47 3.2 Experiments ... .... ..... .... .... .... .... .... ..... .... 48 3.2.1 Synthesis.... ..... .... .... .... .... .... ..... .... 48 3.2.2 Characterization.... .... .... .... .... .... ..... .... 48 3.2.3 Photo-Irradiation Measurements ... .... .... ..... .... 49 3.3 Results ... .... .... ..... .... .... .... .... .... ..... .... 49 3.3.1 Elemental Analysis . .... .... .... .... .... ..... .... 49 3.3.2 Single Crystal X-Ray Analysis at Various Temperatures. ..... .... .... .... .... .... ..... .... 49 3.3.3 IR Spectra... ..... .... .... .... .... .... ..... .... 51 3.3.4 Magnetic Properties. .... .... .... .... .... ..... .... 53 3.3.5 Temperature Dependence of UV-Vis Spectra . ..... .... 54 3.3.6 Photomagnetic Measurements. .... .... .... ..... .... 54 3.3.7 UV-Vis Spectra Under the Light Irradiation at 3 K.. .... 54 3.4 Discussion .... .... ..... .... .... .... .... .... ..... .... 56 3.4.1 The Assignment of Spin-Transition in the Present System . .... ..... .... .... .... .... .... ..... .... 56 3.4.2 The Analysis of Magnetic Susceptibility and the Electronic State.. .... .... .... .... ..... .... 56 3.4.3 Temperature Dependence of Crystal Structure. ..... .... 61 3.4.4 Thermodynamical Properties.. .... .... .... ..... .... 61 3.4.5 Magnetic Properties of Low Temperature State..... .... 65 3.4.6 Photomagnetic Properties .... .... .... .... ..... .... 65 3.5 Conclusion .... .... ..... .... .... .... .... .... ..... .... 67 References.. .... .... .... ..... .... .... .... .... .... ..... .... 67 4 Observation of Coexistence of Super-Ionic Conductivity and Metamagnetism in Mn [NbIV (CN) ] (4-Aminopyridine) 3 8 2 10 (4-Aminopyridinium) (cid:1) 12H O.. .... .... .... .... .... ..... .... 69 2 2 4.1 Introduction ... .... ..... .... .... .... .... .... ..... .... 69 4.2 Experiments ... .... ..... .... .... .... .... .... ..... .... 70 4.2.1 Synthesis.... ..... .... .... .... .... .... ..... .... 70 4.2.2 Characterization.... .... .... .... .... .... ..... .... 70 4.2.3 Impedance Measurement. .... .... .... .... ..... .... 71