Structural, Magnetic, and Electrochemical Characterization of Iron(III) and Cobalt Complexes with Penta-N3O2-dentate Ligands

Six new mononuclear [FeIII(LBr,Cl)X]-complexes (LBr,Cl is the dianionic penta-N3O2-dentate Schiff base ligand N,N′-bis(2’-hydroxy-3-bromo-5-chlorobenzylidene)-1,6-diamino-3-azahexane; X: Cl−, N3−, NCO−, NCS−, NCSe−, CN−) were synthesized and their structures, magnetic and electrochemical properties studied. Structure analysis and magnetic measurements showed that [FeIII(LBr,Cl)CN] is in the low spin state and the other five complexes are in high spin states. Furthermore, the trinuclear mixed valent cobalt complex {[CoIII(LH,H)CN]2[CoII(1-methylimidazole)3(H2O)]} was prepared and its magnetic behavior studied. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH Gmb

A Brønsted ligand molecular switch with five accessible states

A mononuclear Fe(II) complex, prepared with a Brønsted diacid ligand, H2L (H2L = 2-[5-phenyl-1H-pyrazole-3-yl] 6benzimidazole pyridine), shows switchable physical properties and was isolated in five different electronic states. The spin crossover (SCO) complex, [FeII(H2L)2](BF4)2 (1A), exhibits abrupt spin transition at T1/2 = 258 K, and treatment with base yields a deprotonated analogue [FeII(HL)2] (1B), which shows gradual SCO above 350 K. A range of ferric analogues were also characterized. [FeIII(HL)(H2L)](BF4)Cl (1C) has an S = 5/2 spin state, while the deprotonated complexes [FeIII(L)(HL)], (1D), and (TEA)[FeIII(L)2], (1E) exist in the low-spin S = 1/2 state. The electronic properties of the five complexes were fully characterized and we demonstrate in situ switching between multiple states in both solution and the solid-state. The versatility of this simple mononuclear system illustrates how proton donor/acceptor ligands can vastly increase the range of accessible states in switchable molecular devices

Patterning of Nanoparticle‐Based Aerogels and Xerogels by Inkjet Printing

Nanoparticle-based voluminous 3D networks with low densities are a unique class of materials and are commonly known as aerogels. Due to the high surface-to-volume ratio, aerogels and xerogels might be suitable materials for applications in different fields, e.g. photocatalysis, catalysis, or sensing. One major difficulty in the handling of nanoparticle-based aerogels and xerogels is the defined patterning of these structures on different substrates and surfaces. The automated manufacturing of nanoparticle-based aerogel- or xerogel-coated electrodes can easily be realized via inkjet printing. The main focus of this work is the implementation of the standard nanoparticle-based gelation process in a commercial inkjet printing system. By simultaneously printing semiconductor nanoparticles and a destabilization agent, a 3D network on a conducting and transparent surface is obtained. First spectroelectrochemical measurements are recorded to investigate the charge–carrier mobility within these 3D semiconductor-based xerogel networks

Toward switching cyanide- and thiocyanate-bridged compounds derived from mononuclear building blocks

Bistable compounds which exhibit reversible phase transitions under external stimuli accompanied by changes of physical properties are excellent candidates for multifunctional electronic molecular devices and nano-sensors. In this regard, coordination complexes switchable between two or more different electronic states offer great potential due to their flexible design and adjustable properties. Transition metal complexes, mostly containing iron, cobalt, or manganese, can show a spin crossover (SCO). This is a reversible switching between the low and high spin state through physical and chemical stimuli. Additionally, cyanide-bridged complexes can show a reversible electron transfer coupled with a spin transition/SCO (ETCST) between two redox-active transition metals with mixed-valences. Therefore, cyanide-bridged molecular complexes and coordination polymers are of great interest in current research. This dissertation continues the investigations for new switchable complexes. Therefore, novel cyanide-bridged multinuclear complexes and thiocyanate-bridged frameworks were synthesized and characterized. For this purpose, different new and known mononuclear complexes were analyzed in terms of their suitability as building blocks. Appropriate building blocks were combined to form multinuclear complexes, some of them with switching (SCO or ETCST) behavior. The presented results are discussed in four chapters according to the used building blocks and resulting complexes. After a short introduction, the Current State of Research is summarized in Chapter 2. The Chapters 3 and 4 deal with the synthesis of distinct mixed-valence complexes using certain iron and cobalt complexes with pentadentate Schiff base ligands. Dinuclear, trinuclear, and pentanuclear complexes were obtained of which some show SCO and likely ETCST behavior. In Chapter 5, an ETCST-active tetranuclear square complex was used to build up 1D chains through hydrogen bonds with a co-crystallized organic molecule. Significant alterations of the structure were observed in solid-state. Chapter 6 is about the formation of a new kind of coordination framework derived from a thiocyanate-based Prussian blue analog. The aggregation of the building blocks to different framework structures was investigated as well as their properties and how an SCO behavior might be introduced. The analyzed compounds show potential as chemical sensors, and the building blocks might lead to new spin state based electronics.Bistabile Verbindungen, deren physikalische Eigenschaften durch externe Stimuli geändert werden können, sind hervorragende Anwärter für multifunktionale elektronische Anwendungen und Nanosensoren. Übergangsmetallkomplexe, die zwischen zwei oder mehreren elektronischen Zuständen wechseln können, bieten aufgrund ihrer Designvielfalt und Anpassungsmöglichkeiten dahingehend großes Potential. Solche Komplexe beinhalten häufig Eisen, Cobalt oder Mangan und können einen Spin Crossover (SCO) zeigen. Dies bezeichnet den durch chemische oder physikalische Änderungen induzierten reversiblen Übergang vom Low in den High Spin Zustand. Zusätzlich kann in cyanidverbrückten Komplexen ein reversibler Elektronenübertrag mit gekoppeltem Spinübergang/SCO (ETCST, engl. electron transfer coupled spin transition) zwischen zwei redoxaktiven Übergangsmetallen verschiedener Valenzen stattfinden. Aus diesem Grund befasst sich die aktuelle Forschung intensiv mit cyanidverbrückten molekularen Komplexen und Koordinationspolymeren. Diese Dissertation führt die Forschungen zu neuen molekularen Schaltern fort. Es werden die Ergebnisse der Synthesen und Charakterisierungen von verschiedenen cyanidverbrückten molekularen Komplexen und thiocyanatverbrückten Koordinationsnetzwerken diskutiert. Zu diesem Zweck wurden bereits bekannte und neuartige mononukleare Komplexe bezüglich ihrer Eignung als Bausteine analysiert. Ausgewählte Bausteine wurden im Anschluss zu multinuklearen Komplexen kombiniert, von denen einige schalten können (SCO oder ETCST). Die Ergebnisse sind, entsprechend der verwendeten Bausteine und den daraus resultierenden Komplexen, in vier Kapitel unterteilt. Nach einer kurzen Einleitung ist der aktuelle Stand der Forschung in Kapitel 2 zusammengefasst. Die Kapitel 3 und 4 befassen sich mit der Synthese von molekularen Komplexen, die verschiedene Valenzen aufweisen. Zu diesem Zweck wurden ausgewählte Eisen und Cobalt Komplexe mit fünfzähnigen Schiff’schen Base Liganden verwendet, um eine Reihe von di-, tri- und pentanuklearen Komplexen herzustellen, von denen einige einen SCO und wahrscheinlich ETCST zeigen. In Kapitel 5 wurde eine 1D Kettenstruktur durch Wasserstoffbrücken zwischen einem ETCST-aktiven tetranuklearen Komplex und einem organischen Molekül erzeugt, in der signifikante Strukturänderungen zu beobachten sind. Kapitel 6 handelt von neuartigen Netzwerkstrukturen, die von Thiocyanat-basierten Berliner Blau Analogen abgeleitet wurden. Es wurde untersucht, wie die Aggregation der einzelnen Bausteine beeinflusst werden kann, welche Eigenschaften die resultierenden Verbindungen aufweisen und ob ein SCO in diesem System möglich ist. Die untersuchten Verbindungen zeigen großes Potential für die Verwendung als chemische Sensoren und die einzelnen Bausteine können zur Entwicklung neuartiger, auf dem Spinzustand beruhender, Anwendungen beitragen