Dans cette thèse, nous avons développé l'utilisation de l'activation microondes pour fonctionnaliser des pérovskites lamellaires et notamment la phase d'Aurivillius Bi2SrTa2O9 (BST), connue pour ses propriétés ferroélectriques. Nous sommes parvenus à protoner cette phase (HST) et à la fonctionnaliser par diverses amines et polyamines, avec des temps de réaction considérablement réduits par rapport aux fonctionnalisations en conditions classiques. Cette approche nous a permis de fonctionnaliser HST par des amines plus encombrées et plus complexes. Cette stratégie a ensuite été étendue au greffage d'alcools et de polyols. Nous avons également établi une stratégie de modification post-synthèse, pour synthétiser in situ la molécule désirée, en utilisant la chimie "click" et l'activation microondes. Enfin, nous sommes parvenus à insérer des ions métalliques et des complexes de métaux de transition, ce qui constitue une première étape vers la synthèse de nouveaux hybrides multiferroïques. / During this PhD thesis, we have developed the use of microwave activation to functionalize layered perovskites, among which the Aurivillius phase Bi2SrTa2O9 (BST), known for its ferroelectric properties. We managed to protonate this phase (leading to HST) and to functionalize it by various amines and polyamines, with reaction times much shorter than using classical conditions. This approach allowed us to functionalize HST by bulkier and more complex amines. This strategy has further been extended to the grafting of alcohols and polyols. We have also established a postsynthesis modification strategy, in order to synthesize the desired molecule in situ, within the interlamellar space, using "click" chemistry and microwave activation. Finally, we managed to insert transition metal ions and complexes, which constitutes a promising step towards the synthesis of new multiferroic hybrid materials.

One third of world’s total energy is used in production of electricity and one fifth of the total electricity produced in the world is used in lighting. Hence, the materials that have high potential in the field of photovoltaic’s and photoluminescence have recently drawn special attention to meet the ever increasing energy demands. In this thesis, we have studied a few materials that hold tremendous promises in fabricating photovoltaics and photoluminescent devices. Any ferroelectric material is an efficient solar energy converter as it contains an the intrinsic dipolar field which can effectively separate the photo excited electron and hole. We have developed a few materials which possess inherent polarization efficiently absorb over a wide portion of the solar spectrum and hence can find application in the field of photovoltaics. Secondly, we also dealt with semiconductor nonmaterial’s which are technologically very important owing to their improved photoluminescence properties. We tried to improve their light emitting efficiency by engineering crystal structure in nanometer length scales. The thesis deals with such advanced energy materials and is divided in seven chapters. Chapter 1 provides a brief introduction to the fundamental concepts that are relevant in the subsequent chapters. The chapter is started with a brief scenario of current status of energy production and its usage. Next, we have discussed the prospects of ferroelectric materials in photovoltaic devices. This is followed by a brief background on ferroelectricity and related properties which we have studied subsequently. At the end of this chapter a brief overview of photoluminescence properties in semiconductor nonmaterial’s is presented. In this section we have addressed the particular issues that need to be taken care of in order to improve their light emission properties. Chapter 2 describes different experimental and theoretical methods that have been employed to carry out different studies presented in the thesis. Chapter 3 addresses the possibility of employing BaTiO3 (BTO) based composite perovskite oxides as a potent photovoltaic material. It is known that BTO can produce photocurrent upon excitation with suitable light source. However, inability of BTO to absorb sufficient sunlight owing to its near UV band gap prevents to make use of this material in photovoltaic devices. In order to reduce the band gap we have tried to tune the electronic structure at the band edge by doping non-d0 transition metal ions at Ti site. As it is known in the literature an isovalent substitution of Ti4+ stabilizes non-polar phase of BTO we employed a co-doping strategy to substitute tetravalent Ti with equal percentage of a trivalent and a pentavalent metal ion. Keeping in mind off-centering of Ti4+ is primary reason behind the large ferroelectric polarization of BTO, a judicious choice of co-dopant was necessary to minimize reduction of polarization due to replacement of Ti. We have found at least two pairs of co-dopants, namely Mn3+-Nb5+ and Fe3+-Nb5+ which at low doping concentration ( < 10%) effectively reduces the band gap of BTO without affecting its polarization to a large extent. We systematically increase the doping concentration of both the pair of dopants and found Mn3+-Nb5+ pair is more efficient over Fe3+-Nb5+ both in terms of reducing band gap and retaining the polarization of BTO. We have characterized the ferroelectric nature of all the doped compositions with the help of dielectric, polarization and pyroelectric measurements. We have also performed first principle density functional theory (DFT) calculations for an equivalent doped composition and addressed the nature of modulations of electronic structure at the band edges which is responsible for such large reduction of band gap. Chapter 4 deals with composite perovskite materials which posses large tetragonal distortions with reduced optical band gaps. Here we have exploited Cu-Nb and Cu-Ta pair which upon complete substitution of Ti of BTO leads to composite perovskites with enhanced tetragonal distortion of the perovskite lattice. For two resultant compositions, namely BaCu1/3Nb2/3O3 and BaCu 1/3Ta2/3O3 we have characterized the optical and ferroelectric properties. We found though these material possess small band gap (∼ 2 eV), these are not ferroelectric in nature. Results of second harmonic generation measurements and refinement of powder X-ray diffraction both establish Centro symmetric nature of these materials. We infer from these results that presence of large tetragonal distortion is a result of symmetric Jahn-Teller type distortion of Cu2+ and not due to off-centering of any of the metal ions in their MO6 octahedral geometries. In Chapter 5, we have considered the material SrTiO3 (STO) which is stable in cubic paraelectric phase at room temperature. But at the same time this material is considered as an incipient ferroelectric due to presence of an active polar vibrational mode which does not become completely soft even at temperature close to 0 K. While this polar vibrational mode can easily be frozen by making substitution at Sr site, a similar attempt by making substitution at Ti site failed earlier. Keeping in mind Ti is easier to substitute than Sr we employed same co-doping strategy that we have considered in Chapter 3. We found Mn- Nb and Mn-Ta co-dopants at low doping concentration are extremely useful in transforming incipient ferroelectric STO into a dipolar glass. We have characterized the glassy dipolar property of doped STO with the help of tem-perature dependent dielectric response of these material. At the same time we found these co-doped STO possess enhanced static dielectric constant at room temperature with favourable dielectric loss values in comparison to pure STO. We have also ad-dressed the origin of a glassy dipolar state with the help of DFT calculation performed on equivalent doped composition that we have considered for our experiments. In Chapter 6, we have considered another incipient ferroelectric material TiO2 in rutile phase which also possess polar vibrational mode at temperature close to 0 K. A lattice strain along the polar vibrational mode make symmetric non-polar structure unstable with respect to the distorted polar structure. In this context, we found two particular compositions FeTiTaO6 and CrTiTaO6 that are also stable in rutile phases at room temperature but possess similar strain due to presence of larger Fe or Cr and Ta in rutile lattice. Considering the fact these two composite rutile oxides are relaxer ferroelectric in nature, we critically evaluated the effect of the particular kind of strain that these materials introduce in rutile lattice. We also characterized relaxor ferroelectric property and optical band gap of these materials and commented on the potential of these materials in exploiting them in photovoltaic devices. Chapter 7 presents a unique strategy of making use of crystal defects in improving photoluminescent properties of semiconductor nanocrystals. We have shown defects when introduced in nanocrystals in a controlled protected manner efficiently overcome the problem of self absorption which is known to reduce quantum efficiency of emit-ted light. Controlling synthesis conditions we separately prepared CdS nanocrystals with and without intergrowth defects. We characterized the presence of the intergrowth defect with the help of high resolution transmission electron microscope (HRTEM) image. We have also characterized Stokes’ shifted PL emission and ultrafast charge carrier dynamics of these NCs with intergrowth defects. To support these experimental findings we have computed the electronic structures of model nanoclusters possessing similar intergrowth defects that has been observed in HRTEM images. We find that the presence of defects in a nanocluster particularly affect the position of the band edge. However our joint density of state calculation shows that contribution of these defect states to an absorption spectra is negligible. Thus presence of defect states at band edge ensures a Stokes’ shifted emission without affecting the position of absorption. In a separate section of this chapter we have shown apart from intergrowth defects presence of twin boundary also provide similar mid-gap states that can alter its’ optical proper-ties to large extent. In summary, we have studied a few bulk and nano-materials which can show improved photovoltaic and photoluminescence property. We investigated effect of external dopant ions on a classical ferroelectric material BaTiO3 and two incipient ferroelectric materials SrTiO3 and rutile TiO2. We have also shown that efficient defect engineering could be extremely useful in improving photoluminescent property of CdS nanocrystals which is a prototype of II-VI semiconductor nanomaterials. In a separate Appendix Chapter, we have shown an easy and efficient way to suppress coffee ring effect which takes place universally when a drop of colloidal suspension is dried on a solid substrate. We have shown temporary modification of hydropho-bicity of a glass substrate not only can suppress the coffee ring effect but also leaves the particle in a highly ordered self-assembled phase after completion of drying process

Advanced nanomaterials show a significant improvement in certain physical or functional properties compared to conventional materials. Such advanced materials are, for example, lead halide perovskites (LHP). It is a group of hybrid organic-inorganic materials with a direct bandgap exhibiting unique optical properties. The high quantum efficiency of photoluminescence makes nanocrystals or thin films of LHP suitable candidates for the production of light-emitting diodes, solar cells and LCD displays. Their inexpensive and simple fabrication together with their unique optical properties makes LHP one of the most developed materials of the last decade. This diploma thesis aims to study the optical properties of CsPbBr3 perovskite nanocrystals using high lateral resolution methods. CsPbBr3 perovskite nanocrystals show intense anti-Stokes photoluminescence. These nanocrystals can emit light with a lower wavelength than that of the light that causes their photoluminescence. The nanocrystals are prepared in two different ways: by evaporation or by crystallization of the precursor in a solution of dimethylformamide. The morphology, photoluminescence properties and chemical composition of individual nanocrystals are studied. Each nanocrystal is studied individually and its size, shape, photoluminescence properties and chemical compounds are determined, which leads to a deeper understanding of the anti-Stokes photoluminescence of perovskite nanocrystals.

The Master´s thesis deals with the preparation of perovskite oxides by glycine synthesis with following characterization and analysis of catalytic activity. Especially is discussed crystallographic structure. In the theoretical part were first summarized the available information of the properties and usage of perovskite oxides. In the experimental part of the work was carried out the preparation of perovskite oxides and were made chemical analysis. Moreover a catalytic activity of selected perovskites has been studied and have been illustrated their crystal structure.

Die Existenz metallreicher Perowskite der Zusammensetzung (SE3X)M (X = O, N; SE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Er, Ho, Tm, Lu; M = Al, Ga, In, Sn) wurde untersucht. Die Charakterisierung der Proben erfolgte mit Röntgenpulverdiffraktometrie und Elementaranalysen (O und N). Oxide (SE3O)Al mit SE = La, Ce, Pr, Nd und Sm und (SE3O)In mit SE = Ce, Pr und Nd wurden erhalten. Die Reihe der Verbindungen (SE3N)Al (SE = La, Ce, Pr, Nd, Sm) wurde um die Seltenerd-Metalle SE = Gd, Tb, Dy, Ho, Er und Tm erweitert. Die metallreichen Perowskite (SE3N)Sn (SE = La, Ce, Pr, Sm) und (SE3N)Ga (SE = Ce, Pr, Sm, Gd, Tb) wurden erstmals beschrieben. Die thermische Stabilität (DSC) der Phasen (SE3X)M ist für die Nitride allgemein am höchsten. Nitride von Al und Ga zersetzen zwischen 1000 °C und 1200 °C, Stannide bleiben bis 1250 °C thermisch stabil. Messungen der magnetischen Suszeptibilität und der LIII-Absorbtionskanten sind in Einklang mit einer Elektronenkonfiguration SE3+. Die gemessenen elektrischen Widerstände sind charakteristisch für schlechte metallische Leiter. Verschiedene Gehaltschnitte SE3Al-(SE3X)Al und SE3In-(SE3X)In wurden mit Röntgenpulverdiffraktometrie und DTA untersucht. Die Oxide und Nitride (SE3X1-y)M (SE = La, Ce; X = N, O) weisen nur geringe Phasenbreiten auf. Die Carbide (Ce3C1-y)In zeigen hingegen signifikante Phasenbreiten. In den Systemen EA-In-N wurden röntgenografisch phasenreine Pulver von (Ca4N)[In]2 und (EA19N7)[In4]2 (EA = Ca, Sr) erhalten. Durch Elementaranalysen auf H, C, N, O, EA und In und Neutronenbeugung am Pulver können alternative Zusammensetzungen mit einer ausgeglichenen Ladungsbilanz im Sinne des Zintl-Konzepts für diese Phasen ausgeschlossen werden. Im System La-Al wurde die neue Phase La16Al13 beobachtet und an Einkristallen sowie an Pulvern charakterisiert. Das in der Literatur im Cu3Au-Strukturtyp beschrieben kubische Polymorph von Ce3Al wurde auf einen ternären metallreichen Perowskit (Ce3X)Al zurückgeführt.

This dissertation is devoted to the development of novel devices for optoelectronic and photovoltaic applications using the promise of inkjet printing with two-dimensional (2D) materials. A systematic approach toward the characterization of the liquid exfoliated 2D inks comprising of graphene, molybdenum disulfide (MoS2), tungsten diselenide (WSe2), and 2D perovskites is discussed at depth. In the first study, the biocompatibility of 2D materials -- graphene and MoS2 -- that were drop cast onto flexible PET and polyimide substrates using mouse embryonic fibroblast (STO) and human esophageal fibroblast (HEF) cell lines, was explored. The polyimide samples for both STO and HEF showed high biocompatibility with a cell survival rate of up to ~ 98% and a confluence rate of 70-98%. An inkjet printed, biocompatible, heterostructure photodetector was constructed using inks of photo-active MoS2 and electrically conducting graphene, which facilitated charge collection of the photocarriers. The importance of such devices stems from their potential utility in age-related-macular degeneration (AMD), which is a condition where the photosensitive retinal tissue degrades with aging, eventually compromising vision. The biocompatible inkjet printed 2D heterojunction devices were photoresponsive to broadband incoming radiation in the visible regime, and the photocurrent scaled proportionally with the incident light intensity, exhibiting a photoresponsivity R ~ 0.30 A/W. Strain-dependent measurements were also conducted with bending, that showed Iph ~ 1.16 µA with strain levels for curvature up to ~ 0.262 cm-1, indicating the feasibility of such devices for large format arrays printed on flexible substrates. Alongside the optoelectronic measurements, temperature-dependent (~ 80 K to 573 K) frequency shifts of the Raman-active E12g and A1g modes of multilayer MoS2 exhibited a red-shift with increasing temperature, where the temperature coefficients for the E12g and A1g modes were determined to be ~ - 0.016 cm-1/K and ~ - 0.014 cm-1/K, respectively. The phonon lifetime τ was determined to be in the picosecond range for the E12g and A1g modes, respectively, for the liquid exfoliated multilayer MoS2. Secondly, an all inkjet printed WSe2-graphene hetero-structure photodetector on flexible polyimide substrates is also studied, where the device performance was found to be superior compared to the MoS2-graphene photodetector. The printed photodetector was photo responsive to broadband incoming radiation in the visible regime, where the photo responsivity R ~ 0.7 A/W and conductivity σ ~ 2.3 × 10-1 S/m were achieved at room temperature. Thirdly, the synthesis of solution-processed 2D layered organo-halide (CH3(CH2)3NH3)2(CH3NH3)n-1PbnI3n+1 (n = 2, 3, and 4) perovskites is presented here, where inkjet printing was used to fabricate heterostructure flexible photodetector devices on polyimide substrates. The ON/OFF ratio was determined to be high, ~ 2.3 × 103 while the photoresponse time on the rising and falling edges was measured to be rise ~ 24 ms and fall ~ 65 ms, respectively. The strain-dependent measurements, conducted here for the first time for inkjet printed perovskite photodetectors, revealed the Ip decreased by only ~ 27% with bending (radius of curvature of ~ 0.262 cm-1). This work demonstrates the tremendous potential of the inkjet printed, composition tunable, organo-halide 2D perovskite heterostructures for high-performance photodetectors, where the techniques are readily translatable toward flexible solar cell platforms as well. Fourthly, metal contacts and carrier transport in 2D (CH3(CH2)3NH3)2(CH3NH3)n-1PbnI3n+1 (n = 4) perovskites is a critical topic, where the use of silver (Ag) and graphene (Gr) inks as metallic contacts to 2D perovskites was investigated. The all inkjet printed Gr-perovskite and Ag-perovskite photodetectors were found to be photo-responsive to broadband incoming radiation where measurements were conducted from λ ~ 400 nm to 2300 nm. The photoresponsivity R and detectivity D were compared between the Gr-perovskite and Ag-perovskite photodetectors, which revealed the higher performance for the Ag-perovskite photodetector. The superior performance of the Ag-perovskite photodetector was also justified with the Schottky barrier analysis using the thermionic emission model through temperature-dependent transport measurements. Finally, this dissertation ends with the description of the first steps for using solution-processed, inkjet printed perovskites for solar cells. The preliminary investigations include the discussion of the chemical formulations for the carrier separation layers, dispersion route, and the variation of solar cell figures of merit with processing.

Übergangsmetallfluoridverbindungen sind sehr vielversprechende Kandidaten für die nächste Generation von Kathoden für Alkaliionenbatterien. Dennoch verhindern einige Nachteile dieser Materialklasse ihre Anwendung in Energiespeichermedien. Metallfluoride haben eine stark isolierende Wirkung, außerdem bewirken die Mechanismen beim Lade-/Entladevorgang, große Volumenänderungen und somit eine drastische Reorganisation des Materials, welche nur geringfügig umkehrbar ist. Um diese Nachteile zu reduzieren, werden in dieser Arbeit innovative Syntheserouten für die Umwandlung von Metallfluoridverbindungen sowie deren Anwendung in Alkaliionenbatterien vorgestellt. Im ersten Teil werden MFx Verbindungen (M = Co, Fe; x = 2 oder 3) untersucht. Diese Materialien zeigen eine hohe Ausgangskapazität aber nur bei sehr geringen C-Raten und zudem sehr geringe Zyklisierbarkeiten. Ex-situ-XRD und -TEM zeigen, dass die geringe Umkehrbarkeit der Prozesse hauptsächlich aus der Umwandlungsreaktion während des Be-/Entladens resultieren. Im zweiten Teil werden sowohl die Synthesen als auch die elektrochemischen Eigenschaften von Perowskiten aus Übergangsmetallfluoriden vorgestellt. NaFeF3 zeigt hierbei exzellente Leistungen und Reversibilitäten. Die Untersuchung der Mechansimen durch ex-situ und operando XRD während der Be- und Entladeprozesse hinsichtlich verschiedener Alkalisysteme zeigt, dass das kristalline Netzwerk über den Zyklus erhalten bleibt. Dies führt zur hohen Reversibilität und hohen Leistung selbst bei hohen C-Raten. Der Erhalt der Kristallstruktur wird durch elektrochemische Stabilisierung der kubischen Konformation von FeF3 ermöglicht, welche normalerweise erst bei hohen Temperaturen (400 °C) beobachtet wird und durch geringere Reorganisationen innerhalb des Kristallgerüsts erklärt werden kann. Ähnliche elektrochemische Eigenschaften können für KFeF3 und NH4FeF3 beobachtet werden, wobei erstmalig von Ammoniumionen als Ladungsträger in Alkaliionensystemen berichtet wird. / Metal fluoride compounds appear as very appealing candidates for the next generation of alkali-ion battery cathodes. However, many drawbacks prevent this family of compounds to be applicable to storage systems. Metal fluorides demonstrate a high insulating character, and the mechanisms involved during the discharge/charge processes atom engender large volume changes and a drastic reorganization of the material, which induces poor reversibility. In order to answer these problematics, the present thesis reports the elaboration of innovative synthesis routes for transition metal fluoride compounds and the application of these fluoride materials in alkali-ion battery systems. In a first part, MFx compounds (M = Co, Fe; x = 2 or 3) are studied. Those compounds exhibit high initial capacity but very poor cyclability and low C-rate capabilities. Ex-situ X-ray diffraction and transmission electron microscopy demonstrate that the low reversibility of the processes is mainly due to the conversion reaction occurring during their discharge/charge. In the second part, the syntheses of transition metal fluoride perovskites are reported, as well as their electrochemical properties. NaFeF3 demonstrates excellent performances and reversibility. The study of the mechanisms occurring during its charge/discharge processes towards different alkali systems by ex-situ and operando X-ray diffraction reveals that its crystalline framework is maintained along the cycles, resulting in high reversibility and excellent C-rate performance. This retention of the crystal framework is possible by an electrochemical stabilization of a cubic conformation of FeF3, which is usually only observable at high temperature (400 °C), and can be explained by lower reorganizations within the crystal framework. Similar electrochemical properties could be observed for KFeF3 and NH4FeF3, where ammonium ions are reported for the first time as a charge carrier in alkali-ion systems.

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No description available.

<p dir="ltr">The separation of tellurium from cadmium telluride is examined using a unique combination of mild, anhydrous chlorination and complexation of the subsequent tellurium tetrachloride with 3,5-di-<i>tert</i>-butylcatechol. The resulting tellurium complex, Te(dtbc)₂, is isolated in moderate yield and features a 10³ to 10⁴ reduction in cadmium content, as provided by XRF and ICP-MS analysis. Similar results were obtained from zinc telluride. A significant separation between Te, Se, and S was observed after treating a complex mixture of metal chalcogenides with this protocol. These three tunable steps can be applied for future applications of CdTe photovoltaic waste.</p><p dir="ltr">We report the synthesis and characterization of the first series of tellurium and selenium complexes featuring an η⁵-cyclopentadienyl ligand. Reaction of Ph₃TeX (X = Cl, S₂CNEt₂) with MCp^R (M = Li, K; R = H, Me₄, Me₅) results in high yields of [Cp][TePh₃] (<b>1</b>), [Cp^Me4][TePh₃] (<b>2</b>), and [Cp*][TePh₃] (<b>3</b>), respectively. Similarly, reaction of Ph₃SeCl with LiCp and KCp* furnishes [Cp][SePh₃] (<b>4</b>) and [Cp*][SePh₃] (<b>5</b>). Each was characterized by X-ray crystallography, revealing similar η⁵-coordination with little distortion from an idealized half-sandwich geometry, presumably from the remaining lone pair on tellurium and selenium. The Te–centroid distances are relatively long (<b>1</b>: 2.770(3), <b>2</b>: 2.746(1), and <b>3</b>: 2.733(1) Å), suggesting a mostly ionic interaction. Se–centroid distances (<b>4</b>: 2.748(3), <b>5</b>: 2.707(2), 2.730(2) Å) were found to be surprisingly similar despite its smaller atomic radius. Compounds <b>2</b>, <b>3</b>, and <b>5</b> display rapid decomposition at room temperature, extruding a phenylated cyclopentadiene and the and the respective diphenylchalcogenide. The nature of bonding within these complexes was investigated through DFT methods and found to be primarily ionic in nature.</p><p dir="ltr">Synthesis of homoleptic zirconium and hafnium dithiocarbamate via carbon disulfide insertion into zirconium and hafnium amides were investigated for their utility as soluble molecular precursors for chalcogenide perovskites and binary metal sulfides. Treating M(NEtR)₄ (M= Zr, Hf and R= Me, Et) with CS₂ resulted in quantitative yields of homoleptic Group IV dithiocarbamates. Zr(k²-S₂CNMeEt) (<b>1</b>), Zr(k²-S₂CNEt₂)₄ (<b>2</b>), and Hf(k²-S₂CNEt₂)₄(<b>4</b>), a rare example of a crystal of a homoleptic hafnium CS₂ inserted amide species, were characterized. A computational analysis confirmed assignments for IR spectroscopy.<b> </b>To exemplify the utility of the Group IV dithiocarbamates, a solution-phase nanoparticle synthesis was performed to obtain ZrS₃ via the thermal decomposition of Zr(S₂CNMeEt)₄</p><p dir="ltr">Chalcogenide perovskites have garnered interest for applications in semiconductor devices due to their excellent predicted optoelectronic properties and stability. However, high synthesis temperatures have historically made these materials incompatible with the creation of photovoltaic devices. Here, we demonstrate the solution processed synthesis of luminescent BaZrS₃ and BaHfS₃ chalcogenide perovskite films using single-phase molecular precursors at sulfurization temperatures of 575 °C and sulfurization times as short as one hour. These molecular precursor inks were synthesized using known carbon disulfide insertion chemistry to create Group 4 metal dithiocarbamates, and this chemistry was extended to create species, such as barium dithiocarboxylates, that have never been reported before. These findings, with added future research, have the potential to yield fully solution processed thin films of chalcogenide perovskites for various optoelectronic applications.</p><p dir="ltr">Np(IV) Lewis base adducts were prepared by ligand substitution of NpCl₄(DME)₂. Using acetonitrile and pyridine, NpCl₄(MeCN)₄ (<b>1</b>) and NpCl₄(pyr)₄ (<b>2</b>), were isolated, respectively. All species were fully characterized using spectroscopic and structural analyses.</p>