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European journal of inorganic chemistry 2021(11), 1050-1056 (2021). doi:10.1002/ejic.202001091, Published by Wiley-VCH, Weinheim

Chemistry - a European journal 26(6), 1396-1405 (2020). doi:10.1002/chem.201904639, Published by Wiley-VCH, Weinheim

Acta crystallographica / C 72(11), 861 - 866(2016). doi:10.1107/S2053229616015515, Porphyrin assemblies display inter­esting photophysical properties and a relatively high thermal stability. Moreover, meso-functionalized porphyrins with virtually fourfold symmetry can be relatively readily synthesized from pyrrole and the appropriate aldehyde. A number of metallo derivatives of 5,10,15,20-tetra­kis­(4-cyano­phen­yl)porphyrin, where the N atom of the linear cyano group can act both as a donor for coordination bonds or as an acceptor for hydrogen bonds, have been structurally characterized by single-crystal X-ray analysis. The supra­molecular and structural chemistry of the corresponding 2- and 3-cyano­phenyl isomers of the parent porphyrin, however, has remained largely unexplored. The crystal structure of [5,10,15,20-tetra­kis­(3-cyano­phen­yl)porphyrinato]copper(II) (CuTCNPP) nitro­benzene tris­olvate, [Cu(C$_{48}$H$_{24}$N$_8$)]·3C$_6$H$_5$NO$_2$, has been determined at 80 K by synchrotron single-crystal X-ray diffraction. CuTCNPP exhibits a C$_{2h}$-symmetric $\alpha\alpha^{\beta\beta}$ conformation, despite an unsymmetrical crystal environment, and is situated on a crystallographic centre of symmetry. The Cu$^{II}$ ion adopts a genuine square-planar coordination by the four pyrrole N atoms. The 24-membered porphyrin ring system shows no marked deviation from planarity. In the crystal, the CuTCNPP mol­ecules and two nitro­benzene mol­ecules are face-to-face stacked in an alternating fashion, resulting in corrugated layers. The remaining nitro­benzene guest mol­ecule per CuTCNPP resides in the region between four neighbouring columnar stacks of CuTCNPP and sandwiched nitro­benzene mol­ecules, and is disordered over four positions about a centre of symmetry., Published by Wiley-Blackwell, Oxford

Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2022). = Dissertation, RWTH Aachen University, 2022, This dissertation involves fundamental principles of lithium-bridged hierarchical titanium(IV) helicates. These helicates are used to evaluate dispersive interactions in solution, as templates for asymmetric syntheses and as sensors for stereochemical dominance. The presented helicates are based on catechol ligands with an ester function in the 3-position. The titanium(IV) helicates form a monomer-dimer equilibrium in DMSO, which can be observed by NMR spectroscopy and quantified by the dimerisation constant (KDim.). The determined dimerisation constant (KDim.) allows conclusions to be drawn about stabilising dispersive interactions in solution, by taking other interactions into account. As a template for stereoselective reactions, diastereoselectivities of up to 68 % de can be achieved by Diels-Alder reactions on the hierarchical titanium(IV) helicates. Stereoselective additions are carried out on these helicates with an enantioselectivity of up to 32 % ee. Furthermore, the hierarchical titanium(IV) helicates serve as sensors for the visualisation of stereochemical dominance. For this purpose, two chiral ligands with opposite chirality are mixed in different ratios in order to form hierarchical helicates. In this process, the chiral information of one ligand is transferred to the direction of rotation of the superordinate titanium(IV) helicate according to the "induced fit" principle. CD spectroscopy is used to determine the helical sense of the triple-stranded helicates. The investigated directions of rotation follow either the known principle of the "majority rules", the "seargent and soldiers" principle or a new principle, which can also be called the "master and servant" principle. Here, the two chiral ligands compete for the direction of rotation of the superordinate helicate; the "master" species dominates the subordinate "servant" species and determines the direction of rotation of the resulting helicate. This happens even if the "master" species is the one in lower concentration., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2023). = Dissertation, RWTH Aachen University, 2022, Supramolecular cyclic coordination oligomers developed in the working group are excellent hosts for fullerene guest molecules as C60 and C70. It is therefore interesting to explore, whether other guest compounds of comparable size, such as gold clusters, can be stabilized in these host structures, as well. Therefore, the reaction of cyclic coordination oligomers with different gold compounds, i.e. triphenyl phosphine (TPP) Au(I)-complexes, TPP stabilized Au9- and Au55-clusters was investigated. Surprisingly, it could be observed that the reaction, irrespective of the starting compounds, resulted in the formation of TPP-stabilized Au11-clusters, comprising slight structural variations, but having a cluster core size complementary to the cyclic coordination oligomers cavity. In this dissertation the results and the attempts in understanding these unexpected findings are shown. Various coordination compounds such as dimers, triple and quadruple layer structures are used to investigate the influence of cavities and interactions., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2021; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2021). = Dissertation, RWTH Aachen University, 2021, The design of environmentally friendly and efficient catalysts for oxidation processes represents a longstanding research goal. The natural copper protein tyrosinase efficiently activates molecular oxygen, forming reactive copper-oxygen intermediates which catalyze phenolase and catecholase transformations. Inspired by nature, synthetic model systems are designed to imitate the active site of tyrosinase, exploring the structure-reactivity relationship of the copper protein. This doctoral thesis deals with the development of tyrosinase model systems based on aromatic hybrid guanidine ligands. These tailored ligand systems combine strong σ-donor properties of the bulky guanidine moiety with spatially smaller, weaker amine donor moieties, which are bridged by an aromatic spacer to rigidify the ligand backbone. Five structurally related hybrid guanidine ligands were developed to examine correlations between ligand structure and reactivity of the corresponding copper complexes. 29 copper(I) and copper(II) species with weakly coordinating and halide anions were synthesized, of which 15 were structurally characterized by single crystal X-ray diffraction. Oxygenation of suitable copper(I) complexes resulted exclusively in the formation of bis(µ-oxido) dicopper(III) complexes, which were characterized by UV/Vis, resonance Raman and X-ray absorption spectroscopy, cryo-UHR-ESI mass spectrometry as well as DFT simulations. Additionally, the formation of the bis(µ-oxido) species was quantified by spectrophotometric titration with ferrocene monocarboxylic acid. Formation and thermal decay kinetics were studied extensively by UV/Vis spectroscopy to investigate the influence of the ligand system, present anions and different additives on the model system. Several decomposition products were successfully isolated. The hybrid guanidine-stabilized bis(µ-oxido) dicopper(III) complexes are well-suited for tyrosinase-like oxygenation reactions of aromatic alcohols, as the hybrid ligands balance stabilization of the Cu2O2 core and accessibility for external substrates. A library of substrate classes was investigated to exceed the established substrate scope. Many new polycyclic aromatic alcohols including pyridinols, naphthols, quinolinols and indolols were introduced into tyrosinase chemistry. Substrates were hydroxylated and oxidized selectively to generate quinones which were captured exclusively as bent phenazine derivatives. The selectivity of the oxygenation reaction was confirmed by DFT calculations using the Fukui function, enabling a prognosis of the favored hydroxylation position. A simple salt metathesis of the catalyst allowed oxygenation reactions under mild conditions at room temperature, increasing the turnover of the system. Catalytic reactivity and selectivity of the model system were sustained despite enhancing the steric demand of the supporting ligand system. This systematic study opens the door to future developments on tyrosinase model systems to gain deeper insights into molecular mechanisms of the activation and transfer of dioxygen in biological systems., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen Univeristy, 2021; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2021). = Dissertation, RWTH Aachen Univeristy, 2021, This doctoral thesis describes the synthesis and characterization of discrete hybrid structures containing organic and inorganic scaffolds covalently linked through a single-metal ion. In the first part, we show how to combine a phthalocyanine and a monolacunary Keggin phosphotungstate into double-decker structures of 4f-centers (Tb(III) and Dy(III)) that exhibit strong magnetic anisotropy in axial ligand fields. Both tetradentate ligands, differing in their electronic properties and charges, encapsulate 4f-ion in a distorted square-antiprismatic coordination geometry. The magnetic studies reveal marginal magnetic anisotropy of terbium derivative, whereas the dysprosium analogue exhibit significant slow magnetic relaxation. In addition, the impact of electronic nature of phthalocyanine ring on the properties of hybrid complexes has been studied by replacing the peripheral protons with electron-donating (2,6-di-iso-propylphenoxy) and electron-withdrawing (fluorine) groups. UV-Vis spectra and cyclic voltammograms of derivatized complexes show a shift in the signals due to the changes in the electronic structure of complexes. The magnetic ac-data of these complexes reveal the impact of peripheral derivatization by preferring different pathways to the magnetization reversal. The second part describes the integration of a p-tert-butylcalix[4]arene and a monolacunary Keggin phosphotungstate into heteroleptic double-decker complexes of Ce(IV) and Zr(IV), representing the first example of combining these scaffolds through a single-metal ion. The cyclic voltammograms of these complexes display two reversible redox waves at positive potentials that could be attributed to the formation of phenoxy radical and phenoxylium cation on the p-tert-butylcalix[4]arene-skeleton. This represents the first report in which a calix[4]arene shows redox-active behavior upon coordination to metal, suggesting their potential as electroactive materials in single-molecule switches., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2020; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2021). = Dissertation, RWTH Aachen University, 2020, Scorpionates are a ligand class that has been successfully applied for the synthesis of model systems for copper-containing enzymes. If they can also be used for iron-based model systems is the fundamental question of this thesis. In the center of scientific discussion are iron(IV)oxo systems. Starting from bis(pyrazolyl)bipyridinylmethane ligands, functionalization at three locations is investigated and subsequently a new heteroscorpionate with a bis(pyridinyl) function is developed. The ligands and their resulting complexes are characterized in solid state and in solution and successively tested with oxygen transfer reagents. Only iron(II) salts with weak and non-coordinating anions are used. The spin state of the dissolved iron(II) complexes of the known ligands HC(Pz)2BiPy and HC(MePz)2BiPy strongly depend on the used solvent. The complex [Fe(HC(Pz)2BiPy)(MeCN)(OTf)](OTf) demonstrates temperature-induced switching behavior via spin crossover (SCO) in MeCN and a change of the spin state induced by coordination (CISSS) in methanol. A new bismeridional coordination motif for the ligand HC(Pz)2BiPy is found. The cation [{HC(Pz)2BiPy}2]2+ is obtained with three different anions. The sterically demanding methyl groups in HC(MePz)2BiPy prevent this bismeridional coordination. Both systems do not react with oxygen transfer reagents. Furthermore, the structure of the known complex [Fe(HC(Pz)2BiPy)Cl2] is found to be also dependent on the solvent. It decomposes in alcohols under oxidation of the ligand to [(Fe(BiPyCOO)Cl)2(��-OAlc)2]. New fluorinated bis-(pyrazolyl)bipyridinylmethanes are developed with a new CCl4-free synthesis, but so far, no iron complexes are obtained. For tert-butyl substituted ligands, fivefold coordinated complexes are obtained, which do not react with oxygen transfer reagents, yet. Two new hybrid ligands of guanidinoquinolines and bis(pyrazolyl)methanes are developed. Their complexes react with oxygen transfer reagents. Instead of a Fe(IV)oxo complex, only self-hydroxylation products are identified, indicating extremely short-lived Fe(IV)oxo intermediates. Finally, backbone functionalized ligands are examined. While pyrazole-based ligands (MeC(Pz)2BiPy) are not suitable to stabilize a Fe(IV)oxo unit, a pyridine-based ligand (MeC(Py)2Phen) is synthesized, which successfully stabilizes a Fe(IV)oxo species. Extensive comprehensive studies using geometric analysis, spectroscopy, and density functional theory (DFT) indicate octahedral compression/deformation for the bis(pyrazolyl)methane complex, caused by shorter distances between the pyrazolyl donors and the central carbon atom. These ligands wrap the iron center to a lesser extent. This results in an altered orbital splitting of the iron(II) complexes, which might influence the reactivity with oxygen transfer reagents., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2020; Aachen 1 Online-Ressource (XIX, 165 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2020, The present dissertation titled “Coordination compounds based on azine, thiocarbohydrazone and carbohydrazone ligands – supramolecular networks and discrete structures” focuses on the structural investigation of coordination compounds of three different Schiff base ligands with zinc(II) and with zirconium(IV). The main investigation methods used are single crystal structure analysis, nuclear magnetic resonance spectroscopy and ESI mass spectrometry. The synthesis and characterization of a novel pyridine-N-oxide-based azine ligand and the structure of two coordination compounds with known azine ligands and zinc(II) are discussed. In addition, five differently substituted salicylaldehyde-based thiocarbohydrazone ligands are structurally characterized and their coordination compounds with zinc(II)carboxylates in solution and in solid state are investigated. By self-assembly, one- and two-dimensional coordination polymers of different porosity are obtained and a discrete structure is described. In a further study with a tert-butyl-substituted thiocarbohydrazone ligand with zirconium(IV), the resulting zirconium(IV)oxo complex and a decomposition reaction of the ligand are presented. Finally, the synthesis and characterization of a novel pyridine-N-oxide-based carbohydrazone ligand is reported. As a result of the coordination of zinc(II) acetate, the structure of a circular helicate is elucidated. In total, this work contains the discussion of 19 new crystal structures., Published by Aachen

Dissertation, RWTH Aachen University, 2020; Aachen 1 Online-Ressource (VII, 223 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2020, Ruthenium terpyridines (Ru TP) are thanks to their linear structure and their high intensely studied complexes. Their application in nanoelectronics promises enormous potential, as the delocalized electron system offers conductivity, while the redox-active ruthenium centre enables electrical switching. In this thesis different methods to functionalize gold surfaces and gold nanoparticles (AuNP) have been investigated. In the first part of this thesis the syntheses and the characterization of the TP and Ru TP are discussed. The pH-dependent configuration change of the TP ligands could be shown. Further the syntheses and characterization of two new Ru TP complexes was proven using NMR, UV/VIS, IR and Raman spectroscopy, as well as mass spectrometry (MS). By stimulation the metal-ligand charge-transfer transition of the Ru-TP complexes resonant Raman spectra were also recorded. In the second part Ru-TP-wire were growth on Au surfaces in a stepwise approach. This approach was monitored via different surface sensitive methods, namely infrared-reflection-adsorption-spectroscopy and surface enhanced Raman spectroscopy and further followed by variable angle spectroscopic ellipsometry (VASE). To support the resulting spectra DFT calculation were performed and solid phase spectra of model substances recorded. By comparing those spectra and calculation of the dipole derivative unit vector the orientation of the molecules could be deduced. Through this the repetition count to bridge a two nanoelectrodes could be calculated and the suitability of those Ru TP wires could be tested. In the third part of this thesis synthesis conditions for the functionalization of AuNP with TP and Ru TP were found. The TP AuNP and Ru TP AuNP-hybrid systems were studied by means of UV/Vis, DLS, as well as Raman spectroscopy with two excitation wavelengths. Further TEM at high magnification were recorded to measure the distance between the AuNP. The DLS and TEM data indicate an increasing rising ligand layer thickness with increasing number of TP groups, while the UV/Vis date were found to be ambiguous due to solvent effects. Besides isotropically functionalized AuNP Janus-AuNP with TP and Ru TP ligands were synthesized, as well. Both ligands could be identified by measuring Raman at two excitation wavelengths. The distribution of TP and Ru TP could be determined using ICP-MS (induced coupled plasma MS). Further the coverage density and the footprint of all synthesized AuNP was determined through ICP MS. Moreover, the electrical properties of isotropic TP and Ru TP could already be investigated., Published by Aachen

Dissertation, RWTH Aachen University, 2020; Aachen 1 Online-Ressource (XV, 188 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2020, $C_3$-symmetric, triaminoguanidinium-based ligands with three chelating [ONN]-binding pockets are flexible building blocks for the formation of supramolecular coordination compounds. Some complexes with divalent metal ions are known to date, most of which have high negative total charges. For catalytic applications, positively charged compounds would be advantageous, which is why experiments on charge reversal have already been undertaken. In this work, trivalent metal ions (Y(III), Ga(III) and In(III)) as well as Hf(IV) ions were used and converted with known ligands. The decomposition of the $C_3$-symmetric ligand to a $C_2$-symmetric ligand was observed with Hf(IV). The targeted reproduction of this ligand led to a [2x2]-grid with Hf(IV) and in addition the catalytic oxidation of acetylacetone was observed. A preference of this $C_2$-symmetric ligand over the $C_3$-symmetric ligand could be demonstrated for Y(III) ions. However, the coordination of Y(III) ions is also possible by the $C_3$-symmetric ligands, whereby the coordination sphere of the metal ions is saturated by additional coligands and solvent molecules. The use of Ga(III) ions led to various single- or multi-layered coordination compounds. The formation of these complexes was investigated, whereby an influence of the substituents on the ligands and the bound coligands on the resulting compounds could be determined. In principle, it is possible to build one-, three- and four-layered complexes with different chelating and non-chelating specifically applied coligands. By using sodium ions, several such layered structures can be linked to form a 1D-polymer. Also, the coordination of In(III) ions by the $C_3$-symmetric ligands is possible and leads to comparable two-layered compounds. As coligands Acetylacetonate, acetate and methanolate ions were investigated. Two-layered structures can be combined to a dimer via methanolate ions. In the presence of sodium ions, the linkage to a 1D-polymer is also possible. With a sterically less demanding ligand and without sodium ions, a cyclic coordination oligomer consisting of several two-layered complexes is formed. This has a spherical cavity of 2026 $Å^3$ with a diameter of 15.69(2) Å and is therefore interesting as a host for larger molecules., Published by Aachen

Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource (85 Seiten) : Illustrationen, Diagramme (2019). = Dissertation, RWTH Aachen University, 2019, In this thesis three different synthesis strategies for dicyanamides and the successfully synthesized compounds Hg2[N(CN)2]2, Tl[N(CN)2], LiCs2[N(CN)2]3 , M(NH3)2[N(CN)2]2 with M = Ni, Co and their structures are presented and discussed. The synthesis of Hg2[N(CN)2]2 from Na[N(CN)2] and Hg2(NO3)2 was already described in 1922, and here the crystal structure was determined for the first time. Tl[N(CN)2] and LiCs2[N(CN)2]3 were produced by metathesis of the respective metal halides and Ag[dca] monocrystalline. Using the high solubility of NaCl compared to M(NH3)2[N(CN)2]2 with M = Ni, Co in an ammoniacal aqueous solution of Na[N(CN)2] and MCl2, single crystals of the diammine-metal(II)-bisdicyanamide compounds could be isolated. For these structures, it could be shown that the ammonia molecules involved form hydrogen bridges to the dicyanamide, resulting in cross-linking of the two-dimensional M[N(CN)2]2 planes. By SQUID measurements both compounds were characterized as paramagnetic. UV/VIS spectroscopy was also used to characterize the dicyanamide as a medium-field ligand and its incremental volume was calculated from the determined structures. In addition, experiments on the low-temperature synthesis of iron(III)carbodiimide are presented., Published by Aachen

Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource (169 Seiten) : Illustrationen (2020). = Dissertation, RWTH Aachen University, 2019, This doctoral thesis investigates the influence of Lewis acidic metals as ligands for homogeneous Palladium catalysis. Low valent palladium complexes featuring a diphosphinometal-ligand (PMP) are synthesized. The metalloligand contains different Lewis acidic s-orbital acceptors (M = LiI, CuI, ZnII) and is based on a diphosphorylated trispyridylamine (TPA) pre-ligand. The synthesis of two pre-ligand derivates, bis(diphenylphosphine)-trispyridylamine (DPPTPA) and bis(dicyclohexylphosphine)trispyridylamine (DCPTPA) is described in this work.Based on these pre-ligands different heterobimetallic complexes featuring different Lewis acidic metals are synthesized and isolated. A stabilizing co-ligand is needed for a heterobimetallic Li-Pd(0)-complex using pre-ligand DPPTPA while no stabilizing co-ligand is needed for complex [(dpptpa)ZnPd]2+ as well as for heterobimetallic M-Pd(0)-complexes (M = LiI, CuI, ZnII) featuring pre-ligand DCPTPA. Different heterobimetallic Li-Pd(II)-complexes were isolated as well in this work. All feature a trans conformation stabilized by a Li-X-interaction (X = Br-, Cl-).The M-Pd-interaction is quantified by NBO/NLMO-analyses. These analyses show an increasing interaction between the donor dx2-y2-Pd-orbital and the acceptor s-orbital in the order LiI < CuI < ZnII. The influence of the M-Pd-interaction on the reactivity is furthermore investigated in this work. An oxidative addition is observed when 4-bromoanisole is reacted with [(dcptpa)LiPd]+ whereas no reaction takes place when adding 4-bromoanisole to complex [(dcptpa)ZnPd]2+. A reductive elimination of 4-methoxy-biphenyl is proven by GCMS after reacting the isolated oxidative addition product of 4-bromoanisole and [(dcptpa)LiPd]+ with LiPh. The catalytic activity of the heterobimetallic complexes is also tested in different reactions. A similar catalytic activity of heterobimetallic complexes [(dcptpa)ZnPd]2+ and [(dcptpa)LiPd]2+ is observed in the allylic amination reaction. The catalytic activity decreases with an increased steric demand of the substrates.Complex [(dcptpa)ZnPd]2+, in contrary to complexes [(dcptpa)MPd]+ (M = Li, Cu), shows an excellent catalytic activity (TOF1/2 = 3000 1/h) in the hydrosilylation of CO2 with HSiMe2Ph yielding a silyl formate. Preliminary mechanistic investigations suggest the formation of a hydride complex which is stabilized by the Zn-Pd-interaction., Published by Aachen

Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource (125 Seiten) : Illustrationen (2019). = Dissertation, RWTH Aachen University, 2019, Several alkyl bridged bis(catecholketone or catecholester) ligands are designed and made in order to obtain helicates which cations triggered show some spring type dynamic motions.Within the helicates, in the presence of lithium cations the compressed coordination compound is formed, in which lithium cations are bound in the interior of the helicate. If those cations are removed by addition of [2.1.1]cryptand, the helicates expand due to repulsion between the negatively charged titanium triscatecholate units. Thus the helicates show a lithium ion triggered spring type motion. In addition, when the introducing chiral units into helicates, reversible switching is not only possible between those two states, furthermore, the twist of the aggregate also can be controlled. Thus, three out of four possible states of a helicate (expanded/left-handed, expanded/right-handed, compressed/left-handed) based on an enantiomerically pure ester bridged dicatecholate ligand are specifically addressed by introduction, exchange, or removal of countercations., Published by Aachen

Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource ( 108 Seiten) : Illustrationen, Diagramme (2019). = Dissertation, RWTH Aachen University, 2019, This doctoral thesis investigates the synthesis and crystal structures of different layered main group metal chalcogenides. In the first part, the synthesis and crystal structure of Ge4Se3Te are presented, a compound that is known for more than 50 years, but its structure has remained unknown. During this thesis high quality single crystals where synthesised, and the crystal structure of Ge4Se3Te could be determined for the first time. It consists of Se/Te-Ge-Ge-Se/Te layers with unexpected Ge-Ge interactions. The second part of the thesis deals with the polymorphism of In2Se3. Seven different polymorphs were synthesised and structurally characterised, which will help to understand the extraordinary physical properties of this material. In the third part, the Sb2Te3-Sb2Se3 system was structurally characterised by single crystal diffraction. The system crystallises in the Bi2Te3 structure type with A2-Sb-A1-Sb-A2 layers (A: Se/Te mixed sites). A preferred incorporation of Se inside the layer (A1) and unexpected chalcogenide-chalcogenide interactions are observed. In the last part the results of the thesis are discussed in terms of layer-layer distances and compared with literature. While in most layered chalcogenides, the layer-layer distance is in accordance with the van der Waals radius, it was observed, that chalcogenides with a group 5 metal show significantly to small layer-layer distances., Published by Aachen

Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource (XII, 114 Seiten) : Illustrationen, Diagramme (2019). = Dissertation, RWTH Aachen University, 2019, The thesis "High pressure behaviour of inorganic compounds and synthesis of halogenated formamidines" is divided into two parts. The first part deals with the behaviour of inorganic compounds under high pressures as they occur in diamond anvil cells. More precisely, the high-pressure behaviour of mercury and lead cyanamide was investigated. Furthermore, attempts were made to synthesize and characterize solid carbonic acid by high pressures. The two heavy metal cyanamides show the typical anisotropic compression behaviour of layered structures under pressure. For the lead compound, a transition to a more complex behaviour could be determined with increasing compression, in which a sevenfold coordination of the Pb2+ ion was avoided by tilting of the cyanamide unit. The attempt to determine basic crystallographic quantities of the crystal structure of carbonic acid by synthesis at high pressures was accompanied by the construction and development of several apparatuses: a ruby fluorescence spectrometer, a low temperature unit for glove boxes and the improvement of a high-pressure cell for neutron diffraction. These made it possible to index a previously unknown monoclinic phase of CO2 and D2O at 1.82(4) GPa. With a density of ρ = 2.4(1) g/cm3 it is plausible that this is the desired carbonic acid. In part 2 of this thesis, the crystal structures of the already known halogenated formamidinium halides XC(NH2)2X (X = Cl, Br, I) were determined for the first time. The existence of halogen bonds in the structures of Br and I could be proven. In addition, the first synthesis of halogenated formamidinium metalates from hydrogen cyanamide and the corresponding noble metal acids was successful. All compounds of part 2 are composed of halogenated formamidinium cations with two equally long partial C-N double bonds and isolated halides or halide metallates., Published by Aachen

Dissertation, RWTH Aachen University, 2018; Aachen 1 Online-Ressource (IX, 91 Seiten) : Illustrationen (2018). doi:10.18154/RWTH-2018-225391 = Dissertation, RWTH Aachen University, 2018, The utilisation of carbon dioxide and renewable resources as feedstocks for the chemical industry is highly desirable due to fossil fuel depletion and climate change. Chemicals directly produced from these substrates could lead to a circular economy. In this regard, the synthesis of organic carbonates directly from an alcohol and CO2 is a sustainable target transformation since alcohols are readily available from renewable resources. Organic carbonates then can be used as greener alternatives for existing high-boiling polar solvents, carbonation sources or monomers for polycarbonates. The present thesis investigated the direct synthesis of cyclic carbonates and, in particular, glycerol carbonate from glycerol and carbon dioxide by Brønstedt base catalysis. Glycerol is a trivalent alcohol that is a by-product from different biomass conversion processes especially of the biodiesel production and is currently considered as a waste product. The synthesis of the corresponding five-membered cyclic carbonate leads to a value-added compound as it possesses two different functional groups, a hydroxyl group and a 2-oxa-1,3-dioxolane group, leading to a wide reactivity and a broad range of industrial applications. The aim of this thesis is to provide a better understanding of the direct synthesis of glycerol carbonate from glycerol and CO2. The reaction produces water as by-product which should be removed to shift the equilibrium towards the product side. Two different approaches to remove H2O were investigated: I) the reactive dehydration by acetonitrile, and II) the water extraction by a continuous carbon dioxide flow. For both water removal methods, the influence of reaction parameters such as temperature, catalyst, CO2 pressure or additives on the product yield was studied. Furthermore, the reaction mechanism and the formation of side products were investigated. In the case of reactive water removal with acetonitrile as dehydration agent, glycerol carbonate was synthesised in 17 % yield from glycerol and carbon dioxide with potassium carbonate as catalyst. It was found that the glycerol carbonate yield reaches a maximum depending on the reaction conditions due to a complex reaction network leading to side and decomposition reactions. For the non-reactive water removal in the synthesis of glycerol carbonate, a new semi-continuous process was developed with CO2 acting both as reagent and stripping gas. Glycerol carbonate was synthesised in 13 % yield. Investigations on the reaction mechanism identified glycerol hemi-carbonate as intermediate and the subsequent cyclisation to the cyclic carbonate as rate-determining step., Published by Aachen

Dissertation, RWTH Aachen University, 2018; Aachen 1 Online-Ressource (XI, 132 Seiten) : Illustrationen (2018). = Dissertation, RWTH Aachen University, 2018, The two-dimensional structuring at the interface between HOPG (highly oriented pyrolytic graphite) and octanoic acid, was carried out using alkyl-chain substituted ligands. Hexagonally structured surfaces were accessible in which the porous structures are filled with additional molecules of ligand and octanoic acid. For the first time a coordination compound of these ligands with zinc(II)-octanoate was synthesized and deposited at the HOPG/octanoic acid interface. For a structure suggestion, a bromine-substituted ligand was synthesized. With this ligand, easily crystallizable coordination compounds for x-ray diffraction experiments should be accessible with good scattering power. Furthermore, novel reactivates were expected due to steric and electronic properties. The influence of the utilized bases for the deprotonation of the ligand was evaluated with the non-substituted pyridine-N-oxide based ligands due to their better availability. As bases and zinc(II)-precursor the carboxylates of zinc were used. Dimeric structures and coordination polymers were obtained which are in equilibrium with cyclic coordination oligomers [Zn24X24{(pyO)3L}12] (X = F, Cl, Br, N3, BF4, SCN, HCOO, OOct). The latter possess a spherical cavity with a diameter of 10.5 Å that can be used for host-guest-chemistry. The inclusion of fullerenes C60 and C70 was observed by single crystal x-ray diffraction and 13C-NMR experiments. The good reproducibility of this substance class could enable technical applications in the storage of gases like CH4, H2 or CO2., Published by Aachen

Dissertation, RWTH Aachen University, 2018; Aachen 1 Online-Ressource (194 Seiten) : Illustrationen, Diagramme (2018). = Dissertation, RWTH Aachen University, 2018, Due to the increasing use of petrochemical based plastics and the corresponding disadvantages an alternative has to be found. Polylactide (PLA) is a biodegradable polymer and is produced from renewable raw materials. Tin octanoate, which is toxic for the human organism, is nowadays commercially used as catalyst in the industrial PLA synthesis. This catalyst must therefore be replaced by a non-toxic alternative metal (e. g. zinc). Useful ligands are neutral guanidines which show high nucleophilicity, positive donor properties and great combination options of different substituents and bridging units.This dissertation thesis focuses on the optimisation of new aliphatic and aromatic hybridguanidine and aliphatic, chiral bisguanidine ligands with varying bridging units. The reaction of the ligand systems with zinc salts leads to novel zinc halide complexes, which were in detail characterized by means of X-ray crystallography, NMR, IR spectroscopy and mass spectrometer. Afterwards they were compared among each other. The obtained zinc halide complexes polymerise technical lactide after short reaction times without solvent to a colourless polymer which is of large importance for all industrial usecases. Besides, the chirality of the ligands should have an impact on the tacticity of the PLA so that the mechanical properties of the polylactide can be varied. A comparison between chiral bisguanidine and hybrid guanidine complexes relating to polymerisation of lactide and the influence of the bridging unit and of different zinc salts has been elaborated. In addition end group analyses by means of Maldi-ToF measurements were carried out, which provided crucial information for mechanism clarification. To clarify the molecular structures, density functional theory (DFT) calculations and natural bond orbital (NBO) analysis have been performed. The calculated donor-acceptor interactions of the complexes were compared and the donor strength of the coordinating nitrogen atoms was analysed. The influence of the quality of the lactide monomer and the addition of a coinitiator was investigated with two different setups in detail. In addition, one bis(chelate)-complex was tested in the polymerisation which shows outstanding activity in lactide polymerisation. In cooperation with the working group Kögerler robust bis(chelate) zinc complexes with anionic Schiff base ligands were successfully applied as catalysts for the ring-opening polymerisation of lactide., Published by Aachen

Dissertation, RWTH Aachen University, 2017; Aachen, 1 Online-Ressource (vii, 116 Seiten) : Illustrationen (2017). = Dissertation, RWTH Aachen University, 2017, The present work identifies the first canonical spin glasses of ternary iron nitrides MxFe4–xN (0 < x < 1), that are derived from ferromagnetic gamma'-Fe4N by substituting iron atoms with elements of the III. and IV. main group. For M = Sn, Ge, Ga, Al, Si the structural and magnetic properties are studied with experimental and quantum-chemicalmethods. Furthermore, the solid solution SnxGe1–xFe3N is characterized as a quaternary nitride. Combined DC and AC magnetometry reveal the M-rich nitrides Sn0.9Fe3.1N, Ge0.97Fe3.03N0.56 und Ga0.9Fe3.1N as spin glasses with RKKY indirect-exchange interactions. Within their solid solutions, the gradual incorporation of M is accompanied by a drastic weakening of the ferromagnetic interactions, which can be explained in SnxFe4–xN by the Stoner criterion on the basis of electronic structure calculations and a quantum-theoretical bonding analysis. Competing ferromagnetic and antiferromagnetic exchange interactions cause the long-ranged frustration of iron spins, and the spin dynamic below the spin glass transition temperature is characterized by a broad andasymmetrical distribution of relaxation times. This study concentrates on metastable nitrides SnxFe4–xN (0, Published by Aachen

Dissertation, RWTH Aachen University, 2017; Aachen, 1 Online-Ressource (viii, 193 Seiten) : Illustrationen, Diagramme (2017). = Dissertation, RWTH Aachen University, 2017, Gold nanoparticles (AuNP) show unique size-dependent physical and chemical properties. Their size, shape and surface functionalization can be easily modified by adjusting the synthetic procedure or by using specific stabilizing molecules. One parameter influencing the particles’ stability is therefore, the ligand molecule. In the present work, tailor-made ligand molecules were used to enable a cross-linkage of the ligand sphere on the AuNP surface to increase the stability. In order to realize a surface polymerization, diacetylene units within the molecular structure were used. They polymerize upon thermal treatment or ultraviolet (UV)-irradiation to build up so-called polydiacetylenes (PDA). Those DA units were integrated into the molecular scaffold, bound to the AuNP’s surface and subsequently polymerized. For applications in molecular electronics ligand molecules stabilizing AuNP have to fulfill certain requirements. It was elucidated, if these requirements were in coincidence with the ones needed for a successful polymerization. Therefore, a possible stability enhancement as well as the electrical transport characteristics of the AuNP were investigated. Taking the above mentioned considerations into account, the work emphasizes on four points. The first one covers the design and synthesis of the corresponding ligand molecules and their characterization. To gain an insight in the polymerization behavior, polymerization of those molecules was first investigated without AuNP. The next key aspect was the functionalization of AuNP and the characterization of this polymer metal hybrid system. The stability of those functionalized AuNP was investigated directly dependent on the polymerization condition. Those experiments revealed a limitation in stability enhancement. The fourth part covers some application-oriented experiments, which were performed with the functionalized AuNP. The electrical transport characteristics of a nanoelectrode device in which AuNP were integrated showed a nonlinear dependency of current on voltage. It could be described with a tunneling mechanism. Moreover, the possibility to remove the gold core via etching reaction was investigated to keep the ligand sphere as a hollow polymeric nanosphere. The adsorption behavior of nitrile terminated functionalized AuNP on possible electrode materials was also subject of investigation. Moreover, since nitrile groups are able to undergo complexation reactions, the complexation of the nitrile AuNP with a ruthenium complex was performed., Published by Aachen

$C_3$-symmetric, triaminoguanidinium based ligands are able to bind different metal ions strongly in their \textit{tris}-chelating [ONN] coordination pockets. Published structures predominantly consist of bivalent metals leading to negatively charged compounds. However, for a potential application in catalysis, a positive charge is preferred because negative or polarized substrates thus can approach the active sites. Consequently this work concentrates on the use of tetravalent metal ions. Three different imine ligands were synthesized by the reaction of a triaminoguanidinium salt with a salicylaldehyde derivative and the products were fully characterized. Additionally, the reduction of one imine compound to an amine could be performed, resulting in a better stability against hydrolysis. This new type of ligand could be converted to Zr(IV) and Sn(IV) complexes giving an insight into the binding properties of the unknown system. Coordination compounds of the imine ligand with Ti(IV) could be realized, confirming the ability to stabilize the preferred coordination environment. In this context, layered compounds with bridging Ti$_2$($\mu$-O) and Ti$_2$($\mu$-O)$_2$ units were observed. The metal ions exhibit exchangeable coligands indicating a promising use as catalyst. Therefore, the prepared compounds were tested for the polyaldol condensation of acetone. The valorization of acetone, as a low-cost platform molecule, is highly desired. Indeed, the oligomerization of up to 15 molecules could be verified. Resulting products show different contents of terminal hydroxyl groups, revealing branched structures. In addition, Zr(IV) compounds were investigated which lead to an enhancement of the conversion and to branched oligomers of up to 30 molecules. During the conversion of Zr(acac)$_4$ with one $C_3$-symmetric imine compound, the formation of octahedral Zr$_6$(OH)$_4$O$_4 {12+}$ clusters and the simultaneously decomposition of the ligand to an azine compound could be observed. The cluster consists of six octahedral arranged Zr(IV) ions. The faces of the octahedron are alternately capped by \ce{$\mu_3$}-OH$^{-}$ and $\mu_3$}-O$^{2-}$ ions. Four azine and four ethylidene bisacetylacetonate coligands saturate the coordination environment of the metal ions. Ethylidene bisacetylacetonate has formed via the condensation of acetylacetone and acetaldehyde under reaction conditions. The cluster formation was successfully reproduced by using directly the azine and acetylacetone. Two compounds with acetylacetonate in place of ethylidene bisacetylacetonate are present and the two structures differ in the arrangement of the coligands. In summary, coordination compounds of $C_3$-symmetric imine and amine ligands opened a new research field which can be a basis for further projects.

Gold nanoparticles have sparked enormous interest due to their unique properties, synthetic availability and biocompatibility. Especially, the preparation of stable and biocompatible hollow gold nanospheres (HAuNS) and gold nanorods (AuNR) with strong plasmonic near infrared (NIR) absorption in the optical window of biological tissue are on the rise for use in nanomedicine. Their size-dependent optical extinction and ability to absorb light of a certain wavelength and to transform it into heat, which is then delivered to their nearby surroundings, make those particles particular suited for diagnostic and therapeutic approaches. Therefore, this work focuses on the synthesis, characterization and functionalization of NIR-absorbing HAuNS and AuNR for an application as contrast agents in photoacoustic imaging or as photothermal absorbers for Alzheimer’s disease therapy. NIR-absorbing HAuNS were obtained via a reproducible approach starting from cobalt nanoparticles used as sacrificial template. For the control over the gold shell thickness an empirical law correlating the hydrodynamic diameter of the cobalt nanoparticles with the chloroauric acid concentration was developed. NIR-absorbing AuNR were prepared following the seed-mediated growth method. The modification of the ligand shell by commercially-available monodentate and self-synthesized bi- and tridentate methoxy terminated thiol-polyethylenglycol ligands lead to an increase of the stability and biocompatibility of HAuNS and AuNR. The preparation route allowed to obtain cetyltrimethylammonium bromide-free AuNR, which is vital for any clinical applications. The ligand footprint of those multidentate ligands on HAuNS and AuNR was evaluated for the first time.The suitability of HAuNS and AuNR in research on Alzheimer’s disease was enhanced by coupling biological recognition units to the nanoparticle surface. Peptides with the CLPPFD sequence selectively binds to the hydrophobic domains of amyloidogenic structures, being the monomer of Aβ-amyloid fibrils, which are themselves causatively associated with Alzheimer’s disease. The CLPFFD peptide was either bound directly to the particle surface or indirectly to the particle-protecting polyethylenglycol ligand shell. The fundamental suitability of the NIR-absorbing HAuNS and AuNR conjugates for applications in nanomedicine was shown by in vitro studies. This research contributes to the development of new NIR-absorbing contrast agents, potentially allowing the early discovery of tumors, and the development of new photothermal absorbers for Alzheimer’s disease therapy.

Ultrasmall gold nanoparticles (usAuNP) with core diameters below 2 nm have attracted increasing scientific interest due to their special properties, which arise from size quantization effects. They are promising candidates for biomedical applications, because they approach the size of subcellular units. For this kind of application their bioactivity has to be evaluated. In this context this work focuses on the synthesis, characterization and bioactivity of water-soluble phosphine- and diphosphine-stabilized usAuNP. Water-soluble tetrasulfonated bis(diphenylphosphino)alkanes with different alkyl chain lengths were synthesized via the sulfonation of their water-insoluble derivatives. A reduction of AuCl3 in the presence of a tetrasulfonated diphosphine ligand yielded usAuNP with particle core diameters between 1-2 nm. Depending on the used diphosphine ligand different dipsersities were achieved. 31P-NMR spectroscopy revealed a bidentate binding of the ligand to the Au-surface as main binding motif. A ligand exchange reaction on [Au9(PPh3)8](NO3)3 with a water-soluble diphosphine ligand yielded diphosphine-stabilized usAuNP with a particle core diameter around 1 nm. However, no crystals for single-X-ray diffraction (XRD) analysis could be obtained for any of the synthesized usAuNP. The lack of precise structural information prevented their use in bioactivity studies. The synthesis of a recently described 1.1 nm sized triphenylphosphine-monosulfonate (TPPMS)-stabilized Au9-cluster was greatly improved. This particle was used in patch-clamp experiments together with TPPMS-stabilized AuNP of larger size, to evaluate their blocking potential on the human-ether-á-go-go (hERG) ion channel. Therein, AuNP with a particle core diameter of 1.4 nm showed the highest blocking effect. As an alternative to single-XRD analysis, high resolution transmission electron microscopy (HRTEM) was tested as structural characterization method. For a first evaluation of HRTEM as structural characterization method AuNP with a core diameter of 4 nm and ultrathin carbon supports were used, leading to images of the AuNP structures with a high resolution. This concludes that HRTEM might also be used as a structural characterization tool for usAuNP.

Idealized C2 -symmetric 2,2′ -bipyridine based ligands are valuable building blocks for thesynthesis of supramolecular architectures. First of all, new ligands have been synthesized with different functional groups on the ligand’s backbone. Six new ligands based on4,4′ -diamino-2,2′ -bipyridine became available. The most stable one was applied in thesynthesis of coordination compounds.The first applied synthesis plan is based on idealized C2 -symmetric palladium complexes,which are synthesized via several preceding steps. Both, the complexes and their precursor were successfully characterized by crystallography. By applying these complexes ina one-pot synthesis in conjunction with transition metal salts and a base, supramolecular architectures should be designed. While formation of the imine was indeed observed,decomposition of the schiff’s base also occured under the chosen conditions with time.Supramolecular structures were not formed.The second synthesis route was improved by performing all reaction steps under strictinert conditions in a stepwise manner. The previously observed decomposition of the imine was prevented effectivly. Thereby, the synthesis of three ligands by the derivatizationwith different aldehydes succeeded. The 3,5-dibromo derivative was successfully applied inthe synthesis of hetero- and monometallic model complexes. Furthermore, the synthesisof square-planar idealized C2 -symmetric palladium complexes was successfully completed.However the formation of supramolecular architectures could not be proved.In order to stabilize the labile imine bond of the 3,5-dibromo substituted ligands, thesebonds were reduced to amines in the third applied synthetic strategy. The synthesis ofequimolar and 2:1-coordination compounds with palladium and platin salts was successful. In the following synthesis of supramolecular structures with different cadmium(II)salts,octahedral cadmium complexes were obtained, but no supramolecular cages.The synthesis of the idealized C2 -symmetric ligands and their corresponding coordinationcompounds was successful. The formation of supramolecular architectures by application ofthese compounds remains however challenging and provides due to the easy derivatisationthe basis for further research projects.

In this thesis a new derivative of a ligand, Tris-(2,3-Dihydroxybenzene)-triaminoguanidiniumchloride ([H6(OH)3L]Cl, 1), was synthesised. Besides this, the coordination sites of the ligand [H6Br3L]Cl and [H6Br3(OMe)3L]Cl were selectively blocked with [MCl2(PR3)2] (M=Pt2+, Pd2+ und R=Et, Ph) (2 to 7). A second X-Ray measurement of 2 allowed the characterisation of a side product of the selective blocking from [H6Br3L]Cl with [PtCl2(PPh3)2]. In the two complexes 6 and 7, a triazol fomation was observed for the first time. Starting with the synthesised complex 5, heteronuclear complexes with CdCl2·2H2O and ZnCl2 were obtained (8 to 10). Furthermore the first heteronuclear copper complex was synthesised as [{Cu2(µ-OCH3){Pt(PPh3)}(Br3(OMe)3L)}2] ·12 EtOH· 4H2O(11). Besides those complexes various coordination oligomers (12 to 17) were obtained in reactions with other metal salts (EuCl3, GdCl3, Ga(acac)3, SnCl2 and CdCl2). One of this oligomer (17) was not synthesised in a solvent. Instead of this no solvent at all was used and the very first mechanochemicaly sythesised complex based on a derivative of [H6L]Cl was synthesised in the group of I. M. Oppel.