Computational Prediction and Rational Design of Novel Clusters, Nanoparticles, and Solid State Materials

The creation of new materials is absolutely essential for developing new technologies. However, experimental efforts toward the material discovery are usually based on trial-and-error approach and thus require a huge amount of time and money. Alternatively, computational predictions can now provide a more systematic, rapid, inexpensive, and reliable method for the design of novel materials with properties suitable for new technologies. This dissertation describes the technique of theoretical predictions and presents the results on the successfully predicted and already produced (in some cases) unusual molecules, clusters, nanoparticles, and solids. The major part of scientific efforts in this dissertation was devoted to rationalizing of size- and composition-dependent properties of the materials based on understanding of their electronic structure and chemical bonding. It was shown that understanding relations between bonding and geometric structure, bonding and stability, and bonding and reactivity is an important step toward rational design of new, yet unknown materials with unusual properties. Our findings led to the discovery of the first simplest inorganic double helix structures, which can be used in the design of novel molecular devices. A significant part of this work also deals with the pseudo John-Teller effect, which potentially can be a powerful tool for rationalizing and predicting molecular and solid state structures, their deformations, transformations, and properties. Therefore, the works on the pseudo Jahn-Teller effect presented in this dissertation can be considered the steps toward further generalization and elevation of the pseudo Jahn-Teller effect to a higher level of understanding of the origin of molecular and solid state properties

Investigations of the reactivity of selected Pn ligand complexes

In this thesis the reactivity of the pentaphosphaferrocene Cp*FeP5 and the compound Cp'''NiP3 were investigated towards different nucleophiles, salt metathesis of the resulting anionic complexes, aswell as towards reducing agents. As a result various triple decker complexes were obtained and pentaphosphaferrocene was functionalized with organic groups

Halogenation of polypnictogen ligand complexes

After that a previous investigation from our group demonstrated that the iodination and the “classical” oxidation of En ligand complexes can afford different results and are therefore being considered as complementary tools for the synthesis of new polypnictogen complexes, we were interested in extending the investigation to other complexes as well as to other halogens or halogen sources. Therefore, the first object of this work was the investigation of the reactivity of [{CpMo(CO)2}2(μ,ɳ2:ɳ2-P2)] (A) towards halogens (I2, Br2) and halogen sources (PBr5, PCl5). Based on the obtained results, we were interested in expanding the investigation of the reactivity of halogens towards different Pn ligand complexes, whose redox properties have already been elucidated. Accordingly, the next object was the investigation of the reactivity of the triple-decker complex [(Cp*Mo)2(μ,ɳ6:ɳ6-P6)] (B) towards halogens (I2, Br2) and halogen sources (PBr5, PCl5). Finally, we were interested in how the nature of the En ligand and of the pnictogen atom involved could affect the outcome of the reaction. Thus, we wanted to explore a possible alternative way to obtain E-X bonds without using the harsh conditions required for halogenation reactions. Therefore, the next objectives were the investigation of the halogenation of the triple decker complexes [(Cp’’’Co)2(μ,ɳ2:ɳ2-E2)2] (E = As (C), P (D)) bearing two independent E2 units and the exploration of the possibility of quenching the cations of [(Cp’’’Co)2(μ,ɳ4:ɳ4-E4)][TEF]2 (E = P, As) with nucleophilic halides. In conclusion, the investigation of the reactivity of the heterobimetallic triple-decker complexes [(Cp*Fe)(Cp’’’Co)(μ,ɳ5:ɳ4-E5)] (E = P (E), As (F)) towards halogens (I2, Br2) and halogen sources (PCl5) was exploited. The results of these investigation show that the En ligand involved in the halogenation reactions was the variable with the highest influence on the different products obtained. It is not possible to find a general trend based on the halogen used because the outcome was always different from one polypnictogen complex to the other. While in some cases the reactivity of the respective En ligand compound was similar towards Br2 and Cl2 sources but completely different with I2 (e.g. with A and D), in other cases it was comparable to I2 and Br2 and different towards PCl5 (e.g. with E and F), or the same with all the halogens (e.g. with C). On the other hand, with B the reactivity was different towards all the halogen sources, with the formation of similar products among the iodinated or chlorinated derivatives or among the brominated and chlorinated ones. The halogenation of the tetrahedrane complex A, compared to B, has a higher chemoselectivity. The halogenation of the triple decker complexes led in general to a large number of products, especially when PCl5 was involved. Specifically, for B, it was observed that the chlorination reaction requires lower temperatures to isolate some of the products. The investigation of this reactivity for compounds C-F showed that the nature of the pnictogen ligand affects the final products, contrarily to what was observed for the one- or two-electron oxidation of the same compounds. In conclusion, the halogenation can be considered an additional tool for the synthesis of new functionalized En ligand complexes, whose related difficulties (high number of products, low yields) can be partly “balanced” by the opportunity of further functionalization of the products obtained

Oxidation and Coordination Chemistry of En Ligand Complexes under Weakly Coordinating Conditions

This thesis deals with the chemistry of substituent-free En ligand complexes (E = P, As, Sb, Bi) under weakly coordinating conditions. It consists of the following four parts in which different topics are elucidated: 1. Coordination chemistry of En ligand complexes towards monovalent metal cations M+ (M = Cu, Ag, Tl) featuring weakly coordinating anions (WCAs) 2. Oxidation chemistry of selected En ligand complexes and stabilization of the resulting cationic species by WCAs 3. Supramolecular coordination chemistry of trinuclear Cu(I) complexes stabilized by polyphosphine ligands and their reactivity towards En ligand complexes 4. Reactivity of En ligand complexes towards the trinuclear Lewis acid [(o-HgC6F4)3

Transition-Metal-Stabilized Heavy Tetraphospholide Anions

Phosphorus analogues of the ubiquitous cyclopentadienyl (Cp) are a rich and diverse family of compounds, which have found widespread use as ligands in organometallic complexes. By contrast, phospholes incorporating heavier group 14 elements (Si, Ge, Sn, and Pb) are hardly known. Here, we demonstrate the isolation of the first metal complexes featuring heavy cyclopentadienyl anions SnP42– and PbP42–. The complexes [(η4-tBu2C2P2)2Co2(μ,η5:η5–P4Tt)] [Tt = Sn (6), Pb (7)] are formed by reaction of white phosphorus (P4) with cyclooctadiene cobalt complexes [Ar′TtCo(η4-P2C2tBu2)(η4–COD)] [Tt = Sn (2), Pb (3), Ar′ = C6H3-2,6{C6H3-2,6-iPr2}2, COD = cycloocta-1,5-diene] and Tt{Co(η4-P2C2tBu2)(COD)}2 [Tt = Sn (4), Pb (5)]. While the SnP42– complex 6 was isolated as a pure and stable compound, compound 7 eliminated Pb(0) below room temperature to afford [(η4-tBu2C2P2)2Co2(μ,η4:η4–P4) (8), which is a rare example of a tripledecker complex with a P42– middle deck. The electronic structures of 6–8 are analyzed using theoretical methods including an analysis of intrinsic bond orbitals and magnetic response theory. Thereby, the aromatic nature of P5– and SnP42– was confirmed, while for P42–, a specific type of symmetry-induced weak paramagnetism was found that is distinct from conventional antiaromatic species

Effect of Penta-arylated Cp Ligands on Synthesis and Reactivity of Transition Metal Eₙ (E = P, As) Ligand Complexes

Until now, numerous Eₙ (E = P, As) ligand complexes of transition metals are reported, containing different ligand systems. However, examples with sterically highly demanding Cpᴿ ligands and perarylated cyclopentadienyl ligands in particular, are rather rare. They are restricted to compounds of manganese, iron and cobalt due to the lack of appropriate precursors for the preparation. The penta-arylated ligands Cpᴮᴵᴳ (C₅(C₆H₄ⁿBu)₅) and Cpᴾᴱᵗ (C₅(C₆H₄Et)₅) have been chosen for this task, since they provide the high steric demand and show good solubility in all established organic solvents. Furthermore, only few Eₙ (E = P, As) ligand complexes, bearing perarylated Cpᴿ ligands, have been investigated concerning their reaction behavior. This work provides an insight into the preparation and reactivity of transition metal (Mn, Fe, Ni) complexes, bearing the sterically highly demanding perarylated ligands Cpᴮᴵᴳ or Cpᴾᴱᵗ, respectively. Different Eₙ (E = P, As) ligand complexes of nickel were synthesized by E₄ activation or the reaction with the PCO⁻ anion. Moreover, the reactivity of the Eₙ (E = P, As) ligand complexes of manganese, iron and nickel has been investigated towards reactive metal(I) complexes (Fe, Co) at ambient temperatures and under thermolytic conditions

Polyphospholyl ligands as building blocks for the formation of polymeric and spherical assemblies

This thesis is concerned with polyphospholyl ligands as building blocks for the formation of polymeric and spherical assemblies. Within the scope of this work, the coordination chemistry of 1,2,4-triphosphaferrocenes, 1,2,4-triphospholyl anions and pentaphosphaferrocenes towards Cu(I) halides is investigated. Thereby, the first two substance classes preferably tend to the build-up of novel one-, two- and three-dimensional polymers bearing rather uncommon or even unprecedented structural motifs. On the other hand, pentaphosphaferrocenes are capable of the template-directed synthesis of discrete, nano-sized supramolecules. Within a comprehensive study on the template requirements a series of small molecules could be encapsulated in these spheres for the first time. In addition, hitherto unknown host complexes were obtained which all differ in size, charge and topology. Besides the coordination chemistry, also novel complexes and salts were synthesized and characterized, which can now be used as building blocks in supramolecular chemistry

Functionalization and Subsequent Chemical Reactions of Polypnictogen Ligand Complexes

In summary, this dissertation deals with the synthesis and functionalization of polypnictogen ligand complexes. Besides the successful realization of the latter with organic nucleophiles and electrophiles, a conceptually new way for the preparation of phosphines could be found. For the first time, a functionalized phosphorus atom could be removed from the coordination sphere of a transition metal. This finding was transferred to other substituents and the versatility of this method was demonstrated

Structure and Multi-Center Bonding: From Atomic Clusters to Solid Phase Materials

The work presented in this dissertation has been focused on structure, stability, electronic properties, and chemical bonding of atomic clusters and solid-state compounds. The common thread was development of chemically intuitive models and theoretical methods capable of describing and interpreting bonding and hence, structures of these compounds. Understanding how interactions between atoms in sub-nano clusters and solid-state compounds of certain compositions determine their structures, physical properties, and reactivities is essential for rational design of new materials, catalysts, and molecular devices. A significant part of this work presents joint experimental and theoretical studies of doped boron clusters. Several projects on carbon- and aluminum-substituted boron clusters were aimed at establishing their structures, energetic and electronic properties, and understanding bonding interactions. The dissertation introduces a series of peculiar clusters containing transition metal atoms inside perfectly symmetrical boron rings. These clusters, featuring planar octa-, nona-, and decacoordinated transition metal atoms, were designed based on a simple chemical bonding model governing stabilities of such species. One of the most important parts of this dissertation deals with chemical bonding in the solid state. The Adaptive Natural Density Partitioning method previously developed by the Boldyrev group at Utah State University has proven very efficient for understanding chemical bonding in clusters and complex molecules. In this work, a periodic implementation of this method has been developed, yielding a new theoretical tool capable of interpretation of bonding in solid state in chemically intuitive terms of localized and multi-center bonds

En Ligand Complexes - Synthesis, Functionalization and Transfer of Polypnictogen Units

This thesis deals with the synthesis, functionalization and reactivity of En ligand complexes (E = P, As, Sb) as well as the transfer of polypnictogen units. In more detail, it was shown that polypnictogen complexes of zirconium represent promising starting materials to transfer the polypnictogen units to the later transition metals iron, cobalt and nickel. Besides the transfer of the complete units, a degradation as well as aggregation can be observed. Reaction conditions and steric effects have a huge influence on the reaction outcome. Furthermore, the coordination behavior of the zirconium complexes towards Lewis acidic fragments and the reaction behavior towards nucleophiles was investigated. Besides, the formation of En ligand complexes with new structural motifs was possible. This was also the scope of the last part of this thesis. Thereby, the use of Cp*4Sb4 as an antimony source to form Sbn ligand complexes was investigated. The reaction towards ionic compounds and transition metal complexes with labile ligands leads to the desired products