1,721,538 research outputs found
Dilithiation of Bis(benzene)molybdenum and subsequent isolation of a Molybdenum-Containing Paracyclophane
No full textThe homoleptic sandwich complex bis(benzene)molybdenum, [Mo(eta(6)-C6H6)(2)], was successfully dilithiated by employing an excess of BuLi in the presence of N,N,N',N'-tetramethylethylenediamine (up to 6 equiv each) at slightly elevated temperatures furnishing the highly reactive, ring metalated species [Mo(eta(6)-C6H5Li)(2)]center dot tmeda in high yields. Alternatively, this compound was synthesized upon prolonged sonication with 5 equiv of (BuLi)-Bu-t/tmeda without heating. An X-ray crystal structure determination revealed a symmetrical, dimeric composition in the solid state, i.e., a formula of [Mo(eta(6)-C6H5Li)(2)](2)center dot(thf)(6), where the six-membered rings are connected by two pairs of bridging lithium atoms. The synthesis of an elusive ansa-bridged complex failed in the case of a [1]bora and a [1]sila bridge due to the thermal lability of the resulting compounds. Instead, reverse addition of the dilithio precursor to an excess of the appropriate element dihalide facilitated the isolation of several unstrained, 1,1'-disubstituted derivatives, namely, [Mo{eta(6)-C6H5(BN(SiMe3)(2)X)}(2)] (X = Cl, Br) and [Mo{eta(6)-C6H5((SiPr2Cl)-Pr-i)}(2)], respectively. However, the incorporation of a less congesting [2]sila bridge was accomplished. In addition to the formation of [Mo{(eta(6)-C6H5)(2)Si2Me4}], a molybdenum-containing paracylophane complex was isolated and characterized by means of crystal structure analysis. The ancillary formation of 1 equiv of bis(benzene)molybdenum strongly suggests that this species is generated by deprotonation of the ansa-bridged complex by the dilithiated precursor and subsequent reaction with a second equivalent of the disilane
Silver Complexation by Metallacryptates
Full text linkWe report the first complete characterization of metallycryptates encapsulating Ag(I) cations: carboxylato ligands derived from l-proline and l-alanine chelate and bridge six Cu(II) centres arranged in a slightly distorted octahedral fashion. Eight oxygen atoms of these ligands are disposed in square-prismatic geometry and coordinate the monovalent cation. Two alternative metallacryptates based on alanine have been identified which differ with respect to aggregation: a solid in which pairs of encapsulating sites are formed competes with an infinite chain of M(I) coordinating sites. In contrast, the individual encrypting moieties are arranged as overall neutral and isolated molecular species in the proline-based metallacryptate. This proline derivative can accomodate Ag(I) and Na(I) cations and form a solid solution. Susceptibility measurements confirm ferromagnetic interactions between the Cu(II) within the hexanuclear proline cryptate and thus underline the similarity between solids accommodating Na(I) and Ag(I). Spectroscopic results suggest that these metallacryptates hardly dissociate in methanol solution
Organofunctionalization of polyoxometalates and investigation of their reactivity towards heterometals
No full textPolyoxometalates (POMs) are inorganic metal-oxygen cluster anions displaying exclusive nanoscale topologies of a large structural and compositional variety, and exhibiting a multitude of appealing properties like electronic versatility, structural rigidity, adjustable by countercations solubility as well as thermodynamic and redox stability. Among POMs, a sub-class of lacunary polyoxotungstates (POTs) attracts special attention due to their ability to incorporate a vast number of transition metals (TMs) and lanthanides (LnIII) as well as stabilize their multinuclear assemblies. Reports on potential applications of the heterometallic POT derivatives in different areas, such as catalysis, medicine, and materials science, frame a diverse range of properties of these species. Organofunctionalization has been widely recognized as a possibility to further extend the structural variety of polyanions, tune their electronic properties, and can also be used for stabilization of otherwise unstable discrete metal-oxo moieties. Organophosphonates and arsonates RXO32− (X = PV, AsV) providing a rigid tetrahedral XO3 site able to anchor on metal oxide surface as along with an organic group R which could be used for post-functionalization of hybrid organo-POT derivatives as well as for their controlled grafting on various surfaces represent a special interest from this prospect. Motivation behind this research work was to explore the potential of organophosphonate-functionalized POTs as innovative precursors for the design of new hybrid heterometal-substituted POTs and POT-based supramolecular assemblies of interest for applications in magnetism and catalysis as well as preparation of novel organophosphonate- and arsonate-decorated polyanions. Chapter 1 of this dissertation summarizes the history of POMs and discusses their intrinsic properties and developments concerning their applications in magnetism, medicine, catalysis, and preparation of hybrid materials. Chapter 2 gives an overview of materials and methods employed in this research work. The results obtained in the course of the Ph.D. work are presented in Chapters 3 – 5. In Chapter 3 results on the investigation of reactivity of phenylphosphonate-functionalized POTs [P4W24O92(C6H5PO)2]16− ({P4W24(PhP)2}) towards various heterometals in aqueous media are discussed. Innovative synthetic strategies utilized in this work led to the formation of novel transition metal and lanthanide-containing POTs based on unique polyanionic moieties that have not been ever reported before and cannot be synthesized using conventional POT precursors. Five sub-chapters summarize synthesis and investigation of twenty-three discrete polyanions, most of which are complexes of POT with magnetic TMs or LnIII ions. In the course of this research line, I observed a great tendency to the dissociation of organophosphonate groups from the POT precursor following by a rearrangement of the POT skeleton. Only in CoII and VV derivatives the original {P4W2(PhP)2,} structural moiety has retained its integrity. Most novel polyanions showed stability in solution and interesting electrochemical behavior which can serve as an important base for their potential applications. Chapter 4 summarizes the homo- and heterometallic derivatives obtained by self-assembly reactions of [-H2P2W12O48]12− ({-P2W12}) with 2-aminophenylarsonic acid. It appeared that the addition of divalent heterometals (MnII, CoII, and NiII) in the reaction mixture strongly influences the dimerization path of {-P2W12} moieties and leads to coordination polymers based on POTs with a completely different structure than that obtained in the absence of a heterometal. In total, one novel organoarsonate-functionalized homometallic POT, as well as three heterometallic derivatives with chain-like structures, have been prepared and characterized by various analytical techniques. Chapter 5 describes a 3D supramolecular assembly based on unique organophosphonate-functionalized POTs, [-P2W12O48(C6H5PO)2]10−, barrel-shaped -cyclodextrin molecules as well as well-known polyanions of Wells-Dawson type, [-P2W18O62]6−, obtained in one-pot self-assembly reaction of {-P2W12}, phenylphosphonic acid and -cyclodextrin. Solution studies unambiguously confirmed that the interactions between the building units of the supramolecular assembly retain also in aqueous media. Chapter 6 recapitulates the specific conclusions and outlook of individual sub-chapters. It also involves the discussion about the scope of synthesized advanced polyanionic compounds in a broader context, e.g. molecular electronics, spintronics, or in competitive heterogeneous catalytic systems
Rational design of bimetallic coordination polymers by utilizing heteroditopic ligands : synthesis, structural analysis and thermal decomposition
No full textCoordination polymers are handled as promising candidates for future key technologies such as hydrogen storage or catalytic applications; the latter make up a majority of processes in the chemical industry. Compared to polymers solely constructed of covalent bonds like polyethylene (PE), coordination polymers are often crystalline. This opens up the possibility to use single crystal X-ray diffraction, which utilizes the interaction of X-rays with crystalline material to obtain information of the arrangement of atoms within the crystal. This method is a cornerstone of this thesis, as the information on intra- and intermolecular interactions can directly be analyzed and compared. The main focus of this thesis lies on heterobimetallic coordination polymers, which strive to combine properties of two metals in one polymer. Therefore, ligands are designed which selectively join two different metal cation species into one coordination polymer. This selectivity is achieved by using a ligand with two spatially separated and chemically different donor sites. On one site an acetylacetone will be used, while the other site bears an N donor, such as a nitrile or a pyrazole. The difference in Pearson hardness of the two binding sites accomplishes the selectivity towards different metal species. The most promising ligand of this thesis combines the acetylacetone with a trimethylpyrazole. Additionally, these bimetallic coordination polymers are thermally decomposed to obtain a complex heterogeneous solid. This solid is then tested for catalytic activities. Besides this overall target species, every organic molecule and every intermediate product is structurally analyzed where possible and discussed in relation to the literature. The N donor sites are cocrystallized with halogen bond donors. The single crystal diffraction of these cocrystals provides useful insights about the strength and nature of the N donor. For the trimethylpyrazole functionalized ligand all of the aforementioned steps are discussed in this thesis. Its synthesis is optimized and conducted on a multi-gram scale. The ligand selectively binds hard cations like Fe(III) on the acetylacetone site, whilst soft cations like Au(I) are bound on the pyrazole site. Multiple heterobimetallic species are presented, including the interesting combination of Fe(III) and Ag(I), which could lead to a potential catalyst after thermal decomposition. The potential catalysts exhibit reflections of the base metal oxide as well as reflections of the noble metal in oxidation state 0. First studies on of the decomposed species suggest a high surface area as well as small noble metal nanoparticles, which are smaller than those produced by common catalyst preparation methods. The actual tests for catalytic activity could not be conducted in the timeframe of this thesis; however, they are planned for the near future. The halogen bonding adducts exhibit contacts within the expected range for a pyrazole...I contact. Interestingly, the hydrohalides of the ligand do indeed cocrystallize with halogen bond donors. This partly gives rise to extended structures, in which hydrogen as well as halogen bonds coexist. The direct comparison of these related yet different interactions in the same crystal is conducted. An extended discussion of the theoretical electron density in these systems obtained by DFT methods utilizing Bader's theory of "Atoms in Molecules" is also presented
Synthesis, crystal structures and physical properties of metal guanidinate and cyanoguanidine coordination compound
No full textNitrogen-based materials have attracted widespread attention, especially in basic research and applications fields. Among many nitrogen-based compounds, guanidine-based compounds have attracted attention of scientific researchers since the pure guanidine was discovered by Strecker in 1861. As a nitrile derived from guanidine, cyanoguanidine also comes into the public eye since Beilstein and Geuther discovered the cyanoguanidine molecule at the end of the 19th century. This thesis describes the synthesis and structure of several metal guanidinate and transition metal cyanoguanidine coordination compounds, which may be expected to display interesting magnetic and nonlinear optical properties. Guanidine is a very strong organic base, similar to alkali hydroxides, with a pKb = 0.4. Whilst free guanidine is easy to be protonated by an acid, deprotonating free guanidine is a difficult task. Here we utilized ammonothermal syntheses to explore the feasibility of new guanidinates. Indeed, we have obtained a novel magnesium guanidinate phase, Mg(CN3H4)2, from guanidine precursors. The structure was determined from powder X-ray diffraction data to crystallize in the monoclinic space group P21/c. In the structure, every magnesium atom is coordinated to three guanidine molecules and it appears that one guanidine molecule bonds to the magnesium atoms through two nitrogen atoms with coordinated bonds, whilst the other two coordinates through a single nitrogen atom. Moreover, the adjacent magnesium atoms are connected by the guanidine anions, forming infinite chains. From the IR spectrum, we judge that the compound is singly deprotonated guanidinate. For water-sensitive solutes and reactions, ammonothermal synthesis is the best choice. On the contrary, for the stable ligand cyanoguanidine, aqueous synthesis is well suited and was used to good effect in the preparation of new transition metal cyanoguanidine compounds. Due to the existence of lone pairs at four nitrogen atoms of cyanoguanidine, cyanoguanidine is widely employed as a ligand in the synthesis of coordination compounds with transition metals. Via aqueous synthetic routes, we have68 obtained several new cyanoguanidine compounds: Cu(C2N4H4)2Br2·2(H2O) and Co(C2H4N4)2(H2O)4·2Br·2H2O, Co3(C2H4N4)8(H2O)8·6Br, Co(C2N4H4)2Cl(H2O)3·Cl·H2O, Cd(C2H4N4)2Cl2, Cd(C2H4N4)2I2, Mn(C2N4H4)2Cl2(H2O)2, Mn(C2N4H4)2Br2(H2O)2, ZnC2N4H4Br2 and Zn(C2N4H4)2I2 and ZnC2N4H4SO4H2O. There are two coordinated sites in cyanoguanidine, namely, the inner and terminal nitrogen atoms, which may also coordinate to transition metals atoms due to the lone pair of N atoms. With the exception of ZnC2N4H4Br2 and ZnC2N4H4SO4H2O all other cyanoguanidine compounds prepared are bonded exclusively to ligand by the terminal nitrogen atoms (C≡N). IR spectroscopy confirms the presence of the cyanoguanidine ligand which shows an appreciable blue shift of C≡N nitrile group due to the coordination of central metal atoms, compared with the hydrogen bonding present in the free cyanoguanidine ligand. For ZnC2N4H4Br2 and ZnC2N4H4SO4H2O, the central zinc atoms are coordinated to the ligand by both bridging and terminal N atoms, forming infinite chains. It is interesting that Co(C2H4N4)2(H2O)4·2Br·2H2O and Co3(C2H4N4)8(H2O)8·6Br were obtained from distilled water and methanol, respectively. Furthermore, in this work, we also investigated the magnetism. As a result of the d9 electron configuration of Cu(II) (S = 1/2) and d7 (S = 3/2) configuration of Co (II) compounds containing these cations, such phases may possess interesting magnetic properties. Magnetic susceptibility measurements of Cu(C2N4H4)2Br2·2(H2O) and Co3(C2H4N4)8(H2O)8·6Br then go on to reveal weak antiferromagnetic interactions，and Co(C2H4N4)2(H2O)4·2Br·2H2O shows isolated or very weakly interacting Co2+ centers. DFT calculations also confirms the antiferromagnetic ground state with a particular configuration. Finally, we speculate that ZnC2N4H4Br2, which crystallizes in a non-centrosymmetric crystal structure, may show promising NLO properties due to the unusual coordination of the cyanoguanidine ligandwhich may result in a strong optical anisotropy and non-zero nonlinear optical coefficients. Unfortunately, we could not synthesize the phase pure ZnC2N4H4Br2 compound
Exploring dicarboxylic acids as ligands in multidimensional coordination networks
No full textThe coordination chemistry of several different dicarboxylic acids with non-toxic metal cations was investigated. Twelve new crystal structures of discrete complex molecules or coordination polymers were obtained and investigated regarding their structural and physical properties. The experiments conducted for this thesis can be divided into three classes of acids: Using amino acids and en-type coligands yielded the new coordination compounds AM3 and AM4; tartaric acid and its derivatives ditoluoyltartaric acid (dptta) and dibenzoyltartaric acid (dbta) yielded the new crystal compounds TA1 – TA8, some of which feature similar coligands as the amino acids. Finally, coordination compounds of dipicolinic acid and its para-substituted derivatives 4-chloro-dipicolinic acid and 4-hydroxy-dipicolinic acid with Ni(II) and Zn(II) were synthesised (DPA1 – DPA6)
Koordinationsverbindungen basierend auf Azin-, Thiocarbohydrazon- und Carbohydrazon-Liganden : Supramolekulare Netzwerke und diskrete Strukturen
No full textThe 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
Tailoring heteroditopic ligands with S and P donors for heterometallic coordination polymers : ligand design, synthesis and structural properties
No full textCoordination polymers represent a promising class of compounds for innovative solutions in the design of materials. They combine the inherently intriguing properties of coordination compounds with the possibility to adjust material properties with the design and topology of the polymer network. This enables an increased stability and longevity in applications such as catalysis, magnetism, optics, pollutant separation and hydrogen storage. Their insolubility makes a solid state characterisation with diffraction methods like powder and single crystal X-ray diffraction indispensable. The latter is the key technique used for the investigations in this thesis as it reveals how atoms and molecules are arranged in a crystalline solid. The topic of this thesis is the design of organic molecules that are suitable ligands for the formation of coordination polymers which selectively incorporate two different metal cations, namely heteroditopic ligands. For this purpose, the preferential interaction between Lewis acids and bases of matching Pearson character is used. Thus, the ligands have a soft and a hard coordination site. For the hard coordination sit
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