Zur Elektronenstruktur hochsymmetrischer Verbindungen der f‐Elemente. 41 Synthese,Kristall‐, Molekül‐ und Elektronenstruktur eines Bis(cyclohexylisonitril)‐Addukts des Grundkörpers Tris(bis(trimethylsilyl)amido)erbium(III) sowie Elektronenstrukturen ausgewählter Monoaddukte

Electronic Structures of Highly Symmetrical Compounds of f Elements. 41 Synthesis, Crystal, Molecular and Electronic Structure of a Bis(cyclohexylisonitrile) Adduct Derived from the Tris(bis(trimethylsilyl)amido)erbium(III) Moiety and Electronic Structures of Selected Mono Adducts The reaction of tris(bis(trimethylsilyl)amido)erbium(III) (Er(btmsa)₃) with two equivalents of cyclohexylisonitrile yields the corresponding bis adduct [Er(btmsa)₃(CNC₆H₁₁)₂] ( 1 ). Complex 1 crystallizes in the monoclinic space group C2/c with a = 2542.9(11) pm, b = 1208.4(4) pm, c = 1783.0(2) pm, β = 122.39(3)°, V = 4.638(5)·10⁹ pm³, Z = 4 and R = 0.0380. The structure of compound 1 features the five coordinate Er³⁺ central ion in a nearly exact trigonal bipyramidal environment, with three btmsa ligands in the equatorial and the two cyclohexylisonitrile molecules in the axial positions. On the basis of the absorption spectra of bis adduct 1 and the mono(tetrahydrofuran) as well as the mono(triphenylphosphine oxide) adducts [Er(btmsa)₃(THF)] ( 2 ) and [Er(btmsa)₃(OPPh₃)] ( 3 ), respectively, the underlying truncated crystal field (CF) splitting patterns of these compounds could be derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian. Reduced r.m.s. deviations of 13.0 cm^?1 (42 assignments), 16.0 cm^?1 (63 assignments) and 17.5 cm^?1 (55 assignments) could be achieved for compounds 1 , 2 and 3 , respectively. Making use of the phenomenological CF parameters of the fits, the experimentally based non‐relativistic molecular orbital schemes of complexes 1 , 2 and 3 were set up, and compared with that of base‐free Er(btmsa)₃.     

Zur Elektronenstruktur hochsymmetrischer Verbindungen der f‐Elemente. 36 [1] Parametrische Analyse der optischen Spektren eines orientierten Tris(hydrotris(1‐pyrazolyl)borato)praseodym(III)‐Einkristalls

Electronic Structures of Highly Symmetrical Compounds of f Elements. 36 [1] Parametric Analysis of the Optical Spectra of an Oriented Tris(hydrotris(1‐pyrazolyl)borato)praseodymium(III) Single Crystal The absorption and luminescence spectra of polycrystalline tris(hydrotris(1‐pyrazolyl)borato)‐praseodymium(III) (PrTp₃) were measured at room temperature as well as at low temperatures. At room temperature the “polarized” luminescence spectra of a small oriented PrTp₃ single crystal could also be recorded. On the basis of these spectroscopic findings the underlying crystal field splitting pattern could be derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian, achieving a reduced r.m.s. deviation of 17.3 cm^—1 for 37 assignments. On the basis of the parameters used, the global ligand field strength experienced by the Pr³⁺ central ion as well as the individual ligand field strength associated with one Tp ligand are determined, nephelauxetic and relativistic nephelauxetic effects are estimated, and the experimentally orientiented nonrelativistic and relativistic molecular orbital schemes in the f range are set up.     

Substrate‐Modulated Reductive Graphene Functionalization

Covalently functionalizing mechanical exfoliated mono‐ and bilayer graphenides with λ‐iodanes led to the discovery that the monolayers supported on a SiO₂ substrate are considerably more reactive than bilayers as demonstrated by statistical Raman spectroscopy/microscopy. Supported by DFT calculations we show that ditopic addend binding leads to much more stable products than the corresponding monotopic reactions as a result of the much lower lattice strain of the reactions products. The chemical nature of the substrate (graphene versus SiO₂) plays a crucial role.     

Mono‐ and Ditopic Bisfunctionalization of Graphene

For the first time, the bisfunctionalization of graphene by employing two successive reduction and covalent bond forming steps is reported. Bulk functionalization in dispersion and functionalization of individual sheets deposited on surfaces have both been carried out. Whereas in the former case attacks from both sides of the basal plane are possible and can lead to strain‐free architectures, in the latter case, retrofunctionalizations can become important when the corresponding anion of the addend is a sufficiently good leaving group.     

Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 78[1]Ergänzende Informationen von “polarisierten” Raman‐Spektren orientierter Einkristalle und Modellrechnungen auf der Grundlage der Dichtefunktionaltheorie bei der Zuordnung der Schwingungsspektren von Decamethylosmocen

The far and mid infrared (FIR/MIR) spectra of powdered Os(η⁵‐C₅Me₅)₂ (OsCp*₂) as well as the polarized Raman spectra of an oriented single crystal (where the two molecules of D_5h symmetry in the unit cell are uniformly oriented) have been recorded. The latter allow the assignment of the observed Raman lines to irreducible representations (irreps) which agree well with the predictions of a calculation applying density functional theory. This finding suggests additional correlation of the observed (unpolarized) bands in the FIR/MIR spectra with the calculated wavenumbers (and their irreps) of IR active normal modes. Neglecting νCH vibrations an r.m.s. deviation of 15.8 cm^–1 for 40 assignments (Raman and IR) could be achieved. Skeletal and intra‐ligand vibrations could be identified and a number of previous assignments of the latter had to be revised. Because of mixing with skeletal modes some of the low frequency intra‐ligand vibrations display a noticeable dependence on the mass of the central atom which prevents the direct transfer of the identified γCCH₃ and βCCH₃ normal modes from MCp*₂ (M = Fe, Ru, Os) to LnCp*₃ (Ln = La, Ce, Pr, Nd, Sm) complexes.     

Ultrasmall biocompatible nanocomposites: a new approach using seeded emulsion polymerization for the encapsulation of nanocrystals

We report a novel approach of seeded emulsion polymerization in which nanocrystals are used as seeds. Ultrasmall biocompatible polymer-coated nanocrystal with sizes between 15 and 110 nm could be prepared in a process that avoids any treatment with high shear forces or ultrasonication. The number of nanocrystals per seed, the size of the seeds, and the shell thickness can be independently adjusted. Single encapsulated nanocrystals in ultrasmall nanobeads as well as clusters of nanocrystals can be obtained. Polysorbat-80 was used as surfactant. It consists of poly(ethylene glycol) (PEG) chains, giving the particles outstanding biofunctional characteristics such as a minimization of unspecific interactions.     

Electronic structures of organometallic complexes of f elements LXXIV: First Raman spectroscopic polarization measurements on uniformly oriented sandwich complex molecules: Bis(η-pentamethylcyclopentadienyl)ruthenium

The polarized Raman spectra of oriented single crystals as well as far and mid infrared spectra of pellets of RuCp₂* (Cp* = η⁵-C₅Me₅) (1) were recorded. Assuming local C_5v symmetry for the intra-ligand vibrations, pairs of Raman and IR bands of nearly equal energy result for the symmetric and antisymmetric modes, respectively, for the irreducible representations (irreps) a₁, e₁, and partly (the IR part is symmetry forbidden, in principle, but sometimes observed) of e₂ symmetry. By this means, intra-ligand and skeletal vibrations (where no pairs of Raman and IR bands are expected) could be separated, and the Raman active modes were assigned to irreps on the basis of the observed polarizations. The still questionable type of vibration of some intra-ligand modes could be elucidated by the comparison of the vibrational spectra of 1 with the already assigned ones of NaCp*. Transferring the results of 1 to the Raman and IR spectra of OsCp₂* (2) and FeCp₂* (3), a number of previous assignments have to be revised.     

Determination of the surfactant density on SWCNTs by analytical ultracentrifugation

We report on the extensive characterization of single-walled carbon nanotubes (SWCNTs) dispersed in a variety of surfactants, such as sodium dodecyl benzene sulfonate (SDBS), sodium cholate (SC), and three synthesized perylene-based surfactants, by using differential sedimentation in H(2)O and D(2)O. Multidimensional evaluation of the absorption profiles over radius, wavelength, and time allows the determination of the anhydrous specific volumes of the SWCNT-surfactant complexes as well as the concentration of the surfactant reservoir in free micelles with very slow sedimentation coefficients (<1 Svedberg). Among the perylene bisimide surfactants, the smallest derivative is densely adsorbed on the nanotube backbone with an anhydrous specific volume significantly above that of SC or SDBS. Bulky Newkome dendritic groups on one or both ends of the perylene moiety gradually reduce the adsorption density, in accord with the absolute adsorption between 0.66 and 1.7 mmol surfactant per gram SWCNTs. Furthermore, hydrodynamic analysis reveals that SDBS favors the "tails-on" configuration. The distribution of sedimentation coefficients of SWCNTs prepared by high-pressure carbon monoxide decomposition (HiPco) is broader and shifted to faster sedimentation than those prepared by using cobalt-molybdenum catalysis (CoMoCAT), which reflects the polydispersity in diameter and length.     

Enhanced adsorption affinity of anionic perylene-based surfactants towards smaller-diameter SWCNTs

We present evidence from multiple characterization methods, such as emission spectroscopy, zeta potential, and analytical ultracentrifugation, to shed light on the adsorption behavior of synthesized perylene surfactants on single-walled carbon nanotubes (SWCNTs). On comparing dispersions of smaller-diameter SWCNTs prepared by using cobalt-molybdenum catalysis (CoMoCAT) with the larger-diameter SWCNTs prepared by high-pressure carbon monoxide decomposition (HiPco), we find that the CoMoCAT-perylene surfactant dispersions are characterized by more negative zeta potentials, and higher anhydrous specific volumes (the latter determined from the sedimentation coefficients by analytical ultracentrifugation), which indicates an increased packing density of the perylene surfactants on nanotubes of smaller diameter. This conclusion is further supported by the subsequent replacement of the perylene derivatives from the nanotube sidewall by sodium dodecyl benzene sulfonate (SDBS), which first occurs on the larger-diameter nanotubes. The enhanced adsorption affinity of the perylene surfactants towards smaller-diameter SWCNTs can be understood in terms of a change in the supramolecular arrangement of the perylene derivatives on the scaffold of the SWCNTs. These findings represent a significant step forward in understanding the noncovalent interaction of π-surfactants with carbon nanotubes, which will enable the design of novel surfactants with enhanced selectivity for certain nanotube species.