Platinum trans‐Bis(borirene) Complexes Displaying Coplanarity and Communication Across a Platinum Metal Center

Ambient‐temperature photolysis of the aminoborylene complex [(OC)₅Cr?B?N(SiMe₃)₂] in the presence of a series of trans‐bis(alkynyl)platinum(II) precursors of the type trans‐[Pt(CCAr)₂(PEt₃)₂] (Ar=Ph, p‐C₆H₄OMe, and p‐C₆H₄CF₃) successfully leads to twofold transfer of the borylene moiety [ : B?N(SiMe₃)₂] onto the alkyne functionalities. The alkynyl precursors and resultant bis(borirene)platinum(II) complexes formed are of the type trans‐[Pt(B{?N(SiMe₃)₂}C?CAr)₂(PEt₃)₂] (Ar=Ph, p‐C₆H₄OMe, and p‐C₆H₄CF₃). These species have all been successfully characterized by NMR, IR, and UV/Vis spectroscopy as well as by elemental analysis. Single‐crystal X‐ray diffraction has verified that these trans‐bis(borirene)platinum(II) complexes display coplanarity between the twin three‐membered rings across the platinum core in the solid state and stand as the first examples of coplanar conformations of twin borirene systems. These complexes were modeled using density functional theory (DFT), providing information helpful in determining the ability of the transition metal core to interact with each individual borirene ring system and allowing for the observed coplanarity of these rings in the solid state. This proposed transition metal interaction with the twin borirene systems is manifested in the electronic characterization of these borirene species, which display divergent photophysical UV/Vis spectroscopic profiles compared to a previously published mono(borirene)platinum(II) complex.     

Selective polycarboxylation of semiconducting single-walled carbon nanotubes by reductive sidewall functionalization

The efficient and controllable synthesis, the detailed characterization, and the chemical postfunctionalization of polycarboxylated single-walled carbon nanotubes SWCNT(COOH)(n) are reported. This innovative covalent sidewall functionalization method is characterized by (a) the preservation of the integrity of the entire σ-framework of SWCNTs; (b) the possibility of achieving very high degrees of addition; (c) control of the functionalization degrees by the variation of the reaction conditions (reaction time, ultrasonic treatment, pressure); (d) the identification of conditions for the selective functionalization of semiconducting carbon nanotubes, leaving unfunctionalized metallic tubes behind; (e) the proof that the introduced carboxylic acid functionalities can serve as versatile anchor points for the coupling to functional molecules; and (f) the application of a subsequent thermal degradation step of the functionalized semiconducting tubes leaving behind intact metallic SWCNTs. Functional derivatives have been characterized in detail by means of Raman, UV-vis/nIR, IR, and fluorescence spectroscopy as well as by thermogravimetric analysis combined with mass spectrometry, atomic force microscopy, and zeta-potential measurements.     

Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 68 Absorptions‐ sowie erstmalige lumineszenz‐ und Raman‐spektroskopische Polarisationsmessungen an einem orientierten metallorganischen Einkristall: Pr(C5Me4H)3

Electronic Structures of Organometallic Complexes of f Elements. 68 Absorption and First Luminescence and Raman Spectroscopic Polarization Measurements of an Oriented Organometallic Single Crystal: Pr(C₅Me₄H)₃ Optical polarization measurements of oriented single crystals of Pr(C₅Me₄H)₃ ( 1 ) were performed at room temperature. In order to separate “cold” and “hot” f‐f‐transitions and νC–H combination vibrations, the absorption spectra of KBr pellets of compound 1 and La(C₅Me₄H)₃ ( 2 ) were additionally recorded at ca. 77 K. To gather additional information about the wavefunctions of the crystal field (CF) states of complex 1 , a magnetic circular dichroism spectrum of 1 was recorded too. From the spectra obtained, a partial CF splitting pattern of 1 was derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian, leading to a reduced r.m.s. deviation of 24.8 cm⁻¹ for 24 assignments. On the basis of these phenomenological CF parameters, the global CF strength experienced by the Pr³⁺ central ion was estimated, and seems to be the largest one ever encountered in Pr^III chemistry. The obtained Slater parameter F² and the spin‐orbit coupling parameter ζ_4f allow the insertion of compound 1 into empirical nephelauxetic and relativistic nephelauxetic series, respectively, of Pr^III compounds. With its low F² value, complex 1 is the most covalent Pr^III compound (considering only f electrons) found to date. The experimentally‐based non‐relativistic molecular orbital scheme (in the f range) of complex 1 was determined and compared with the results of a previous Xα‐SW calculation on the ψ trigonal planar model compound Pr(η⁵‐C₅H₅)₃. In the framework of the search for “polarized” luminescence transitions, polarized Raman spectra of 1 were recorded too, and compared to the corresponding FIR and IR spectra run by means of pellets.     

Novel λ3‐Iodane‐Based Functionalization of Synthetic Carbon Allotropes (SCAs)—Common Concepts and Quantification of the Degree of Addition

The covalent functionalization of carbon allotropes represents a main topic in the growing field of nano materials. However, the development of functional architectures is impeded by the intrinsic polydispersibility of the respective starting material, the unequivocal characterization of the introduced functional moieties, and the exact determination of the degree of functionalization. Based on a novel carbon allotrope functionalization reaction, utilizing λ³‐iodanes as radical precursor systems, we were able to demonstrate the feasibility to separate and to quantify thermally detached functional groups, formerly covalently linked to carbon nanotubes and graphene through thermogravimetric GC‐MS.     

Ueber eine falsche Sandarac-Sorte

Ohne Zusammenfassung     

Ueber die Werthbestimmung der Myrrha

Ohne Zusammenfassung     

Substituent Effects on the Spin-Transition Temperature in Complexes with Tris(pyrazolyl) Ligands

Summary.  Iron (II) complexes with substituted tris(pyrazolyl) ligands, which exhibit a thermally driven transition from a low-spin state at low temperatures to a high-spin state at elevated temperatures, have been studied by M?ssbauer spectroscopy and magnetic susceptibility measurements. From the observed spectra the molar high-spin fraction and the transition temperature have been extracted. All substituents, except for bromine, lead to a decrease of the transition temperature. Density functional calculations have been carried out to compare the experimentally observed shifts of the transition temperature with those derived from theory. Corresponding author. E-mail: paulsen@physik.uni-luebeck.de Received June 26, 2002; accepted July 22, 2002     

Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 60 [1] Strukturelle,einkristalloptische und magnetooptische Untersuchungen von Trialkylphosphat‐Addukten des Grundkörpers Tris(cyclopentadienyl)lanthanid(III) (Ln = La,Pr) sowie Ergebnisse vergleichender optischer Studien an [Pr(Ind)3(OP(OEt)3)] (Ind = Indenyl)

Electronic Structures of Organometallic Complexes of f Elements. 60 [1] Structural, Single Crystal Optical and Magnetooptical Investigations on Trialkylphosphate Adducts of the Tris(cyclopentadienyl)lanthanide(III) (Ln = La, Pr) Moiety as well as Results of Comparing Optical Studies of [Pr(Ind)₃(OP(OEt)₃)] (Ind = indenyl) [Ln(Cp)₃(OP(OR)₃)] (Cp = η⁵‐cyclopentadienyl; Ln = La, R = Et ( 1 ); Ln = Pr, R = Me ( 2 ); Ln = Pr, R = Et ( 3 )) and [Pr(Ind)₃(OP(OEt)₃)] ( 4 ) have been synthesized and spectroscopically as well as partly structurally (only compounds 1 and 2 ) characterized. On the basis of variable temperature measurements of α absorption spectra of an oriented single crystal, the magnetic circular dichroism spectra of dissolved, and the luminescence spectra of powdered material, a nearly complete crystal field (CF) splitting pattern could be derived for 3 , and simulated by fitting the free parameters of a phenomenological Hamiltonian. The parameters used in the fit allowed the calculation of the global CF strength experienced by the Pr³⁺ central ion, the estimation of the nephelauxetic and relativistic nephelauxetic parameters, as well as the setup of experimentally based non‐relativistic and relativistic molecular orbital schemes in the f range. The optical spectra of compound 4 suggest that two different species exist at low temperatures, thus preventing a successful CF analysis.