Porous interpenetrated zirconium-organic frameworks (PIZOFs): a chemically versatile family of metal-organic frameworks

We present the synthesis and characterization of porous interpenetrated zirconium-organic frameworks (PIZOFs), a new family of metal-organic frameworks obtained from ZrCl(4) and the rodlike dicarboxylic acids HO(2)C[PE-P(R(1),R(2))-EP]CO(2) H that consist of alternating phenylene (P) and ethynylene (E) units. The substituents R(1),R(2) were broadly varied (alkyl, O-alkyl, oligo(ethylene glycol)), including postsynthetically addressable substituents (amino, alkyne, furan). The PIZOF structure is highly tolerant towards the variation of R(1) and R(2). This together with the modular synthesis of the diacids offers a facile tuning of the chemical environment within the pores. The PIZOF structure was solved from single-crystal X-ray diffraction analysis. The PIZOFs are stable under ambient conditions. PIZOF-2, the PIZOF prepared from HO(2)C[PE-P(OMe,OMe)-EP]CO(2)H, served as a prototype to determine thermal stability and porosity. It is stable up to 325 °C in air as determined by using thermogravimetry and powder X-ray diffraction. Argon sorption isotherms on PIZOF-2 revealed a Brunauer-Emmett-Teller (BET) surface area of 1250 m(2) g(-1) and a total pore volume of 0.68 cm(3) g(-1).     

Modulated synthesis of Zr-based metal-organic frameworks: from nano to single crystals

We present an investigation on the influence of benzoic acid, acetic acid, and water on the syntheses of the Zr-based metal-organic frameworks Zr-bdc (UiO-66), Zr-bdc-NH(2) (UiO-66-NH(2)), Zr-bpdc (UiO-67), and Zr-tpdc-NH(2) (UiO-68-NH(2)) (H(2) bdc: terephthalic acid, H(2) bpdc: biphenyl-4,4'-dicarboxylic acid, H(2) tpdc: terphenyl-4,4'-dicarboxylic acid). By varying the amount of benzoic or acetic acid, the synthesis of Zr-bdc can be modulated. With increasing concentration of the modulator, the products change from intergrown to individual crystals, the size of which can be tuned. Addition of benzoic acid also affects the size and morphology of Zr-bpdc and, additionally, makes the synthesis of Zr-bpdc highly reproducible. The control of crystal and particle size is proven by powder XRD, SEM and dynamic light scattering (DLS) measurements. Thermogravimetric analysis (TGA) and Ar sorption experiments show that the materials from modulated syntheses can be activated and that they exhibit high specific surface areas. Water proved to be essential for the formation of well-ordered Zr-bdc-NH(2) . Zr-tpdc-NH(2), a material with a structure analogous to that of Zr-bdc and Zr-bpdc, but with the longer, functionalized linker 2'-amino-1,1':4',1'-terphenyl-4,4'-dicarboxylic acid, was obtained as single crystals. This allowed the first single-crystal structural analysis of a Zr-based metal-organic framework.     

A Chemiluminescent Metal–Organic Framework

The synthesis and characterization of a chemiluminescent metal–organic framework with high porosity is reported. It consists of Zr₆O₆(OH)₄ nodes connected by 4,4′-(anthracene-9,10-diyl)dibenzoate as the linker and luminophore. It shows the topology known for UiO-66 and is therefore denoted PAP-UiO. The MOF was not only obtained as bulk material but also as a thin film. Exposure of PAP-UiO as bulk or film to a mixture of bis-(2,4,6-trichlorophenyl) oxalate, hydrogen peroxide, and sodium salicylate in a mixture of dimethyl and dibutyl phthalate evoked strong and long lasting chemiluminescence of the PAP-UiO crystals. Time dependent fluorescence spectroscopy on bulk PAP-UiO and, for comparison, on dimethyl 4,4′-(anthracene-9,10-diyl)dibenzoate provided evidence that the chemiluminescence originates from luminophores being part of the PAP-UiO, including the luminophores inside the crystals.     

Direct conversion of EPR dipolar time evolution data to distance distributions

Shallow electron spin echo envelope modulations due to dipole-dipole couplings between electron spins provide information on the radial distribution function of the spins in disordered systems while angular correlations between spin pairs are negligible. Under these conditions and in the absence of orientational selection, the dipolar time evolution data can be quantitatively simulated for arbitrary radial distribution functions by shell factorization, i.e., by performing the orientational average separately for thin spherical shells and multiplying the signals of all the shells. For distances below 5 nm, a linear superposition of the signals of the shells is sufficient. The dipolar time evolution data can be separated into this linear contribution and a nonlinear background. The linear contribution can then be converted directly to a radial distribution function. For a series of shape-persistent and flexible biradicals with end-to-end distances between 2 and 5 nm, shell factorization and direct conversion of the data are in good agreement with each other and with force-field computations of the end-to-end distances. The neglect of orientation selection does not cause significant distortions of the determined distance distributions.     

Synthese und Struktur von Komplexen mit Nitridobrücken zwischen Rhenium und Zink

Synthesis and Structure of Complexes with Nitrido Bridges between Rhenium and Zinc The reaction of [ReNCl₂(PMePh)₃] with ZnX₂ (X = Cl, Br) in CH₂Cl₂ yields the tetranuclear complexes [(Me₂PhP)₃X₂Re≡N–ZnX₂]₂. In case of the reaction with ZnBr₂ an exchange of the halogen atoms coordinated to the Re atom occurs. [(Me₂PhP)₃Cl₂Re≡N–ZnCl₂]₂ ( 1 ) crystallizes with one centrosymmetric tetranuclear complex in the triclinic unit cell. [(Me₂PhP)₃Br₂Re≡N–ZnBr₂]₂ ( 2 ) forms triclinic crystals with the composition 2 · 2 CH₂Cl₂. The centrosymmetric tetranuclear complexes exhibit analogous structures. Two complexes [ReNX₂(PMe₂Ph)₃] coordinate with the terminal nitrido ligands the Zn atoms of a central unit XZn(μ-X)₂ZnX. The resulting linear nitrido bridges Re≡N–Zn (Re–N–Zn = 178.4° ( 1 ) und 178.0° ( 2 )) are asymmetric with distances Re–N = 170 pm and Zn–N = 199 pm for 1 , and Re–N = 167 pm as well as Zn–N = 201 pm for 2 . The reaction of [ReNCl₂(PMe₂Ph)₃] with ZnI₂ in CH₂Cl₂ presumably first affords [(Me₂PhP)₃ClIRe≡N–ZnI₂]₂, which, however, in the course of crystallization decomposes to yield [(Me₂PhP)₃ClIRe≡N–ZnI₂(OPMe₂Ph)] ( 3 ). Of the two Cl atoms originally coordinated at the Re atom the one in cis position to the nitrido ligand is substituted by iodine. 3 forms monoclinic crystals with the space group P2₁/n. The distances in the linear nitrido bridge (Re–N–Zn = 171.5°) are Re–N = 167.9 pm and Zn–N = 204.9 pm. By the reaction of [ReNCl₂(PMe₂Ph)₃] with ZnX₂ (X = Cl, I) in THF the dinuclear complexes [(Me₂PhP)₃Cl₂Re≡N–ZnCl₂(THF)] ( 4 ) and [(Me₂PhP)₃ClIRe≡N–ZnI₂(THF)] ( 5 ) are obtained. They crystallize isotypically as 4 · THF or 5 · THF in the triclinic space group P1. Their nitrido bridges have the following parameters: Re–N–Zn = 175.2°, Re–N = 167.7 pm, and Zn–N = 202.1 pm for 4 , resp. Re–N–Zn = 174.7°, Re–N = 168.3 pm, and Zn–N = 201.2 pm for 5 .     

The Chemistry of Phenylimidotechnetium(V) Complexes with Isocyanides: Steric and Electronic Factors

Organometallic approaches are of ongoing interest for the development of novel functional ^99mTc radiopharmaceuticals, while the basic organotechnetium chemistry seems frequently to be little explored. Thus, structural and reactivity studies with the long-lived isotope ⁹⁹Tc are of permanent interest as the foundation for further progress in the related radiopharmaceutical research with this artificial element. Particularly the knowledge about the organometallic chemistry of high-valent technetium compounds is scarcely developed. Here, phenylimido complexes of technetium(V) with different isocyanides are introduced. They have been synthesized by ligand-exchange procedures starting from [Tc(NPh)Cl₃(PPh₃)₂]. Different reactivity patterns and products have been obtained depending on the steric and electronic properties of the individual ligands. This involves the formation of 1:1 and 1:2 exchange products of Tc(V) with the general formulae [Tc(NPh)Cl₃(PPh₃)(isocyanide)], cis- or trans-[Tc(NPh)Cl₃(isocyanide)₂], but also the reduction in the metal and the formation of cationic technetium(I) complex of the formula [Tc(isocyanide)₆]⁺ when p-fluorophenyl isocyanide is used. The products have been studied by single-crystal X-ray diffraction and spectroscopic methods, including IR and multinuclear NMR spectroscopy. DFT calculations on the different isocyanides allow the prediction of their reactivity towards electron-rich and electron-deficient metal centers by means of the empirical SADAP parameter, which has been derived from the potential energy surface of the electron density on their potentially coordinating carbon atoms.     

Post‐Synthetic Modification of Zr‐Metal–Organic Frameworks through Cycloaddition Reactions

Cycloaddition reactions are highly attractive for post‐synthetic modification of metal–organic frameworks (MOFs). We report herein on cycloaddition reactions with PIZOF(R¹,R²)s, which are porous interpenetrated Zr‐based MOFs with Zr₆O₄(OH)₄(CO₂)₁₂ as the nodes and the dicarboxylates ^?O₂C[PE‐P(R¹,R²)‐EP]CO₂^? (P: phenylene, E: ethynylene; R¹, R²: side chains at the central phenylene unit) as the linkers. 1,3‐Dipolar cycloaddition between the pendant ethyne moieties of PIZOF(OMe,OCH₂C?CH) and 4‐methylbenzyl azide resulted in 98 % conversion of the ethyne groups. Reactions of PIZOF(OMe,O(CH₂)₃furan) with maleimide, N‐methylmaleimide, and N‐phenylmaleimide converted 98, 99, and 89 % of the furan moieties into the Diels–Alder adducts. However, no reaction occurred with maleic anhydride. High‐resolution ¹H NMR spectra were crucial in determining the conversion and identifying the reaction products. Of all the reagents (NaOD/D₂O, D₂SO₄, Bu₄NF, CsF, CsF/DCl, and KHF₂) tested for the disassembly of the PIZOFs in [D₆]DMSO, the combination of CsF and DCl was found to be the best. The disassembly at room temperature was fast (5–15 min), and after the addition of K₂CO₃ the ¹H NMR data were identical to those of the diacids (=protonated linkers) dissolved in pure DMSO. This allowed for simple structure elucidation through data comparison. CsF/DCl dissolves not only PIZOFs but also the hydrolytically very stable UiO‐66.