Fr Francium

A novel method to prepare TiO₂-coated Ag nanowire arrays for use as multifunctional surface enhanced Raman scattering (SERS) active substrates is introduced. Such an array is made by the synthesis of an Ag nanowire array utilizing an anodic aluminum oxide (AAO) template, followed by coating of the Ag wires with a layer of titania that is several nanometers thick. Employing these TiO₂-coated Ag nanowire substrates in the detection of organic contaminants allows high SERS enhancement to be achieved. Moreover, owing to the high photocatalytic activity of titania, the substrate can degrade target molecules into small inorganic molecules under UV irradiation, and in this manner the arrays are able to self-clean. The unique properties of this integrated substrate enable it to exhibit its feasibility as an analytical tool for the assessment of environmental pollution and thus to assist in the detection and disposal of contaminants.

A novel method to prepare TiO₂-coated Ag nanowire arrays for use as multifunctional surface-enhanced Raman scattering (SERS) active substrates is introduced. Employing this substrate for the detection of organic contaminants can lead to high SERS enhancement. Owing to the high photocatalytic activity of TiO₂, the substrate can degrade target molecules into small inorganic molecules, and in this way the arrays are able to self-clean.

Redox and coordination processes are coupled in the course of reactions of the organic electron donors 1,2,4,5-tetrakis(tetramethylguanidino)benzene (1) and 1,2,4,5-tetrakis(N,N′-dimethyl-N,N′-ethyleneguanidino)benzene (2) with silver salts. Experiments with several different silver salts show that the product structure is significantly affected by the properties of the anion in these salts. Chain polymers are the products of reactions with AgPF₆ or AgBF₄, in which dicationic organic building blocks are connected by silver ions. Experiments with AgNO₃ yielded either dinuclear complexes (with 1) or 2D networks (with 2). If the salt Ag[Al{OC(CF₃)₃}₄], featuring a weakly coordinating anion, was used, simple silver-free salts of the guanidine dication were obtained. The thermal stability, optical properties, and electrical conductivity were studied in detail for the product polymer {[(1)Ag](PF₆)₃}_n. From the temperature dependence of the electric conductivity, this compound was found to be a semiconductor with a band gap of approximately 3 eV. The experiments were complemented by quantum chemical calculations at density-functional-theory level on the band structure of this and a related polymer. The electronic situation was further analyzed with the aid of molecular model complexes, which were either synthesized or calculated.

1D coordination polymers of oxidized guanidino-functionalized aromatic ligands were prepared by coupled oxidation and coordination with silver salts. The structures and electronic properties of these semiconducting materials were analyzed.

Two new hybrid ligands that exhibit organic as well as siloxane chains between four phosphorus atoms in bridge-head positions were synthesized. These species show a very different ability with regard to the formation of coordination compounds. Whereas compound 1 with the short (C₂H₄)₂O ether units shows no ability to act as a ligand, the compound with the longer (C₂H₄O)₂C₂H₄ chains between the siloxane fragments could be obtained as the free ligand and with incorporated Li₂I₂ and Ag₂I₂ units. The observed coordination modi of the lithium and silver ions in these complexes corresponds to the HSAB- or Pearson concept. The silver ions prefer the soft phosphorus atoms as a bonding partner, while, for lithium, coordination by the hard oxygen atoms is favoured.

Empty and filled hybrid cage compounds with siloxane as well as ether units between four phosphorus bridge-head atoms were obtained from the deprotonation of the cyclic siloxadiphosphane [O(SiiPr₂)₂PH]₂ and subsequent reaction with diiodo ethers. These compounds show very different coordination behaviour depending on the length of the ether chain and the metal cation used.

The cover picture shows a ball-and-stick model of the larger cage of the vanadium-based metal–organic framework (MOF) having the MIL-101 topology (MIL: Materials of the Institute Lavoisier; V: yellowish green octahedra, C: yellow, O: red). Similar to its chromium analogue, the structure is built up of trimeric [Va ball-and-stick model of the larger cage of the vanadium-based metal?organic framework (MOF) having the MIL-101 topology (MIL: Materials of the Institute Lavoisier; V: yellowish green octahedra, C: yellow, O: red). Similar to its chromium analogue, the structure is built up of trimeric [V₃(μ₃-O)Cl(DMF)₂]⁶⁺ (DMF: N,N′-dimethylformamide) units that are interconnected by 1,4-benzenedicarboxylate (BDC^2–) linkers to form supertetrahedra (ST). The ST are further connected to each other to obtain the augmented zeolite Mobil Thirty-Nine (MTN) type of framework, which consists of smaller and larger mesoporous cages having diameters of 29 and 34 Å, respectively. The redox-active MOF material exhibits a high uptake of nitrogen and of carbon dioxide. Details are discussed in the article by P. Van Der Voort et al. on p. 2481 ff.

The known MOF UiO-67 of general formula [Zr₆O₄(OH)₄(bpdc)₆] [bpdc = biphenyldicarboxylate, O₂C(C₆H₄)₂CO₂] has been synthesized on a 3 g scale and characterized by BET, TGA, XRD, IR and ¹³C NMR spectroscopy, and elemental analyses. The chemical accessibility of the hydroxy ligand Zr₃(μ-OH) was assessed by the addition of D₂O: The expected isotopic shift of ν(OH) = 3673 cm^–1 to ν(OD) = 2709 cm^–1 in the IR spectrum was observed. The OH content in bulk UiO-67, previously mildly activated at 120 °C under vacuum (10^–5 Torr) overnight, was quantitatively determined by three methods: (1) By integration of the IR ν(OH) region and comparison with calibrated spectra of MCM-41 previously dehydroxylated at 500 °C, which gave a spectroscopically measured OH content in bulk UiO-67 of 2.2 mmol/g (37 mg OH/g); (2) by extrapolation of the OH content from the measured weight loss between 250 and 400 °C in TGA, which corresponded to 1.6 mmol OH/g (27 mg OH/g); and (3) by chemical titration of UiO-67 with CH₃MgBr and GC determination of the evolved methane, which gave 1.8 mmol OH/g (31 mg OH/g). The three methods, and in particular the latter chemical titration, are in very good to excellent agreement with the nominal OH content based on the molecular formula [Zr₆O₄(OH)₄(bpdc)₆] (expected: 1.9 mmol OH/g, 32 mg OH/g; experimental/calculated OH content = 110, 85, and 95 %, respectively, for the three methods). The weak acidity of the OH moiety in UiO-67 was assessed by IR and ³¹P NMR monitoring of the physisorption of PMe₃ in the UiO-67 cavities. Inclusion of the organometallic Au^I complex [AuMe(PMe₃)] in a 1:1 molar ratio with respect to [Zr₆O₄(OH)₄(bpdc)₆] was achieved. Some chemisorption at 20 % of the cornerstone hydroxy sites also occurred to yield [Zr₆O₄(OH)₃(bpdc)₆(OAuPMe₃)].

Thermally stable MOF UiO-67, [Zr₆O₄(OH)₄(bpdc)₆], is well-behaved chemically in the bulk: Cornerstone (μ₃-OH) hydroxy groups react quantitatively with MeMgBr with stoichiometric release of methane. Post-synthetic modification with [AuMe(PMe₃)] results in partial covalent grafting of the Au^I center onto the cornerstone hydroxy groups.

The syntheses of new potentially tetradentate ligands of the type RN(CH₂CMe₂OH)₂ (1, R = Me₂NCH₂CH₂; 2, R = MeOCH₂CH₂), their tin(II) derivatives RN(CH₂CMe₂O)₂Sn (3, R = Me₂NCH₂CH₂; 4, R = MeOCH₂CH₂), the pentacarbonyltungsten complexes RN(CH₂CMe₂O)₂SnW(CO)₅ (5, R = Me₂NCH₂CH₂; 6, R = MeOCH₂CH₂) and their oxidation products with bromine, RN(CH₂CMe₂O)₂SnBr₂ (7, R = Me₂NCH₂CH₂; 8, R = MeOCH₂CH₂), are reported. The compounds were characterized by multinuclear NMR spectroscopy, elemental analysis, electrospray ionization mass spectrometry and single-crystal X-ray diffraction analysis. DFT calculations on compounds 3, 7 and 8 suggest the preference of dimeric over monomeric structures.

From dimers to monomers by oxidative addition: The alkoxido-bridged dimeric tin(II) compound 3 undergoes oxidative addition by the reaction with bromine to give compound 7 that in turn is monomeric by an additional intramolecular N→Sn interaction. The methoxy-substituted analogue 8, however, is a dimer.

(4S)-2-(4-Isopropyl-4,5-dihydrooxazol-2-yl)-4-nitrobenzenethiol {(S)-TS} and its tert-butyl derivative {(S)-TS′} were developed as chiral auxiliaries for the asymmetric synthesis of polypyridyl ruthenium complexes. In their deprotonated form, these (mercaptophenyl)oxazolines were used as bidentate ligands and allowed the efficient transfer of chirality from the oxazoline moiety to the ruthenium stereocenter. After the induction of the absolute metal-centered configuration, the auxiliaries were labilized by converting the coordinated thiolate into a thioether ligand upon methylation with Meerwein salt, followed by the thermal replacement with 2,2′-bipyridine or 1,10-phenanthroline ligands under retention of configuration to afford octahedral polypyridyl ruthenium complexes with high enantiomeric excesses. These thiol-based auxiliaries complement our previously developed acid-labile chiral auxiliaries and thus expand the toolbox for the asymmetric synthesis of chiral ruthenium complexes.

(Mercaptophenyl)oxazolines were used as chiral auxiliaries for the asymmetric synthesis of polypyridyl ruthenium complexes. Key step was the conversion of a coordinated thiolate into a labilized thioether upon methylation with Meerwein salt, followed by a thermal substitution with an achiral ligand under retention of configuration.

NN–Pt^II–bis(acetylide) complexes [NN = 4,4′-bis(tert-butyl-2,2′-bipyridine) (dbbpy)] with ethynylpyrene (Pt-2) or 4-ethynyl-1,8-naphthalimide ligands (Pt-3) that show long-lived ³IL triplet excited states (τ_T = 118.0 μs) were used as new triplet sensitizers for triplet–triplet annihilation (TTA) based upconversion (UC). UC quantum yields of up to 18.1 % were observed. We found that the triplet–triplet energy-transfer (TTET) processes, which are crucial for the TTA UC, were improved by up to 150-fold and 250-fold with Pt-2 (Stern–Volmer quenching constant K_SV = 5.70 × 10⁵M^–1) and Pt-3 (K_SV = 9.64 × 10⁵M^–1), respectively, relative to the model complex dbbpy–Pt^II–bis(phenylacetylide) (Pt-1) (K_SV = 3.80 × 10³M^–1). The efficient upconversion is attributed to the long-lived triplet excited states as well as the high T₁-state energy level of the sensitizers Pt-2 and Pt-3.

NN–Pt^II–bis(acetylide) complexes [NN = 4,4′-bis(tert-butyl-2,2′-bipyridine)] that show long-lived ³IL triplet excited states (τ_T = 118.0 μs) were used as new triplet sensitizers for triplet–triplet annihilation (TTA) based upconversion (UC). An UC quantum yield of up to 18.1 % was observed. The triplet–triplet energy-transfer process was improved by up to 250-fold relative to that of the model complex.