Synthesis, electronic structure and redox properties of the diruthenium sandwich complexes [Cp*Ru(µ-C10H8)RuCp*]x (x = 0, 1+; Cp* = C5Me5; C10H8 = naphthalene).

The dinuclear ruthenium complex [Cp*Ru(µ-C10H8)RuCp*] (1; Cp* = η5-C5Me5) was prepared by reduction of the cationic precursor [Cp*Ru(η6-C10H8)]PF6 with KC8. Diamagnetic 1 has a symmetric molecular structure with an anti-facial configuration of the Cp*Ru moieties coordinating to naphthalene. Density Functional Theory (DFT) studies showed an electronic structure similar to that of the analogous diiron complex [Cp*Fe(µ-C10H8)FeCp*]. Cyclic voltammetry and UV-vis spectroelectrochemistry showed that 1 can be reversibly oxidized to 1+ and 12+. Chemical oxidation with [Cp2Fe]BArF4 afforded the paramagnetic compound [1]BArF4, which was investigated by EPR, single-crystal X-ray diffractometry and DFT calculations. Reaction of 1 with Brookhart's acid gave the hydride complex [3]BArF4, which was characterized spectroscopically and crystallographically. Cyclic voltammetry showed that [3]+ is converted back to 1 upon reduction and oxidation.

Selective P4 Activation by a Highly Reduced Cobaltate: Synthesis of Dicobalt Tetraphosphido Complexes.

Although the chemistry of transition metal polyphosphide anions has attracted significant attention, there are few reports of studies in which such species have been synthesized directly from white phosphorus. [K(OEt2 )2 {Co(BIAN)(cod)}] (1, BIAN=1,2-bis(2,6-diisopropylphenylimino)acenaphthene, cod=1,5-cyclooctadiene), which is readily prepared by ligand exchange from [K(thf)x {Co(cod)2 }], reacts with P4 to afford [{K(thf)}2 {(BIAN)Co}2 (µ-η4 :η4 -P4 )] (2 a) in 61 % yield (isolated product). [{K(OEt2 )}2 {(BIAN)Co}2 (µ-η4 :η4 -P4 )] (2 b) and [K([18]crown-6)(MeCN)]2 [{(BIAN)Co}2 (µ-η4 :η4 -P4 )] (2 c) were obtained by recrystallizing 2 a from diethyl ether and acetonitrile (and using [18]crown-6 in case of 2 c). Oxidation of 2 a with [Cp2 Fe]BArF4 (one equivalent) and subsequent recrystallization of the product from different solvents gave [K(OEt2 ){(BIAN)Co}2 (µ-η4 :η4 -P4 )] (3 a) and [K(dme)4 ][{(BIAN)Co}2 (µ-η4 :η4 -P4 )] (3 b; dme=1,2-dimethoxyethane). Neutral [{(BIAN)Co}2 (µ-η4 :η4 -P4 )] (4) was obtained in moderate yield by oxidizing 2 a with two equivalents of [Cp2 Fe]BArF4 . The new complexes were characterized by NMR, EPR (in the case of 3 a), and UV/Vis spectroscopy, and elemental analysis. The molecular structures revealed by X-ray crystallography display planar cyclic or open-chain P44- units sandwiched between {(BIAN)Co} fragments.

Selective P4 activation by an organometallic nickel(I) radical: formation of a dinuclear nickel(II) tetraphosphide and related di- and trichalcogenides.

The reaction of the 17e nickel(I) radical [CpNi(IDipp)] (1, IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with P4 results in a nickel tetraphosphide [{CpNi(IDipp)}2(µ-η(1):η(1)-P4)] with a butterfly-P4(2-) ligand; related chalcogenides [{CpNi(IDipp)}2(µ-E2)] (E = S, Se, Te) and [{CpNi(IDipp)}2(µ-E3)] (E = S, Se) are formed with S8, Se∞ and Te∞.

A tetradentate metalloligand: synthesis and coordination behaviour of a 2-pyridyl-substituted cyclobutadiene iron complex.

The salt [K([18]crown-6){Cp*Fe(η(4)-C4py4)}] (K1, py = 2-pyridyl, Cp* = C5Me5) is accessible by the reaction of an iron(0) naphthalene precursor and bis(2-pyridyl)acetylene. Cyclic voltammetry and preparative investigations demonstrate the electron-rich nature of K1, which is reversibly oxidized to neutral [Cp*Fe(η(4)-C4py4)] (1) at a low potential. The first coordination studies with iron(II) and zinc(II) chloride show that all four 2-pyridyl units may be employed for metal coordination.

Diffusion- and convection-based activation of Wnt/ß-catenin signaling in a gradient generating microfluidic chip.

Stem cells and developing tissues respond to long-range signaling molecules (morphogens), by starting different nuclear programs that decide about the cell fate. Cells sense the local morphogen concentration and the shape of the gradient. We developed a two-chambered microfluidic chip to reproduce the in vivo situation under shear stress free conditions. The gradient is generated in the lower part of our device and recognized by cells grown in the upper part in the microchamber. We tested our device by activating the Wnt/ß-catenin signaling pathway in HeLa cells as proven by nuclear ß-catenin accumulation in response to the Wnt pathway activator 6-bromoindirubin-3'-oxime (BIO). Applying the same readout system to a recombinant Wnt3a and Dkk-1 bipolar gradient we demonstrate that our microfluidic chip is suitable for morphogens as well as small molecules. More interestingly, our microfluidic device is highly flexible. While the generated gradients are stable for several hours and reproducible, we can change the kind and the shape of the gradient actively on demand. We also can switch from diffusion- to convection-based transport, thus applying the morphogen gradient either in a polarized or non-polarized manner.

A simple magneto-optical method for the restoration of erased markings in metals.

There are different techniques for the restoration of erased markings in metals. Non-destructive methods are generally preferable. The only frequently used non-destructive method is the magnetic technique. The different kinds of magnetic restoration methods are discussed in the article. In the experiments described, the applicability of magneto-optical methods for the restoration of obliterated markings was examined. The results show that the methods are suitable and the required equipment does not cause high expenses.

Evolution of climate niches in European mammals?

Our ability to predict consequences of climate change is severely impaired by the lack of knowledge on the ability of species to adapt to changing environmental conditions. We used distribution data for 140 mammal species in Europe, together with data on climate, land cover and topography, to derive a statistical description of their realized climate niche. We then compared climate niche overlap of pairs of species, selected on the basis of phylogenetic information. In contrast to expectations, related species were not similar in their climate niche. Rather, even species pairs that had a common ancestor less than 1 Ma already display very high climate niche distances. We interpret our finding as a strong interspecific competitive constraint on the realized niche, rather than a rapid evolution of the fundamental niche. If correct, our results imply a very limited usefulness of climate niche models for the prediction of future mammal distributions.