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Paul Müller

Publications and source records attributed to Paul Müller.

At least 19 recordsLinked to original sources
PubMed2006

Addressing metal centres in supramolecular assemblies.

Supramolecular metal ion assemblies are deposited from their solutions onto highly orientated pyrolytic graphite (HOPG) substrates to be imaged by scanning tunnelling microscopy (STM). Since the structural and electronic information of STM measurements are strongly entangled, the spectroscopic interpretation and analysis of the images of such molecular assemblies has proven to be challenging. This tutorial review focuses on a general room temperature scanning tunnelling spectroscopy (STS) protocol, current induced tunnelling spectroscopy (CITS), applied to free-standing 1D and 2D arrangements of supramolecular metal ion assemblies rendering local tunnelling probabilities with submolecular resolution. The size of the investigated molecular assemblies was confirmed by comparison with X-ray crystallographic data, while the consistency of the spectroscopic investigations and of the determined positions of the metal ions within the assemblies was checked by DFT calculations. Due to the genuine level structure of coordinated metal centers, it was possible to map exclusively the position of the coordination bonds in supramolecular transition metal assemblies with submolecular spatial resolution using the CITS technique. CITS might thus constitute an important tool to achieve directed bottom-up construction and controlled manipulation of fully electronically functional, two-dimensional molecular designs.

Journal Article↗
PubMed2006

Supramolecular Co(II)-[2 x 2] grids: metamagnetic behavior in a single molecule.

The magnetic anisotropy of the supramolecular [2 x 2] grid [Co(II)4L4]8+, with a bis(bipyridyl)-pyrimidine-based ligand L, was investigated by single-crystal magnetization measurements at low temperatures. The magnetization curves exhibit metamagnetic-like behavior and are explained by the weak-exchange limit of a minimal spin Hamiltonian including Heisenberg exchange, easy-axis ligand fields, and the Zeeman term. It is also shown that the magnetic coupling strength can be varied by the substituent R1 in the two-position on the central pyrimidine group of the ligand L.

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PubMed2006

Supramolecular 'flat' Mn9 grid complexes--towards functional molecular platforms.

Flat, quantum dot like arrays of closely spaced, electron rich metal centres are seen as attractive subunits for device capability at the molecular level. Mn(II)9 grids, formed by self-assembly processes using 'tritopic' pyridine-2,6-dihydrazone ligands, provide easy and pre-programmable routes to such systems, and have been shown to exhibit a number of potentially useful physical properties, which could be utilized to generate bi-stable molecular based states. Their ability to form surface monolayers, which can be mapped by STM techniques, bodes well for their possible integration into nanometer scale electronic components of the future. This report highlights some new Mn(II)9 grids, with functionalized ligand sites, that may provide suitable anchor points to surfaces and also be potential donor sites capable of further grid elaboration. Structures, magnetic properties, electrochemical properties, surface studies on HOPG (highly ordered pyrolytic graphite), including the imaging of individual metal ion sites in the grid using CITS (current imaging tunneling spectroscopy) are discussed, in addition to an analysis of the photophysics of a stable mixed oxidation state [Mn(III)4Mn(II)5] grid. The grid physical properties as a whole are assessed in the light of reasonable approaches to the use of such molecules as nanometer scale devices.

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PubMed2006

Surface-assisted coordination chemistry and self-assembly.

This article discusses different approaches to build up supramolecular nanoarchitectures on surfaces, which were simultaneously investigated by scanning tunneling microscopy (STM) on the single-molecule level. Following this general road map, first, the hydrogen-bonding guided self-assembly of two different, structural-equivalent molecular building blocks, azobenzene dicarboxylic acid and stilbene dicarboxylic acid, was studied. Secondly, the coordination chemistry of the same building blocks, now acting as ligands in metal coordination reactions, towards co-sublimed Fe atoms was studied under near surface-conditions. Extended two-dimensional tetragonal network formation with unusual Fe2L(4/2)-dimers at the crossing points was observed on copper surfaces. Complementary to the first two experiments, a two-step approach based on the solution-based self-assembly of square-like tetranuclear complexes of the M4L4-type with subsequent deposition on graphite surfaces was investigated. One- and two-dimensional arrangements as well as single molecules of the M4L4-complexes could be observed. Moreover, the local electronic properties of a single M4L4-complexes could be probed with submolecular resolution by means of scanning tunnelling spectroscopy (STS).

Journal Article↗
PubMed2006

The [Fe(III)[Fe(III)(L1)2]3] star-type single-molecule magnet.

Star-shaped complex [Fe(III)[Fe(III)(L1)2]3] (3) was synthesized starting from N-methyldiethanolamine H2L1 (1) and ferric chloride in the presence of sodium hydride. For 3, two different high-spin iron(III) ion sites were confirmed by Mössbauer spectroscopy at 77 K. Single-crystal X-ray structure determination revealed that 3 crystallizes with four molecules of chloroform, but, with only three molecules of dichloromethane. The unit cell of 3.4CHCl3 contains the enantiomers (delta)-[(S,S)(R,R)(R,R)] and (lambda)-[(R,R)(S,S)(S,S)], whereas in case of 3.3CH2Cl2 four independent molecules, forming pairs of the enantiomers [lambda-(R,R)(R,R)(R,R)]-3 and [lambda-(S,S)(S,S)(S,S)]-3, were observed in the unit cell. According to SQUID measurements, the antiferromagnetic intramolecular coupling of the iron(III) ions in 3 results in a S = 10/2 ground state multiplet. The anisotropy is of the easy-axis type. EPR measurements enabled an accurate determination of the ligand-field splitting parameters. The ferric star 3 is a single-molecule magnet (SMM) and shows hysteretic magnetization characteristics below a blocking temperature of about 1.2 K. However, weak intermolecular couplings, mediated in a chainlike fashion via solvent molecules, have a strong influence on the magnetic properties. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were used to determine the structural and electronic properties of star-type tetranuclear iron(III) complex 3. The molecules were deposited onto highly ordered pyrolytic graphite (HOPG). Small, regular molecule clusters, two-dimensional monolayers as well as separated single molecules were observed. In our STS measurements we found a rather large contrast at the expected locations of the metal centers of the molecules. This direct addressing of the metal centers was confirmed by DFT calculations.

Journal Article↗
PubMed2006

STM/STS observation of polyoxoanions on HOPG surfaces: the wheel-shaped [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- and the ball-shaped [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A-PW9O34)12]36-.

A combination of scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) techniques have been performed on the wheel-shaped [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- and the ball-shaped [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A-PW9O34)12]36- deposited on highly oriented pyrolytic graphite surfaces. Small, regular molecule clusters, as well as separated single molecules, were observed. The size of the molecules is in agreement with the data determined by X-ray crystallography. In STS measurements, we found a rather large contrast at the expected location of the Cu metal centers in our molecules, i.e., the location of the individual Cu ions in their organic matrix is directly addressable by STS.

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PubMed2006

Genetic differentiation of the marbled white butterfly, Melanargia galathea, accounts for glacial distribution patterns and postglacial range expansion in southeastern Europe.

Isolation of Mediterranean species in the southern European peninsulas during the cold glacial phases often resulted in differentiation of several genetic lineages confined to the respective peninsulas. However, whilst there is good genetic evidence for multiple refugia in Iberia, there are only limited data available for the Balkans. Therefore, we wish to examine the hypothesis of a strong genetic structuring within southeastern Europe for the existence of multiple Balkan differentiation centres and/or several leading edges. As a model we use the marbled white butterfly, Melanargia galathea. We studied 18 allozyme loci of 564 individuals from 16 populations distributed over a large part of southeastern Europe. The single populations showed moderately high genetic diversity and no northward decline of genetic diversity was detected. The overall genetic differentiation between populations was considerable (F(ST) 7.0%). Cluster analysis discriminated three genetic groups: (i) a western flank in the former Yugoslavia, parts of eastern Austria and Hungary; (ii) an eastern flank with populations from Bulgaria and Romania (south of the southern Carpathians and eastern Carpathians); and (iii) the eastern Carpathian Basin. Hierarchical variance analysis distributed 53% of the variance among populations between these three groups. One sample from the Greek-Bulgarian border clustered within the eastern flank, but showed some tendency towards the eastern Carpathian Basin populations. Two populations from Carinthia clustered together with the eastern Carpathian Basin ones and a population from Styria showed an intermediate genetic composition between the three groups. Most probably, the eastern and the western flank groups are due to postglacial range expansion from the northeastern and the northwestern edges of the glacial differentiation centre (so-called leading edges). The eastern Carpathian Basin group may have resulted from postglacial expansion from northern Greece through valley systems of the central Balkan peninsula, maybe even expanding westwards north of the Balkan mountains reaching some parts of eastern Austria (e.g. Carinthia). Therefore, the Balkanic refugium of M. galathea may or may not have been continuous along the coastal areas of the Mediterranean, but must have been strongly genetically structured.

Animal Migration↗
PubMed2005

Synthesis, crystal structure, and properties of MnNCN, the first carbodiimide of a magnetic transition metal.

Synthesis, single-crystal structure determination, and magnetic properties are reported for manganese carbodiimide, MnNCN. The presumably unstable but inert phase adopts the trigonal system (R3m) with a = 3.3583(4) A, c = 14.347(2) A, V = 140.13(3) A3, and Z = 3. Divalent manganese is octahedrally coordinated by nitrogen atoms at 2.26 A, and the NCN(2-) unit adopts the linear [N=C=N](2-) carbodiimide shape with two C=N double bonds of 1.23 A. MnNCN contains high-spin Mn(II) with five unpaired electrons and behaves like an antiferromagnet with an ordering temperature below 30 K.

Journal Article↗
PubMed2005

One-pot synthesis and chiral analysis of cyclopropane derivatives.

A user-friendly, one-pot procedure was developed to access racemic as well as enantiomerically enriched cyclopropanes. Thus, the cyclopropanation of olefin (3) was performed using Meldrum's acid (4) or dimethyl malonate (5) and diacetoxyiodobenzene PhI(OAc)2 (6) or iodosyl benzene PhI=O (7) for in situ generation and decomposition of the phenyliodonium ylide 1 and 2, respectively. The reaction proceeds well with 5 mol% of achiral rhodium (II)-catalyst [Rh2(OAc)4] and a 10-fold excess of olefin affording the cyclopropane derivates 10 and 11, respectively, with high yield. The system is compatible with chiral Rh(II)-catalysts 8 and 9 and an enantiomeric excess up to 66% was achieved. An effective baseline separation of the enantiomers of the resulting cyclopropane derivatives was achieved using gas chromatography on the chiral stationary phase Chirasil-beta-dex.

Cyclopropanes↗
PubMed2005

Bandgap widening of titania through semiconductor support interactions.

Silica-supported titania powders with 50, 36, 13 and 4 wt% of TiO2 (TiO2-50/SiO2, TiO2-36/SiO2, TiO2-13/SiO2 and TiO2-4/SiO2) were prepared by hydrolysis of TiCl4 in the presence of silica, followed by calcination at 500 degrees C. The formation of Ti-O-Si linkages was confirmed by diffuse reflectance infrared Fourier transform spectroscopy. Atomic force microscopy indicated the presence of titania crystals larger than 15 nm. All supported materials exhibited a blue-shift of the TiO2 absorption edge, which was attributed to an electronic semiconductor support interaction. Bandgap energies of TiO2-50/SiO2, TiO2-36/SiO2, TiO2-13/SiO2 and TiO(2)4/SiO2 were measured to be 3.28, 3.36, 3.40 and 3.42 eV, respectively, as compared to 3.15 eV for unsupported TiO2. From these values, and from the quasi-Fermi level of electrons, a high anodic shift of both the valence and the conduction band was estimated. X-ray photoelectron spectroscopy (XPS) measurements of oxygen 1s- and titanium 2p-binding energies confirmed the anodic shift of the band edges.

Journal Article↗
PubMed2004

Rh(II)-catalyzed enantioselective cyclopropanation of olefins with dimethyl malonate via in situ generated phenyliodonium ylide.

Olefins are cyclopropanated with dimethyl malonate (1a) iodosylbenzene (PhI=O) and a Rh(II) carboxylate catalyst via an in situ generated phenyliodonium ylide (1c). Enantioselectivities of up to 90% for 4-bromostyrene and 98% for pent-1-ene have been observed with (S)-N-4-bromo-1,8-naphthanoyl-tert-leucine (4c) as the chiral ligand. The same catalyst was effective for olefin cyclopropanation with Meldrum's acid, giving cyclopropanes with 96% (with styrene) and 87% ee (with pent-1-ene), respectively.

Journal Article↗
PubMed2004

Binary mixture of DDT and Arochlor1254: effects on sperm release by Danio rerio.

A long-term toxicity test with zebrafish was carried out with different concentrations of DDT, Arochlor1254 (A54), and their 1:1 mixture under flow-through conditions. By collecting and counting the number of sperm released during separate mating events we observed that gametes are released asynchronously. Sperms are released in the form of sperm trails laid on the nest surface; subsequently active spermatozoa leave the trails and move in the water for several minutes. Sperm trails consist of bands of viscous material in which sperm are embedded. The water samples for the estimation of sperm presence were collected gradually within 180 min after 24 h, 2 weeks, 1 month, and 2 months of exposure. It was established that the reductions in count, activity of sperm, and average life span of sperm trails were significant (P<0.05) at the tested concentrations, 5 and 50 microg/L after 1 month and 2 weeks of exposure to each chemical tested and to their mixture, respectively. In conclusion, this study demonstrates that DDT and A54 could react synergically and increase the alteration in sperm release and activity as well as the life span of their trails.

Animals↗