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The mainstream magnetic iron oxide particles used as contrast media for magnetic resonance (MR) imaging are composed of a magnetic iron oxide core surrounded by a dextran or carboxydextran coat. The core size ranges from 2 nm to less than 10 nm, and the hydrodynamic diameter ranges from 20 nm to about 120 nm. The coat prevents aggregation and sedimentation of the particles in aqueous solutions, achieves high biological tolerance, and prevents toxic side effects.Two kinds of particles are considered: (i) large particles (>30 nm), called superparamagnetic iron oxide particles (SPIOs) for liver imaging; (ii) smaller particles (<30 nm hydrodynamic diameter), called ultrasmall SPIOs (USPIOs), e.g. for MR angiography.To characterize the particles, Mössbauer spectra are presented for the two particle ensembles. These spectra allow insight into the magnetic coupling, the valency of the iron ions and a rough estimate of the core size to be deduced. On the basis of the concentration dependence of the MR signal intensities, two applications are discussed together with two representative clinical examples.Future indications for MR diagnostics, e.g. the labeling and tracking of stem cells during stem-cell therapy control, are outlined.

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Self-assembly of Fe(II) and the ditopic ligand 1,4-bis(2,2:6,2؆-terpyridine-4-yl)benzene results in equilibrium structures in solutions, so-called metallosupramolecular coordination polyelectrolytes (MEPEs). It is exceedingly difficult to characterize such macromolecular assemblies, because of the dynamic nature. Therefore, hardly any structural information is available for this type of material. Here, we show that from dilute solutions, where small aggregates predominate, it is possible to grow nanoscopic crystals at an interface. A near atomic resolution structure of MEPE is obtained by investigating the nanoscopic crystals with electron diffraction in combination with molecular modeling. The analysis reveals a primitive monoclinic unit cell (P2 1͞c space group, a ‫؍‬ 10.4 Å, b ‫؍‬ 10.7 Å, c ‫؍‬ 34.0 Å, ␣ ‫؍‬ ␥ ‫؍‬ 90°, ␤ ‫؍‬ 95°, ‫؍‬ 1.26 g͞cm 3 , and Z ‫؍‬ 4). The MEPE forms linear rods, which are organized into sheets. Four sheets intersect the unit cell, while adjacent sheets are rotated by 90°with respect to each other. The pseudooctahedral coordination geometry of the Fe(II) centers is confirmed by Mö ssbauer spectroscopy. The combination of diffraction and molecular modeling presented here may be of general utility to address problems in structural materials science.electron diffraction ͉ Mö ssbauer spectroscopy ͉ molecular modeling ͉ supramolecular chemistry W eak competing interactions provide an efficient and elegant route to self-assemble supramolecular modules in tailored architectures with a tremendous range of value-adding (1) and dynamic (2) properties. Metal ion-assisted self-assembly is one of the major recognition motives in supramolecular chemistry (3). The resulting metallosupramolecular modules possess structural, kinetic, magnetic, optic, electronic, and reactive properties that are relevant for functional devices and materials of technological interest (4).Although polymers based on kinetically inert transition-metal complexes are readily characterized in solution by standard analytical means, polymeric assemblies formed by kinetically labile transition-metal complexes have successfully evaded characterization in solution (5). The overwhelming majority of metal-organic frameworks are isolated and characterized as crystalline solids (6). The diversity of the resulting framework architectures is remarkable (7). Solids with well defined voids with molecular dimensions give an opportunity to manipulate, separate, arrange, and react molecules. Now, there are a large number of porous solids available that exhibit permanent porosity suitable for technological applications (8-10).In 1992, Constable et al. (11) published the synthesis and characterization of various multinucleating terpyridines (tpy), including 1,4-bis(2,2Ј:6Ј,2Љ-terpyridine-4Ј-yl)benzene (11). A high binding affinity to many transition metal ions and a well defined stereochemistry make this building block an attractive component for the assembly of dynamic and functional metallosupramolecular polyelectrolytes (MEPEs) (Scheme 1)...

Oligomeric and polymeric polyether polyols, especially poly(propylene oxide), are used for the production of detergents, nonionic surfactants, washing agents, and cleaners, but they are predominantly used in polyurethane production processes. Tin phosphate coordination polymers show good activity in the selective polymerization of epoxides. The catalyst can be easily synthesized by the condensation of tributyl phosphate and butyl tin trichloride. Investigations of this achiral organotin phosphate condensate in the stereoregular polymerization of propylene oxide, including the properties controlling the molecular weight of the resulting poly(propylene oxide) and structural and mechanistic studies, are presented. Additionally, the polymerization of propylene oxide occurs with high activity, no allyl end groups, just a small number of irregularities, and a high percentage of isotacticity (88%) in the polymer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3032–3041, 2007

Systematic 119m Sn-Mössbauer spectroscopy studies of three different types of five and six coordinated molybdenum and tungsten stannylidyne complexes are presented. The measured isomer shifts (IS) range from 2.38 to 2.50 mm/s and the quadrupole splittings (QS) from 1.8 to 2.8 mm/s. The values are dependent on the metal centre, the ligand sphere and the charge of the complexes. The influence of the neighbouring metal atoms (Mo, W) and their coordination sphere on the electron density at the tin atom is observed and will be discussed.

The syntheses, crystal structures, and physical properties of [HFe19 O14 (OEt)30 ] and {Fe11 (OEt)24 }∞ are reported. [HFe19 O14 (OEt)30 ] has an octahedral shape. Its core with a central Fe metal ion surrounded by six μ6 -oxo ligands is arranged in the rock salt structure. {Fe11 (OEt)24 }∞ is a mixed-valence coordination polymer in which Fe(III) metal ions form three 3D interpenetrating (10,3)-b nets. The arrangement of the Fe(III) ions can also be compared to that of Si ions in α-ThSi2 . Thus, the described structures are at the interface between molecular and solid-state chemistry.