Fe-TMA

Figure 6 Coadsorption of TMA and Fe adatoms on Cu(lOO). (a) At 300 K, chiral Fe(TMA)4 clusters form which exist as S and R enantiomers, (b) Annealing the sample at 400 K lesnlts in the formation of homochiral nanocavity domains which are built up from Fe(TMA)4 clustes in a hierarchical fashion. The inset shows a high-resolution STM image of a S-type nanocavity, (c) and (d) Corresponding models for the chiral Fe(TMA)4 clusters and for the S enantiomCT of the nanocavity array. (Reproduced from Ref. 43. American Chemical Society, 2003.)...

Cu(lOO), chiral Fe(TMA)4 clusters are formed. This is associated with the deprotonation of the carboxylic acid groups of TMA upon adsorption on the Cu substrate at temperatures above 250 K. Upon annealing at 400 K, homochiral porous network structures can be built up from these Fe(TMA)4 clusters in a hierarchical manner (Figure 6). The nanocavities of these networks have been used as hosts for the accommodation of Ceo and small biomolecules. The same group also investigated such important key factors for self-assembly as self-recognition, self-selection, self-repair, and dynamic self-organization for a library of linear dicarboxylates and bipyridines codeposited with Fe atoms onto a Cu(lOO) surface. ... 

Erba, sodium hydroxide pellets (Normapur from Prolabo), tetramethylammonium hydroxide pentahydrate (TMA, Fluka purum grade), non-porous silica (Zeosil 175 MP from Rhone Poulenc, pore volume 0.08 ml/g, grain size 2-20 pm, H O 6.5 wt%) kaolinite des Charentes (from Kaolins d Arvor, surface area 24 m /g, grain size 4-15 pm, wt% Al 19.3, Si 21.3, Fe 0.29, Ca 0.1, Mg 0.13, K 0.5, Na 300 ppm), and deionized water. 

The changes in the ferromagnetic phases during the 72-hour carburization of catalyst B-6 (Figure 5) were measured by TMA at the times indicated in Figure 1. As the a-Fe phase decreased, the Fe2C (Hagg) phase increased, and the FesC (cementite) phase exhibited a transient existence, reached a maximum at about five hours. 

We did not observe two ferromagnetic phases, Fe2.2C (c phase) and Fes04, as previously observed by TMA in carburized iron (1,2). This diflFerence in the studies is probably attributable to differences in catalyst compositions and reaction conditions. In a few but not all instances of Ref. 2, the assignment of Fes04 of an inflection at about 825 K in the TMA curve appears to be incorrect because the inflection disappeared upon cooling. This disappearance is a strong indication of a thermal reaction between Fe and FesC. 

The cavities of the FeTMA arrays presented above, emerging from the hierarchical self-assembly of TMA molecules in the presence of Fe adatoms, feature identically shaped hosts of about 1 nm, equally spaced by 3.43 nm and functionalized by eight carboxylate groups. It was successfully demonstrated that this network is capable of selective and reversible adsorption of a series of guest species, including Ceo and small biomolecules (Fig. 10c) [221]. 

Besides the elucidation of the adsorbate structure of the metal-TMA chains, DFT calculations give also insight into the electronic structure of the coordination centers, in particular the spin states [203]. It was foimd that the projected density of states displays an appreciable splitting between the majority and minority spin electronic d states. Moreover, the spin polarization of 3.3 p.B is comparable to the polarization of an isolated Fe adatom (3.2 p b). Consequently the coordination to the carboxylate groups does not affect the electron localization at the coordination center, i.e., does not quench the spin magnetic moment. 

CxxCxxC Fe-S binding Ferredoxin, TMA DH Three Cys are involved in two turns of an a-hehx, in addition to a four-residue loop that surrounds a single Fe-S cluster. 

Kvim] X-ray diffiaction, thermomagnetic analysis (TMA-2 apparatus technique), metallography 1000 50°C, > 3 mass% Fe, > 3 mass% P... 

Carboxylates represent a versatile and frequently used class of molecules for the construction of 2D as well as 3D coordination networks. In particular, the research group of Klaus Kern has studied the formation of 2D networks from Fe atoms and different polyaromatic carboxylates systematically. For TMA codeposited with Fe atoms on... 

A material used frequently for the construction of the connecting rod and also as the reference material is quartz (expansivity of 0.6x10 K ). This is a rather small expansivity when compared to other solids and can often be neglected. For comparison, several typical expansivities are listed in Fig. 6.2. Of particular interest is Invar, an alloy of Fe, Ni, Co, and Mn that was especially developed to have a low e q>ansivity. The organic materials, at the bottom of the list, show much greater expansivities and are thus good candidates for TMA. 

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