Room-temperature molecular magnets

An important achievement concerning the challenge of obtaining high Curie temperatures was reported for the compound V [TCNE]xyCH2Cl2 [62]. This is the first room-temperature molecular magnet reported so far. Tc is estimated to be 400 K, and the coercive field is Hc = 60 G. This material has a considerable conductivity, crRX = 10 3 S-cm1. Figure 13 shows the hysteresis curve at room temperature. 

The room temperature electrical conductivity of single crystals of M03S7 (dmit)3 along the c axis is 25 S cm, which is very high for a neutral molecular crystal. The variation of the magnetic susceptility (/) with the temperature does not follow a Curie-Weis law with a continuous decrease of /T vs. Tupon cooling... 

The electrocrystallization and characterization of a novel molecular metal which displays both electronic and ionic conduction has been reported. The complex Li0.6(15-crown-5-ether)[Ni-(dmit)2] H20 is composed of stacks of [Ni(dmit)2] units which provide pathways for electronic conduction. The stacks are separated by parallel stacks of 15-crown-5-ether moieties in a channellike formation which facilitates ion conduction. The salt has a room temperature conductivity of 240 Scm-1. Temperature-dependent magnetic susceptibility and NMR measurements were used to prove the existence of Li+ movement within the crown ether channels.1030... 

In a 10 mL round-bottomed flask equipped with a magnetic stirrer bar were placed activated molecular sieves 4A (44.9 mg), (R)-BINOL (6.4 mg), triphenylphosphine oxide (18.7 mg), and anhydrous tetrahydrofuran (0.9 mL) and the mixture was stirred for 5 minutes under argon. To this suspension was added a suspension of La(0 z-Pr)3 (7.1 mg) in tetrahydrofuran (1.4 mL) by a syringe. After stirring for 1 hour at room temperature, cumene hydro-... 

Figure 3 Molecular relaxivities of liposomes with different Gd-containing membranotropic chelators. Liposomes (egg lecithin cholesterol chelator = 72 25 3) were prepared by consecutive extrusion of lipid suspension in HEPES buffered saline, pH 7.4, through the set of polycarbonate filters with pore size of 0.6, 0.4, and 0.2 mm. Liposome final size was between 205 and 225 nm. Gd content determination was performed by Galbraith Laboratories, Inc. The relaxation parameters of all preparations were measured at room temperature using a 5-MHz RADX nuclear magnetic resonance proton spin analyzer. The relaxivity of liposomes with polymeric chelators is noticeably greater because of the larger number of Gd atoms bound to a single lipid residue [16].

The compounds Ln(C5H5)2Cl also have been made only with the lanthanides above samarium (772). These compounds are stable in the absence of air and moisture, sublime near 200 °C, are insoluble in non-polar solvents, and exhibit room temperature magnetic moments near the free ion values (772, 113). The chloride ion may be replaced by a variety of anions including methoxide, phenoxide, amide and carboxylate. Some of these derivatives are considerably more air-stable than the chloride — the phenoxide is reported to be stable for days in dry air. Despite their apparent stability, little is known about the physical properties of these materials. The methyl-substituted cyclopentadiene complexes are much more soluble in non-polar solvents than the unsubstituted species. Ebulliometric measurements on the bis(methylcyclopentadienyl)lanthanide(III) chlorides indicated the complexes are dimeric in non-coordinating solvents (772). A structmre analysis of the ytterbium member of this series has been completed (714). The crystal and molecular parameters of this and related complexes are compared in Table 5. 

Powdered 4 A molecular sieves (2.0 g) and PDC (2.5 g, 6.65 mmol) were placed in a 100 mL round-bottomed flask equipped with a magnetic stirrer bar and then stoppered with a rubber septum under nitrogen. A solution of 2, 3 -diisobutyl acetal (2) (1.0 g, 2.28 mmol) in dry CH2CI2 (60 mL) in a 100 mL round-bottomed flask stoppered with a rubber septum was transferred to the above-mentioned lOOmL round-bottomed flask via a glass syringe. The mixture was stirred at room temperature for 12 h. 

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