Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

The Chemistry and Applications of Metal-Organic Frameworks

The development in the field of coordination polymers or metal-organic coordination networks, MOCNs (metal-organic frameworks, MOFs) is assessed in terms of property investigations in the areas of catalysis, chirality, conductivity, luminescence, magnetism, spin-transition (spin-crossover), non-linear optics (NLO) and porosity or zeolitic behavior upon which potential applications could be based.

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Engineering coordination polymers towards applications

The semiconductor industry has seen a remarkable miniaturization trend, driven by many scientific and technological innovations. But if this trend is to continue, and provide ever faster and cheaper computers, the size of microelectronic circuit components will soon need to reach the scale of atoms or molecules—a goal that will require conceptually new device structures. The idea that a few molecules, or even a single molecule, could be embedded between electrodes and perform the basic functions of digital electronics—rectification, amplification and storage—was first put forward in the mid-1970s. The concept is now realized for individual components, but the economic fabrication of complete circuits at the molecular level remains challenging because of the difficulty of connecting molecules to one another. A possible solution to this problem is ‘mono-molecular’ electronics, in which a single molecule will integrate the elementary functions and interconnections required for computation.

Electronics using hybrid-molecular and mono-molecular devices

The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

http://depa.fquim.unam.mx/amyd//archivero/FidelmarLechugaSanabria_4940.pdf

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

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Lanthanide single-molecule magnets.

Investigation of the static and dynamic magnetic properties of CoFe2O4 nanoparticles

Preparation of size-controllable magnetite (Fe3O4) nanoparticles by alkaline oxidation of ferrous ion adsorbed in sulfonated mesoporous styrenedivinylbenzene copolymer is described. It was observed that the magnetite nanoparticle size increases by ion-charging the sulfonated polymeric template with ferrous aqueous solution at increasing iron concentration. A simple model describing the amount of iron incorporation in the polymeric template is proposed. The magnetite-based composite was investigated by atomic absorption, transmission electron microscopy, Mo 1ssbauer spectroscopy, X-ray diffraction, and magnetization data.

Preparation of Magnetite Nanoparticles in Mesoporous Copolymer Template

Ferromagnetic order in the sulfur‐containing nitronyl nitroxide radical, 2‐(4‐thiomethyl)phenyl‐4,4,5,5‐tetramethylimidazoline‐l‐oxyl‐3‐oxide, NIT(SMe)Ph

We present static and dynamical magnetic properties of a new organic cluster compound, Mn12Ac. High field magnetization and susceptibility data indicate that the clusters have a S=10 ground state with a high anisotropy and are magnetically well isolated from each other. Low temperature specific heat results are in agreement with this picture. Those properties make this system ideal to study superparamagnetic relaxation and possible quantum effects at the nanoscopic scale at very low temperatures. Above 4K the relaxation times follow an Arrhenius law \( \tau = {\tau _o}{e^{\Delta /k}}{_b^T} \) with Δ/kb~64 K, in agreement with high field magnetization, and τO~10-7 S. AC susceptibility data under dc field show a new and unexpected field dependence of the relaxation time that seems to indicate that thermally activated Quantum Tunneling of the Magnetization through the anisotropy energy barrier occurs.

AC Susceptibility Relaxation Studies on a Manganese Organic Cluster Compound: Mn12Ac

Magnetic relaxation experiments constitute a unique method of determining the nature of fluctuations in dissipative magnetic systems. At high temperatures these fluctuations are thermal and strongly temperature dependent. At low temperatures, where quantum fluctuations dominate, magnetic relaxation becomes independent of temperature. Such behavior has been observed in many systems. In this review we emphasize the study of low temperature relaxation in ferromagnetic nanoparticles, layers, and multilayers (including ‘‘domain wall junctions’’), and large single crystals. The results of magnetic relaxation experiments are shown to agree with theoretical predictions of quantum tunneling of the magnetization. When dissipation becomes important, in large and complex systems, a time dependent WKB exponent needs to be introduced.

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Miguel A. Novak

Papers

Investigation of the static and dynamic magnetic properties of CoFe2O4 nanoparticles

Preparation of Magnetite Nanoparticles in Mesoporous Copolymer Template

Ferromagnetic order in the sulfur‐containing nitronyl nitroxide radical, 2‐(4‐thiomethyl)phenyl‐4,4,5,5‐tetramethylimidazoline‐l‐oxyl‐3‐oxide, NIT(SMe)Ph

AC Susceptibility Relaxation Studies on a Manganese Organic Cluster Compound: Mn12Ac

Quantum tunneling in magnetic systems of various sizes (invited)