Lanthanides

Lanthanides

The lanthanide elements comprise a unique series of metals in the periodic table. These metals are distinctive in terms of size, valence orbitals, electrophilicity, and magnetic and electronic properties, such that some members of the series are currently the best metals for certain applications. Increased use of the lanthanides in the future is likely since their unusual combination of physical properties can be exploited to accomplish new types of chemical transformations not possible with transition and main group metals.

Since the lanthanides are relatively abundant in nature, their current price on the worldwide market is low and they are affordable in terms of practical applications. Since substantial ore deposits are available in the United States, the lanthanides constitute a national resource.

Utilization of these metals depends on our ability to manipulate them into the appropriate compounds and materials and to optimize their reactivity. This requires a basic understanding of their chemistry. Hence, the general objective of our research is to develop a fundamental understanding of this available set of heavy metals such that their special chemistry can be fully utilized.

The distinctive properties of the lanthanides include the following:

The lanthanides are some of the largest non-radioactive metals in the periodic table. For reactions in which a large trivalent ion is needed, they may be the best. Superior performance of the lanthanides in ring opening polymerization of lactones, butadiene polymerization, and catalytic phosphate hydrolysis may be related to this feature.

The lanthanides 4f valence orbitals have a limited radial extension. As a result orbital factors do not affect the chemistry as much as in transition metal chemistry. This means that substrates can approach the metal center in a variety of orientations and reaction pathways are not orbitally forbidden. The high reactivity of lanthanides in olefin polymerization and hydrogenation may be related to the fact that their are no orbital limitations to slow down the reactions.

The lanthanides are quite electropositive and as such have a high affinity for oxygen and the halides. Utilization in the catalytic converters of automobiles and in fuel cells is related to this.

The limited radial extension of the f orbitals reduces vibronic broadening of optical transitions and this leads to sharp 4f-4f emission and absorption spectra. The sharp nature of these transitions leads to very precise and efficient optical processes such that the lanthanides are often the components of choice in optical devices ranging from lasers (e.g. Nd;YAG) to color television (Eu provides the red) to energy saving phosphors (Eu, red, blue; Tb green).

The magnetic moments of the trivalent lanthanides range from 0 to 10.5 Bohr magnetons. This means that there are diamagnetic metals in the series which can be studied by NMR and other metals which can provide high magnetic moments for applications ranging from magnetic resonance imaging, MRI (e.g. Gd), to low weight high power magnets used in cars, airplanes, and appliances (NdFeB and SmCo magnets).