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Ytterbium, a Lanthanide series element, was discovered in 1878 byMarignac who named the element after a town (Ytterby) in Sweden. The first synthesis of YbCl3 did not appear in literature until 1946 by Hoogschagen. YbCl3 is now a readily available source of Yb+3 ions, which is why the study of YbCl3 is chemically relevant.
Additional recommended knowledge
The valence electron configuration of Yb+3 (from YbCl3) is 4f135s25p6, which has crucial implications in chemical behavior of Yb+3. Also, the size of Yb+3 governs it’s catalytic behavior and biological applications. For example, while both Ce+3 and Yb+3 have a single unpairedf electron, Ce+3 is much larger than Yb+3 because Lanthanides become much smaller with increasing effective nuclear charge sincef electrons are not well shielded, compared tod electrons. This behavior is known as the Lanthanide contraction. The small size of Yb+3 produces fast catalytic behavior and an atomic radius (0.99 Ǻ) comparable to many important biological ions.
The thermodynamic properties tabulated herein were difficult to obtain since many of the measurements were made in the gas phase where YbCl3 can exist as ([YbCl6]-3) or Yb2Cl6. The Yb2Cl6 species was detected by electron impact (EI) mass spectrometry as (Yb2Cl5+). Additional complications in obtaining experimental data arise from the myriad of low-lying f-d andf-f electronic transitions. Despite these issues, the thermodynamic properties of YbCl3 have been obtained and the C3V symmetry group has been assigned based upon the four active infrared vibrations.
In practice there are better ways to prepare YbCl3 for lab use. The aqueous HCl/ammonium chloride route is low tech but very effective. Alternatively hydrated YbCl3 may be dehydrated using a variety of reagents, particularly trimethylsilyl chloride. Other methods have been published including reacting the finely powdered metal with mercuric chloride at high temperature in a sealed tube. A variety of routes to solvated YbCl3 have been reported including reaction of the metal with various halocarbons in the present of a donor solvent such as THF, or dehydration of the hydrated chloride using trimethylsilyl or thionyl chloride, again in a solvent such as THF.
YbCl3, with a single unpairedf electron, acts as a Lewis acid in order to fill the 4f orbital. The Lewis acidic nature of YbCl3 allows YbCl3 to coordinate (usually as [YbCl2]+) in transition states to catalyze alkylation reactions, such as the Aldol reaction and the Pictet-Spengler reaction.
The Aldol reaction is a versitle reaction in synthetic organic chemistry. YbCl3 serves a Lewis acid catalyst which aids the Pd(0) catalyzed decarboxylative Aldol reaction between a ketone enolate and an aldehyde. Transition statesA andB show the coordination method of the ytterbium salt as a Lewis acid. For the depicted decarboxylative Aldol reaction with R = tert-butyl andR’ = -(CH2)2Ph, the reaction yields show YbCl3 is an effective Lewis acid catalyst:
The Pictet-Spengler reaction produces a valuable tetrahydro-β-carboline ring system which can be later used for synthetically prepared indole alkaloids. The Lewis acid catalyzed reaction with YbCl3 gave excellent yields and reduced reaction times from four days to 24 hours.
The small size of Yb3+ provides fast catalysis, but at the cost of selectivity. For example, the mono-acetylation ofmeso-1,2-diols is fastest (2 h) with YbCl3, but chemoselectivity for the mono-acetylated product is low (50%) compared to CeCl3 (23 h, 85%).
YbCl3 is a NMR shift reagent that produces different resonances with nuclei in contact with the YbCl3 versus those nuclei not in contact with the shift reagent. Generally paramagnetic species, such as a (Lanthanide)+3 ion, are desirable shift reagents. Membrane biology has been greatly influenced by YbCl3, where39K+ and23Na+ ion movement is critical in establishing electrochemical gradients. Nerve signaling is a fundamental aspect of life that may be probed with YbCl3 using NMR techniques. YbCl3 may also be used as a calcium ion probe, in a fashion similar to a sodium ion probe.
YbCl3 is also used to track digestion in animals. Certain additives to swine feed, such as probiotics, may be added to either solid feed or drinking liquids. YbCl3 travels with the solid food and therefore helps determine which food phase is ideal to incorporate the food additive. The YbCl3 concentration is quantified from ICP (inductively coupled plasma) mass spectrometry to within 0.0009 μg/mL. YbCl3 concentration versus time yields the flow rate of solid particulates in the animal’s digestion. The animal is not harmed by the YbCl3 since YbCl3 is simply excreted in fecal matter and no change in body weight, organ weight, or hematocrit levels has been observed in mice.
The catalytic nature of YbCl3 also has an application in DNA microarrays, or so called DNA “chips”. YbCl3 led to a 50-80 fold increase in flourescein incorporation into target DNA, which could revolutionize infectious disease detection (such as a rapid test for tuberculosis).
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ytterbium(III)_chloride". A list of authors is available in Wikipedia.|