Ytterbium(III) chloride

The synthesis of YbCl₃ was first reported by Jan Hoogschagen in 1946.[3] It is now a commercially available source of Yb³⁺ ions and therefore of significant chemical interest.

The valence electron configuration of Yb⁺³ (from YbCl₃) is 4f¹³5s²5p⁶, which has crucial implications for the chemical behaviour of Yb⁺³. Also, the size of Yb⁺³ governs its catalytic behaviour and biological applications. For example, while both Ce⁺³ and Yb⁺³ have a single unpaired f electron, Ce⁺³ is much larger than Yb⁺³ because lanthanides become much smaller with increasing effective nuclear charge as a consequence of the f electrons not being as well shielded as d electrons.[4] This behavior is known as the lanthanide contraction. The small size of Yb⁺³ produces fast catalytic behavior and an atomic radius (0.99 Å) comparable to many biologically important ions.[4]

The gas-phase thermodynamic properties of this chemical are difficult to determine because the chemical can disproportionate to form [YbCl₆]⁻³ or dimerize.[5] The Yb₂Cl₆ species was detected by electron impact (EI) mass spectrometry as (Yb₂Cl₅⁺).[5] Additional complications in obtaining experimental data arise from the myriad of low-lying f-d and f-f electronic transitions.[6] Despite these issues, the thermodynamic properties of YbCl₃ have been obtained and the C_3V symmetry group has been assigned based upon the four active infrared vibrations.[6]

Anhydrous ytterbium(III) chloride can be produced by the ammonium chloride route.[7][8][9] In the first step, ytterbium oxide is heated with ammonium chloride to produce the ammonium salt of the pentachloride:

Yb₂O₃ + 10 NH₄Cl → 2 (NH₄)₂YbCl₅ + 6 H₂O + 6 NH₃

In the second step, the ammonium chloride salt is converted to the trichlorides by heating in a vacuum at 350-400 °C:

(NH₄)₂YbCl₅ → YbCl₃ + 2 HCl + 2 NH₃

YbCl₃ is a paramagnetic Lewis acid, like many of the lanthanide chlorides. It gives rise to pseudocontact shifted NMR spectra, akin to NMR shift reagents

Membrane biology has been greatly influenced by YbCl₃, where³⁹K⁺ and²³Na⁺ ion movement is critical in establishing electrochemical gradients.[10] 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.[11]

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.[12] The YbCl₃ concentration is quantified by inductively coupled plasma mass spectrometry to within 0.0009 μg/mL.[4] 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.[11]

The catalytic nature of YbCl₃ also has an application in DNA microarrays, or so called DNA “chips”.[13] YbCl₃ led to a 50–80 fold increase in fluorescein incorporation into target DNA, which could revolutionize infectious disease detection (such as a rapid test for tuberculosis).[13]