I am on a mission to persuade my colleagues that the statistical analysis of crystal structures is a useful teaching tool. One colleague asked for a demonstration and suggested exploring the classical Jahn-Teller effect (thanks Milo!). This is a geometrical distortion associated with certain molecular electronic configurations, of which the best example is illustrated by octahedral copper complexes which have a d9 electronic configuration. The eg level shown below is occupied by three electrons and which can therefore distort in one of two ways to eliminate the eg degeneracy by placing the odd electron into either a x2-y2 or a z2 orbital. Here I explore how this effect can be teased out of crystal structures.
Posts Tagged ‘chemical bonding’
The mechanism of borohydride reductions. Part 1: ethanal.
Sunday, April 12th, 2015Sodium borohydride is the tamer cousin of lithium aluminium hydride (LAH). It is used in aqueous solution to e.g. reduce aldehydes and ketones, but it leaves acids, amides and esters alone. Here I start an exploration of why it is such a different reducing agent.
Hafnium and Niels Bohr
Sunday, June 5th, 2011In 1923, Coster and von Hevesy[1] claimed discovery of the element Hafnium, atomic number 72 (latin Hafnia, meaning Copenhagen, where the authors worked) on the basis of six lines in its X-ray spectrum. The debate had long raged as to whether (undiscovered) element 72 belonged to the rare-earth group 3 of the periodic table below yttrium, or whether it should be placed in group 4 below zirconium. Establishing its chemical properties finally placed it in group 4. Why is this apparently arcane and obscure re-assignment historically significant? Because, in June 1922, in Göttingen, Niels Bohr had given a famous series of lectures now known as the Bohr Festspiele on the topic of his electron shell theory of the atom. Prior to giving these lectures he had submitted his collected thoughts in January 1922[2].
References
- D. COSTER, and G. HEVESY, "On the Missing Element of Atomic Number 72", Nature, vol. 111, pp. 79-79, 1923. http://dx.doi.org/10.1038/111079a0
- N. Bohr, "Der Bau der Atome und die physikalischen und chemischen Eigenschaften der Elemente", Zeitschrift f�r Physik, vol. 9, pp. 1-67, 1922. http://dx.doi.org/10.1007/BF01326955