Uploaded December 2017 | Updated September 2026, 1 week ago
This is going to be the first video of a whole new video section dedicated to solid state thermochromism. We tested out several combinations of heavy metal Iodides, Chromates, and Iodomercurates in the past 4 weeks, isolated all these compounds and ampoule them. Here are the best results (as some weren't thermochromic at all). Note, we could not show this here without thermally shattering the glass but all of these thermochromic compounds shown here are also reversible, meaning they will turn to the original color if cooled.
Much like many other mercury-related compounds, HgI2 is thermochromic. Upon heating the color switches from red to yellow. What happens is that the crystal structure changes as the former dihedral angle between Hg and I is increased to a nearly linear geometry.
The red color is, according to literature, due to a strong ligand to metal charge transfer. Now, this linear geometry is something very common for Hg(I), although Hg(I) has Hg-Hg-bonds, a linear geometry is a well-known motif. And in fact, we can even postulate something like that here. Much like in our video on Tetraiodomercurates, we can formulate the reaction as a temperature controlled electron to jump from the Iodide to the Mercury resulting in:
I(-)-------Hg(2+) to I(0)-------Hg(+)
This also changes the LMCT-band positions a bit, in this case with a blue-shift.
For all the upcoming videos several explanations can be given. A solid-state chemist will argue with different occupation of empty sites in the crystal structure, coordination chemists will think about changes in the coordination and some inorganic chemists will rather think about electron transfers. We will try to assign the different ideas and theories to the videos but mostly it is usually really a change in the crystal structure as we are still dealing with solid compounds.
This is going to be the first video of a whole new video section dedicated to solid state thermochromism. We tested out several combinations of heavy metal Iodides, Chromates, and Iodomercurates in the past 4 weeks, isolated all these compounds and ampoule them. Here are the best results (as some weren't thermochromic at all). Note, we could not show this here without thermally shattering the glass but all of these thermochromic compounds shown here are also reversible, meaning they will turn to the original color if cooled.
Much like many other mercury-related compounds, HgI2 is thermochromic. Upon heating the color switches from red to yellow. What happens is that the crystal structure changes as the former dihedral angle between Hg and I is increased to a nearly linear geometry.
The red color is, according to literature, due to a strong ligand to metal charge transfer. Now, this linear geometry is something very common for Hg(I), although Hg(I) has Hg-Hg-bonds, a linear geometry is a well-known motif. And in fact, we can even postulate something like that here. Much like in our video on Tetraiodomercurates, we can formulate the reaction as a temperature controlled electron to jump from the Iodide to the Mercury resulting in:
I(-)-------Hg(2+) to I(0)-------Hg(+)
This also changes the LMCT-band positions a bit, in this case with a blue-shift.
For all the upcoming videos several explanations can be given. A solid-state chemist will argue with different occupation of empty sites in the crystal structure, coordination chemists will think about changes in the coordination and some inorganic chemists will rather think about electron transfers. We will try to assign the different ideas and theories to the videos but mostly it is usually really a change in the crystal structure as we are still dealing with solid compounds.
![Copper Chemistry: K3[Cu(NO2)5]](https://i.ytimg.com/vi/zz23zENTWXk/mqdefault.jpg "Copper Chemistry: K3[Cu(NO2)5]
Explanation will follow soon")
