Uploaded May 2017 | Updated September 2026, 1 week ago
Just a short clip from a side product we made. We did not film the preparation but basically, we took the PdCl2 in HCl solution we made and neutralized it with an excess of NaOH. At basic conditions, Pd(II) tends to form the Oxide-Hydrate. In comparison to the anhydrous Oxide is the Hydrate still soluble in Acids while the anhydrous form isn't. Another interesting property is here that the pure anhydrous oxide can be made thermally without decomposition of the product.
But why can you sometimes dehydrate a compound and sometimes not? Let's take Calcium chloride in water as an example. This compound cannot be fully dehydrated without the formation of other products. If you look more closely at the structure of the compound in the water you will understand why.
In CaCl2 x 6H2O the Calcium is surrounded by 9 water ligands, six of them form a trigonal prism where all three rectangular sites are capped by an additional H2O. These prisms stack via their triangular sites so 6 H2O are always shared between two Calcium giving the total composition of CaCl2 x 6H2O. The Chloride counter-ions are connected to the positive hydrogen atoms in the water molecules but have no direct contact to the calcium which is why you cannot simply boil off the water.
But how is PdO x H2O different? The same question had Oskar Glemser and Gerd Peuchel as well when they wrote their paper on this subject (DOI: 10.1002/zaac.19552810105). PdO crystallizes in the famous PtS-Structure. They found that from the size of H2O and the little distortion it cannot be positioned in channels or holes in the structure. Some could eventually take atom positions where Pd should rest (Pd(II) and H2O are quite similar in size) or on unoccupied positions. Still, this would be too little which is why they assumed most of the water is only bound due to absorption on the surface probably due to hydrogen bonds with the Oxides. So the structure itself always remains, coming from the anhydrous form to the hydrated one the lattice parameters do not change significantly. And this is why you can make anhydrous PdO thermally quite easily.
Just a short clip from a side product we made. We did not film the preparation but basically, we took the PdCl2 in HCl solution we made and neutralized it with an excess of NaOH. At basic conditions, Pd(II) tends to form the Oxide-Hydrate. In comparison to the anhydrous Oxide is the Hydrate still soluble in Acids while the anhydrous form isn't. Another interesting property is here that the pure anhydrous oxide can be made thermally without decomposition of the product.
But why can you sometimes dehydrate a compound and sometimes not? Let's take Calcium chloride in water as an example. This compound cannot be fully dehydrated without the formation of other products. If you look more closely at the structure of the compound in the water you will understand why.
In CaCl2 x 6H2O the Calcium is surrounded by 9 water ligands, six of them form a trigonal prism where all three rectangular sites are capped by an additional H2O. These prisms stack via their triangular sites so 6 H2O are always shared between two Calcium giving the total composition of CaCl2 x 6H2O. The Chloride counter-ions are connected to the positive hydrogen atoms in the water molecules but have no direct contact to the calcium which is why you cannot simply boil off the water.
But how is PdO x H2O different? The same question had Oskar Glemser and Gerd Peuchel as well when they wrote their paper on this subject (DOI: 10.1002/zaac.19552810105). PdO crystallizes in the famous PtS-Structure. They found that from the size of H2O and the little distortion it cannot be positioned in channels or holes in the structure. Some could eventually take atom positions where Pd should rest (Pd(II) and H2O are quite similar in size) or on unoccupied positions. Still, this would be too little which is why they assumed most of the water is only bound due to absorption on the surface probably due to hydrogen bonds with the Oxides. So the structure itself always remains, coming from the anhydrous form to the hydrated one the lattice parameters do not change significantly. And this is why you can make anhydrous PdO thermally quite easily.
![Copper Chemistry: K3[Cu(NO2)5]](https://i.ytimg.com/vi/zz23zENTWXk/mqdefault.jpg "Copper Chemistry: K3[Cu(NO2)5]
Explanation will follow soon")
