A perusal of the PDB reveals that the game of Periodic Table bingo still has eleven rounds to run:
scandium, titanium, germanium, zirconium, niobium, neodymium, dysprosium, thulium, hafnium, bismuth and thorium remain absent from PDB entries. OK, many of these are elements that would rather be refractory oxides or jet-engine components than hexammines, and niobium chloride clusters don't seem to be as water-stable as Ta6Br14, but why have neodymium, dysprosium and thulium so consistently been left out there in the cold rather than admitted to the warmish embrace of carboxyl groups? There must somewhere be a protein with a site that cries out for ThCl2(2+), an unexpectedly water-stable cation. Tom
