According to textbook knowledge, the usual oxidation states of gold in compounds are +I and +III. The divalent form (+II), on the other hand, prefers to form polynuclear compounds or simply undergoes transformation into the mono- and trivalent forms. However, the elements next to gold in the periodic table are quite different in this respect. The ions of the coinage metals, copper(+II) and silver(+II), are usually present in divalent form and this is also the case for gold’s neighbors to its left and right, platinum(+II) and mercury(+II). It has been postulated that when gold undergoes photochemical catalysis reactions, the +II state may form, but definitive evidence has not been provided to date. The corresponding proof has just been advanced by researchers at Johannes Gutenberg University Mainz (JGU) in a recent publication.