u201d when used to designate a ligand having a nominal u2212 1 charge is considered to be derived from the neutral parent compound u201c hl u201d by the loss of a hydrogen ion the term u201c complex u201d when used as a noun is intended to mean a compound having at least one metallic ion and at least one ligand the term u201c u03b2 dicarbonyl u201d is intended to mean a neutral compound in which two ketone groups are present separated by a chr group the term u201c u03b2 enolate u201d is intended to mean the anionic form of the u03b2 dicarbonyl in which the h from the chr group between the two carbonyl groups has been abstracted the term u201c group u201d is intended to mean a part of a compound such as a substituent in an organic compound or a ligand in a complex the phrase u201c adjacent to u201d when used to refer to layers in a device does not necessarily mean that one layer is immediately next to another layer on the other hand the phrase u201c adjacent r groups u201d is used to refer to r groups that are next to each other in a chemical formula i e r groups that are on atoms joined by a bond the term u201c photoactive u201d refers to any material that exhibits electroluminescence and or photosensitivity in addition the iupac numbering system is used throughout where the groups from the periodic table are numbered from.