Metal carbonyl 18-electron complexes is sometimes catalysed by catalytic amounts of oxidants, via electron-transfer. Metal carbonyls react with reducing agents such as metallic sodium or sodium amalgam to give carbonylmetalate (or carbonylate) anions: For iron pentacarbonyl, one obtains the tetracarbonylferrate with loss of CO: Mercury can insert into the metal-metal bonds of some polynuclear metal carbonyls: The CO ligand is often susceptible to attack by nucleophiles. For example, trimethylamine oxide and bistrimethylsilylamide convert CO ligands to CO and CN, respectively. In the "Hieber base reaction", hydroxide ion attacks the CO ligand to give a metallacarboxylic acid, followed by the release of carbon
Mercury(IV) fluoride more recent theoretical studies cast doubt on the possible existence of mercury(IV) and even copernicium(IV) fluoride. HgF is produced by the reaction of elemental mercury with fluorine: HgF is only stable in matrix isolation at ; upon heating, or if the HgF molecules touch each other, it decomposes to mercury(II) fluoride and fluorine: HgF is a diamagnetic, square planar molecule. The mercury atom has a formal 6s5d6p electron configuration, and as such obeys the octet rule but not the 18-electron rule. HgF is isoelectronic with the tetrafluoroaurate anion, , and is valence isoelectronic with the tetrachloroaurate (), tetrabromoaurate (), and