Metal hydroxide
Metal hydroxides are also known as strong bases. Many common metal hydroxides are made up from hydroxide ions and the ion of the particular metal that it is made up of. Example: When NaOH (sodium hydroxide) is dissolved in water, it forms OH ions and Na ions. Metal hydroxides ionize completely when dissolved, so that is why they are known as strong bases. Their pH is above 7, labeling them as bases. Since ions conduct electricity, metal hydroxides carry electricity very well when they are dissolved.In soils, it is assumed that larger amounts of natural phenols are released from decomposing plant litter rather than from throughfall in any natural plant community. Decomposition of dead plant material causes complex organic compounds to be slowly oxidized (lignin-like humus) or to break down into simpler forms (sugars and amino sugars, aliphatic and phenolic organic acids), which are further transformed into microbial biomass (microbial humus) or are reorganized, and further oxidized, into humic assemblages (fulvic and humic acids), which bind to clay minerals and metal hydroxides.
Iridium
No monohalides or dihalides are known, whereas trihalides, , are known for all of the halogens. For oxidation states +4 and above, only the tetrafluoride, pentafluoride and hexafluoride are known. Iridium hexafluoride, , is a volatile and highly reactive yellow solid, composed of octahedral molecules. It decomposes in water and is reduced to , a crystalline solid, by iridium black. Iridium pentafluoride has similar properties but it is actually a tetramer, , formed by four corner-sharing octahedra. Iridium metal dissolves in molten alkali-metal cyanides to produce the (hexacyanoiridate) ion.
Hexachloroiridic(IV) acid, , and its ammonium salt are the most important iridium compounds from an industrial perspective. They are involved in the purification of iridium and used as precursors for most other iridium compounds, as well as in the preparation of anode coatings. The ion has an intense dark brown color, and can be readily reduced to the lighter-colored and vice versa. Iridium trichloride, , which can be obtained in anhydrous form from direct oxidation of iridium powder by chlorine at 650 °C, or in hydrated form by dissolving in hydrochloric acid, is often used as a starting material for the synthesis of other Ir(III) compounds. Another compound used as a starting material is ammonium hexachloroiridate(III), . Iridium(III) complexes are diamagnetic (low-spin) and generally have an octahedral molecular geometry.