Give formulas for the following. a. potassium tetrachlorocobaltate(II) b. aquatricarbonylplatinum(II) bromide c. sodium dicyanobis(oxalato)ferrate(III) d. triamminechloroethylenediaminechromium(III) iodide

Coordination compounds, also known as complex compounds, consist of a central metal atom or ion bound to one or more ligands. Ligands are atoms, ions, or molecules that can donate a pair of electrons to the metal center, forming coordinate covalent bonds. These compounds are typically represented by formulas in square brackets to show the coordination sphere, which includes the metal and its directly attached ligands. For example, in the compound potassium tetrachlorocobaltate(II), denoted as \(K_4[CoCl_4]\), cobalt acts as the central metal ion, while the chloride ions act as ligands.

To understand coordination compounds, one must grasp the concept of coordination number, which is the number of ligand attachment sites to the metal ion, and the types of ligands involved, which can range from simple ions like chloride \(Cl^-\) to more complex molecules like ethylenediamine. These compounds have a vast range of colors, properties, and applications in various fields, including chemistry, biology, and medicine.

The oxidation number, also called oxidation state, is an assigned number that reflects the number of electrons an atom has gained, lost, or shared when it forms chemical compounds or bonds. It is essential in determining how these atoms combine to form chemical compounds. For example, in sodium dicyanobis(oxalato)ferrate(III), represented as \(Na_3[Fe(CN)_2(C_2O_4)_2]\), the Roman numeral III indicates that iron has an oxidation number of +3.

In coordination compounds, the oxidation number of the central metal ion helps determine the formula of the compound by ensuring that the total charge in the coordination complex is balanced by the counterions. The ligands also have oxidation numbers, which are generally fixed for simple ions and neutral molecules, while organic ligands can have varied oxidation states depending on their structure and the atoms involved.

Ligands are crucial participants in coordination complexes. They are ions or molecules with one or several donor atoms containing lone pairs that can be donated to an empty orbital of a metal atom or ion, forming a coordinate bond. The nature of ligands greatly influences the properties and reactivity of the coordination compound.

There are several types of ligands, including monodentate ligands, which bind through a single atom like the chloride ion \(Cl^-\), multidentate or polydentate ligands, which can attach through multiple atoms at once, such as ethylenediamine in triamminechloroethylenediaminechromium(III) iodide, and ambidentate ligands, which can attach through two different atoms but only one at a time. The ability of ligands to create stable complexes with metal ions finds applications across various scientific fields, from industrial catalysis to the development of new pharmaceuticals.