Give the coordination number of the metal ion and the number of ions per formula unit in each compound in Problem 23.67.

A coordination complex is made up of a core atom or ion, known as the coordination center, which is typically metallic, and an array of attached molecules or ions that are known as ligands or complexing agents.

The coordination number is the number of ligands directly attached to the central metal ion in a coordination compound. These ligands can be ions, atoms, or molecules. The most common coordination number is 0, but it is also not rare to see 2 and 4 as coordination numbers.

$\left(\text{Cr}{\left({\text{H}}_2{\text{O}}_6\right)}_2{\left({\text{SO}}_4\right)}_3\right.$- There are six ligands bonded with a central metal ion, so the coordination number is 6. This compound consists of 5 ions (2Cr a+ and $3{\text{SO}}_4^{2-}$).

$\text{Ba}{\left({\text{FeBr}}_4\right)}_2$- There are four ligands bonded with a central metal ion, so the coordination number is 4 This compound consists of 11 ions (Ba+, 2Feand $8{\text{Br}}^{-}$).

role="math" localid="1663316902643" $\left(\text{Pt}{\left(\text{en}\right)}_2\right){\text{CO}}_3$- There are two ligands bonded with a central metal ion (en is bidentate), so the coordination number is 4. This compound consists of 2 ions $\left({\text{Pt}}^{2+}\right.$and$\left.{\text{CO}}_3^{2-}\right)$