Question

Do the alkaline earth metal ions form many complexes? Are group

2

better or worse than group

1

at forming complexes? What is the reason for the difference? Which of the metal ions in the group are best at forming complexes? Which are the best complexing agents? Name one complex of a group

2

metal which is of biological importance.

Accepted Answer

Alkaline earth metals have greater tendency to form complexes with Lewis bases than that of alkali metals. The heavier alkaline earth metals also form complexes but usually with a coordination number of $6$ or higher.

Factors which favours complex formation are small highly charged ions with suitable empty orbitals of low energy that are used for bonding. Group $2$ elements form divalent ions and these are smaller than that of group $1$ ions. So, group $2$ elements are better at forming complexes than group $1$ elements.

Beryllium is smaller than the other elements, so, beryllium form many complexes. Of the other elements only calcium and magnesium show the tendency to form complexes and these are usually with other oxygen donor ligands. In most cases, beryllium is four coordinate in complexes.

Calcium and rest of the elements of the group only form complexes with strong complexing agents like acetyl acetone and ethylenediaminetetraacetic acid $(EDTA)$ . Calcium and magnesium complex with $(EDTA)$ and titrations are performed using $EDTA$ in buffered solutions to estimate the amount of ${Ca}^{+ 2}$ and ${Mg}^{+ 2}$ .

${Mg}^{+ 2}$ ions are concentrated in animal cells and ${Ca}^{+ 2}$ are concentrated in body fluids outside the cell. ${Mg}^{+ 2}$ is important in chlorophyll. ${Ca}^{+ 2}$ is important in bones and teeth as apatite and it is important in blood clotting and required to maintain the regular heart beat.

Important Questions on Group 2 - the Alkaline Earth Elements

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