Question

Give the coordination numbers and write the formulas for each of the following, including all isomers where appropriate:

(a) tetrahydroxozincate(II) ion (tetrahedral)

(b) hexacyanopalladate(IV) ion

(c) dichloroaurate(I) ion (note that aurum is Latin for “gold”)

(d) diamminedichloroplatinum(II)

(e) potassium diamminetetrachlorochromate(III)

(f) hexaamminecobalt(III) hexacyanochromate(III)

(g) dibromobis(ethylenediamine) cobalt(III) nitrate

Short answer

The number of ligands attached to the central metal ion attached through the secondary valencies and are present inside the coordination sphere is called coordination number of central metal ion.

Step-by-step solution

Explanation

(a)

• We have tetrahydroxozincate\(\left( {{\bf{II}}} \right)\)ion from which we could see that we have\({\bf{4}}\)monodentate hydroxyl ligands inside the coordination sphere.
• It means that the coordination number of the central metal ion\({\rm{Zn}}\)is\({\bf{4}}\).
• Hence, the formula of ion is\({\left( {{\rm{Zn}}{{({\rm{OH}})}_4}} \right)^{2 - }}\)

(b)

• We have\(hexacyanopalladate(IV) ion\)ion from which we could see that we have\(6\)monodentate cyano ligands inside the coordination sphere.
• It means that the coordination number of the central metal ion\({\rm{Pd}}\)is\(6\).
• Hence, the formula of ion is\({\left( {Pd{{(CN)}_6}} \right)^{2 - }}\)

(c)

• Here, we have\(dichloroaurate(I) ion\)from which we can see that we have\( {\bf{2}} \)monodentate ligands inside the coordination sphere.
• It clearly means that the coordination number of the central metal ion\({\bf{Au}}\)is\( {\bf{2}} \).
• The formula of the ion is\({\left( {AuC{l_2}} \right)^ - }\)

(d)

• We have\(diamminedichloroplatinum(II)\)from which we can see that we have\({\bf{4}}\)monodentate ligands inside the coordiantion sphere.
• It means that the coordination number of the central metal ion\( {\bf{Pt}}\)is\({\bf{4}}\).
• The formula of the compound is\(\left( {{\rm{Pt}}{{\left( {{\rm{N}}{{\rm{H}}_3}} \right)}_2}{\rm{C}}{{\rm{l}}_2}} \right)\)

(e)

• We have\(potassium diamminetetrachlorochromate(III)\)from which we can see that we have\(6\)monodentate ligands (\({\bf{4}}\)chloride and\( {\bf{2}} \)amine ) inside the coordination sphere.
• It clearly means that the coordination number of the central metal ion\( {\rm{Cr}}\)is\(6\)
• The formula of the compound is\({\rm{K}}\left( {{\rm{Cr}}{{\left( {{\rm{N}}{{\rm{H}}_3}} \right)}_2}{\rm{C}}{{\rm{l}}_4}} \right)\)

(f)

• We have\(hexaamminecobalt(III) hexacyanochromate(III)\)from that we can see that we have\(6\)monodentate ligands, in both cases, inside the coordination sphere.
• It gives us a clue that the coordination number of the central metal ion\({\bf{Co}}\)and\({\bf{Cr}}\)is\(6\)
• The formula of the compound is\(\left( {{\rm{Co}}{{\left( {{\rm{N}}{{\rm{H}}_3}} \right)}_6}} \right)\left( {{\rm{Cr}}{{({\rm{CN}})}_6}} \right)\)

(g)

• We have\(dibromobis(ethylenediamine) cobalt(III) nitrate\)and from that we can see that we have\( {\bf{2}} \)monodentate ligands (\( {\bf{2}} \)bromide ) and\( {\bf{2}} \)bidentate ligands (en) inside the coordination sphere.
• It leaves us a clue that the coordination number of the central metal ion\({\bf{Co}}\)is\(6\).
• The formula of the compound is\( \left( {{\rm{CoBr}}{r_2}{{(en)}_2}} \right){\rm{N}}{{\rm{O}}_3}\)

Result

\(\begin{aligned}{l}a){\left( {{\rm{Zn}}{{({\rm{OH}})}_4}} \right)^{2 - }}\\b){\left( {Pd{{(CN)}_6}} \right)^{2 - }}\\c){\left( {AuC{l_2}} \right)^ - }\\d)\left( {{\rm{Pt}}{{\left( {{\rm{N}}{{\rm{H}}_3}} \right)}_2}{\rm{C}}{{\rm{l}}_2}} \right)\\e)K\left( {Cr{{\left( {{\rm{N}}{{\rm{H}}_3}} \right)}_2}C{l_4}} \right)\\f)\left( {{\rm{Co}}{{\left( {{\rm{N}}{{\rm{H}}_3}} \right)}_6}} \right)\left( {{\rm{Cr}}{{({\rm{CN}})}_6}} \right)\\g)\left( {{\rm{CoBr}}{r_2}{{(en)}_2}} \right)N{\rm{N}}{{\rm{O}}_3}\end{aligned}\)