Question

Complex X of composition $Cr(H_2O)_6Cl_n$ has a spin only magnetic moment of 3.83 BM. It reacts with $AgNO_3$ and shows geometrical isomerism. The IUPAC nomenclature of X is :

• A. Tetraaquadichlorido chromium(IV) chloride dihydrate
• B. Hexaaqua chromium(III) chloride
• C. Dichloridotetraaqua chromium(IV) chloride dihydrate
• D. Tetraaquadichlorido chromium(III) chloride dihydrate

Answer 1

Answer: (D)

Tetraaquadichlorido chromium(III) chloride dihydrate

Answer 2

$Cr\left(H_{2}O\right)_{6} Cl_{n}$ if magnetic mement is 3.83 BM then it contain three unpaired electrons. It means chromium in +3 oxidation state so molecular formula is $Cr\left(H_{2}O\right)_{6} Cl_{3}$
$\therefore\,$ This formula have following isomers
(a)$\left[Cr\left(H_{2}O\right)_{6}\right]Cl_{3} :$ react with $AgNO_{3}$ but does not show geometrical isomerism.
(b) $\left[Cr\left(H_{2}O\right)_{5} Cl\right]Cl_{2}. H_{2}O$ react with $AgNO_{3}$ but does not show geometrical isomerism.
(c) $\left[Cr\left(H_{2}O\right)_{4} Cl_{2}\right]Cl.2H_{2}O$ react with $AgNO_{3} \&$ show geometrical isomerism.
(d) $\left[Cr\left(H_{2}O\right)_{3}Cl_{3}\right]. 3H_{2}O$ does not react with $AgNO_{3} \&$ show geometrical isomerism.
$\left[Cr\left(H_{2}O\right)_{4}Cl_{2}\right]Cl. 2H_{2}O$ react with $AgNO_{3} \&$ show geometrical isomerism and it's IUPAC nomenclature is Tetraaquadichlorido chromium (III) Chloride dihydrate.