CBSE Class 12 Chemistry Chapter 17: Coordination Compounds NCERT Solutions

To write the formulas for coordination compounds, we need to identify the central metal ion, its oxidation state, the ligands, and the counter ions. The ligands are written inside the square brackets, and the counter ions are written outside to balance the charge.

1. The compound is Tetraamminediaquacobalt(III) chloride. The central metal ion is Cobalt (Co) with an oxidation state of +3. The ligands are tetraammine (4 NH3) and diaqua (2 H2O). The charge on the complex ion is [Co(H2O)2(NH3)4]^(3+). To balance this charge, three chloride ions (Cl-) are needed. Therefore, the formula is $[CO(H\_2O)\_2(NH\_3)\_4]CI\_3$.

2. The compound is Potassium tetracyanonickelate(II). The central metal ion is Nickel (Ni) with an oxidation state of +2. The ligand is tetracyano (4 CN-). The charge on the complex ion is [Ni(CN)4]^(2-). The counter ion is Potassium (K+). To balance the charge, two potassium ions are needed. Therefore, the formula is $K\_2[Ni(CN)\_4]$.

3. The compound is Tris(ethane-1,2-diamine) chromium(III) chloride. The central metal ion is Chromium (Cr) with an oxidation state of +3. The ligand is tris(ethane-1,2-diamine), which means three molecules of ethylenediamine (en). Ethylenediamine is a neutral ligand. The charge on the complex ion is [Cr(en)3]^(3+). The counter ion is chloride (Cl-). To balance the charge, three chloride ions are needed. Therefore, the formula is $\backslash left[\backslash operatorname\{Cr\}(\backslash operatorname\{en\})\_\{3\}\backslash right]\backslash operatorname\{Cl\}\_\{3\}$.

4. The compound is Amminebromidochloridonitrito-N-platinate(II). The central metal ion is Platinum (Pt) with an oxidation state of +2. The ligands are ammine (NH3), bromido (Br-), chlorido (Cl-), and nitrito-N (NO2-). The charge on the complex ion is [Pt(NH3)BrCl(NO2)]^-. The counter ion is not specified, implying the complex itself is an anion. Therefore, the formula is $[Pt(NH)\_3\; BrCl(NO\_2)]^-$.

5. The compound is Dichloridobis(ethane-1,2-diamine)platinum(IV) nitrate. The central metal ion is Platinum (Pt) with an oxidation state of +4. The ligands are dichlorido (2 Cl-) and bis(ethane-1,2-diamine) (2 en). The charge on the complex ion is [PtCl2(en)2]^(2+). The counter ion is nitrate (NO3-). To balance the charge, two nitrate ions are needed. Therefore, the formula is $\backslash left[\; PtCl\_2(en)\_2\; \backslash right]\; (NO\_3)\_2$.

6. The compound is Iron(III) hexacyanoferrate(II). This is a coordination compound where both ions are iron complexes. The cation is Iron(III) (Fe^3+). The anion is hexacyanoferrate(II), meaning it contains Iron in the +2 oxidation state coordinated with six cyanide ligands ([Fe(CN)6]^(4-)). To balance the charges, we need three Fe^3+ ions to balance the charge of two [Fe(CN)6]^(4-) anions (3 * +3 = +9 and 2 * -4 = -8, this is incorrect. Let's re-evaluate. The name implies Fe(III) is the cation and hexacyanoferrate(II) is the anion. The anion is [Fe(CN)6]^(4-). The cation is Fe^(3+). To balance the charges, we need 4 Fe^(3+) ions and 3 [Fe(CN)6]^(4-) anions. 4 * (+3) = +12 and 3 * (-4) = -12. Thus, the formula is $Fe\_4[Fe(CN)\_6]\_3$.

The IUPAC nomenclature of coordination compounds follows specific rules. Ligands are named first, followed by the central metal ion. The oxidation state of the metal is indicated in Roman numerals in parentheses. Cations are named before anions.

1. In $[Co(NH\_3)\_6]Cl\_3$, the central metal is Cobalt (Co). There are six ammine ligands (NH3). The oxidation state of Co is +3 (since 6 * 0 + x + 3 * (-1) = 0, x = +3). The counter ion is chloride. The IUPAC name is Hexaamminecobalt(III) chloride.

2. In $[Co(NH\_3)\_5Cl]Cl\_2$, the central metal is Cobalt (Co). There are five ammine ligands (NH3) and one chloride ligand (Cl). The oxidation state of Co is +3 (since 5 * 0 + 1 * (-1) + x + 2 * (-1) = 0, x = +3). The counter ion is chloride. The IUPAC name is Pentaamminechloridocobalt(III) chloride.

3. In $K\_3[Fe(CN)\_6]$, the counter ion is Potassium (K+), and the complex ion is $[Fe(CN)\_6]^(3-)$. The central metal is Iron (Fe). There are six cyano ligands (CN-). The oxidation state of Fe is +3 (since 3 * (+1) + x + 6 * (-1) = 0, x = +3). The IUPAC name is Potassium hexacyanoferrate(III).

4. In $K\_3[Fe(C\_2O\_4)\_3]$, the counter ion is Potassium (K+), and the complex ion is $[Fe(C\_2O\_4)\_3]^(3-)$. The central metal is Iron (Fe). The ligand is oxalate ($C\_2O\_4^2-$), and there are three of them. The oxidation state of Fe is +3 (since 3 * (+1) + x + 3 * (-2) = 0, x = +3). The IUPAC name is Potassium trioxalatoferrate(III).

5. In $K\_2[PdCl\_4]$, the counter ion is Potassium (K+), and the complex ion is $[PdCl\_4]^(2-)$. The central metal is Palladium (Pd). There are four chloride ligands (Cl-). The oxidation state of Pd is +2 (since 2 * (+1) + x + 4 * (-1) = 0, x = +2). The IUPAC name is Potassium tetrachloridopalladate(II).

6. In $[Pt(NH\_3)\_2Cl(NH\_2CH\_3)]Cl$, the central metal is Platinum (Pt). The ligands are two ammine (NH3), one chloride (Cl-), and one methylamine ($NH\_2CH\_3$, which is neutral). The oxidation state of Pt is +2 (since x + 2 * 0 + 1 * (-1) + 1 * 0 + 1 * (-1) = 0, x = +2). The counter ion is chloride. The ligands are named alphabetically: ammine, chlorido, methylamine. The IUPAC name is Diamminechlorido(methylamine)platinum(II) chloride.

Isomerism in coordination compounds arises from the different spatial arrangements of ligands or different composition of coordination sphere. Let's analyze each complex:

1. For the complex $K[Cr(H\_2O)\_2(C\_2O\_4)\_2]$, the central metal ion is Chromium (Cr). It is coordinated with two water ligands ($H\_2O$) and two oxalate ligands ($C\_2O\_4^2-$). Oxalate is a bidentate ligand. This complex can exhibit geometrical isomerism because the two water ligands can be adjacent (cis) or opposite (trans) to each other. The cis-isomer, where the two water molecules are adjacent, can also exist as optical isomers because it is chiral and not superimposable on its mirror image. The trans-isomer, where the two water molecules are opposite, has a plane of symmetry and is optically inactive.

   Geometrical Isomers:

   Trans-isomer: The two $H\_2O$ ligands are opposite each other.

   Cis-isomer: The two $H\_2O$ ligands are adjacent to each other.

   Optical Isomers:

   The cis-isomer is chiral and exists as a pair of enantiomers (optical isomers).

   Trans-isomer is optically inactive.

2. For the complex $[Co(en)\_3]Cl\_3$, the central metal ion is Cobalt (Co), and the ligand is ethylenediamine (en), which is a bidentate ligand. Since all the ligands are identical and bidentate, only optical isomerism is possible. This complex exists as two optical isomers (enantiomers) because the arrangement of the three bidentate ethylenediamine ligands around the cobalt ion creates a chiral structure that is not superimposable on its mirror image.

   Optical Isomers:

   The complex $[Co(en)\_3]^\{3+\}$ exists as a pair of enantiomers (optical isomers), denoted as $\backslash Delta$ and $\backslash Lambda$ forms.

3. For the complex $[Co(NH\_3)\_5(NO\_2)](NO\_3)\_2$, the central metal ion is Cobalt (Co). It has five ammine ligands ($NH\_3$) and one nitrito ligand ($NO\_2$). The nitrite ion ($NO\_2$) is an ambidentate ligand, meaning it can coordinate through either the nitrogen atom (nitrito-N) or an oxygen atom (nitrito-O). This leads to linkage isomerism.

   Linkage Isomers:

   1. Nitrito-N isomer: $[Co(NH\_3)\_5(NO\_2)](NO\_3)\_2$ (where $NO\_2$ is bonded through N).

   2. Nitrito-O isomer: $[Co(NH\_3)\_5(ONO)](NO\_3)\_2$ (where $NO\_2$ is bonded through O).

   Additionally, if the ligands were different, geometrical isomerism could be possible, but with five identical ammine ligands and one variable nitrite ligand, only linkage isomerism is significant here.

4. For the complex $[Pt(NH\_3)(H\_2O)Cl\_2]$, the central metal ion is Platinum (Pt). It is a square planar complex with two chloride ligands ($Cl$), one ammine ligand ($NH\_3$), and one water ligand ($H\_2O$). This complex can exhibit geometrical isomerism because the two chloride ligands can be adjacent (cis) or opposite (trans) to each other. The cis-isomer, where the two chloride ligands are adjacent, is chiral and can exhibit optical isomerism. The trans-isomer, where the chloride ligands are opposite, is optically inactive.

   Geometrical Isomers:

   Cis-isomer: The two $Cl$ ligands are adjacent.

   Trans-isomer: The two $Cl$ ligands are opposite.

   Optical Isomers:

   The cis-isomer is optically active.

   The trans-isomer is optically inactive.