Class 12 Chemistry MCQs | Chapter 5: Coordination Compounds – Part 2

Explanation: In coordination nomenclature, \(CO\) as a ligand is called carbonyl. It is a neutral ligand and is commonly seen in metal carbonyl complexes such as \([Ni(CO)_4]\). The word carbonato is used for carbonate-based species, not for coordinated carbon monoxide. So the correct ligand name here is carbonyl.

Explanation: In coordination nomenclature, coordinated \(NO\) is called nitrosyl. The ligand \(NO_2^-\) is named nitro or nitrito depending on the donor atom, \(CN^-\) is cyanido, and \(OH^-\) is hydroxido.

Explanation: The modern preferred ligand name for coordinated \(Cl^-\) is chlorido. Older texts often used chloride in complex names, but chlorido is the systematic form expected in modern coordination nomenclature. This change helps keep ligand naming consistent with other anionic ligand names. So chlorido is the preferred form in naming coordination entities.

Explanation: The correct modern ligand names here are chlorido for \(Cl^-\), hydroxido for \(OH^-\), and cyanido for \(CN^-\). These are all anionic ligands, and their names end in forms used specifically for coordination nomenclature. The other options mix in incorrect or non-systematic names. Remembering these standard mappings makes later complex naming much easier.

Explanation: The ligand \(C_2O_4^{2-}\) is named oxalato in coordination nomenclature. It commonly coordinates through two donor oxygen atoms, so it is treated as a bidentate ligand at this level. This is different from monodentate ligands such as \(CN^-\), \(Cl^-\), or \(OH^-\). The name carbonyl belongs to coordinated \(CO\), not oxalate. Therefore the correct pairing is oxalato and bidentate.

Explanation: The ligand \(SCN^-\) is generally named thiocyanato in coordination nomenclature. It is an ambidentate ligand and can coordinate through sulfur or nitrogen. When the donor atom is specified more precisely, special names such as isothiocyanato may be used. At the general recognition level, thiocyanato is the standard ligand name.

Explanation: The ligand \(NO_2^-\) can coordinate through either nitrogen or oxygen, so it is ambidentate. When coordination occurs through oxygen, the name used is nitrito. If it coordinates through nitrogen, the name changes to nitro. This difference is important because the two forms are linkage isomers.

Explanation: For simple ligand names, the multiplicative prefixes used are di-, tri-, tetra-, penta-, and hexa-. These prefixes show how many identical ligands are attached to the metal. The prefix tetra is therefore used for four such ligands. Prefixes like bis and tris are reserved for special situations involving more complicated ligand names.

Explanation: The ligand \(en\) is polydentate, so its multiplicity is usually shown with prefixes such as bis, tris, or tetrakis rather than di, tri, or tetra. This avoids confusion in naming and keeps the coordination name clearer. So two \(en\) ligands are indicated by the prefix bis. The choice depends on the nature of the ligand name, not on the metal.

Explanation: When the coordination entity is anionic, the metal name is modified to end in \(-ate\). For iron, the special form used is ferrate rather than ironate. This is one of the important traditional exceptions that remains standard in coordination nomenclature. So an anionic iron complex is named using ferrate.

Explanation: Copper follows a special naming pattern in anionic coordination entities. Instead of using the ordinary metal name, the name changes to cuprate. This is similar to ferrate for iron and argentate for silver. Such special forms must be memorised because they are used directly in systematic names.

Explanation: The Roman numeral in parentheses shows the oxidation state of the central metal ion. It is written after the metal name in the systematic name of the complex. This value is found from charge balance using the charges of the ligands and the overall complex charge. It does not represent coordination number or the number of ligands.

Explanation: The ligands are named first in alphabetical order, and multiplicative prefixes are ignored for alphabetisation. So ammine is written before chlorido. There are four \(NH_3\) ligands and two \(Cl^-\) ligands, giving tetraammine and dichlorido. The oxidation state of cobalt in \([Co(NH_3)_4Cl_2]^+\) is \(+3\), so the metal part is written as cobalt(III).

Explanation: The coordination entity \([Fe(CN)_6]^{3-}\) is anionic, so the metal name changes from iron to ferrate. Each \(CN^-\) ligand is named cyanido, giving hexacyanido for six such ligands. The three \(K^+\) ions are named first as potassium. Charge balance shows iron is in the \(+3\) oxidation state, so the full name becomes potassium hexacyanidoferrate(III).

Explanation: In naming salts, the cation is written first and the anion is written afterward. The same rule applies when the cation is a coordination entity. So a complex cation such as \([Cu(NH_3)_4]^{2+}\) is named before a simple anion such as sulfate. This keeps coordination compound naming consistent with general ionic nomenclature.

Explanation: The ligand \(CO\) is neutral and is named carbonyl. Since there are four such ligands, the prefix tetra is used. The whole complex is neutral, so the metal name remains nickel rather than nickelate. Because each carbonyl ligand is neutral, the oxidation state of nickel is \(0\), giving tetracarbonylnickel(0).

Explanation: \(\textbf{Given:}\) Name: potassium hexacyanidoferrate(II) \(\textbf{Required:}\) Formula of the compound \(\textbf{Relevant Principle:}\) The name gives the ligand, number of ligands, metal, oxidation state, and counter ion needed to build the formula. \(\textbf{Interpret the coordination entity:}\) Hexacyanido means \(6\) \(CN^-\) ligands. Ferrate(II) means iron has oxidation state \(+2\). \(\textbf{Find the charge on the coordination entity:}\) \[+2 + 6(-1) = -4\] So the complex ion is \([Fe(CN)_6]^{4-}\). \(\textbf{Balance with counter ions:}\) Potassium is \(K^+\), so \(4\) potassium ions are needed to balance \(-4\). \(\textbf{Final Answer:}\) The formula is \(K_4[Fe(CN)_6]\).

Explanation: The complex part is the cation \([Cu(NH_3)_4]^{2+}\), so it is named first. The ligand \(NH_3\) is ammine, and with four such ligands the name becomes tetraammine. Sulfate is a simple counter anion outside the coordination sphere, so it is named as sulfate, not sulfato. Copper is in the \(+2\) oxidation state in the complex cation, giving tetraamminecopper(II) sulfate.

Explanation: \(\textbf{Given:}\) Name: tetraamminedichloridocobalt(III) chloride \(\textbf{Required:}\) Formula of the compound \(\textbf{Relevant Principle:}\) Ligands named before the metal are inside the coordination sphere; the anion written after the coordination entity name is outside the bracket. \(\textbf{Build the coordination entity:}\) Tetraammine gives \(4\) \(NH_3\) ligands. Dichlorido gives \(2\) coordinated \(Cl^-\) ligands. Cobalt(III) means metal oxidation state \(= +3\). \(\textbf{Find the charge on the complex ion:}\) \[+3 + 4(0) + 2(-1) = +1\] So the coordination entity is \([Co(NH_3)_4Cl_2]^+\). \(\textbf{Balance with the counter ion:}\) One outer chloride ion is needed to balance the \(+1\) charge. \(\textbf{Final Answer:}\) The formula is \([Co(NH_3)_4Cl_2]Cl\).

Explanation: The ligand \(SCN^-\) is ambidentate, so it can coordinate through different donor atoms. When coordination occurs through sulfur, the general name thiocyanato is used. When coordination occurs through nitrogen, the donor-atom-sensitive name is isothiocyanato. This distinction matters because the two binding modes represent different linkage possibilities.