Coordination Compounds flash cards

1. 1.State the main postulates of Werner's coordination theory.

   Metals show two valencies: primary (ionizable, satisfied by anions) and secondary (non-ionizable, satisfied by ligands, = coordination number). Secondary valencies are directional, giving definite geometry. In $[\text{Co}(\text{NH}_3)_6]\text{Cl}_3$ primary $=3$, secondary $=6$.

   Hint: Two types of valency: ionizable vs directional.

2. 2.Differentiate primary and secondary valency in Werner's theory.

   Primary valency = oxidation state, ionizable, satisfied by negative ions, non-directional. Secondary valency = coordination number, non-ionizable, satisfied by ligands (neutral/negative), directional and fixes geometry.

   Hint: Oxidation state vs coordination number.

3. 3.Define a ligand and coordination number.

   A ligand is an ion or molecule with at least one lone pair that donates electrons to the central metal via a coordinate bond. Coordination number = number of ligand donor atoms directly bonded (sigma) to the metal.

   Hint: Electron-pair donor; count donor atoms.

4. 4.What is the coordination sphere? How is it written?

   The central metal plus its directly bonded ligands, enclosed in square brackets, e.g. $[\text{Co}(\text{NH}_3)_6]^{3+}$. It behaves as a single unit; species outside brackets are counter (ionizable) ions.

   Hint: Everything inside the square brackets.

5. 5.Classify ligands by denticity with one example each (monodentate, bidentate, polydentate).

   Monodentate: one donor atom, e.g. $\text{NH}_3$, $\text{Cl}^-$. Bidentate: two donors, e.g. ethylenediamine (en), oxalate $\text{C}_2\text{O}_4^{2-}$. Polydentate/hexadentate: EDTA$^{4-}$ (6 donors).

   Hint: Count how many donor atoms attach.

6. 6.What is an ambidentate ligand? Give examples.

   A monodentate ligand that can bind through either of two different donor atoms (but only one at a time). Examples: $\text{NO}_2^-$ (N = nitro, O = nitrito), $\text{SCN}^-$ (S = thiocyanato, N = isothiocyanato), $\text{CN}^-$ (C or N).

   Hint: Two possible donor atoms, one used at a time.

7. 7.What is a chelate ligand and the chelate effect?

   A chelate is a polydentate ligand forming a ring with the metal (e.g. en gives a 5-membered ring). The chelate effect = extra thermodynamic stability of chelated complexes vs comparable monodentate ones, driven mainly by a favourable positive entropy change.

   Hint: Ring formation; entropy-driven stability.

8. 8.Why is EDTA$^{4-}$ called a hexadentate ligand? Draw its donor set.

   EDTA$^{4-}$ binds through 2 nitrogen atoms and 4 carboxylate oxygen atoms = 6 donor atoms, wrapping octahedrally around the metal (e.g. $[\text{Ca(EDTA)}]^{2-}$).

   Hint: 2 N + 4 O donors.

9. 9.Name the ligands: $\text{H}_2\text{O}$, $\text{NH}_3$, $\text{CO}$, $\text{OH}^-$, $\text{NO}^+$ in coordination nomenclature.

   $\text{H}_2\text{O}$ = aqua, $\text{NH}_3$ = ammine (double m), $\text{CO}$ = carbonyl, $\text{OH}^-$ = hydroxido, $\text{NO}^+$ = nitrosyl.

   Hint: Neutral ligands often keep special names.

10. 10.Give the IUPAC ligand names for $\text{Cl}^-$, $\text{CN}^-$, $\text{SO}_4^{2-}$, $\text{C}_2\text{O}_4^{2-}$, $\text{CH}_3\text{COO}^-$.

    $\text{Cl}^-$ = chlorido, $\text{CN}^-$ = cyanido, $\text{SO}_4^{2-}$ = sulfato, $\text{C}_2\text{O}_4^{2-}$ = oxalato, $\text{CH}_3\text{COO}^-$ = acetato.

    Hint: Anionic ligands end in -o (-ido).

11. 11.State the IUPAC rules for ordering and naming ligands in a complex.

    Name ligands alphabetically (ignore multiplying prefixes), then the metal. Use di/tri/tetra for simple ligands, bis/tris/tetrakis for complex ones (with named ligands in parentheses). Cationic/neutral complex: metal name unchanged; anionic complex: metal gets -ate suffix. Oxidation state in Roman numerals in parentheses.

    Hint: Alphabetical ligands, then metal (+ate if anionic).

12. 12.Give the IUPAC name of $[\text{Co}(\text{NH}_3)_5\text{Cl}]\text{Cl}_2$.

    Pentaamminechloridocobalt(III) chloride. Cation charge: overall neutral, 2 outer $\text{Cl}^-$ so cation is $2+$; Co $= +3$ (since one coordinated $\text{Cl}^-$ is $-1$).

    Hint: 5 ammine + 1 chlorido inside; 2 chloride outside.

13. 13.Give the IUPAC name of $\text{K}_4[\text{Fe}(\text{CN})_6]$.

    Potassium hexacyanidoferrate(II). Anionic complex $\Rightarrow$ ferrate; Fe oxidation state: $x + 6(-1) = -4 \Rightarrow x = +2$.

    Hint: Anionic complex of iron = ferrate.

14. 14.Write the formula for potassium tetrahydroxidozincate(II) and hexaamminecobalt(III) chloride.

    $\text{K}_2[\text{Zn}(\text{OH})_4]$ and $[\text{Co}(\text{NH}_3)_6]\text{Cl}_3$.

    Hint: Balance the counter ions to neutrality.

15. 15.Give the Latin/-ate names used for anionic complexes of Fe, Cu, Pb, Sn, Ag, Au.

    Fe = ferrate, Cu = cuprate, Pb = plumbate, Sn = stannate, Ag = argentate, Au = aurate.

    Hint: These metals use Latin roots in the -ate form.

16. 16.How do you determine the oxidation number of the metal in $[\text{Cr}(\text{H}_2\text{O})_4\text{Cl}_2]\text{Cl}$?

    Sum of charges = overall charge. Outer $\text{Cl}^- = -1$ so complex ion is $+1$. Inside: aqua = 0, each chlorido $= -1$. $x + 0 + 2(-1) = +1 \Rightarrow x = +3$. Chromium is $+3$.

    Hint: Ligand charges + metal = ion charge.

17. 17.List the four main types of structural isomerism in coordination compounds.

    Ionization isomerism, hydrate (solvate) isomerism, linkage isomerism, and coordination isomerism. (Also ligand isomerism.) They differ in how atoms are connected.

    Hint: Ionization, hydrate, linkage, coordination.

18. 18.Explain ionization isomerism with an example.

    Isomers give different ions in solution by swapping a ligand with the counter ion. Example: $[\text{Co}(\text{NH}_3)_5\text{Br}]\text{SO}_4$ (gives $\text{SO}_4^{2-}$, tests positive for sulfate) vs $[\text{Co}(\text{NH}_3)_5\text{SO}_4]\text{Br}$ (gives $\text{Br}^-$).

    Hint: Counter ion and a ligand exchange places.

19. 19.Explain hydrate (solvate) isomerism using the chromium chloride hexahydrate example.

    $\text{CrCl}_3\cdot 6\text{H}_2\text{O}$ exists as $[\text{Cr}(\text{H}_2\text{O})_6]\text{Cl}_3$ (violet), $[\text{Cr}(\text{H}_2\text{O})_5\text{Cl}]\text{Cl}_2\cdot\text{H}_2\text{O}$ (blue-green), and $[\text{Cr}(\text{H}_2\text{O})_4\text{Cl}_2]\text{Cl}\cdot 2\text{H}_2\text{O}$ (dark green). They differ in number of coordinated vs lattice water and in free/precipitable $\text{Cl}^-$.

    Hint: Water inside vs outside the coordination sphere.

20. 20.Explain linkage isomerism with an example.

    Arises with ambidentate ligands binding through different atoms. Example: $[\text{Co}(\text{NH}_3)_5(\text{NO}_2)]^{2+}$ (nitrito-N, yellow) vs $[\text{Co}(\text{NH}_3)_5(\text{ONO})]^{2+}$ (nitrito-O, red).

    Hint: Same ligand, different donor atom.

21. 21.Explain coordination isomerism with an example.

    In a salt of a complex cation and complex anion, ligands are distributed differently between the two metals. Example: $[\text{Co}(\text{NH}_3)_6][\text{Cr}(\text{CN})_6]$ vs $[\text{Cr}(\text{NH}_3)_6][\text{Co}(\text{CN})_6]$.

    Hint: Both cation and anion are complexes; swap ligands.

22. 22.What is geometrical (cis-trans) isomerism? In which geometries does it occur?

    Isomerism from different spatial arrangement of ligands. Cis = identical ligands adjacent ($90^\circ$), trans = opposite ($180^\circ$). Common in square planar $\text{MA}_2\text{B}_2$ and octahedral $\text{MA}_4\text{B}_2$/$\text{MA}_3\text{B}_3$. Tetrahedral complexes do NOT show it.

    Hint: Adjacent vs opposite; not tetrahedral.

23. 23.What is fac-mer isomerism? For which formula does it arise?

    In octahedral $\text{MA}_3\text{B}_3$: facial (fac) has three identical ligands on one triangular face (mutually cis); meridional (mer) has them around a meridian (spanning a plane). Example: $[\text{Co}(\text{NH}_3)_3\text{Cl}_3]$.

    Hint: Face vs meridian arrangement in MA3B3.

24. 24.Why do tetrahedral complexes not show geometrical isomerism?

    In a tetrahedron all four positions are equivalent and mutually adjacent (all bond angles $\approx 109.5^\circ$), so there is no cis/trans distinction — every arrangement is identical.

    Hint: All four corners are equidistant/adjacent.

25. 25.When does a coordination complex show optical isomerism?

    When it is chiral (non-superimposable on its mirror image, lacks a plane/centre of symmetry). Common in octahedral complexes with bidentate chelates, e.g. $[\text{Co}(\text{en})_3]^{3+}$ and cis-$[\text{Co}(\text{en})_2\text{Cl}_2]^+$; the trans isomer is optically inactive.

    Hint: Non-superimposable mirror images; think en chelates.

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