Practice problems drawn from Housecroft, Atkins, JD Lee, and others. Select an answer or click "Show Answer" to reveal the explanation.
Name the coordination compound [Co(NH3)6]Cl3 using IUPAC nomenclature rules.
Under IUPAC rules, ligands are named first (alphabetically by ligand name) followed by the metal with its oxidation state in Roman numerals. The six NH3 ligands give “hexaammine” and cobalt is in the +3 oxidation state. The counter ion is simply “chloride” — the number of counter ions is not explicitly stated because it is implied by charge balance.
Consider the compound [PtCl2(NH3)2]. This compound exists as two geometric isomers. How does IUPAC nomenclature distinguish between the cis and trans forms?
Geometric isomers are distinguished using italicised stereochemical descriptors placed before the name. The cis isomer (identical ligands adjacent) is named cis-diamminedichloroplatinum(II), while the trans isomer (identical ligands opposite) is trans-diamminedichloroplatinum(II). The cis form is the anticancer drug cisplatin.
Write the formula for potassium hexacyanoferrate(III). What is the complex ion?
The name tells us: potassium is the cation, “hexacyano” means six CN− ligands, “ferrate” uses the Latin-root suffix “-ate” indicating an anionic complex, and (III) means iron is in the +3 oxidation state. Since Fe is +3 and each CN− carries −1, the complex ion is [Fe(CN)6]3−, requiring three K+ counter ions.
In IUPAC nomenclature of coordination compounds, what determines the order in which ligands are listed in the name?
IUPAC 2005 recommendations state that ligands are listed alphabetically by their name, disregarding the multiplying prefixes (di-, tri-, tetra-, bis-, tris-, etc.). For example, in [CoCl2(en)2]+, “bis(ethylenediamine)” comes before “dichloro” because “e” precedes “c” — wait, actually “c” precedes “e”, so it would be dichlorobis(ethylenediamine)cobalt(III). The key rule: alphabetical by ligand name, not by prefix.
Under the 2005 IUPAC recommendations, which set of endings correctly describes the naming conventions for anionic ligands in coordination compounds?
The 2005 IUPAC recommendations introduced systematic endings for anionic ligands. Monatomic anions use -ido (Cl− → chlorido, O2− → oxido). Polyatomic anions ending in -ate become -ato (SO42− → sulfato). Some traditional short forms persist in common usage, such as cyano for CN− and oxo for O2−, though the strict 2005 forms are cyanido and oxido respectively.
How are bridging ligands denoted in IUPAC nomenclature? Consider the dinuclear complex [(NH3)5Cr–OH–Cr(NH3)5]5+.
Bridging ligands are indicated by the Greek letter μ (mu) placed before the ligand name and separated by a hyphen. The given complex would be named μ-hydroxido-bis[pentaamminechromium(III)] (5+). When multiple bridging ligands of the same type are present, the notation becomes μ-ligand with an appropriate multiplying prefix. The μ descriptor is listed alphabetically among the other ligands.
How are polydentate (chelating) ligands handled in IUPAC nomenclature? Consider ligands such as ethylenediamine (en), edta4−, and acetylacetonate (acac−).
Polydentate ligands whose names already contain multiplying prefixes (such as ethylenediamine, which contains “di”) use the alternative multiplicative prefixes bis-, tris-, tetrakis- to avoid ambiguity, and the ligand name is enclosed in parentheses. For example, [Co(en)3]3+ is named tris(ethylenediamine)cobalt(III). Similarly, [Cr(acac)3] is tris(acetylacetonato)chromium(III).
What is the purpose of κ (kappa) notation in IUPAC nomenclature, and how would you use it to distinguish SCN− bound through sulfur versus nitrogen?
The κ (kappa) convention identifies the specific donor atom through which an ambidentate ligand coordinates to the metal. For the thiocyanate ion (SCN−), coordination through sulfur is denoted thiocyanato-κS, while coordination through nitrogen is thiocyanato-κN (historically called isothiocyanato). This notation is essential whenever a ligand has more than one potential donor atom and the binding mode is not obvious from context.
How is ferrocene, [Fe(C5H5)2], named using full IUPAC nomenclature rules?
In ferrocene, each cyclopentadienyl ring binds to iron through all five carbon atoms in a π-bonding mode. The η5 (eta-five or pentahapto) prefix indicates that five contiguous atoms of the ring are coordinated. The prefix “bis” is used instead of “di” because the ligand name is enclosed in parentheses. Although “ferrocene” is acceptable as a trivial name, the systematic IUPAC name is bis(η5-cyclopentadienyl)iron(II).
What does the η (eta, or hapto) notation indicate in organometallic nomenclature? Consider the difference between η1-allyl and η3-allyl coordination modes.
The ηn (hapto) notation specifies how many contiguous atoms of a ligand are directly coordinated to the metal. An η1-allyl ligand bonds through only one carbon (acting as a simple σ-donor), while η3-allyl bonds through all three carbons in a delocalised π-fashion. This distinction is critical because it affects electron counting, geometry, and reactivity of the complex.
Name [Cr(CO)6] and [Mn2(CO)10] using IUPAC rules. Which pair of names is correct?
Carbonyl (CO) is a neutral ligand, so the metal retains its zero oxidation state in homoleptic carbonyls. [Cr(CO)6] is hexacarbonylchromium(0) — six CO ligands with chromium in the zero oxidation state. For [Mn2(CO)10], the “di” prefix on manganese indicates two metal centres, giving decacarbonyldimanganese(0). The “-ate” suffix is not used because the complex is neutral, not anionic.
Given the IUPAC name “tetraaquadichlorocobalt(III) chloride”, write the correct formula.
Parsing the name: “tetraaqua” means four H2O ligands, “dichloro” means two Cl− ligands in the coordination sphere, and cobalt(III) is Co3+. The complex ion is [CoCl2(H2O)4]+ (charge: +3 − 2 = +1). The “chloride” outside is one Cl− counter ion to balance the +1 charge, giving [CoCl2(H2O)4]Cl.
IUPAC Nomenclature