Write the formula for each of the following compounds, being sure to use brackets to indicate the coordination sphere:
(a) tetraaquadibromomanganese(III) perchlorate
(b) bis(bipyridyl)cadmium(II) chloride
(c) potassium tetrabromo(ortho-phenanthroline)- cobaltate (III)
(d) cesium diamminetetracyanochromate(III)
(e) tris(ethylenediammine)rhodium(III) tris(oxalato)-cobaltate(III)
The correct answer and explanation is :
Here are the formulas for the given compounds, using appropriate notation for the coordination sphere:
(a) tetraaquadibromomanganese(III) perchlorate
Formula: ([MnBr_2(H_2O)_4]ClO_4)
Explanation:
- Tetraaqua refers to four water molecules (H₂O) as ligands, which are denoted in square brackets as part of the coordination sphere.
- Dibromo indicates two bromine ions (Br⁻) are also coordinated to the manganese.
- Manganese(III) indicates the metal ion is Mn³⁺.
- The perchlorate ion (ClO₄⁻) is a counter ion outside the coordination sphere and is written outside the square brackets.
(b) bis(bipyridyl)cadmium(II) chloride
Formula: ([Cd(C_10H_8N_2)_2]Cl_2)
Explanation:
- Bis(bipyridyl) refers to two bipyridyl ligands, where each bipyridyl is a bidentate ligand (C₁₀H₈N₂).
- Cadmium(II) indicates the metal ion is Cd²⁺.
- The formula indicates two chloride (Cl⁻) counterions outside the coordination sphere.
(c) potassium tetrabromo(ortho-phenanthroline)-cobaltate(III)
Formula: ([Co(C₁₈H₁₄N₂)Br₄]K)
Explanation:
- Tetrabromo refers to four bromine ions (Br⁻) coordinated to cobalt.
- Ortho-phenanthroline is a bidentate ligand (C₁₈H₁₄N₂), which coordinates with the metal via its nitrogen atoms.
- Cobaltate(III) indicates the cobalt is in the +3 oxidation state (Co³⁺).
- The potassium ion (K⁺) is a counter ion outside the coordination sphere.
(d) cesium diamminetetracyanochromate(III)
Formula: ([Cr(NH_3)_2(CN)_4]Cs)
Explanation:
- Diamminetetra indicates two ammonia (NH₃) molecules and four cyanide (CN⁻) ions as ligands in the coordination sphere.
- Chromate(III) indicates the chromium ion (Cr³⁺).
- The cesium (Cs⁺) ion is the counter ion outside the coordination sphere.
(e) tris(ethylenediamine)rhodium(III) tris(oxalato)-cobaltate(III)
Formula: ([Rh(C_2H_8N_2)_3][Co(C_2O_4)_3])
Explanation:
- Tris(ethylenediamine) refers to three ethylenediamine (C₂H₈N₂) ligands coordinated to the rhodium ion (Rh³⁺).
- Rhodium(III) indicates the metal ion is Rh³⁺.
- Tris(oxalato)-cobaltate(III) refers to the cobalt ion (Co³⁺) coordinated with three oxalate ions (C₂O₄²⁻) and being the counter ion for the complex. The oxalate is a bidentate ligand, meaning each oxalate ion binds through two oxygen atoms.
General Explanation:
The notation for coordination compounds distinguishes between the metal center, its coordination sphere, and the counterions. The coordination sphere is represented in square brackets with ligands explicitly listed with their chemical formulas (and sometimes names for clarity), while the counterions appear outside the brackets. In these examples:
- Ligands: Water, ammonia, cyanide, oxalate, bipyridyl, etc.
- Counterions: Perchlorate, chloride, cesium, etc.
- The oxidation state of the metal is shown in Roman numerals. Each ligand has a defined number of bonds it forms with the central metal, and the coordination number (how many bonds the metal forms) influences the overall geometry and properties of the complex.