trigger 3

February 16, 2009 at 1:16 pm (Uncategorized)

Group 15 members:

Bernadette Chara anak Jemat (22752)
Chandrasuriya Lingam (20771)
Fatimah Sani (20957)
Julan Baling (21163)
Mimi Nadhira binti Mustapha (21454)
Ng Zhi Zheng (21694)
Nurfahana binti Kamez (21985)
Nurul ‘Izzati binti Chik (22874)
Patsy Rani (22110)
Siti Nurfathikah binti Abu Bakar (22379)
Toh Geh Heng (22560)

Problem 1

In experiment 1, two students prepared an ion complex from cobalt(ii), ammonia, and nitrogen dioxide. Before the experiment the students have made a hypothesis that the coordination compound will produce the same colored solid. However, the two students obtained solids which are different in color.

a) Determine the name and geometrical shape of the ion complex in experiment 1. Calculate the ion charge. Explain the rules and steps in naming coordination compounds.

b) Then, explain why the difference in color occurred in experiment 1. Give other examples that are caused by the same reason in coordination compounds.

ANSWERS:

Name: Pentaamminenitrocobalt (II)

[Co(NO₂)(NH₃)₅]⁺

Geometrical Shape: Octahedron

There are two compounds:

Ion charge:

Co ²⁺ + NH₃ + (NO₂)-   –>   [Co(NO₂)(NH₃)₅]⁺
(+2) + 5(0) + 1(-1) = +1

STEPS IN NAMING COORDINATION COMPOUNDS:

There are 5 rules and steps:

1. Name the ligands first, in alphabetical order, then the metal atom or ion. Note: The metal atom or ion is written before the ligands in the chemical formula.

2. The names of some common ligands are listed in Table 1.

• Anionic ligands end in “-o”; for anions that end in “-ide”, “-ate”, and “-ite”, change the endings

as follows: -ide -o; -ate -ato; -ite -ito

• Neutral ligands, the common name of the molecule is used.

Table 1. Names of Some Common Ligands

name of some common ligands

numerical prefixes

3. Greek prefixes are used to designate the number of each type of ligand in the complex ion, e.g. di-, tri- and tetra-. If the ligand already contains a Greek prefix or if it is polydentate ligands the prefixes bis-, tris-, tetrakis-, pentakis-, are used instead.

4. After naming the ligands, name the central metal. If the complex ion is a cation, the metal is named same as the element. If the complex ion is an anion, the name of the metal ends with the suffix -ate. For some metals, the Latin names are used in the complex anions.

5. Following the name of the metal, the oxidation state of the metal in the complex is given as a Roman numeral in parentheses.

•To name a neutral complex molecule, follow the rules of naming a complex cation. For historic reasons, some coordination compounds are called by their common names.

Questions 1(b)

Why the difference colored occurred in experiment 1?

•The difference in color occurred in experiment 1 because of the linkage isomerism that are formed in coordination compound of [Co(NO₂)(NH₃)₅]⁺.

•Linkage isomerism is relatively rare but interesting type that arises when a particular ligand is capable of coordinating to a metal in 2 different ways.

•The nitrite ion, NO₂ ⁻ can coordinate through either a nitrogen or an oxygen atom. When it coordinates through nitrogen atom, the NO₂ ⁻ ligand is called nitro while when it coordinates through the oxygen atom, it is called nitrito and is generally written ONO⁻. The N-bonded isomer is yellow whereas the O-bonded isomer is red.

Other examples:

•Other example that are caused by linkage isomerism in coordination compound is [Co(NH₃)₅SCN⁻].