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Naming Coordination Compounds: A Comprehensive Tutorial, Lecture notes of Chemistry

University of Isfahan (UI)Chemistry

Naming Coordination Compounds and lecture 2 about ATMOSPHERIC CHEMISTRY AND AIR POLLUTION

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Naming Coordination Compounds
Author: Kit Mao
Department of Chemistry, Washington University
St. Louis, MO 63130
For information or comments on this tutorial, please contact K. Mao at [email protected].
Please click here for a pdf version of this tutorial.
A coordination complex is a substance in which a metal atom or ion accepts electrons from (and
thus associates with) a group of neutral molecules or anions called ligands. A complex can be an
anion, a cation ion, or a neutral molecule. Coordination compounds are neutral substances (i.e.
uncharged) in which at least one ion is present as a complex. You will learn more about
coordination compounds in the lab lectures for experiment 5 in this course.
The coordination compounds are named in the following way. (At the end of this tutorial,
there are additional examples that demonstrate how coordination compounds are named.)
A. When naming coordination compounds, always name the cation before the anion. This
rule holds regardless of whether the complex ion is the cation or the anion. (This is just
like naming an ionic compound.)
B. In naming the complex ion:
1. Name the ligands first, in alphabetical order, and then name 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”(e.g. chloride,
hydroxide), “-ate” (e.g. sulfate, nitrate), and “-ite” (e.g. nirite), change the
endings as follows:
-ide → -o; e.g., chloride → chloro and hydroxide → hydroxo
-ate → -ato; e.g., sulfate → sulfato and nitrate → nitrato
-ite → -ito; e.g., nitrite → nitrito
• For neutral ligands, the common name of the molecule is used (e.g.
H2NCH2CH2NH2 (ethylenediamine)). Important exceptions: water is
called ‘aqua’, ammonia is called ‘ammine’, carbon monoxide is called
‘carbonyl’, and the N
2 and O
2 molecules are called ‘dinitrogen’ and
‘dioxygen’.
Table 1. Names of Some Common Ligands
Anionic Ligands
Names Neutral Ligands Names
Br- bromo NH3 ammine
F- fluoro H2O aqua
O2- oxo NO Nitrosyl
OH- hydroxo CO Carbonyl
CN- cyano O2 dioxygen
C2O42- oxalato N2 dinitrogen
CO32- carbonato C5H5N pyridine
CH3COO- acetato H2NCH2CH2NH2 ethylenediamine
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Download Naming Coordination Compounds: A Comprehensive Tutorial and more Lecture notes Chemistry in PDF only on Docsity!

Naming Coordination Compounds

Author: Kit Mao Department of Chemistry, Washington University St. Louis, MO 63130

For information or comments on this tutorial, please contact K. Mao at [email protected]. Please click here for a pdf version of this tutorial.

A coordination complex is a substance in which a metal atom or ion accepts electrons from (and thus associates with) a group of neutral molecules or anions called ligands. A complex can be an anion, a cation ion, or a neutral molecule. Coordination compounds are neutral substances (i.e. uncharged) in which at least one ion is present as a complex. You will learn more about coordination compounds in the lab lectures for experiment 5 in this course.

The coordination compounds are named in the following way. (At the end of this tutorial, there are additional examples that demonstrate how coordination compounds are named.)

A. When naming coordination compounds, always name the cation before the anion. This rule holds regardless of whether the complex ion is the cation or the anion. (This is just like naming an ionic compound.) B. In naming the complex ion:

  1. Name the ligands first, in alphabetical order, and then name 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”(e.g. chloride, hydroxide), “-ate” (e.g. sulfate, nitrate), and “- ite” (e.g. nirite), change the endings as follows: -ide → -o; e.g., chloride → chloro and hydroxide → hydroxo -ate → -ato; e.g., sulfate → sulfato and nitrate → nitrato -ite → - ito; e.g., nitrite → nitrito
    • For neutral ligands, the common name of the molecule is used (e.g. H 2 NCH 2 CH 2 NH 2 (ethylenediamine)). Important exceptions : water is called ‘aqua’, ammonia is called ‘ammine’, carbon monoxide is called ‘carbonyl’, and the N 2 and O 2 molecules are called ‘dinitrogen’ and ‘dioxygen’.

Table 1. Names of Some Common Ligands

Anionic Ligands Names Neutral Ligands Names Br-^ bromo NH 3 ammine F-^ fluoro H 2 O aqua O2-^ oxo NO Nitrosyl OH-^ hydroxo CO Carbonyl CN-^ cyano O 2 dioxygen C 2 O 4 2-^ oxalato N 2 dinitrogen CO 3 2-^ carbonato C 5 H 5 N pyridine CH 3 COO-^ acetato H 2 NCH 2 CH 2 NH 2 ethylenediamine

  1. The Greek prefixes di-, tri-, tetra-, etc. are used to designate the number of each type of ligand in the complex ion. If the ligand already contains a Greek prefix (e.g. ethylene di amine) or if it is a polydentate ligand (i.e. it can attach at more than one coordination site), the prefixes bis-, tris-, tetrakis-, and pentakis- are used instead (See examples 3 and 4). The numerical prefixes are listed in Table 2.

Table 2. Numerical Prefixes

Number Prefix Number Prefix Number Prefix 1 mono 5 penta (pentakis) 9 nona (ennea) 2 di (bis) 6 hexa (hexakis) 10 deca 3 tri (tris) 7 hepta 11 undeca 4 tetra (tetrakis) 8 octa 12 dodeca

  1. After naming the ligands, name the central metal. If the complex ion is a cation, the metal is named same as the element. For example, Co in a complex cation is called cobalt and Pt is called platinum. (See examples 1-4.) If the complex ion is an anion, the name of the metal ends with the suffix -ate. (See examples 5 and 6.) For example, Co in a complex anion is called cobaltate and Pt is called platinate. For some metals, the Latin names are used in the complex anions (e.g. Fe is called ferrate and not ironate).

Table 3: Name of Metals in Anionic Complexes Name of Metal Name in an Anionic Complex Iron Ferrate Copper Cuprate Lead Plumbate Silver Argentate Gold Aurate Tin Stannate

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

C. To name a neutral complex molecule, follow the rules of naming a complex cation. Remember: Name the (possibly complex) cation BEFORE the (possibly complex) anion. See examples 7 and 8.

For historic reasons, some coordination compounds are called by their common names. For example, Fe(CN) 63 −^ and Fe(CN) 64 −^ are named ferricyanide and ferrocyanide respectively, and Fe(CO) 5 is called iron carbonyl.

Examples Give the systematic names for the following coordination compounds:

  1. [Cr(NH 3 ) 3 (H 2 O) 3 ]Cl 3

Answer: triamminetriaquachromium(III) chloride Solution:

  • The complex ion is found inside the parentheses. In this case, the complex ion is a cation.
  • The ammine ligands are named first because alphabetically, “ammine” comes before “aqua.”

Answer: diamminetetrachloroplatinum(IV) Solution:

  • This is a neutral molecule because the charge on Pt+4^ equals the negative charges on the four chloro ligands.
  • If the compound is [Pt(NH 3 ) 2 Cl 2 ]Cl 2 , even though the number of ions and atoms in the molecule are identical to the example, it should be named: diamminedichloroplatinum(IV) chloride because the platinum in the latter compound is only four coordinated instead of six coordinated.
  1. Fe(CO) 5 Answer: pentacarbonyliro n(0) Solution:
  • Since it is a neutral complex, it is named in the same way as a complex cation. The common name of this compound, iron carbonyl, is used more often.
  1. (NH 4 ) 2 [Ni(C 2 O 4 ) 2 (H 2 O) 2 ] Answer: ammonium diaquabis(oxalato)nickelate(II) Solution: The oxalate ion is a bidentate ligand.
  2. [Ag(NH 3 ) 2 ][Ag(CN) 2 ] Answer: diamminesilver(I) dicyanoargentate(I) You can have a compound where both the cation and the anion are complex ions. Notice how the name of the metal differs even though they are the same metal ions.

Can you give the molecular formulas of the following coordination compounds?

  1. hexaammineiron(III) nitrate
  2. ammonium tetrachlorocuprate(II)
  3. sodium monochloropentacyanoferrate(III)
  4. potassium hexafluorocobaltate(III)

Can you give the name of the following coordination compounds?

  1. [CoBr(NH 3 ) 5 ]SO 4
  2. [Fe(NH 3 ) 6 ][Cr(CN) 6 ]
  3. [Co(SO 4 )(NH 3 ) 5 ]+
  4. [Fe(OH)(H 2 O) 5 ]2+

Answers:

**_1. [Fe(NH 3 ) 6 ](NO 3 ) 3

  1. (NH 4 ) 2 [CuCl 4 ]
  2. Na 3 [FeCl(CN) 5 ]
  3. K 3 [CoF 6 ]
  4. pentaamminebromocobalt(III) sulfate
  5. hexaammineiron(III) hexacyanochromate (III)
  6. pentaamminesulfatocobalt(III) ion
  7. pentaaquahydroxoiron(III) ion_**