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naming Transition metals

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Naming Transition Metals
Many transition metals exist as more than one type of cation. For example, iron exists as Fe2+ and Fe3+. Therefore, when you are naming an ionic compound containing iron, it is necessary to indicate which oxidation number the metal has. The oxidation number appears as a Roman numeral in parenthesis after the cation. For metals, the oxidation number is the same as the charge. Fe2+ in a compound with chloride would have a formula FeCl2 and would be named iron(II) chloride. The cation Fe3+ paired with oxygen would have the formula Fe2O3 and would have the name iron(III) oxide.
The procedure for naming ionic compounds containing polyatomic ions is the same as that for naming simple ions. Thus, CaCO3 is named calcium carbonate; (NH4)2HPO4, a compound with two polyatomic ions, is named ammonium hydrogen phosphate; and Pb2+ paired with SO42- (PbSO4) is named lead(II) sulfate.
Example 1: Write a correct chemical formula for each of the following ionic compounds: a. Aluminum oxide; b. Copper(II) chloride; c. Iron(III) oxide.
Solution 1: a. Aluminum is 3+, oxide is 2-; Al2O3. b. From the oxidation state that is given, copper is 2+, chloride is 1-; CuCl2. c. From the oxidation state, iron is 3+, oxide is 2-; Fe2O3.
Example 2: Write the proper chemical name for each of the following ionic compounds: a. Li2S; b. NiCl2; c. FeO.
Solution 2: a. We do not use multipliers, so this is simply lithium sulfide. b. We must specify that nickel is 2+ in this compound, so this is nickel(II) chloride. c. We must specify that iron is 2+ in this compound, so this is iron(II) oxide.
Naming Coordination Compounds
More complicated coordination compounds are composed of an atom or ion (usually a metal) and a surrounding array of bound molecules or anions, known as ligands. The atom within a ligand that is bonded to the central atom or ion is called the donor atom. A typical complex is bound to several donor atoms, which can be the same or different. Coordination refers to the coordinate covalentbonds (dipolar bonds) between the ligands and the central atom.
The set of rules for naming a coordination compound is:
  1. When naming a complex ion, the ligands are named before the metal ion.
  2. Write the names of the ligands in the following order: neutral, negative, positive. If there are multiple ligands of the same charge type, they are named in alphabetical order. (Numerical prefixes do not affect the order.)
  3. Multiple occurring monodentate ligands receive a prefix according to the number of occurrences: di-, tri-, tetra-, penta-, or hexa. Polydentate ligands (e.g., ethylenediamine, oxalate) receive bis-, tris-, tetrakis-, etc.
  4. Anions end in -ido. This replaces the final "e" when the anion ends with "-ate" (e.g, sulfate becomes sulfato) and replaces "-ide" (cyanide becomes cyanido).
  5. Neutral ligands are given their usual name, with some exceptions: NH3 becomes ammine; H2O becomes aqua or aquo; CO becomes carbonyl; NO becomes nitrosyl.
  6. Write the name of the central atom/ion. If the complex is an anion, the central atom's name will end in -ate, and its Latin name will be used if available (except for mercury).
  7. If the central atom's oxidation state needs to be specified (when it is one of several possible, or zero), write it as a Roman numeral (or 0) in parentheses.
  8. End with "cation" or "anion" as separate words (if applicable).
Example coordination compound
Chromium(III) 2-ethylhexanoate molecule.

Example:
Write a proper chemical name for each of the following coordination compounds:
a. [NiCl4]2−
b. Pt(NH3)2Cl4
c. [Pt(NH3)2Cl2]Cl2.
Solution:
a. Tetrachloridonickelate(II) ion. The complex ion, an anion, is inside the parentheses. We have to add the suffix -ate in the name of the metal.
b. Diamminetetrachloroplatinum(IV). This is a neutral molecule. The total charge on the ligands is -4. Therefore, the platinum oxidation number is +4.
c. Diamminedichloroplatinum(II) chloride. Here, the number of ions and atoms are the same. However, the brackets as well as the different oxidation number of the platinum result in a very different name.
The coordination number of ligands attached to more than one metal (bridging ligands) is indicated by a subscript to the Greek symbol μ placed before the ligand name. Thus the dimer of aluminum trichloride is described by Al2Cl4(μ2-Cl)2.
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Coordination complexes have their own classes of isomers, different magnetic properties and colors, and various applications (photography, cancer treatment, etc), so it makes sense that they would have a naming system as well. Consisting of a metal and ligands, their formulas follow the pattern [Metal Anions Neutrals]±Charge, while names are written Prefix Ligands Metal(Oxidation State).
Introduction
According to the Lewis base theory, ligands are Lewis bases since they can donate electrons to the central metal atom. The metals, in turn, are Lewis acids since they accept electrons. Coordination complexes consist of a ligand and a metal center cation. The overall charge can be positive, negative, or neutral. Coordination compounds are complex or contain complex ions, for example: 
  • Complex Cation: [CO(NH3)6]3+[CO(NH3)6]3+
  • Complex Anion: [CoCl4(NH3)2]−[CoCl4(NH3)2]−
  • Neutral Complex: [CoCl3(NH3)3][CoCl3(NH3)3]
  • Coordination Compound: K4[Fe(CN)6]K4[Fe(CN)6]
A ligand can be an anion or a neutral molecule that donates an electron pair to the complex (NH3, H2O, Cl-). The number of ligands that attach to a metal depends on whether the ligand is monodentate, bidentate, or polydentate. For more information, see Ligands and Chelation.
Naming Coordination Complexes
To begin naming coordination complexes, here are some things to keep in mind.  
  1. Ligands are named first in alphabetical order.
  2. The name of the metal comes next.
  3. The oxidation state of the metal follows, noted by a Roman numeral in parentheses (II, IV).                                                               
Rule 1: Anionic Ligands
Ligands that act as anions which end in "-ide" are replaced with an ending "-o" (e.g., Chloride → Chloro). Anions ending with "-ite" and "-ate" are replaced with endings "-ito" and "-ato" respectively (e.g., Nitrite → Nitrito, Nitrate → Nitrato).
Table 1.11.1: Anionic Monodentate Ligands
Molecular Formula
Ligand Name
Molecular Formula
Ligand Name
F-
Fluoro
OH-
Hydroxo
Cl-
Chloro
SO42-
Sulfato
Br-
Bromo
S2O32-
Thiosulfato
I-
Iodo
NO2-
Nitrito-N-; Nitro
O2-
Oxo
ONO-
Nitrito-O-; Nitrito
CN-
Cyano
SCN-
Thiocyanato-S-; Thiocyanato
NC-
Isocyano
NCS-
Thiocyanato-N-; Isothiocyanato
Rule 2: Neutral Ligands
Most neutral molecules that are ligands carry their normal name. The few exceptions are the first four on the chart: ammine, aqua, carbonyl, and nitrosyl.
Table 1.21.2: Select Neutral Monodentate Ligands. Note: Ammine is spelled with two m's when referring to a ligand. Amines are a class of organic nitrogen-containing compounds.
Molecular Formula of Ligand
Ligand Name
NH3
Ammine
H2O
Aqua
CO
Carbonyl
NO
Nitrosyl
CH3NH2
Methylamine
C5H5N
Pyridine
Polydentate ligands follow the same rules for anions and neutral molecules.
Table 1.31.3: Select Polydentate ligands
En
 Ethylenediamine
ox2-
Oxalato
EDTA4-
Ethylenediaminetetraacetato
Rule 3: Ligand Multiplicity
The number of ligands present in the complex is indicated with the prefixes di, tri, etc. The exceptions are polydentates that have a prefix already in their name (en and EDTA4- are the most common). When indicating how many of these are present in a coordination complex, put the ligand's name in parentheses and use bis, tris, and tetrakis.
Table 1.41.4: Prefixes for indicating number of ligands in a complex.
Number of Ligands
Monodentate Ligands
Polydentate Ligands
1
Mono
-
2
Di
Bis
3
Tri
Tris
4
Tetra
Tetrakis
5
Penta
-
6
Hexa
-
Prefixes always go before the ligand name; they are not taken into account when putting ligands in alphabetical order. Note that "mono" often is not used. For example, [FeCl(CO)2(NH3)3]2+ would be called triamminechlorodicarbonyliron(III) ion. Remember that ligands are always named first, before the metal is. 
Example 1.11.1
What is the name oft his complex ion: [CrCl2(H2O)4]+[CrCl2(H2O)4]+?
SOLUTION
Let's start by identifying the ligands. The ligands here are Cl and H2O. Therefore, we will use the monodentate ligand names of "chloro" and "aqua". Alphabetically, aqua comes before chloro, so this will be their order in the complex's name. There are 4 aqua's and 2 chloro's, so we will add the number prefixes before the names. Since both are monodentate ligands, we will say "tetra[aqua]di[chloro]".
Now that the ligands are named, we will name the metal itself. The metal is Cr, which is chromium. Therefore, this coordination complex is called tetraaquadichlorochromium(III) ion. See the next section for an explanation of the (III).
Example 1.21.2
What is the name oft his complex ion: [CoCl2(en)2]+[CoCl2(en)2]+?
SOLUTION
We take the same approach. There are two chloro and ethylenediamine ligands. The metal is Co, cobalt. We follow the same steps, except that enen is a polydentate ligand with a prefix in its name (ethylenediamine), so "bis" is used instead of "bi", and parentheses are added. Therefore, this coordination complex is called dichlorobis(ethylenediamine)cobalt(III) ion.
Rule 4: The Metals
When naming the metal center, you must know the formal metal name and the oxidation state. To show the oxidation state, we use Roman numerals inside parenthesis. For example, in the problems above, chromium and cobalt have the oxidation state of +3, so that is why they have (III) after them. Copper, with an oxidation state of +2, is denoted as copper(II). If the overall coordination complex is an anion, the ending "-ate" is attached to the metal center. Some metals also change to their Latin names in this situation. Copper +2 will change into cuprate(II). The following change to their Latin names when part of an anion complex:
Table 1.51.5: Latin name so of select common metals
Transition Metal
Latin
Iron
Ferrate
Copper
Cuprate
Tin
Stannate
Silver
Argentate
Lead
Plumbate
Gold
Aurate
The rest of the metals simply have -ate added to the end (cobaltate, nickelate, zincate, osmate, cadmate, platinate, mercurate, etc. Note that the -ate tends to replace -um or -ium, if present).
Finally, when a complex has an overall charge, "ion" is written after it. This is not necessary if it is neutral or part of a coordination compound (Examaple 3). Here are some examples with determining oxidation states, naming a metal in an anion complex, and naming coordination compounds.
Example 1.31.3
What is the name of [Cr(OH)4]- ?
SOLUTION
Immediately we know that this complex is an anion. There is only one monodentate ligand, hydroxide. There are four of them, so we will use the name "tetrahydroxo". The metal is chromium, but since the complex is an anion, we will have to use the "-ate" ending, yielding "chromate". The oxidation state of the metal is 3 (x+(-1)4=-1). Write this with Roman numerals and parentheses (III) and place it after the metal to get tetrahydroxochromate(III) ion.
Example 1.41.4
What is the name of  [CuCl4]2- ?
SOLUTION
If you got tetrachlorocuprate(II) ion, you are correct.
A last little side note: when naming a coordination compound, it is important that you name the cation first, then the anion. You base this on the charge of the ligand. Think of NaCl. Na, the positive cation, comes first and Cl, the negative anion, follows.
Example 1.51.5
What is the name of  [Pt(NH3)4)][Pt(Cl)4] ?
SOLUTION
NH3 is neutral, making the first complex positively charged overall. Cl has a -1 charge, making the second complex the anion. Therefore, you will write the complex with NH3 first, followed by the one with Cl (the same order as the formula). This coordination compound is called tetraammineplatinum(II) tetrachloroplatinate(II).
Distinguishing between linkage isomers.
Example 1.61.6
What is the name of [CoCl(NO2)(NH3)4]+ ?
SOLUTION
This coordination complex is called tetraamminechloronitrito-N-cobalt(III). N comes before the O in the symbol for the nitrite ligand, so it is called nitrito-N. If an O came first, as in [CoCl(ONO)(NH3)4]+, the ligand would be called nitrito-O, yielding the name tetraamminechloronitrito-O-cobalt(III).
Nitro (for NO2) and nitrito (for ONO) can also be used to describe the nitrite ligand, yielding the names tetraamminechloronitrocobalt(III) and tetraamminechloronitritocobalt(III).
Writing Formulas of Coordination Complexes
The formula of a coordination complex is written in a different order than its name. The chemical symbol of the metal center is written first. The ligands are written next, with anion ligands coming before neutral ligands. If there is more than one anion or neutral ligand, they are written in alphabetical order according to the first letter in their chemical formula.

In a coordination compound's name, when one of the ions is just an element, the number of atoms is not indicated with a prefix. Since it still has to be written in the formula, it is determined by balancing the overall charge of the compound. (For example, tetrafluorochromium(VI) chloride becomes [CrF4]Cl2.
Examples 1.71.7
  1. Amminetetraaquachromium(II)
  2. Amminesulfatochromium(II)
  3. Amminetetraaquachromium(II) sulfate
  4. Potassium hexacyanoferrate(III)
SOLUTION
  1. Amminetetraaquachromium(II) ion would be written as [Cr(H2O)4(NH3)]+2. Both ligands are neutral, so they are ordered alphabetically with H2O before NH3. Their order in the formula is the opposite of that in the complex's name since one uses their chemical symbols and the other uses the names of the ligands.
  2. Amminesulfatochromium(II) is written as [Cr(SO4)(NH3)]. SO4 is an anion, so it comes before NH3.
  3. Amminetetraaquachromium(II) sulfate -> Try this on your own. Did you get [Cr(H2O)4(NH3)]SO4? If you did, you are correct.
  4. Potassium hexacyanoferrate(III) -> Try this on your own. Did you get K3[Fe(CN)6]? Remember to balance the K!
References
Write the name of the following complexes (Chapter 24 / Custom Edition Chapter 21 Exercises):
  1. [CoCl3(NH3)3]
  2. [Co(ONO)3(NH3)3]
  3. [Fe(ox)2(H2O)2]-
  4. Ag2[HgI4]
Answers
  1. triamminetrichlorocobalt(III)
  2. triamminetrinitrito-O-cobalt(III); or triamminetrinitritocobalt(III)
  3. diaquadioxalatoferrate(III) ion
  4. silver(I) tetraiodomercurate(II


Naming Transition Metals
Many transition metals exist as more than one type of cation. For example, iron exists as Fe2+ and Fe3+. Therefore, when you are naming an ionic compound containing iron, it is necessary to indicate which oxidation number the metal has. The oxidation number appears as a Roman numeral in parenthesis after the cation. For metals, the oxidation number is the same as the charge. Fe2+ in a compound with chloride would have a formula FeCl2 and would be named iron(II) chloride. The cation Fe3+ paired with oxygen would have the formula Fe2O3 and would have the name iron(III) oxide.
The procedure for naming ionic compounds containing polyatomic ions is the same as that for naming simple ions. Thus, CaCO3 is named calcium carbonate; (NH4)2HPO4, a compound with two polyatomic ions, is named ammonium hydrogen phosphate; and Pb2+ paired with SO42- (PbSO4) is named lead(II) sulfate.
Example 1: Write a correct chemical formula for each of the following ionic compounds: a. Aluminum oxide; b. Copper(II) chloride; c. Iron(III) oxide.
Solution 1: a. Aluminum is 3+, oxide is 2-; Al2O3. b. From the oxidation state that is given, copper is 2+, chloride is 1-; CuCl2. c. From the oxidation state, iron is 3+, oxide is 2-; Fe2O3.
Example 2: Write the proper chemical name for each of the following ionic compounds: a. Li2S; b. NiCl2; c. FeO.
Solution 2: a. We do not use multipliers, so this is simply lithium sulfide. b. We must specify that nickel is 2+ in this compound, so this is nickel(II) chloride. c. We must specify that iron is 2+ in this compound, so this is iron(II) oxide.
Naming Coordination Compounds
More complicated coordination compounds are composed of an atom or ion (usually a metal) and a surrounding array of bound molecules or anions, known as ligands. The atom within a ligand that is bonded to the central atom or ion is called the donor atom. A typical complex is bound to several donor atoms, which can be the same or different. Coordination refers to the coordinate covalentbonds (dipolar bonds) between the ligands and the central atom.
The set of rules for naming a coordination compound is:
  1. When naming a complex ion, the ligands are named before the metal ion.
  2. Write the names of the ligands in the following order: neutral, negative, positive. If there are multiple ligands of the same charge type, they are named in alphabetical order. (Numerical prefixes do not affect the order.)
  3. Multiple occurring monodentate ligands receive a prefix according to the number of occurrences: di-, tri-, tetra-, penta-, or hexa. Polydentate ligands (e.g., ethylenediamine, oxalate) receive bis-, tris-, tetrakis-, etc.
  4. Anions end in -ido. This replaces the final "e" when the anion ends with "-ate" (e.g, sulfate becomes sulfato) and replaces "-ide" (cyanide becomes cyanido).
  5. Neutral ligands are given their usual name, with some exceptions: NH3 becomes ammine; H2O becomes aqua or aquo; CO becomes carbonyl; NO becomes nitrosyl.
  6. Write the name of the central atom/ion. If the complex is an anion, the central atom's name will end in -ate, and its Latin name will be used if available (except for mercury).
  7. If the central atom's oxidation state needs to be specified (when it is one of several possible, or zero), write it as a Roman numeral (or 0) in parentheses.
  8. End with "cation" or "anion" as separate words (if applicable).
Example coordination compound
Chromium(III) 2-ethylhexanoate molecule.

Example:
Write a proper chemical name for each of the following coordination compounds:
a. [NiCl4]2−
b. Pt(NH3)2Cl4
c. [Pt(NH3)2Cl2]Cl2.
Solution:
a. Tetrachloridonickelate(II) ion. The complex ion, an anion, is inside the parentheses. We have to add the suffix -ate in the name of the metal.
b. Diamminetetrachloroplatinum(IV). This is a neutral molecule. The total charge on the ligands is -4. Therefore, the platinum oxidation number is +4.
c. Diamminedichloroplatinum(II) chloride. Here, the number of ions and atoms are the same. However, the brackets as well as the different oxidation number of the platinum result in a very different name.
The coordination number of ligands attached to more than one metal (bridging ligands) is indicated by a subscript to the Greek symbol μ placed before the ligand name. Thus the dimer of aluminum trichloride is described by Al2Cl4(μ2-Cl)2.
Give us feedback on this content:
Coordination complexes have their own classes of isomers, different magnetic properties and colors, and various applications (photography, cancer treatment, etc), so it makes sense that they would have a naming system as well. Consisting of a metal and ligands, their formulas follow the pattern [Metal Anions Neutrals]±Charge, while names are written Prefix Ligands Metal(Oxidation State).
Introduction
According to the Lewis base theory, ligands are Lewis bases since they can donate electrons to the central metal atom. The metals, in turn, are Lewis acids since they accept electrons. Coordination complexes consist of a ligand and a metal center cation. The overall charge can be positive, negative, or neutral. Coordination compounds are complex or contain complex ions, for example: 
  • Complex Cation: [CO(NH3)6]3+[CO(NH3)6]3+
  • Complex Anion: [CoCl4(NH3)2]−[CoCl4(NH3)2]−
  • Neutral Complex: [CoCl3(NH3)3][CoCl3(NH3)3]
  • Coordination Compound: K4[Fe(CN)6]K4[Fe(CN)6]
A ligand can be an anion or a neutral molecule that donates an electron pair to the complex (NH3, H2O, Cl-). The number of ligands that attach to a metal depends on whether the ligand is monodentate, bidentate, or polydentate. For more information, see Ligands and Chelation.
Naming Coordination Complexes
To begin naming coordination complexes, here are some things to keep in mind.  
  1. Ligands are named first in alphabetical order.
  2. The name of the metal comes next.
  3. The oxidation state of the metal follows, noted by a Roman numeral in parentheses (II, IV).                                                               
Rule 1: Anionic Ligands
Ligands that act as anions which end in "-ide" are replaced with an ending "-o" (e.g., Chloride → Chloro). Anions ending with "-ite" and "-ate" are replaced with endings "-ito" and "-ato" respectively (e.g., Nitrite → Nitrito, Nitrate → Nitrato).
Table 1.11.1: Anionic Monodentate Ligands
Molecular Formula
Ligand Name
Molecular Formula
Ligand Name
F-
Fluoro
OH-
Hydroxo
Cl-
Chloro
SO42-
Sulfato
Br-
Bromo
S2O32-
Thiosulfato
I-
Iodo
NO2-
Nitrito-N-; Nitro
O2-
Oxo
ONO-
Nitrito-O-; Nitrito
CN-
Cyano
SCN-
Thiocyanato-S-; Thiocyanato
NC-
Isocyano
NCS-
Thiocyanato-N-; Isothiocyanato
Rule 2: Neutral Ligands
Most neutral molecules that are ligands carry their normal name. The few exceptions are the first four on the chart: ammine, aqua, carbonyl, and nitrosyl.
Table 1.21.2: Select Neutral Monodentate Ligands. Note: Ammine is spelled with two m's when referring to a ligand. Amines are a class of organic nitrogen-containing compounds.
Molecular Formula of Ligand
Ligand Name
NH3
Ammine
H2O
Aqua
CO
Carbonyl
NO
Nitrosyl
CH3NH2
Methylamine
C5H5N
Pyridine
Polydentate ligands follow the same rules for anions and neutral molecules.
Table 1.31.3: Select Polydentate ligands
En
 Ethylenediamine
ox2-
Oxalato
EDTA4-
Ethylenediaminetetraacetato
Rule 3: Ligand Multiplicity
The number of ligands present in the complex is indicated with the prefixes di, tri, etc. The exceptions are polydentates that have a prefix already in their name (en and EDTA4- are the most common). When indicating how many of these are present in a coordination complex, put the ligand's name in parentheses and use bis, tris, and tetrakis.
Table 1.41.4: Prefixes for indicating number of ligands in a complex.
Number of Ligands
Monodentate Ligands
Polydentate Ligands
1
Mono
-
2
Di
Bis
3
Tri
Tris
4
Tetra
Tetrakis
5
Penta
-
6
Hexa
-
Prefixes always go before the ligand name; they are not taken into account when putting ligands in alphabetical order. Note that "mono" often is not used. For example, [FeCl(CO)2(NH3)3]2+ would be called triamminechlorodicarbonyliron(III) ion. Remember that ligands are always named first, before the metal is. 
Example 1.11.1
What is the name oft his complex ion: [CrCl2(H2O)4]+[CrCl2(H2O)4]+?
SOLUTION
Let's start by identifying the ligands. The ligands here are Cl and H2O. Therefore, we will use the monodentate ligand names of "chloro" and "aqua". Alphabetically, aqua comes before chloro, so this will be their order in the complex's name. There are 4 aqua's and 2 chloro's, so we will add the number prefixes before the names. Since both are monodentate ligands, we will say "tetra[aqua]di[chloro]".
Now that the ligands are named, we will name the metal itself. The metal is Cr, which is chromium. Therefore, this coordination complex is called tetraaquadichlorochromium(III) ion. See the next section for an explanation of the (III).
Example 1.21.2
What is the name oft his complex ion: [CoCl2(en)2]+[CoCl2(en)2]+?
SOLUTION
We take the same approach. There are two chloro and ethylenediamine ligands. The metal is Co, cobalt. We follow the same steps, except that enen is a polydentate ligand with a prefix in its name (ethylenediamine), so "bis" is used instead of "bi", and parentheses are added. Therefore, this coordination complex is called dichlorobis(ethylenediamine)cobalt(III) ion.
Rule 4: The Metals
When naming the metal center, you must know the formal metal name and the oxidation state. To show the oxidation state, we use Roman numerals inside parenthesis. For example, in the problems above, chromium and cobalt have the oxidation state of +3, so that is why they have (III) after them. Copper, with an oxidation state of +2, is denoted as copper(II). If the overall coordination complex is an anion, the ending "-ate" is attached to the metal center. Some metals also change to their Latin names in this situation. Copper +2 will change into cuprate(II). The following change to their Latin names when part of an anion complex:
Table 1.51.5: Latin name so of select common metals
Transition Metal
Latin
Iron
Ferrate
Copper
Cuprate
Tin
Stannate
Silver
Argentate
Lead
Plumbate
Gold
Aurate
The rest of the metals simply have -ate added to the end (cobaltate, nickelate, zincate, osmate, cadmate, platinate, mercurate, etc. Note that the -ate tends to replace -um or -ium, if present).
Finally, when a complex has an overall charge, "ion" is written after it. This is not necessary if it is neutral or part of a coordination compound (Examaple 3). Here are some examples with determining oxidation states, naming a metal in an anion complex, and naming coordination compounds.
Example 1.31.3
What is the name of [Cr(OH)4]- ?
SOLUTION
Immediately we know that this complex is an anion. There is only one monodentate ligand, hydroxide. There are four of them, so we will use the name "tetrahydroxo". The metal is chromium, but since the complex is an anion, we will have to use the "-ate" ending, yielding "chromate". The oxidation state of the metal is 3 (x+(-1)4=-1). Write this with Roman numerals and parentheses (III) and place it after the metal to get tetrahydroxochromate(III) ion.
Example 1.41.4
What is the name of  [CuCl4]2- ?
SOLUTION
If you got tetrachlorocuprate(II) ion, you are correct.
A last little side note: when naming a coordination compound, it is important that you name the cation first, then the anion. You base this on the charge of the ligand. Think of NaCl. Na, the positive cation, comes first and Cl, the negative anion, follows.
Example 1.51.5
What is the name of  [Pt(NH3)4)][Pt(Cl)4] ?
SOLUTION
NH3 is neutral, making the first complex positively charged overall. Cl has a -1 charge, making the second complex the anion. Therefore, you will write the complex with NH3 first, followed by the one with Cl (the same order as the formula). This coordination compound is called tetraammineplatinum(II) tetrachloroplatinate(II).
Distinguishing between linkage isomers.
Example 1.61.6
What is the name of [CoCl(NO2)(NH3)4]+ ?
SOLUTION
This coordination complex is called tetraamminechloronitrito-N-cobalt(III). N comes before the O in the symbol for the nitrite ligand, so it is called nitrito-N. If an O came first, as in [CoCl(ONO)(NH3)4]+, the ligand would be called nitrito-O, yielding the name tetraamminechloronitrito-O-cobalt(III).
Nitro (for NO2) and nitrito (for ONO) can also be used to describe the nitrite ligand, yielding the names tetraamminechloronitrocobalt(III) and tetraamminechloronitritocobalt(III).
Writing Formulas of Coordination Complexes
The formula of a coordination complex is written in a different order than its name. The chemical symbol of the metal center is written first. The ligands are written next, with anion ligands coming before neutral ligands. If there is more than one anion or neutral ligand, they are written in alphabetical order according to the first letter in their chemical formula.

In a coordination compound's name, when one of the ions is just an element, the number of atoms is not indicated with a prefix. Since it still has to be written in the formula, it is determined by balancing the overall charge of the compound. (For example, tetrafluorochromium(VI) chloride becomes [CrF4]Cl2.
Examples 1.71.7
  1. Amminetetraaquachromium(II)
  2. Amminesulfatochromium(II)
  3. Amminetetraaquachromium(II) sulfate
  4. Potassium hexacyanoferrate(III)
SOLUTION
  1. Amminetetraaquachromium(II) ion would be written as [Cr(H2O)4(NH3)]+2. Both ligands are neutral, so they are ordered alphabetically with H2O before NH3. Their order in the formula is the opposite of that in the complex's name since one uses their chemical symbols and the other uses the names of the ligands.
  2. Amminesulfatochromium(II) is written as [Cr(SO4)(NH3)]. SO4 is an anion, so it comes before NH3.
  3. Amminetetraaquachromium(II) sulfate -> Try this on your own. Did you get [Cr(H2O)4(NH3)]SO4? If you did, you are correct.
  4. Potassium hexacyanoferrate(III) -> Try this on your own. Did you get K3[Fe(CN)6]? Remember to balance the K!
References
Write the name of the following complexes (Chapter 24 / Custom Edition Chapter 21 Exercises):
  1. [CoCl3(NH3)3]
  2. [Co(ONO)3(NH3)3]
  3. [Fe(ox)2(H2O)2]-
  4. Ag2[HgI4]
Answers
  1. triamminetrichlorocobalt(III)
  2. triamminetrinitrito-O-cobalt(III); or triamminetrinitritocobalt(III)
  3. diaquadioxalatoferrate(III) ion
  4. silver(I) tetraiodomercurate(II

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