Name: how transition metal complexes are named
Uploaded: 2020-09-24T15:06:53.000Z
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Bonding and compounds

Coordination Compounds and Nomenclature

Coordination compounds are neutral species consisting of either a neutral complex or charged complex ions and oppositely-charged counter ions. The complex ion is a central metal ion bound to molecules or ions, known as ligands.
Ligands are compounds with one or more electron pairs. They act as Lewis bases by donating a pair of electrons to the metal ion, which acts as a Lewis acid to form a coordinate covalent bond. Together, they constitute a coordination sphere. 
In 1893, Alfred Werner proposed a coordination theory to explain why specific stable molecules react and violate the valence theory, to form coordination compounds. By studying various cobalt-ammonia complexes, Werner postulated that the central metal atom exhibits two types of valence interactions.
The primary valence is the oxidation number of the central metal, while the secondary valence is the number of ligands bound to it, also called the coordination number. Thus, if the number of bounded ligands decreases, counter ions can bind directly to the metal ion, maintaining the secondary valence. 
Werner&#8217;s coordination theory is nowadays used to write chemical formulas of coordination compounds. Start with the symbol of the metal ion, then list all ligands in alphabetical order. Put square brackets around the complex ion, and list counter ions last. Use numerical subscripts to indicate the number of ligands and the counterions involved.
For a systematic nomenclature of coordination compounds, first, name the complex ions. Start by enlisting the ligands alphabetically. An anionic ligand ends with the letter -o, while a neutral ligand is denoted by its molecular name with a few exceptions such as aqua and ammine.
Use Greek-prefixes such as di-, tri- or tetra- to denote the number of ligands. If a prefix is present in the ligand name already, alternate prefixes to bis- tri- or tetrakis with the ligand name in parentheses.
Then name the metal name and its oxidation state using Roman numerals in parentheses. In the case of an anionic complex, the metal name is suffixed with -ate.
Lastly, the coordination compound is named by adding the cation name first, followed by the anion. Thus, the two coordination compounds are called amminechlorobis(ethylenediammine)cobalt(III) bromide and ammonium diaquatetrachlorocobaltate(III).

coordination compounds and nomenclature

In most main group element compounds, the valence electrons of the isolated atoms combine to form chemical bonds that satisfy the octet rule. For instance, the four valence electrons of carbon overlap with electrons from four hydrogen atoms to form CH4. The one valence electron leaves sodium and adds to the seven valence electrons of chlorine to form the ionic formula unit NaCl (Figure 1a). Transition metals do not normally bond in this fashion. They primarily form coordinate covalent bonds, a form of the Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base, e.g. ammonia molecule ) to an electron acceptor (Lewis acid, e.g. cobalt ion) (Figure 1b). The Lewis acid in coordination complexes, called a central metal ion (or atom), is often a transition metal or inner transition metal. The Lewis base donors, called ligands, can be a wide variety of chemicals - atoms, molecules, or ions. The only requirement is that they have one or more electron pairs, which can be donated to the central metal. Most often, this involves a donor atom (nitrogen atom, Figure 1b) with a lone pair of electrons that can form a coordinate bond to the metal.
<img alt="Chemical bonding diagram, electron dot formulas, sodium acetylide reaction, coordination complex." src="/files/ftp_upload/11455/11455_Image_1.svg" style="text-align: center; height: 150px;" data-altupdatedat="1761830439000" data-alt="Image1" />
Figure 1 (a) Covalent bonds involve the sharing of electrons, and ionic bonds involve the transferring of electrons associated with each bonding atom, as indicated by the colored electrons. (b) However, coordinate covalent bonds involve electrons from a Lewis base being donated to a metal center. The lone pairs from six ammonia molecules form bonds to the cobalt ion to form an octahedral complex.
The coordination sphere consists of the central metal ion or atom plus its attached ligands. Brackets in a formula enclose the coordination sphere; species outside the brackets are not part of the coordination sphere. The coordination number of the central metal ion or atom is the number of donor atoms bonded to it. The coordination number for the silver ion in [Ag(NH3)2]+ is two; for the copper(II) ion in [CuCl4]2&#8722;, the coordination number is four; whereas for the cobalt(II) ion in [Co(H2O)6]2+ the coordination number is six.
The Naming of Complexes
The nomenclature of the complexes is patterned after a system suggested by Alfred Werner, a Swiss chemist and Nobel laureate, whose outstanding work more than 100 years ago laid the foundation for a clearer understanding of these compounds. The following five rules are used for naming complexes:
<ol>
	<li>If a coordination compound is ionic, name the cation first and the anion second, in accordance with the usual nomenclature.</li>
	<li>Name the ligands first, followed by the central metal. Name the ligands alphabetically. Negative ligands (anions) are named by adding -o to the stem name of the group. For most neutral ligands, the name of the molecule is used. The four common exceptions are aqua (H2O), ammine (NH3), carbonyl (CO), and nitrosyl (NO). For example, name [Pt(NH3)2Cl4] as diamminetetrachloroplatinum(IV).</li>
	<li>If more than one ligand of a given type is present, the number is indicated by the prefixes di- (for two), tri- (for three), tetra- (for four), penta- (for five), and hexa- (for six). Sometimes, the prefixes bis- (for two), tris- (for three), and tetrakis- (for four) are used when the name of the ligand already includes di-, tri-, or tetra-, or when the ligand name begins with a vowel. For example, the ion bis(bipyridyl)osmium(II) uses bis- to signify that there are two ligands attached to Os, and each bipyridyl ligand contains two pyridine groups (C5H4N).</li>
</ol>
When the complex is either a cation or a neutral molecule, the name of the central metal atom is spelled exactly like the name of the element and is followed by a Roman numeral in parentheses to indicate its oxidation state.
When the complex is an anion, the suffix -ate is added to the stem of the name of the metal, followed by the Roman numeral designation of its oxidation state. Sometimes, the Latin name of the metal is used when the English name is awkward. For example, ferrate is used instead of ironate, plumbate instead leadate, and stannate instead of tinate.
The oxidation state of the metal is determined based on the charges of each ligand and the overall charge of the coordination compound. For example, in [Cr(H2O)4Cl2]Br, the coordination sphere (in brackets) has a charge of 1+ to balance the bromide ion. The water ligands are neutral, and the chloride ligands are anionic with a charge of 1&#8722; each. To determine the oxidation state of the metal, the overall charge is set equal to the sum of the ligands and the metal: +1 = &#8722;2 + x, so the oxidation state (x) is equal to +3.
This text is adapted from <a href="https://openstax.org/books/chemistry-2e/pages/19-2-coordination-chemistry-of-transition-metals">Openstax, Chemistry 2e, Chapter 19.2 Coordination Chemistry of Transition Metals</a>.

In most main group element compounds, the valence electrons of the isolated atoms combine to form chemical bonds that satisfy the octet rule. For ...

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Transition Metals and Coordination Complexes

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KEY TERMS AND CONCEPTS

how transition metal complexes are named

Transition metal complexes are named by following rules for ligands, metal ions, and oxidation state. These compounds form when a central metal ion or atom, often a transition metal or inner transition metal, accepts electron pairs from ligands. A ligand is a Lewis base that can be an atom, molecule, or ion with one or more lone pairs to donate.

In these complexes, the bond is a coordinate covalent bond. That means both electrons in the bond come from the donor, such as ammonia, and are accepted by the metal center, such as a cobalt ion. The coordination sphere includes the metal plus its attached ligands. Brackets show the coordination sphere in a formula, and anything outside the brackets is not part of it.

The coordination number tells how many donor atoms are bonded to the central metal. For example, [Ag(NH3)2]+ has a coordination number of two, [CuCl4]2− has a coordination number of four, and [Co(H2O)6]2+ has a coordination number of six. These examples show how different ligands can surround the metal in different numbers.

The naming system for complexes follows rules suggested by Alfred Werner. If the coordination compound is ionic, name the cation first and the anion second. Then name the ligands first, followed by the central metal, and list the ligands in alphabetical order.

Negative ligands are named by changing the stem of the name to end in -o. Most neutral ligands keep their usual molecular name, but aqua, ammine, carbonyl, and nitrosyl are common exceptions. If more than one ligand is present, use prefixes such as di-, tri-, tetra-, penta-, and hexa-. The prefixes bis-, tris-, and tetrakis- are used when the ligand name already contains a prefix or begins with a vowel.

A cationic or neutral complex keeps the metal name unchanged and adds a Roman numeral for the oxidation state. An anionic complex uses the -ate ending on the metal name, followed by the Roman numeral. Latin-based names are sometimes used when the English form sounds awkward, such as ferrate, plumbate, and stannate.

The oxidation state of the metal is found from the charges of the ligands and the total charge of the complex. In [Cr(H2O)4Cl2]Br, the bracketed coordination sphere has a 1+ charge to balance bromide. The water ligands are neutral, and each chloride ligand has a 1− charge, so the chromium oxidation state is +3.

How Transition Metal Complexes Are Named

properties of transition metals

Transition Metals in the Periodic Table

Transition metals are the d-block elements and the inner transition metals in the f-block. They are defined by partially filled d orbitals. In the periodic table, the transition elements are in groups 3 through 11, and the inner transition metals appear in the two rows below the main body of the table. The d-block is often grouped into transition series. The first transition series runs from Sc through Cu. The second series runs from Y through Ag. The third series includes La and Hf through...

Transition metal complexes are named by following rules for ligands, metal ions, and oxidation state. These compounds form when a central metal ion or atom, often a transition metal or inner transition metal, accepts electron pairs from ligands. A ligand is a Lewis base that can be an atom, molecule, or ion with one or more lone pairs to donate. In these complexes, the bond is a coordinate covalent bond. That means both electrons in the bond come from the donor, such as ammonia, and are...

metal-ligand bonds

Coordination Complexes and Chelation

Coordination complexes form when a metal ion bonds to ligands. These compounds appear in familiar examples such as hemoglobin in blood, chlorophyll in green plants, vitamin B-12, and the catalyst used to make polyethylene. Transition metal ions are especially likely to form these complexes. In a coordination complex, the metal acts as a Lewis acid. The ligand acts as a Lewis base and donates both electrons in the coordinate covalent bond. A ligand can be an atom, molecule, or ion, as long as...

coordination number and geometry

Transition Metal Shapes from Coordination Number

Transition metal complexes are often identified by their coordination number and the shape around the metal ion. The coordination number is the number of donor atoms bonded to the central metal. In many complexes, the most common shapes are octahedral, tetrahedral, and square planar. Coordination number and molecular geometry are linked in a clear pattern. A coordination number of 2 gives a linear shape, as in [Ag(NH3)2]+. A coordination number of 3 gives a trigonal planar shape, as in...

structural isomerism

Linkage and Ionization Isomers

Isomers are different chemical species that share the same chemical formula. In coordination compounds, structural isomerism includes linkage isomers and coordination-sphere isomers. These two forms show how the same atoms can be arranged in different ways around a metal center. Linkage isomers form when a ligand can attach to a transition metal through two different atoms. The cyanide ligand, CN−, can bind through carbon or nitrogen. The thiocyanate ligand, SCN−, can bind through sulfur or...

stereoisomerism

Isomer Shapes in Coordination Complexes

Isomer shapes in coordination complexes can change a compound’s properties even when the chemical formula stays the same. Isomers are different chemical species with the same formula. In transition metal complexes, the atoms stay connected through the same types of bonds, but their arrangement in space can differ. One common form is geometric isomerism. In these complexes, ligands (the ions or molecules attached to the metal) can sit in cis or trans positions. The octahedral [Co(NH3)4Cl2]+ ion...

valence bond theory

Metal Ligand Bonds in Coordination Complexes

Coordination complexes form metal-ligand bonds through valence bond theory. In this model, Linus Pauling explained bonding with hybridization and overlap of atomic orbitals. The central metal atom or ion acts as a Lewis acid. It uses empty orbitals of suitable energy to accept electron pairs from ligands, which act as Lewis bases. These coordinate covalent bonds help explain the color, geometry, and magnetic behavior seen in coordination compounds. The type of hybridization helps determine the...

crystal field theory - octahedral complexes

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Octahedral d-Orbital Splitting in Crystal Fields

Crystal field theory explains how ligands affect the d orbitals in transition metal complexes. This electrostatic model helps predict the colors, magnetic behavior, and some structures of coordination compounds. It focuses on the nonbonding electrons on the central metal ion, not on the metal-ligand bonds. In crystal field theory, the metal ion and ligands are treated as very small point charges. Because electrons are negative, electrons donated by the ligands repel the electrons in the...

crystal field theory - tetrahedral and square planar complexes

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Crystal Field Splitting in Non-Octahedral Shapes

Crystal field theory also explains d orbital splitting in tetrahedral and square planar complexes. These shapes do not follow the same pattern as an octahedral complex, so the d orbitals respond to ligand placement in different ways. In tetrahedral complexes, the four ligands sit between the axes. None of the d orbitals points directly at the ligands, but the d x2−y2 and d z2 orbitals lie along the Cartesian axes and overlap less with the ligands than the d xy, d xz, and d yz orbitals. The d...

colors and magnetism

Color and Spin in Coordination Complexes

Color in coordination complexes comes from how metal electrons absorb light. When atoms or molecules absorb light at the right frequency, electrons move to higher-energy orbitals. For many main-group atoms and molecules, the absorbed light is ultraviolet and cannot be seen. In coordination compounds, the energy gap between d orbitals often matches visible light, so the compound can absorb and emit colors that the human eye detects. Small changes in orbital energy can cause large shifts in the...

key terms and concepts

Learn how transition metal complexes are named, including ligands, coordination number, oxidation state, and rules like di-, bis-, and -ate.

How Transition Metal Complexes Are Named | JoVE K12

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Atomic Radii and Effective Nuclear Charge

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Bond Polarity

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Lewis Structures of Molecular Compounds and Polyatomic Ions

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Resonance

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Exceptions to the Octet Rule

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	...

Bond Energies and Bond Lengths

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Bonding in Metals

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Ionic Compounds: Formulas and Nomenclature

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Molecular Compounds: Formulas and Nomenclature

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Content elaboration: Middle school content introduced the concept that compounds are composed of atoms of two or more different elements joined together chemically. In this course, the chemical joining of atoms is studied in more detail. Atoms may be bonded together by losing, gaining or sharing valence electrons to form molecules or three-dimensional lattices. An ionic bond involves the attraction of two oppositely charged ions, typically a metal cation and a nonmetal anion formed by transferring electrons between the atoms. An ion attracts oppositely charged ions from every direction, resulting in the formation of a three-dimensional lattice. Covalent bonds result from the sharing of electrons between two atoms, usually nonmetals. Covalent bonding can result in the formation of structures ranging from small individual molecules to three-dimensional lattices (e.g., diamond). The bonds in most compounds fall on a continuum between the two extreme models of bonding: ionic and covalent. Using the periodic table to determine ionic charge, formulas of ionic compounds containing elements from groups 1, 2, 17, hydrogen and oxygen can be predicted. Given a chemical formula, a compound can be named using conventional systems that include Greek prefixes where appropriate. Prefixes will be limited to represent values from one to 10. Given the name of an ionic or covalent substance, formulas can be written. Naming organic molecules is beyond this grade level and is reserved for an advanced chemistry course. Prediction of bond types from electronegativity values, polar covalent bonds, and writing formulas/naming compounds that contain polyatomic ions or transition metals are reserved for Chemistry.

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• Chemical reactions
• Nuclear reactions

Content elaboration: In middle school, the law of conservation of matter was expanded to chemical reactions, noting that the number and type of atoms and the total mass are the same before and after the reaction. In this course, conservation of matter is expressed by writing balanced chemical equations. At this level, reactants and products can be identified from an equation and simple equations can be written and balanced given either the formulas of the reactants and products or a word description of the reaction. [cite: 143, 149] Stoichiometric relationships beyond the coefficients in a balanced equation and classification of types of chemical reactions are reserved for Chemistry. During chemical reactions, thermal energy is either transferred from the system to the surroundings (exothermic) or transferred from the surroundings to the system (endothermic). Since the environment surrounding the system can be large, temperature changes in the surroundings may not be detectable. Nuclear reactions involve changes to the nucleus and typically produce much larger energies than chemical reactions. The strong nuclear force is an attractive force that binds protons and neutrons together in the nucleus. While the nuclear force is extremely weak at most distances, over the very short distances present in the nucleus the force is greater than the repulsive electrical forces among protons. When the attractive nuclear forces and repulsive electrical forces in the nucleus are not balanced, the nucleus is unstable. Through radioactive decay, the unstable nucleus emits radiation in the form of very fast-moving particles and energy to produce a new nucleus. Nuclei that undergo this process are said to be radioactive. Radioactive decay can result in the release of different types of radiation (alpha, beta, gamma), each with a characteristic mass, charge, and potential to alter and penetrate the material it strikes. Alpha decay changes the identity of the element. Beta decay results from the decay of a neutron. When a radioisotope undergoes alpha or beta decay, the resulting nucleus can be predicted and the balanced nuclear equation can be written. For any radioisotope, the half-life is unique and predictable. Graphs can be constructed that show the amount of a radioisotope that remains as a function of time and can be interpreted to determine the value of the half-life. Half-life values are used in radioactive dating. Only whole number integers of half-lives will be addressed in this course. Other examples of nuclear processes include nuclear fission and nuclear fusion. Nuclear fission involves splitting a large nucleus into smaller nuclei, releasing large quantities of energy. Nuclear fusion is the joining of smaller nuclei into a larger nucleus accompanied by the release of large quantities of energy. Nuclear fusion is the process responsible for formation of elements in the universe beyond hydrogen and is the source of energy in the sun and other stars. Using nuclear reactions as an energy resource can be addressed. Further details about nuclear processes, including mass-energy equivalence and nuclear power applications, are addressed in Physics.

Reactions of matter

How Transition Metal Complexes Are Named

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