19.2 Coordination Chemistry of Transition Metals
4 min read•june 25, 2024
are fascinating molecules with a atom bonded to surrounding . These compounds play crucial roles in biology and industry, from carrying oxygen to catalysts driving chemical reactions.
The structure and properties of depend on the metal, ligands, and bonding. Understanding their nomenclature, isomerism, and electronic structure helps explain their diverse applications in medicine, manufacturing, and beyond.
Coordination Compounds
Characteristics of coordination compounds
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- Molecules consisting of a central metal atom or ion bonded to surrounding molecules or ions called ligands
- Central metal atom or ion usually a transition metal (iron, copper, cobalt) or inner transition metal (lanthanides, actinides)
- Ligands can be neutral molecules (, ) or ions (, )
- Bonds between metal and ligands are coordinate covalent bonds where both electrons in the bond come from the ligand
- Entire coordination compound enclosed in square brackets in chemical formulas with metal listed first followed by ligands ()
- Can be cationic, anionic, or neutral depending on charges of metal and ligands
- Cationic example:
- Anionic example:
- Neutral example:
- The and its surrounding ligands form the
Monodentate vs polydentate ligands
- ligands bond to central metal atom through only one atom forming a single coordinate covalent bond
- Examples: , , ,
- Polydentate ligands bond to central metal atom through two or more atoms forming multiple coordinate covalent bonds
- bond through two atoms (, )
- Hexadentate ligands bond through six atoms (, ethylenediaminetetraacetic acid)
- Polydentate ligands form more stable complexes due to where entropy of system increases when multiple ligands replaced by a single
Nomenclature for coordination compounds
- Name consists of ligands followed by central metal atom or ion
- Ligands named first in alphabetical order followed by metal
- Anionic ligands end in "-o" (chloro for , cyano for )
- Neutral ligands named as molecule (aqua for , ammine for )
- Greek prefixes (di-, tri-, tetra-) used to indicate number of each type of ligand ( named hexaamminecobalt(III) ion)
- Oxidation state of metal indicated by Roman numeral in parentheses after metal name
- Oxidation state calculated by considering charges of ligands and overall charge of complex
- The , which is the number of ligand donor atoms bonded to the central atom, is often included in the name
Isomerism in coordination complexes
- Geometric isomers have same chemical formula but different spatial arrangements of ligands around central metal atom
- complexes with formula can have cis and trans isomers where A and B ligands are adjacent or opposite each other
- are non-superimposable mirror images of each other arising from presence of chiral centers in complex
- complexes with formula where A and B are different ligands can have optical isomers
- Isomers designated as Δ (delta) and Λ (lambda) based on direction of twist of ligands around metal center
- Coordination compounds with optical isomers can exhibit different biological activities and chemical properties due to different spatial arrangements
Electronic Structure and Properties
- The ranks ligands based on their ability to cause in the central metal atom
- D-orbital splitting occurs when ligands interact with the central metal, causing energy differences between d orbitals
- Complexes can be classified as high-spin or low-spin depending on how electrons fill the split d orbitals
- High-spin complexes have electrons occupying all d orbitals before pairing
- Low-spin complexes have electrons pairing in lower energy d orbitals before occupying higher energy ones
Applications of coordination compounds
- Hemoglobin, oxygen-carrying protein in red blood cells, contains iron(II) ion coordinated to porphyrin ligand
- Oxygen binds to iron center allowing hemoglobin to transport oxygen throughout body
- , green pigment in plants, contains magnesium ion coordinated to porphyrin ligand
- Complex plays crucial role in photosynthesis by absorbing light energy
- is coordination compound with cobalt ion center essential for red blood cell formation and proper nervous system function
- , square planar platinum(II) complex, used as anticancer drug
- Compound binds to DNA interfering with cell division and causing apoptosis in cancer cells
- Used as catalysts in various industrial processes such as for production of acetic acid
- Catalyst, rhodium complex cis-, facilitates reaction between methanol and carbon monoxide to produce acetic acid
Key Terms to Review (64)
[Co(NH3)6]3+: [Co(NH3)6]3+ is a coordination complex consisting of a central cobalt(III) ion surrounded by six ammonia ligands. It is an important example of coordination chemistry in transition metals, where the metal ion forms stable bonds with multiple ligands to create a complex ion.
[Cu(NH3)4]2+: [Cu(NH3)4]2+ is a coordination complex formed by a central copper(II) ion surrounded by four ammonia ligands. It is an important example of the coordination chemistry of transition metals, which involves the formation of complex species with a central metal atom and attached ligands.
[Fe(CN)6]4-: [Fe(CN)6]4- is a complex ion consisting of an iron(II) center coordinated to six cyanide ligands. It is an important example of coordination chemistry in transition metal complexes and is studied in the context of 19.2 Coordination Chemistry of Transition Metals.
[Pt(NH3)2Cl2]: [Pt(NH3)2Cl2] is a coordination complex consisting of a central platinum (Pt) atom bonded to two ammonia (NH3) ligands and two chloride (Cl) ligands. This complex is an important example of coordination chemistry, which describes the formation of compounds involving a central metal atom or ion surrounded by other atoms or molecules known as ligands.
Alfred Werner: Alfred Werner was a Swiss chemist who is considered the founder of coordination chemistry, a field that examines the structure and properties of metal complexes. His groundbreaking work in the late 19th and early 20th centuries laid the foundation for understanding the coordination behavior of transition metals, which is a central topic in 19.2 Coordination Chemistry of Transition Metals.
Bidentate: Bidentate refers to a ligand that is bound to a central metal atom through two separate donor atoms, typically forming a chelate ring. This type of coordination is commonly observed in transition metal complexes.
Bidentate ligands: Bidentate ligands are molecules or ions that can form two bonds to a central metal atom in a coordination complex. They have two donor atoms that each share an electron pair with the metal center.
Central Atom: The central atom is the main atom in a molecule or complex ion that is bonded to other atoms or ligands. It is the focal point around which the molecular structure is organized and plays a crucial role in determining the overall shape and properties of the chemical species.
Central metal: A central metal is the metal atom or ion in a coordination complex to which ligands are directly bonded. It acts as the core around which the structure of the coordination compound is formed.
Chelate: Chelate is a complex formed when a single ligand binds to a central metal atom at multiple points. This creates ring-like structures that enhance the stability of the complex.
Chelate effect: The chelate effect refers to the increased stability of coordination complexes formed by multidentate ligands compared to those formed by monodentate ligands. This effect is primarily due to the formation of a ring structure when a ligand coordinates to a metal ion at multiple binding sites, resulting in stronger metal-ligand interactions and greater overall complex stability.
Chelating: Chelating is the formation of multiple bonds between a central metal ion and a ligand, creating a cyclic structure that is more stable than simple ionic or covalent bonds. This process is particularly important in the coordination chemistry of transition metals.
Chelating ligands: Chelating ligands are molecules that can form multiple bonds to a single metal ion, creating a ring structure. They increase the stability of coordination compounds through the chelate effect.
Chlorophyll: Chlorophyll is a green pigment found in the chloroplasts of plants and some other photosynthetic organisms. It is essential for the process of photosynthesis, which converts light energy from the sun into chemical energy that can be used by the plant.
Cis configuration: Cis configuration describes the arrangement of two identical or similar ligands adjacent to each other in a coordination complex. It is commonly seen in square planar and octahedral geometries.
Cis Isomer: A cis isomer is a type of geometric isomer where two identical substituents are positioned on the same side of a carbon-carbon double bond or a cyclic structure. This arrangement contrasts with the trans isomer, where the identical substituents are on opposite sides.
Cis-[Rh(CO)2I2]-: cis-[Rh(CO)2I2]- is a coordination complex consisting of a rhodium (Rh) metal center surrounded by two carbonyl (CO) ligands and two iodide (I) ligands arranged in a cis configuration.
Cisplatin: Cisplatin is a platinum-based chemotherapy drug used to treat a variety of cancers. It is a coordination complex that forms covalent bonds with DNA, leading to cell death and inhibition of tumor growth.
Color: Color is a fundamental property of light that is perceived by the human eye and brain. It is the result of the interaction between light and matter, and it plays a crucial role in the field of coordination chemistry of transition metals.
Coordination compounds: Coordination compounds are complex molecules consisting of a central metal atom or ion bonded to surrounding molecules or anions, called ligands. These compounds exhibit unique chemical and physical properties due to the interactions between the central metal and its ligands.
Coordination Compounds: Coordination compounds are a class of chemical compounds that consist of a central metal atom or ion surrounded by a number of ligands, which are molecules or ions that are attached to the central metal. These compounds are an important aspect of transition metal chemistry and exhibit unique spectroscopic and magnetic properties.
Coordination number: The coordination number is the number of atoms, ions, or molecules that a central atom or ion holds as its nearest neighbors in a complex or lattice structure. It indicates the connectivity and spatial arrangement around the central entity.
Coordination Number: The coordination number is the number of atoms, ions, or molecules that are directly bonded to a central atom or ion in a coordination complex or crystal structure. This concept is fundamental in understanding the solid state of matter, lattice structures in crystalline solids, and the coordination chemistry of transition metals.
Coordination sphere: The coordination sphere includes the central metal atom or ion and its directly attached ligands, enclosed in square brackets. It defines the immediate chemical environment of the central atom in a complex.
Coordination Sphere: The coordination sphere refers to the arrangement of atoms, ions, or molecules that are directly bonded to a central metal atom in a coordination complex. It describes the spatial organization of the ligands around the metal center, which is a crucial aspect of coordination chemistry.
Crystal field theory: Crystal Field Theory (CFT) describes the breaking of degeneracies of electronic orbitals in transition metal complexes due to the presence of ligands. It explains how the arrangement of ligands around a central metal ion affects the energy levels and properties like color and magnetism.
Crystal Field Theory: Crystal Field Theory is a model that explains the electronic structure and bonding in coordination complexes formed between transition metal ions and surrounding ligands. It provides a framework for understanding the spectroscopic and magnetic properties of these complexes.
D-Orbital Splitting: d-Orbital splitting refers to the energy level splitting of the five degenerate d-orbitals of a transition metal atom when it forms a coordination complex with ligands. This splitting pattern is a key concept in understanding the electronic structure and properties of transition metal complexes.
Donor atom: A donor atom is an atom in a ligand that donates a pair of electrons to a central metal atom or ion, forming a coordinate bond. Donor atoms are essential in the formation of coordination complexes.
EDTA: EDTA, or ethylenediaminetetraacetic acid, is a synthetic compound used as a chelating agent to bind metal ions in solution. It plays a critical role in coordination chemistry, especially with transition metals, as it forms stable complexes that can effectively sequester harmful ions, making it important in various chemical, medical, and industrial applications.
Enantiomers: Enantiomers are a pair of molecules that are mirror images of each other and cannot be superimposed. They have identical physical properties but differ in the direction they rotate plane-polarized light.
Ethylenediamine: Ethylenediamine (en) is a bidentate ligand, meaning it has two nitrogen atoms that can coordinate to a metal center in coordination compounds. It is a colorless, flammable liquid with a strong ammonia-like odor, and it is widely used in the synthesis of coordination complexes, particularly in the field of transition metal chemistry.
Geometric Isomerism: Geometric isomerism, also known as cis-trans isomerism, is a type of stereoisomerism that occurs when two or more atoms or groups are arranged differently in space around a central atom or group, resulting in molecules with the same chemical formula but different spatial arrangements. This phenomenon is particularly relevant in the context of coordination chemistry of transition metals.
Hemoglobin: Hemoglobin is a complex protein found in red blood cells that is responsible for transporting oxygen from the lungs to the body's tissues and facilitating the return of carbon dioxide from the tissues back to the lungs. This protein contains iron, which plays a crucial role in its ability to bind to oxygen, linking it closely with the properties of transition metals and their coordination chemistry.
Hexaamminecopper(II) ion: The hexaamminecopper(II) ion, with the chemical formula $[Cu(NH_3)_6]^{2+}$, is a coordination complex formed by the central copper(II) ion surrounded by six ammonia ligands. This complex is an important example in the study of coordination chemistry of transition metals.
High-Spin Complex: A high-spin complex is a type of coordination complex in which the transition metal center has the maximum number of unpaired electrons, resulting in a high total spin quantum number. This occurs when the energy difference between the t2g and eg orbitals is relatively small, allowing the electrons to occupy the available orbitals with parallel spins.
Ionization isomers: Ionization isomers are coordination compounds that have the same composition but yield different ions in solution. This occurs due to the interchange of ligands between the inner coordination sphere and the counter-ions.
IUPAC Nomenclature: IUPAC nomenclature is a systematic method of naming chemical compounds developed and recommended by the International Union of Pure and Applied Chemistry (IUPAC). It provides a standardized way to name organic and inorganic compounds based on their structure and composition.
K3[Fe(CN)6]: K3[Fe(CN)6], also known as potassium ferrocyanide, is a coordination compound consisting of a central iron(III) ion surrounded by six cyanide ligands. It is an important compound in the field of coordination chemistry, particularly in the study of transition metal complexes.
Ligands: Ligands are ions or molecules that can donate a pair of electrons to a central atom or ion to form a coordination complex. They act as Lewis bases in this interaction.
Linkage isomers: Linkage isomers are coordination compounds that have the same composition but differ in the connectivity of a ligand to the central metal atom. This occurs when a ligand can coordinate to the metal through two or more different atoms.
Low-Spin Complex: A low-spin complex is a type of coordination complex in which the transition metal center has a low number of unpaired electrons, typically two or less, due to the arrangement of electrons in the metal's d-orbitals. This configuration results from the stabilization of the d-orbitals in the presence of a strong ligand field.
Magnetism: Magnetism is the fundamental force of attraction or repulsion between particles with electric charge. It is a key concept in the field of coordination chemistry, as transition metals exhibit unique magnetic properties due to their partially filled electron shells.
Monodentate: Monodentate describes a ligand that forms a single bond with a central metal atom or ion in a coordination complex. It can donate only one pair of electrons to the metal center.
Monodentate: Monodentate refers to a ligand that binds to a metal center through a single donor atom. These ligands form coordination complexes with transition metals, contributing to the unique properties and reactivity of these complexes.
Monsanto Process: The Monsanto process is a method for the industrial production of ammonia, a key component in fertilizers and other chemical products. It is a critical process in the field of coordination chemistry of transition metals, as it involves the use of a transition metal catalyst to facilitate the reaction between nitrogen and hydrogen gases.
NMR Spectroscopy: NMR (Nuclear Magnetic Resonance) spectroscopy is an analytical technique that utilizes the magnetic properties of atomic nuclei to provide detailed information about the structure and composition of chemical compounds. It is a powerful tool for studying the coordination chemistry of transition metals.
Octahedral: Octahedral is a molecular geometry where a central atom is surrounded by six atoms or ligands placed at the vertices of an octahedron. This arrangement results in 90° bond angles between adjacent atoms.
Octahedral: Octahedral is a geometric shape in which a central atom or ion is surrounded by six other atoms or ions arranged in a three-dimensional, octagonal configuration. This shape is commonly observed in the context of Lewis Symbols and Structures, Hybrid Atomic Orbitals, and Coordination Chemistry of Transition Metals.
Optical isomerism: Optical isomerism refers to the phenomenon where compounds have the same molecular formula and connectivity but differ in their spatial arrangement, resulting in non-superimposable mirror images known as enantiomers. This type of isomerism is particularly relevant in coordination chemistry, as transition metal complexes can exhibit optical isomerism due to their chiral arrangements, affecting their physical properties and biological activity.
Optical isomers: Optical isomers are molecules that are non-superimposable mirror images of each other, also known as enantiomers. They have identical physical and chemical properties except for their interaction with plane-polarized light and reactions in a chiral environment.
Polydentate ligand: A polydentate ligand is a molecule or ion that can form multiple bonds to a single metal ion simultaneously. It has two or more donor atoms that can coordinate to the metal center.
Potassium ferricyanide: Potassium ferricyanide, also known as potassium hexacyanoferrate(III), is a coordination complex compound with the chemical formula K3[Fe(CN)6]. It is an important compound in the field of coordination chemistry of transition metals, particularly in the study of metal-ligand bonding and the electronic properties of transition metal complexes.
Sophus Mads Jørgensen: Sophus Mads Jørgensen was a Danish chemist who made significant contributions to the field of coordination chemistry, particularly in the study of transition metal complexes.
Spectrochemical series: The spectrochemical series is an empirically derived list of ligands ordered by the magnitude of the crystal field splitting energy ($\Delta$) they produce when coordinating to a metal ion. Ligands at the high end of the series cause a larger splitting of d-orbital energies, resulting in stronger field effects.
Spectrochemical Series: The spectrochemical series is a ranking of ligands based on their ability to split the d-orbital energy levels in coordination complexes, which is directly related to the strength of the ligand field. This concept is crucial in understanding the coordination chemistry of transition metals and the spectroscopic and magnetic properties of coordination compounds.
Square planar: Square planar is a molecular geometry where a central atom is surrounded by four other atoms positioned at the corners of a square, forming a flat, two-dimensional shape. This geometry is commonly seen in coordination compounds of transition metals, where the arrangement affects the properties and reactivity of the complex. The square planar shape results from specific hybridization and ligand arrangements that influence bond angles and electron distribution.
Stability: Stability refers to the ability of a system or compound to resist change or maintain its structure and properties under various conditions. It is a fundamental concept in chemistry, particularly in the context of coordination chemistry of transition metals.
Trans configuration: Trans configuration describes a type of geometric isomerism in coordination complexes where two identical ligands are positioned across from each other, at a 180-degree angle. This arrangement contrasts with the cis configuration, where identical ligands are adjacent.
Trans Isomer: A trans isomer, also known as a trans configuration, is a type of geometric isomerism that occurs in organic compounds. It refers to the spatial arrangement of atoms or functional groups around a carbon-carbon double bond, where the substituents are on opposite sides of the double bond.
UV-Vis Spectroscopy: UV-Vis spectroscopy is an analytical technique that measures the absorption of ultraviolet (UV) and visible (Vis) light by a sample. It is widely used in chemistry to identify and quantify various compounds based on their unique absorption patterns in the UV and visible regions of the electromagnetic spectrum.
Vitamin B12: Vitamin B12, also known as cobalamin, is an essential nutrient that plays a crucial role in various physiological processes within the human body. It is a water-soluble vitamin that is involved in the coordination chemistry of transition metals, particularly in the context of cellular metabolism and red blood cell formation.
Δ Isomer: A Δ isomer, also known as a cis-trans isomer, is a type of stereoisomer that arises from the restricted rotation around a carbon-carbon double bond or a cyclic structure. These isomers differ in the spatial arrangement of their substituents on either side of the double bond or within the cyclic framework.
Λ Isomer: A Λ isomer, also known as a lambda isomer, is a type of stereoisomer that arises in coordination compounds of transition metals. It refers to the spatial arrangement of the ligands around the central metal atom, which can adopt a left-handed, spiral-like configuration resembling the Greek letter Λ (lambda).