coordination number

Examples of coordination number in the following topics:

• Coordination Number, Ligands, and Geometries

  • The coordination number determines the number of ligands attached to the central ion and the overall shape of the complex.
  • In coordination chemistry, the coordination number is the number of ligands attached to the central ion (more specifically, the number of donor atoms).
  • Coordination numbers are normally between two and nine.
  • Different ligand structural arrangements result from the coordination number.
  • Calculate the coordination number of the metal in a coordination complex.

• Crystal Structure: Packing Spheres

  • The structure seen within the crystalline lattice of a material can be described in a number of ways.
  • Each sphere that participates in a crystal structure has a coordination number, which corresponds to the number of spheres within the crystalline structure that touch the sphere that is being evaluated.
  • For a sphere in the interior of a crystal lattice, the number of spheres contacting the sphere that is being evaluated is known as the bulk coordination number.
  • For a sphere at the surface of a crystal, the number of spheres contacting the sphere being evaluated is known as the surface coordination number.
  • By considering how atomic spheres are arranged relative to one another, their coordination numbers, and the dimensions of the unit cell, it is possible to form a general view of the structure and complexity of particular crystal structures.

• Applying the VSEPR Model

  • In the VSEPR model, the number of electron pairs around a central atom dictates a molecule's general shape.
  • The number of atoms bonded to a central atom combined with the number of pairs of its nonbonding valence electrons is called its steric number.
  • When calculating the coordination number around the central atom, count both the bonded atoms and the nonbonding pairs, because the nonbonding electrons are also in orbitals that occupy space and repel the other orbitals.
  • Molecules with a coordination number of 5 are in the shape of a trigonal bipyramid; this consists of two triangular-based pyramids joined base-to-base.
  • A coordination number of 6 is one of the most commonly encountered in inorganic chemistry, specifically in transition metal hydrates such as Fe(H2O)63+.

• Metal Cations that Act as Lewis Acids

  • Ligands create a complex when forming coordinate bonds with transition metals ions; the transition metal ion acts as a Lewis acid, and the ligand acts as a Lewis base.
  • The number of coordinate bonds is known as the complex's coordination number.
  • For instance, Mg2+ can coordinate with ammonia in solutions, as shown below:
  • The product is known as a complex ion, and the study of these ions is known as coordination chemistry.
  • Examples of several metals (V, Mn, Re, Fe, Ir) in coordination complexes with various ligands.

• Lone Electron Pairs

  • Coordination number refers to the number of electron pairs that surround a given atom, often referred to as the central atom.
  • The oxygen atom will therefore be tetrahedrally coordinated, meaning that it sits at the center of the tetrahedron.
  • This means that there are three bonded atoms and one lone pair for a coordination number of four around the nitrogen, the same as occurs in H2O.
  • Substituting nonbonding pairs for bonded atoms reduces the triangular bipyramid coordination to even simpler molecular shapes.
  • Although the oxygen atom is tetrahedrally coordinated, the bonding geometry (shape) of the H2O molecule is described as bent.

• Naming Coordination Compounds

  • Transition-metal and coordination compounds are named using a set of rules that describe oxidation numbers and anion and cation composition.
  • Coordination refers to the coordinate covalent bonds (dipolar bonds) between the ligands and the central atom.
  • Therefore, the platinum oxidation number is +4.
  • Here, the number of ions and atoms are the same.
  • 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.

• Oxidation Numbers of Metals in Coordination Compounds

  • O2- and S2- have oxidation numbers of -2.
  • In a molecule or compound, the oxidation number is the sum of the oxidation numbers of its constituent atoms.
  • The oxidation number of H is +1 (H+ has an oxidation number of +1).
  • The oxidation number in coordination chemistry has a slightly different meaning.
  • Calculate the oxidation state of a metal in a coordination compound.

• Biomolecules

  • Coordination complexes (also called coordination compounds) and transition metals are widespread in nature.
  • In addition to donor groups that are provided by amino acid residues, a large number of organic cofactors function as ligands.
  • Metalloenzymes contain a metal ion bound to the protein with one labile coordination site.
  • The structure of the active site in carbonic anhydrases is well known from a number of crystal structures.
  • The fourth coordination site is occupied by a water molecule.

• Chelating Agents

  • Chelating agents are ligands for metals that bind via multiple atoms, thus taking up several coordination sites on the metal.
  • Chelation is the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central atom.
  • Chelate complexes are contrasted with coordination complexes composed of monodentate ligands, which form only one bond with the central atom.
  • Chelating agents, unlike the other ligands in coordination compounds, bind via multiple atoms in the ligand molecule, not just one.
  • The effect increases with the number of chelate rings, so the concentration of the EDTA complex, which has six chelate rings, is much higher than a corresponding complex with two monodentate nitrogen donor ligands and four monodentate carboxylate ligands.

• Isomers in Coordination Compounds

  • Coordination stereoisomers have the same bonds in different orientations; structural isomers have different bonding orientations.
  • As with other compounds, there are several kinds of coordination complex isomers.
  • In solvate or hydrate isomerism, the isomers have the same composition but differ with respect to the number of solvent ligand molecules as well as the counter ion in the crystal lattice.
  • In coordination isomerism, both positive and negative ions of a salt are complex ions and the two isomers differ in the distribution of ligands between the cation and the anion.
  • Explain the effect of isomerization on the properties of a coordination complex.