coordinate bond

Examples of coordinate bond in the following topics:

• 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.

• Bonding in Coordination Compounds: Valence Bond Theory

  • Valence bond theory is used to explain covalent bond formation in many molecules.
  • Valence bond theory is a synthesis of early understandings of how chemical bonds form.
  • Where bond order is concerned, single bonds are considered to be one sigma bond, double bonds are considered to contain one sigma and one pi bond, and triple bonds consist of one sigma bond and two pi bonds.
  • When we apply valence bond theory to a coordination compound, the original electrons from the d orbital of the transition metal move into non-hybridized d orbitals.
  • Calculate the theoretical hybridization of a metal in a coordination complex based on valence bond theory

• Reactions of Coordination Compounds

  • Many metal-containing compounds consist of coordination complexes.
  • The atom within a ligand that is bonded to the central atom or ion is called the donor atom.
  • These are generally bound to the central atom by a coordinate covalent bond (donating electrons from a lone electron pair into an empty metal orbital).
  • There are also organic ligands such as alkenes whose pi (π) bonds can coordinate to empty metal orbitals.
  • Coordination refers to the coordinate covalent bonds (dipolar bonds) between the ligands and the central atom.

• Applications of Transition Metals to Organic Chemistry

  • As a first step in the analysis of transition metal complexes, it is necessary to distinguish covalently bonded substituents from coordinatively bonded ligands.
  • Here, a single covalent bond buttressed by electron pair coordination from the two double bonds may be imagined.
  • This coordinate bonding, together with the electron pairs donated by the carbon monoxide ligands, allows each metal to achieve an 18 electron valence shell (characteristic of the inert gas krypton).
  • The Fe(0) atom has eight valence electrons, and the cyclobutadiene and CO ligands provide ten more by coordinate bonding.
  • Note that, for simplicity, the ring-to-metal coordinate bonding is designated by a single dashed line rather than multiple lines as in ferrocene.

• Lone Electron Pairs

  • Two of the coordination positions are occupied by the shared electron-pairs that constitute the O–H bonds, and the other two by the non-bonding pairs.
  • Therefore, although the oxygen atom is tetrahedrally coordinated, the bonding geometry (shape) of the H2O molecule is described as bent.
  • 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.

• Applying the VSEPR Model

  • Two of the coordination positions are occupied by the shared electron-pairs that constitute the O–H bonds, and the other two by the non-bonding pairs.
  • Therefore, although the oxygen atom is tetrahedrally coordinated, the bonding geometry (shape) of the H2O molecule is described as bent.
  • The four equivalent bonds point in four geometrically equivalent directions in three dimensions corresponding to the four corners of a tetrahedron; this is called tetrahedral coordination.
  • In 5-coordinated molecules containing lone pairs, these non-bonding orbitals will preferentially reside in the equatorial plane at 90° angles, with respect to no more than two axially-oriented bonding orbitals.
  • An AX4E molecule (one in which the central atom is coordinated to four other atoms and to one nonbonding electron pair) has a "see-saw" shape; substituting more nonbonding pairs for bonded atoms reduces the triangular bipyramid coordination to even simpler molecular shapes.

• Coordination Number, Ligands, and Geometries

  • The number of bonds depends on the size, charge, and electron configuration of the metal ion and the ligands.
  • Denticity refers to the number of times a ligand bonds to a metal through donor atoms.
  • All unsaturated molecules are also ligands, utilizing their π-electrons in forming the coordinate bond.
  • Also, metals can bind to the σ bonds in, for example, silanes, hydrocarbons, and dihydrogen.
  • Calculate the coordination number of the metal in a coordination complex.

• 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.
  • Stereoisomers occur when the ligands have the same bonds, but the bonds are in different orientations relative to one another.
  • Structural isomerism occurs when the bonds are different.
  • Explain the effect of isomerization on the properties of a coordination complex.

• Naming Coordination Compounds

  • Transition-metal and coordination compounds are named using a set of rules that describe oxidation numbers and anion and cation composition.
  • The atom within a ligand that is bonded to the central atom or ion is called the donor atom.
  • Coordination refers to the coordinate covalent bonds (dipolar bonds) between the ligands and the central atom.
  • Write a proper chemical name for each of the following coordination compounds:
  • Identify the proper name for a coordination complex given its molecular formula.

• Alkylidene Complexes

  • Transition metal complexes incorporating a formal metal-carbon double bond are termed alkylidene or carbene complexes.
  • This results in a strong metal-to-carbon double bond.
  • The overall bonding in the complex leaves the carbon atom nucleophilic.
  • The metal is electron rich, in part because of coordinate donation of an electron pair from the carbene carbon atom and CO ligands.
  • The resulting C=M multiple bond is weakened, and has a low barrier to rotation.