Coordination of compounds ‐ definition, composition, stability, isomerism. Bonding in coordination compounds – theories. Chelate compounds. Biological and medical importance.
Covers the formation of complex compounds from d-block and some p- and s-block elements, and the coordinate covalent bond that links ligands to a central atom. It then explains complex-ion stability through formation and dissociation constants, gives a table of coordination numbers against geometry, and sets out structural (coordination and linkage) and stereoisomerism, including cis-trans and optical forms. It closes with monodentate, bidentate and polydentate ligands and chelate compounds, illustrated by example ligands.
Topic 4 of 47 in the MU Pleven syllabus for Chemistry (Medicine, Year 1). The free AceMed note covers it in 6 sections, about 467 words (4 min of reading), with 20 flashcards.
In this note
Coordination of compounds ‐ definition, composition, stability, isomerism. Bonding in coordination compounds – theories. Chelate compounds. Biological and medical importance.
Definition of terms used in coordinative chemistry.
Stability of coordination compounds.
Stereochemistry of coordination compounds.
Isomerism in complexes
Chelate compounds
Definition of terms used in coordinative chemistry.
The d-block elements, some p-elements and some s-elements form coordination compounds or otherwise called complex compounds. Let us consider how these complex compounds are formed.
A coordinate bond is formed between A and B, when both bonding electrons are donated by one atom A+ B = A B
Examples: NH3 reacts with BCl3 to form the compound BCl3.NH3, because the unshared pair on nitrogen can be shared with the boron atom.
BCl3 +: NH3 Cl3B – NH3
Stability of coordination compounds.
The stability of coordination compounds is characterized by the stability of its complex ion. For the compound [Ag((NH3)2]Cl the process of dissociation is presented by the equations:
[Ag(NH3)2]Cl [Ag(NH3)2] + Cl-
[Ag(NH3)2] + ⇄ Ag++ 2NH3
The constant is sometimes referred to as the stability constant or association constant. The larger the formation constant, the more stable the complex.
The smaller the dissociation constant, the more stable the complex. Kf is inversely proportional to Kd.
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