Chemistry. Session. COORDINATION COMPOUNDS AND ORGANOMETALLICS - 1. Session Objectives. Werner’s coordination theory IUPAC nomenclature Isomerism in Coordination Compounds. Coordination compounds. Coordination compound, central metal ion, ligand, coordination sphere, coordination number.
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COORDINATION COMPOUNDS AND ORGANOMETALLICS - 1
Coordination compound, central metal ion, ligand, coordination sphere, coordination number
Metal has two types of valencies.
An isomer of CrCl3 6H2O reacts with one mole AgNO3 to give one mole of precipitate of AgCl. What is the compound?
Only those ions which are present outside the coordination sphere can be ionised.
[CrCl2(H2O)4]Cl . H2O + AgNO3 AgCl
Therefore the compound is [CrCl2(H2O)4]Cl.H2O.
Coordination entity: it constitutes a central atom/ion, usually of a metal, to which are attached a fixed number of other atoms or groups each of which is called a ligand.
For example [PtCl4]2- and [Fe(CN)6]3-.
Central atom/ion: in a coordination entity the atom/ion to which are bound a fixed number of ligands in a definite geometrical arrangement around it.
For example: Ni2+ in [NiCl2(OH2)4], Fe3+ in [Fe(CN)6]3-.
Coordination number: it is determined by the sigma bonds between the ligands and the central atom/ion.
For example coordination number in [Fe(CN)6]3- is six.
[Co(NH3)4 Cl (NO2)]K3[Fe(CN)6]
x + 4(o) + 1 (–1) + 1 (–1) = 0 3(1) + x + 6(–1) = 0
x = + 2 x = + 3.
The ligands are the ions or molecules bound to the central atom/ion in the coordination entity.
Ligands are Lewis base because they works as electron donor.
Ligands which can ligate through two different atoms present in it.
For example SCN- ion can coordinate through the sulphur or nitrogen atom.
Denticity and chelation: when coordination of more than one sigma electron pair donor group from the ligand to the same central atom/ion takes place, it is called chelation.
The number of such ligating groups indicate the denticity of the ligand, e.g., ethylenediamine, EDTA For example unidentate, didentate, terdentate tetradentate etc.
Pentaammineisothiocyanatocobalt (III) chloride
Tetraaquadichlorochromium (III) ion
Potassium tetraiodomercurate (II)
Sodium tetrafluorooxochromate (IV)
Bis(ethylenediamine)cobalt (III)- m - imido - m – hydroxo bis(ethylenediammine)cobalt (III) ion.
(i) Ag in Tollen’s reagent exists as Ag2O
2x + 1(–2) = 0
x = +1
(ii) 2x + 4(–2) + 2 × 0 = –2
x = +3
Follow IUPAC rules.
Write the formula of the following coordination compounds.
i. Bis(acetylacetonato) oxovanadium (IV)
ii. Pentaammine carbonatocobalt (III) chloride
iii. Sodium tetratacyanonitrosylsulphidoferrate (III)
iv. Dichlorobis (urea) copper (II)
Atomic number of cobalt is 27.As such Co3+ has 24 electrons. Each of the six NH3 will donate one pair of electron to cobalt. So EAN of Co3+ is 24 + 12 = 36.
(2) EAN of [Fe(CN)6]4–
26 – 2 + 2 × 6 = 36
(3) EAN of [Cu(NH3)4]2–
29 – 2 + 2 × 4 = 35
[Co(NH3)6] [Cr (CN)6] and [Cr(NH3)6] [Co (CN)6]
This type of isomerism occurs in ambidentate ligands like and CO.
[Co(NH3)5NO2]Cl2 and [Co(NH3)5ONO]Cl2
Coordination position isomerism
Write the type of isomerism in the compounds [Co(NH3)4Cl2]NO2 and [Co(NH3)4ClNO2]Cl.
As the two complexes give different ions in solution, they show ionization isomerism.
Complexes with general formula, Ma2b2
Complexes with general formula Ma2bc can have cis- and trans-isomers.
Complexes with general formula, Mabcd, can have three isomers.
Octahedral complexes of the type Ma4b2
Octahedral complexes of the type Ma3b3
three NH3 molecules can be situated (1) on the same face
of the octahedron (fac isomer) or (2) around a perimeter of the octahedron (mer isomer
(Where AA = Symmetrical bidentate ligand)
(Where AB = Unsymmetrical ligands)
A metal complex having composition Cr(NH3)4Cl2Br has been isolated in two forms (A) and (B). The form (A) reacts with AgNO3 to give a white precipitate readily soluble in dilute aqueous ammonia whereas (B) gives a pale yellow precipitate soluble in concentrated ammonia. Write the formula of (A) and (B) and state the hybridisation of chromium in each. Calculate the magnetic moment (spin only value).
Since A is readily soluble in dilute aqueous ammonia. It must have Cl-outside the coordination sphere I.e. its formula is [Cr(NH3)4ClBr] Cl
Similarly, form B gives pale yellow precipitate of AgBr which are sparingly soluble in NH4OH.
The state of hybridisation of chromium in both the complexes is d2sp3. Both the forms have chromium in +3 oxidation state.
As there are three unpaired electrons so magnetic moment
(a) No isomers are possible for a square planar complex of the type MA3B
(b) No isomers are possible for an octahedral complex of the type of MAB5.
(c). Cis and trans isomers are possible for a square planar complex of the type MA2BC.
(d). Cis and trans isomers are possible for an octahedral complex of the type MA4BC.