Coordination compound notes

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Classification of ligands on the basis of bonding
Ligands are of two types ---

1. Loan pair donar
   They form sigma or single coordinate bond by donating loan pair to central metal atom. (as you read previous)
   
2. Pie- electron donar
   Those compound which contain pie-bond, may donate their pie electrons. They form no bond by donating their pie electron unless they regain their electron in their antibonding orbitals. While regain their pie electron, they form back bond named as Sinergic Bond with central metal atom.

Example :-

CH2CH2 (monodentate)
C6H6 (tridentate) represented by n-C6H6.	[Cr(C6H6)2] (dibenzene Chromium)

Sinergic Bonding
Sometimes electron may be transferred from filled orbitals of central atom to vacant orbitals of the ligands and this type of back bonding is known as Sinergic bonding.
On the basis of Sinergic bonding, ligands are of two types :--

1. Classical ligands
   They only donate pie bond to central atom and there is no back bonding.
   Example :- F^-, OH^-, H₂O, NH₃ etc.
   
2. Non-Classical ligands (pie-acid ligand)
   They donate pie electron but they form pie-bond with central atom by taking electron from filled orbital of central atom as Sinergic bonding.
   Example :-

   CO	vacant pie* (pie-antibonding orbital)		PH3	vacant d-orbital
   CN-			PF3
   NC-			PR3
   NO+			PPH3
   C2H4			H2S
   C6H6			CH3X (X-halogens)
   C5H5

   

   Question - When CO form coordination complex, bond length of CO increases. Explain.
   Answer -During Sinergic bonding, CO accept electron in pie^* (pie-antibonding orbital) due to which bond order decreases, hence bond length increases.

   ===> If Z-effect of central atom decreases, Sinergic bonding increases.

   
   

   Sidwick's EAN rule
   EAN = Effective atomic number.
   

   EAN = atomic number of central atom - Primary valancy (charge on central atom) + 2 * secondary valancy.

   Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	--------------------	36Kr
   Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	--------------------	54Xe
   La	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	--------------------	86Rn

   Central atom for coordination compound to achieve inert gas configuration of same period but it is not a necessary condition.
   Example :-
   K₄[Fe(CN)₆]
   EAN = atomic number of Fe - charge on Fe + 2 * secondary valency of Fe
   EAN = 26 - 2 + 2 * 6 = 36. (follow EAN rule)

   [Co(gly)3]	27 - 3 + 2 * 6 = 36
   [Ag(NH3)2]+	47 - 1 + 2 * 2 = 50
   [Fe(en)2ClBr]I	26 - 3 + 2 * 4 + 2 + 2 = 35

   Fact :- All the elements of 3-d series will form a metal carbonyl. They obey EAN rule.
   

   [Cr(CO)x] EAN = 36 36 = 24 - 0 - 2 * x x = 6. [Cr(CO)6]

   [Fe(CO)x] EAN = 36 36 = 26 - 0 + 2 * x x = 5. [Fe(CO)5]

   [Ni(CO)x] EAN = 36 36 = 28 - 0 + 2 * x x = 4. [Ni(CO)4]

   Hx[Co(CO)4] EAN = 36 36 = 27 -(-x) + 2 * 4 x = 1. H[Co(CO)4]

   EAN may be achieved in two ways :-
   A] By Redox Reaction :-
   
   • [Mn(CO)₅] ------- + e^- -------> [Mn(CO)₅]^- (act as oxidising agent)
     EAN for [Mn(CO)₅] is = 35 and that of [Mn(CO)₅]^- is = 36.
     Here reduction take place for Mn.
   B] By Dimerization :-
   
   • 2[Mn(CO)₅] --------------------------------> [Mn₂(CO)₁₀]
     EAN for [Mn(CO)₅] is = 35 and that of [Mn₂(CO)₁₀] is = 36.

     Organo Metallic compound
     M <------ C { C from alkyl, aryl or CO }.
     Example :-

     Compound	Organo Metallic
     [Cr(C6H6)2]	Yes
     [Fe(C5H5)2]	Yes
     [Ni(CO)4]	Yes
     [PtCl3(C2H4)2] Zesse's salt	Yes
     K4[Fe(CN)6]	No
     [CH3MgCl]	Yes
     [CH3ZnCl]	Yes

     Werner's Coordination theory :-
     

     1. In complex compound central atom shows two type of valancy :- 1] Primary valancy. 2] Secondary valancy.
        
     2. Primary valancy is satisfied by negative ion and secondary valancy is satisfied by negative, positive or neutral ion.
        
     3. Primary valancy is ionisable and non-directional whereas secondary valancy is non-ionisable and directional.
        Example :-
        CrCl₃.6H₂O. = Primary valancy (PV) = +3, Secondary valancy = 6.

        A) [Cr(H2O)6]+3Cl3 after ionisation, 4 ion will form	B) [Cr(H2O)5Cl]+2Cl2.H2O after ionisation, 3 ion will form	C) [Cr(H2O)4Cl2]+Cl.2H2O after ionisation, 2 ion will form
        dotted line indicates that here Cl only satisfied primary valancy and solid line satisfied secondary valancy.	here one Cl is joined by solid and dotted line which indicate that one Cl satisfied primary and secondary valancy both while other two satisfied only secondary valancy. One H2O molecule lie outside the coordination sphere.	here two Cl is joined by solid and dotted line which indicate that two Cl satisfied primary and secondary valancy both while other one satisfied only secondary valancy. Two H2O molecule lie outside the coordination sphere.
        Electrical conductance depend on no. of ion formed. If produced ions are same in number, then compound which contain higher charge, will have more Electrical Conductance. Electrical conductance ----- (A) > (B) > (C)
        We do not have to find exact value of electrical conductance. We have to just compare the electrical conductance. We have to compare how many ions will form after ionisation.
        You may think that why not all Cl come inside coordination sphere and put 3H2O outside the sphere. But you have to always remember that water molecule are neutral and it will not lie outside without any ion. As you see above in fig. 2 & 3, atleast one Cl atom lie outside the sphere so H2O lie outside. If all Cl lie inside sphere then there will no charge on sphere. Hence no attraction between sphere and H2O molecule.

        IUPAC name of Coordination Compound :-
        Name of complex if formula is given :-
        

        • Name of positive part written is followed by name of ligands.
          
        • For simple ion, we write its simple name.
          
        • In complex ion, name of ligands is written first followed by name of central atom.
          
        • There should be a single letter gap between name of cation and anion.
          
        • First letter of name should be capital.
        
        Example :- K₄[Fe(CN)₆] = Potassium hexacynoferrate.

        Rules for naming of Central atom :-
        

        • If coordination sphere is neutral or positively charged, then central atom is given its simple name followed by primary valancy in Roman numerals.
        
        Example :- [Cu(NH₃)₄]SO₄ = tetraaminecopper(ii)sulphate.
        • If coordination sphere is negatively charged, then the term 'ate' in the name of central atom is added.
        
        Example :- K₄[Fe(CN)₆] = Potassium hexacynoferrate.

        Atom	Name		Atom	Name
        Lead (Pb)	Plumbate		Vanadium (V)	Vanadate
        Tin (Sn)	Stanate		Chromium (Cr)	Chromate
        Boron (B)	Borate		Molybdenum (Mo)	Molybdate
        Aliminium (Al)	Aluminate		Manganese (Mn)	Manganate
        Scandium (Sc)	Scandanate		Iron (Fe)	Ferrate
        Titanium (Ti)	Titanate		Osmium (Os)	Osmate
        Cobalt (Co)	Cobaltate		Rhodium (Rh)	Rhodate
        Iridium (Ir)	Irridate		Nickel (Ni)	Nickilate
        Palladium (Pd)	Palladate		Platinum (Pt)	Platinate
        Copper (Cu)	Cuprate		Gold (Au)	Aurate
        Zinc (Zn)	Zincate		Cadmium (Cd)	Caddimate
        Mercury (Hg)	Mercurate		Ruthenium (Rh)	Rhodate

        Rules for naming of Ligands :-
        

        • Different ligands are arranged in alphabetical order.
          
        • Number of ligands is written in Greek numerals.
          Example :-
          2 - bi
          3 - tri
          4 - tetra etc.
          
        • If the name of ligand itself contain Greek numerals then for -
          2 - bis
          3 - tris
          4 - tetracis
          5 - pentacis etc.
          
        • Name of ligands depends on charge present
          
          1. Neutral ligands :-
             Simple name will written.
             Example :-
             

             CO -	carbonyl
             PH3 -	Phosphine
             PPH3 -	triphenylphosphine
             PMe3 -	trimethylphosphine
             C2H4 -	ethylene
             C6H6 -	benzene
             en -	ethylenediamine
             * H2O -	aqua
             * NH3 -	ammine
             Me-O-Me -	dimethylether
             Me-S-Me -	dimethylthioether

          2. Positive ligands :-
             the term 'ium' is added.
             Example :-
             NO⁺ = nitrosonium or nitrosylium
             N₂H₅⁺ = hydrazenium

          3. Negative ligands :-
             Till 2004, at the place of 'ide', 'o' is added but after 2004, at the place of 'ide', 'ido' is added.
             Like

             	till 2004	after 2004
             ide	o	ido
             ite	ito	ito
             ate	ato	ato

             ide - ido
             	Till 2004	After 2004
             Cl-	Chloro	Chlorido
             O2-	oxo	oxido
             O22-	peroxo	peroxido
             O2-	superoxo	superoxido
             O3-	ozonido	ozonido
             S2-	sulphido	sulphido
             N3-	azido	azido
             N3-	nitrido	nitrido
             OH-	hydroxo	hydrido
             ite - ito (it is same for before & after 2004)
             NO2-	nitrito
             ClO2-	chlorato
             SO32-	sulphito
             ate - ato (it is same for before & after 2004)
             SO42-	sulphato
             CO32-	carbonato
             C2O42-	oxalato
             CH3COO-	acetato
             gly-	glycenato
             dmg-	dimethylglyoximato
             acac-	acetylacetonato
             edta4-	ethylenediaminetetraacetato
             S2O32-	thiosulphato

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