Title COORDINATION COMPOUNDS.pdf ✅

 Digital www.allendigital.in [ 121 ] Introduction and terminology and classification of ligands Introduction (a) The concept of coordination compounds arises from the complex formation tendency of transition elements. (b) These compounds play a vital role in our lives. Haemoglobin of blood and chlorophyll of plants are also coordination compounds of Fe, Mg respectively. Type of compounds Molecular or Addition Compounds (a) When two or more simple salts are chemically combined together in fixed proportion by weight the molecular or addition compounds are formed. (b) Some common examples are as follows. K2SO4 + Al2(SO4)3 + 24H2O K2SO4.Al2(SO4)3. 24H2O Alum (c) Depending upon the behaviour in an aqueous solution they are of two types (i) Double salt (ii) Coordination or complex compounds. (I) Double Salt The addition compounds which loose their identity in aq. solution and get completely ionised in water. Ex. (i) K2SO4.Al2(SO4)3.24H2O (Potash Alum) (ii) FeSO4(NH4)2SO4.6H2O (Mohr's salt) (iii) KCl.MgCl2.6H2O (Carnallite) (II) Coordination or Complex Compounds (i) Those molecular or addition compounds which retain their identity in aq. solution or loose the identity of constituents are called complex salt. (ii) Complexes retain their identity in aqueous solution. i.e., they do not dissociate into separate ion. K4[Fe(CN)6] 4K+ + [Fe(CN)6] –4 H2O Potassium ferrocyanide Ferrocyanide ion (iii) On the basis of type of ligands complex compounds are divided as follows : (i) Homoleptic complexes : Complex in which all the ligands are identical is called homoleptic complex. Ex. [Co(NH3)6] +2 (ii) Heteroleptic complexes : Complex in which all the ligands are not identical is known as heteroleptic complex. Ex. [Fe(en)2Cl2] +1 Coordination Compounds 03
NEET : Chemistry [ 122 ] www.allendigital.in  Digital Terminology of complex compounds (A) Complex Ion/Coordination sphere (a) An aggregate of metal ion with anions, cation or neutral molecules is called as complex ion. (b) It is a non-ionisable part of complex compound. (B) Central Metal Ion (a) The metal ion which forms complex ion in combination with anions, cation or neutral molecules is called as central metal ion. (b) Central metal ion acts as an electron pair acceptor and forms coordinate bonds with donor species. (c) Generally belongs to d block because d block elements have tendency to form complex due to their high charge density and availability of vacant orbitals. (C) Coordination Number The total number of coordinate bonds formed by central metal ion with donor species is called as coordination number of central metal ion. (D) Ionisation Sphere The part of complex compound which get ionised is known as ionisation sphere. Central metal ion Coordination sphere [Cu(NH3)4]SO4 Ionization sphere Ligand Coordination number [Cu(NH3)4]SO4 (E) Oxidation State It is a number which represents the electrical charge on the central metal atom of a complex ion. Ex. the oxidation number of Fe, Co and Ni in [Fe(CN)6] 4– , [Co(NH3)6] 3+ and Ni(CO)4 is +2, +3 and zero respectively. (F) Charge On the Complex Ion It is the algebraic sum of the total charge of the donor species and central metal ion. (G) Ligands (a) The anions, cation or neutral molecules which combine with central metal ion to form complex ion are called as ligands. (b) They act as electron pair donor (Lewis bases) which donate e– pair to central metal ion and form coordinate bonds. (c) Number of e– pair donated by a ligand to central metal ion is equal to its denticity. (H) Naming of ligands (a) o-suffix is used in the name of anionic ligands. (b) ium-suffix is used in the name of cationic ligands.
Coordination Compounds  Digital www.allendigital.in [ 123 ] Classification of ligands :- On the basis of denticity. 1. Monodentate ligands : Which donate one e– pair to the central metal ion. Neutral monodentate ligands NH3 ammine H2O aqua NO nitrosyl PH3 phosphine PPh3 triphenyl phosphine O2 dioxygen N2 dinitrogen CH3–OH methyl alcohol CH3–NH2 methyl amine NH2CONH2 urea NH2NH2 hydrazine CH3–O–CH3 dimethyl ether CO carbonyl CS thiocarbonyl Cationic monodentate ligands : O2 + oxygenium NO+ nitrosylium or nitrosonium NO2 + nitronium N2H5 + hydrazinium Anionic monodentate ligands : F – Fluorido / fluoro Cl– Chlorido / chloro Br– bromido / bromo I – iodido / iodo O –2 oxido/oxo S –2 sulphido/sulpho OH– hydroxido / hydroxo O2 – superoxido / superoxo O2 –2 peroxido / peroxo N –3 nitrido N3 – azido (NH2) – amido NH–2 imido H – hydrido
NEET : Chemistry [ 124 ] www.allendigital.in  Digital 2. Bidentate ligands : Ligands which donates two e– pair to the central metal ion. Ligands having denticity 2 or more than 2 form a stable ring with central metal ion that's why they are known as chelating ligands. no. of rings = Denticity – 1 NH2 – CH2 – CH2 – NH2 M+ ⋅⋅ ⋅⋅ Ethylene diamine (en) M+ dipyridyl (dipy) N N O O O O – – M+ oxalate(ox) or C2O4 –2 H2N — CH2 — C M+ glycinato(gly)– (unsymmetrical) O O– CH3–C = CH–C–CH3 M+ acetyl acetonato (acac)– O– O CH3–C= N M+ dimethyl glyoximato (dmg)– O– O CH3–C= N H 3. Polydentate ligands CH2—CH2—NH—CH2—CH2 M+ Diethylenetriamine(dien) Tridentate H2N NH2 CH2—CH2—NH—CH2—CH2— NH—CH2—CH2 M+ Triethylenetetraamine (trien) Tetradentate H2N NH2 N—CH2—CH2—N Ethylene diaminetetraacetato (EDTA4–) Hexadenatate CH2—COO– –OOC— CH2 – CH2—COO– OOC— CH2 4. Ambidentate ligand: Ligands which have two different donor atoms but at one time one donor atom can donate electron pair are called ambidentate ligands. Ambidentate ligands have same molecular formula but have different donor atom. (i) M C N   cyanido (CN) M N C   isocyanido(NC) (ii) M O C N  −  cyanato / cyanato-O M N C O   − isocyanato / cyanato-N (iii) M S C N  −  Thiocyanato / Thiocyanato-S M N C S   − Isothiocyanato/thiocyanato-N