Coordination Compounds Notes PDF

# Coordination Compounds ## Introduction * Coordination compounds: * textile dyeing * medicinal chem * electroplating * industrial catalyst * analytical reagents * metallurgical processes * Chlorophyll * Haemoglobin * Vit B12 * c.c of Mg, Fe and Co. ##...

# Coordination Compounds ## Introduction * Coordination compounds: * textile dyeing * medicinal chem * electroplating * industrial catalyst * analytical reagents * metallurgical processes * Chlorophyll * Haemoglobin * Vit B12 * c.c of Mg, Fe and Co. ## Werner's theory of Coordination compounds * Alfred Werner - Swiss chemist - Ist to formulate strl. of c.c. * Proposed the concept of 1°, 2° valence for a metal ion. * Ex: I valence - CrCl3 - 3 * PdCl2 - 2 * Exp: On addition of excess AgNO3 in cold, * Series of compound of CoCl3 with NH3 precipitated AgCl * 1 mol CoCl3.6NH3 → 3 mol AgCl * 1 mol CoCl3.5NH3 → 2 mol AgCl * 1 mol CoCl3.4NH3(green) → 1 mol AgCl * 1 mol CoCl3.4NH3(violet) → 1 mol AgCl. * Here 6 grps in all (either Cl or NH3 or both) remain bonded to cobalt ion during the reaction. The compounds are formulated: * Sol. conductivity corresponds: | Colour | Formula | Electrolyte | |---|---|---| | Yellow | [Co(NH3)6]3+ 3Cl- | 1:3 | | Purple | [CoCl(NH3)5]*2Cl- | 1:2 | | Green | [CoCl2 (NH3)4] "Cl2- | 1:1 | | Violet | [COCl2 (NH3)4]+CI- | 1:1 | ## Werner's Theory of Coordination Compounds * In 1898, Werner propounded his theory of c.c with 4 postulates: * In c.c metals show two types of linkages (valences) - primary and secondary * Primary valences are normally ionizable and are satisfied by negative ions. * Secondary valences are non ionizable * bound directly to metal. * equal to coordination number and is fixed for a metal. * satisfied by neutral molecules or negative ions. * Ions/groups bound by secondary linkages to the M have characteristic spatial arrangement/coordination polyhedra corresponding to different coordination no. * Geometrical shapes for different transition metals * Octahedral - [Co(NH3)6]3+, [CoCl(NH3)5] 2+, [COCl2 (NH3)4] * Tetrahedral - [Ni(CO)4] * Square Planar - [PtCl4]2- ## Difference between :- * **DOUBLE SALT** * Dissociates into simple ions in H2O completely. * Ex: Potash Alum - KAI [SO4]2.12 H2O * Mohr's Salt - FeSO4 (NH4)2 SO4.6H2O * Carnallite - RCI.MgCl2.6H20 * **COORDINATION COMPLEX** * Doesn't dissociate into ions. * Ex: [Fe(CN)6]4- * [CO(NH3)6]3+ ## Definitions of some imp. terms pertaining to coordination compounds: **A) Coordination Entity** * Central metal atomlion bonded to fixed no. of ions/molecules * Ex: [Ni(CO)4], [COCl3 (NH3)3], [Fe(CN)6]4- **B) Central atom/ion** * The atomlion to which fixed no. of ions/grps are bound in definite geometrical arrangement. * Also referred to as Lewis acids. * Ex: [NiCl2(H2O)4] → Ni2+ [Fe(CN)6]3- → Fe3+ **C) Ligands** * The ion /molecule bound to central atomlion. * Ex: Simple ions - Cl- Small molecules - H2O, NH3 Large molecules - N(CH2CH2NH2) Macromolecules - proteins * Types: 1. Unidentate - bound through I donor (Cl, H2O.NH3) 2. Didentate - " " " 2 donors (en, ox) 3. Polydendate - " " " many " " [N(CH2CH2NH2)3, EDTA] * en - ethane -1,2-diamine (H2N), CH2CH2NH2) * ox-oxalate [C2O42-] * EDTA - ethylene diammine tetra acetate (4 Oxygen. 2 nitrogen) - CH2COO - H2C - N - CH2COO - H2C - CH2COO - N ## In di- or polydentate ligand * **DENDICITY** * (no. of ligating grps present) * **Chelate** * 2 or more donor atom simultaneously bind to single metal ion. * Chelate complexes are more stable. * Ex: en which bonds to metal ion ↑ each of the 2 nitrogens. * **Ambidentate** * Either of the donor atoms ligetes in the complex. * Ex: NO2- , SCN- * M≡N≡O * M≡S≡C≡N **D) Coordination number (<span style="text-decoration: overline;">CN</span>)** * <span style="text-decoration: overline;">CN</span> of a metal ion is the no. of ligand donor atoms to which the metal is directly bonded. * Ex: * [PtCl6]2- - 6 * [Ni(NH3)4]2+ - 4 * [Fe(C2O4) 3]3- - 6 * [CO(en)3]3+ - 6. * [Didendate] * Only the no of sigma bonds formed by the ligand with the central ion (atom) is counted. **E) Coordination sphere** * The central atomlion + ligands are enclosed in the square bracket and called coordination sphere. * Ionisable ion outside the bracket - counter ion. * Ex: K4[Fe(CN)6] - [Fe(CN)6]4- coordination sphere * K+ counter ioD. **F) Coordination polyhedron** * Spatial arrangement of ligand atoms directly attached to central atomlion. L L L L L L L L L L L L | | | | | | | | | | | _ _ _ M _ _ _ | | | | | | | | | | | L - M - L | | | | | | | | | | | L L L L L L L L L L L L L L L L _ _ _ M _ _ _ | | | | | | | | | | | L L L L L L L L L L L L L L L L L L L L L L L | | | | | | | | | | | _ M _ | | | | | | | | L L L L L L * Octahedral - [Co(NH3)6]3+ * Tetrahedral - [Ni(CO)4] * Square Planar - [PtCl4]2- * Trigonal bipyramidal * Square pyramidal **G) Oxidation No. of Central Atom** * Charge it would carry if all the ligands are removed along with the co pairs that are shared with central atom. * Represented by roman numeral in parenthesis. * Ex: [CO (CN)4] 3- → CU(I) **H) Homoleptic and heteroleptic complexes** * Complexes in which a metal is bound to only one kind of donor groups - Homoleptic [Co(NH3)6]3+ * Complexes in which a metal is bound to more than one kind of donor groups - Heteroleptic [Co(NH3)4C12] + ## Some common ligands & their charge: | Name | Formula | Donor Atom | Charge | |------|--------------|-------------|--------| | Water | H2O | O | 0 | | Ammonia | NH3 | N | 0 | | Pyridine | C6H5N | N | 0 | | Carbonyl | CO | C | 0 | | Nitrosyl | NO | N | 0 | | Triphenyl phosphine | (C6H5)3 P | P | 0 | | Halide ion | X- | X | -1 | | Hydroxide ion | OH- | O | -1 | | Cyanide ion | CN- | N or C | -1 | | Nitto | NO2- | N | -1 | | Nitrito | ONO- | N | -1 | | Oxide ion | O2- | O | -2 | | Thiocyanate | SCN- | S or N | -1 | | Acetate | CH3COO- | O | -1 | | Carbon monoxide | CO | C | 0 | | Sulphate ion | SO42- | S | -2 | | en | | | 0 | | Ox | | | -2 | | EDTA | | | -4 | ## Note * Central Atom * [Pd(NH3)4]Cl2→ Counter ion ↑ Ligand Coordination entity - oxi. no. of Pd → 2 + 0 - 2 = 0 ... x = 2 - homdeptic - CN = 4. ## Nomenclature of coordination compounds #### **i) Formulas of mononuclear coordination entities** 1. Central Atom is listed first. 2. Ligands are listed in alphabetical order. 3. Polydendate ligands are also listed alphabetical. For abbreviated ligands, first letter of abbreviation is used. 4. Enclosed in square brackets. Ligands abb. or polyatomic ions are enclosed in parenthesis. 5. There should be no space blw ligands & metalg in coordination sphere. 6. Charge is indicated outside the [ as a right superscript with the number before the sign. 7. The charge of the cation(s) is balanced by the charge of the anion(s). #### **ii) Naming of mononuclear coordination compounds:** 1. The cation is named first in both positively and negatively charged coordination enities. 2. Ligands are named in alphabetical order before name of central atomlion. 3. Name of anionic ligands - end in * "-ate" - neutral, cationic ligands - same [Exception - H2O - Aqua, NH3 - ammine, CO- carbonyl, NO - nitrosyl] 4. Prefix - mono, di, tri... to indicate no. of individual ligands * Prefix - bis, tris, tetrakis to indicate ligands that have numerical prefix. 5. oxi. state of metal is represented by roman numeral in parenthesis. 6. In cationic complex - metal is named same as the element. * In anionic " " - name of metal ends with suffix -ate. * Exception - te - Ferrate * Ag - Argentate 7. name of counter ion. * at first - anionic complex. * at last - cationic complex. ## Examples: 1. [Cr(NH3)3(H2O)3]Cl3 * Complex is cationic * Ligands - Ammine (3), Aqua (3) * Calculate the oxi state of Cr x-0-0-3=0 x =+3 So, triammine triaquachromium (III) chloride. 2. [Co(H2NCH2CH2NH2)3]2(SO4)3 * complex - cationic. * Ligands - en (3) * oxi state 2x-0-6 = 0 ⇒ x = +3 So, tris (ethane-1,2-diamine) cobalt (III) sulphate. 3. [Ag(NH3)2][Ag(CN)2] [Ag(NH3)2]+[ Ag (CN)2]- ↓ x-0=1 x=1 ↓ x-2=-1 x = 1 diamminesilver (I) diayanidoargentate (I) 4. K3[Cr(C204)3] - Potassium trioxalato chromate (III) 5. Tetracarbonyl nickel (0) - [Ni(CO)4] 6. Dichloridobis (ethane-1,2-diamine) coball(III)chloride - [CoCl2(en)2] Cl. ## Bonding in Coordination Compounds * Nature of bonding in c.c * VBT (Valence Bond Theory) * LFT (Ligand Field theory) * CFT (crystal field theory) * MOT (Molecular Orbital theory). ## Valence bond theory * Metal atom/ion under the influence of ligands can use (n-1)d, ns.np or nsinpind orbitals for hybridization to yield a set of equivalent orbitals of definite geometry. * Hybridised orbitals are allowed to overlap with ligand orbitals. | CN | Type of hybridisation | Distribution of hybrid orbitals | |---- | --------------------- | ------------------------------ | | 4 | sp³ | tetrahedral | | 4 | dsp² | Square Planar | | 5 | sp³d | Trigonal Bipyramidal | | 6 | sp³d² (ooc) | Octahedral | | 6 | d²sp³ (ioc) | Octahedral | ## Magnetic behaviour * Paramagnetic - unpaired eo. * Diamagnetic-no unpaired eo ## Hybridisation * d²sp³- inner orbital / low spin / spin paired complex. * sp³d²-outer orbital / high spin Ispin free complex ## Magnetic moment y = √n (n+1) BM. ## Magnetic properties: * 3d series * Ti 3+ (d'), v³+ (d2), Cr3+ (d3) - 2 vacant d orbitals are available for octahedral hyb. with 4s & 4p. * d4 (Cr2+, Mn3+), d5 (Mn2+, Fe3+, (Fe2+, CO3+) - cases, we get vacant d orbitals by pairing 3d eo leaving 2, 1, 0 unpaired eo. * Due to Ioc * [Mn (CN)6]3- - 2 unpaired eo (IOC) * [Mn C16 J3- - 4 " " (OOC) * [Fe(CN)6]3-- 1 " " (IOC) * [Fe F6] 3- - 5 " " (OOO) * [COF6J3- - 4 " " (OOO) * [CO(C204)3]³ - 0 " " (IOC) ## Examples: 1. [Co(NH3)6]3+ | | | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------|---------|---------| | 27 Co | 1L | 1L | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | | ↑ | ↓ | ↑ | | | | | | | | | ↑ | | ↑ | | | | | | | | | ↑ | | ↑ | | | | | | | | | ↑ | | ↑ | | | | | | | | | ↑ | | ↑ | | | | | | | | | ↑ | | ↓ | | | | | | | | | ↑ | | | | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | | NH3 | NH3 | NH3 | NH3 | NH3 | NH3| NH3| NH3| NH3| | | ↑ | ↑ | ↑ | | | | | | | | | ↑ | ↑ | ↑ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | | | ↓ | ↓ | ↓ | | | | | | | | | d2 | | | d2 | d2 | d2 | d2 | d2 | d2 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | * Oxi state of Co in [Co(NH3)6]3+ x-0=3 x = +3 * Co3+ | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------| | 27 Co | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↓ | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↓ | | | | | | | ↑ | | | | | | | * [CO(NH3)6]3+ * Hyb: d2sp3 (IOC) * Geometry: Octahedral * Magnetic: Diamagnetic ## 2. [COF6] 3- | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------| | 27 Co | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↓ | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↓ | | | | | | | ↑ | | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | ↑ | ↑ | ↑ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | | | ↓ | ↓ | ↓ | | | | | | | | | d2 | | | d2 | d2 | d2 | d2 | d2 | d2 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | * Oxi state of Co in [COF6] 3- x-6 = -3 x = +3 * Co3+ | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------| | 27 Co | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↓ | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↓ | | | | | | | ↑ | | | | | | | * [COF6]3- | | | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------|---------|---------| | 27 Co | 1L | 1L | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | | ↓ | ↓ | ↓ | ↑ | ↑ | ↑ | ↑ | ↑ | ↑ | | | ↓ | ↓ | ↓ | ↑ | ↑ | ↑ | ↑ | ↑ | ↑ | | | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | | | d2 | | | d2 | d2 | d2 | d2 | d2 | d2 | * sp3d2 (ooc), Octahedral, Paramagnetic * μ = √4x5 = √20 ## 3.[NiCl4]2- | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------| | 28 Ni | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↓ | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↓ | | ↓ | | | | | | | | | | | | | | * Oxi state of Ni in [NiCl4]2- x-4=-2 x=2 * Ni +2 | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------| | 28 Ni | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↓ | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↓ | | ↓ | | | | | | | | | | | | | | * [NiCl4]2- | | | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------|---------|---------| | 28 Ni | 1L | 1L | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | | ↓ | ↓ | ↓ | ↑ | ↑ | ↑ | ↑ | ↑ | ↑ | | | ↓ | ↓ | ↓ | ↑ | ↑ | ↑ | ↑ | ↑ | ↑ | | | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | | | d2 | | | d2 | d2 | d2 | d2 | d2 | d2 | * sp3, Tetrahedral, Paramagnetic, μ = √2x3 = √6, high spin complex. ## 4. [Ni(CN)4]2- | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------| | 28 Ni | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↓ | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↓ | | ↓ | | | | | | | ↓ | | | | | | | * Oxi State of Ni in [Ni(CN)4]2- x-4=-2 ⇒x=2 * Ni+2 | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------| | 28 Ni | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↑ | ↑ | | | | | | | ↑ | ↓ | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↑ | | ↑ | | | | | | | ↓ | | ↓ | | | | | | | | | | | | | | * [Ni(CN)4]2- | | | | | | | | | | | |---------|---------|---------|---------|---------|---------|---------|---------|---------|---------| | 28 Ni | 1L | 1L | 1L | 1L | 1L | 1L | 1L | 1L | 1L | | | 3d | 4s | 4p | | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | | ↑ | ↑ | ↑ | | | | | | | | | ↓ | ↓ | ↓ | ↑ | ↑ | ↑ | ↑ | ↑ | ↑ | | | ↓ | ↓ | ↓ | ↑ | ↑ | ↑ | ↑ | ↑ | ↑ | | | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | ↓ | | | d2 | | | CN | CN | CN | CN | CN | CN | * dsp² (Low spin complex) * diamagnetic * Square planar. ## Limitations of VBT * Involves a no. of assumptions. * Dosen't give quantitative interpretation of magnetic data. * Dosen't explain colour of C.C. * Dosen't give quantitative interpretation of thermodynamic, Kinetic Stabilities of C.C. * Dosen't distinguish blw weak & strong ligands. * Dosen't make exact predictions regarding tetrahedral & square planar stt/. OF 4-C.C. ## Crystal Field Theory * Considers metal-ligand bond to be ionic. * Ligands - point charges (anions) * Point dipole (neutral) * 5 d orbitals - degenerate * When negative Field surrounding M➝ symmetrical → degeneracy is maintained. * When regative Field is due to ligands → asymmetrical → degeneracy is lifted → splitting of d orbitals. ## A) Crystal Field splitting in octahedral coordination entities * 6 ligands surround the metal atomlion. * Repulsion blw eo in d-orbitals and e in ligands. * Max when a orbital is directed towards ligand. So, dx²-y², dzz experience more repulsion. * Min when d orbital is away from the ligand. So, day, dyz