LECTURE 4 THEME: Complex compound in biological systems. associate prof. Dmukhalska Ye. B.

Outline Concept of complex compounds and complexing process. Nomenclature of complex compounds. Types of complexes Structure of complex compounds. Isomerism of complex compounds. Chemical bonds in complex compounds molecule Stability of complexes and influence of different factors on it Biological role of complex compounds. Usage of complexing in chemistry.

(usually metallic), Coordination compounds are the compounds in which the central atom (usually metallic), is linked to а number of ions or neutral molecules by coordinate bonds i.е. by donation of lone pairs of electrons by these ions or neutral molecules to the central metal atom. nickel tetracarbonyl, [Ni(CO) 4 ] A coordination complex

Complex compounds А) Structure CuSO NH 3 = [Cu (NH 3 ) 4 ] SO 4 [Cu (NH 3 ) 4 ] SO 4 Complex compound Cu 2+ - central atom NH 3 – ligand [Cu (NH 3 ) 4 ] 2+ - complex ion SO anion

Aqueous solutions that contain [Ni(H 2 O) 6 ] 2+, [Ni(NH 3 ) 6 ] 2+ and [Ni(en) 3 ] 2+ (from left to right). The two solutions on the right were prepared by adding ammonia and ethylenediamine, respectively, to aqueous nickel(II) nitrate.

Werner’s Theory Alfred Werner suggested in 1893 that metal ions exhibit what he called primary and secondary valences. Alfred Werner suggested in 1893 that metal ions exhibit what he called primary and secondary valences. –Primary valences were the oxidation number for the metal (+3 on the cobalt at the right). –Secondary valences were the coordination number, the number of atoms directly bonded to the metal (6 in the complex at the right).

Charge coordination number example of the metal ion +1 2 Ag +, Cu , 6 Cu 2+, Zn 2+, Pd 2+, Pt , 4 Pt 4+, Cr 3+, Co 3+, Fe Sn 4+ Co-ordination Werner’s theory

The species formed by linking of а number of ions or molecules by co-ordinate bonds to the central metal atom (or ion) carries positive or negative charge, it is called a complex ion (coordination sphera). [Fe(СN) 6 ] 4-, [Cu(NH 3 ) 4 ] 2+, [Ag(CN) 2 ] -

Coordination sphere. The central atom and the ligands which are directly attached to it are enclosed in square brackets and are collectively termed as the coordination sphere. The central atom and the ligands which are directly attached to it are enclosed in square brackets and are collectively termed as the coordination sphere.

Metal-Ligand Bond This bond is formed between a Lewis acid and a Lewis base. This bond is formed between a Lewis acid and a Lewis base. –The ligands (Lewis bases) have nonbonding electrons. –The metal (Lewis acid) has empty orbitals.

Transition metals act as Lewis acids Transition metals act as Lewis acids Form complexes/complex ions Form complexes/complex ions Fe 3+ (aq) + 6CN - (aq)  [Fe(CN) 6 ] 3- (aq) Ni 2+ (aq) + 6NH 3 (aq)  [Ni(NH 3 ) 6 ] 2+ (aq) Complex with a net charge = complex ion Complexes have distinct properties Lewis acid Lewis baseComplex ion Lewis acid Lewis base Complex ion

Coordination compound Coordination compound –Compound that contains 1 or more complexes –Example [Co(NH 3 ) 6 ]Cl 3 [Co(NH 3 ) 6 ]Cl 3 [Cu(NH 3 ) 4 ][PtCl 4 ] [Cu(NH 3 ) 4 ][PtCl 4 ] [Pt(NH 3 ) 2 Cl 2 ] [Pt(NH 3 ) 2 Cl 2 ]

The donor atoms, molecules or anions, which donate а pair of electrons to the metal atom and form co-ordinate bond with it are called ligands.

Ligands Ligands –classified according to the number of donor atoms –Examples monodentate = 1 monodentate = 1 bidentate = 2 bidentate = 2 tetradentate = 4 tetradentate = 4 hexadentate = 6 hexadentate = 6 polydentate = 2 or more donor atoms polydentate = 2 or more donor atoms chelating agents

Ligands Monodentate Monodentate –Examples: H 2 O, CN -, NH 3, NO 2 -, SCN -, OH -, X - (halides), CO, O 2- H 2 O, CN -, NH 3, NO 2 -, SCN -, OH -, X - (halides), CO, O 2- –Example Complexes [Co(NH 3 ) 6 ] 3+ [Co(NH 3 ) 6 ] 3+ [Fe(SCN) 6 ] 3- [Fe(SCN) 6 ] 3-

Ligands Bidentate Bidentate –Examples oxalate ion = C 2 O 4 2- oxalate ion = C 2 O 4 2- ethylenediamine (en) = NH 2 CH 2 CH 2 NH 2 ethylenediamine (en) = NH 2 CH 2 CH 2 NH 2 ortho-phenanthroline (o-phen) ortho-phenanthroline (o-phen) –Example Complexes [Co(en) 3 ] 3+ [Co(en) 3 ] 3+ [Cr(C 2 O 4 ) 3 ] 3- [Cr(C 2 O 4 ) 3 ] 3- [Fe(NH 3 ) 4 (o-phen)] 3+ [Fe(NH 3 ) 4 (o-phen)] 3+

Ligands oxalate ion ethylenediamine ortho-phenanthroline Donor Atoms: * ** * * * *

Ligands oxalate ion ethylenediamine O C M M N C H

Ligands

Chelation is a process in which a polydentate ligand bonds to a metal ion, forming a ring. The complex produced by this process is called a chelate, and the polydentate ligand is referred to as a chelating agent. Chelation is a process in which a polydentate ligand bonds to a metal ion, forming a ring. The complex produced by this process is called a chelate, and the polydentate ligand is referred to as a chelating agent. – ethylenediaminetetraacetate (EDTA) = (O 2 CCH 2 ) 2 N(CH 2 ) 2 N(CH 2 CO 2 ) 2 4- –Example Complexes [Fe(EDTA)] -1 [Fe(EDTA)] -1 [Co(EDTA)] -1 [Co(EDTA)] -1

EDTA Ligands * Donor Atoms * ** * **

EDTA Ligands C O N H M

Ligands

Some important characteristics of chelates. Some important characteristics of chelates. (i) Chelating ligands form more stable complexes than the monodentate analogs. This is called chelating effect. (i) Chelating ligands form more stable complexes than the monodentate analogs. This is called chelating effect. (ii) Chelating ligands, which do not contain double bonds e.g. ethylenediamine form five membered stable rings. The chelating ligands such as acetylacetone form six membered stable ring complexes. (ii) Chelating ligands, which do not contain double bonds e.g. ethylenediamine form five membered stable rings. The chelating ligands such as acetylacetone form six membered stable ring complexes. (iii) Ligands with large groups form unstable rings than the ligands with smaller groups due to steric hindrance. (iii) Ligands with large groups form unstable rings than the ligands with smaller groups due to steric hindrance.

The complexes formed by Cu (II) and Pt (II) ions with ethylenediamine are metal chelates represented as follows: The complexes formed by Cu (II) and Pt (II) ions with ethylenediamine are metal chelates represented as follows:

Coordination number The number of ligand donor atoms that surround a central metal ion in a complex is called the coordination number of the metal The number of ligand donor atoms that surround a central metal ion in a complex is called the coordination number of the metal Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds. Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds. [Ag(СN) 2 ] -, [Cu(NН 3 ) 4 ] 2+ and [Cr(Н 2 О) 6 ] 3+ [Ag(СN) 2 ] -, [Cu(NН 3 ) 4 ] 2+ and [Cr(Н 2 О) 6 ] 3+

Common Geometries of Complexes Linear Coordination Number Geometry 2 Example: [Ag(NH 3 ) 2 ] +

Common Geometries of Complexes Coordination Number Geometry 4 tetrahedral square planar Example: [Ni(CN) 4 ] 2- Examples: [Zn(NH 3 ) 4 ] 2+, [FeCl 4 ] -

Common Geometries of Complexes Coordination Number Geometry 6 octahedral Examples: [Co(CN) 6 ] 3-, [Fe(en) 3 ] 3+

Charge on the complex ion. The charge carried by а complex ion is the algebraic sum of the charges carried by central metal ion and the ligands coordinated to the central metal ion. The charge carried by а complex ion is the algebraic sum of the charges carried by central metal ion and the ligands coordinated to the central metal ion. [Ag (CN) 2 ]- [Ag (CN) 2 ]- [Cu (NH 3 ) 4 ] 2+ [Cu (NH 3 ) 4 ] 2+

[Fe(CN) 6 ] 3- Complex charge = sum of charges on the metal and the ligands

[Fe(CN) 6 ] 3- Complex charge = sum of charges on the metal and the ligands +3 6(-1)

[Co(NH 3 ) 6 ]Cl 2 Neutral charge of coordination compound = sum of charges on metal, ligands, and counterbalancing ions neutral compound (0) 2(-1)

Oxidation number or oxidation state. It is а number that represents an electric charge which an atom or ion actually has or appears to have when combined with other atoms, oxidation number of copper in [Cu(NH 3 ) 4 ] 2+ is +2 but coordination number is 4. oxidation number of Fe in [Fe(СN) 6 ] 3- is + 3 but the coordination number is 6. (i) [Cu (NН З ) 4 ]SO 4. (ii) Fe in [Fe (СN) 6 ] 3- (iii)К 3 [Fe(С 2 О 4 ) 3 ]. (iv) [Ni(CO) 4 ].

[Co(NH 3 ) 6 ]Cl 2 Neutral charge of coordination compound = sum of charges on metal, ligands, and counterbalancing ions neutral compound (0) 2(-1)

Nomenclature of Coordination Compounds: IUPAC Rules The cation is named before the anion The cation is named before the anion When naming a complex: When naming a complex: –Ligands are named first alphabetical order alphabetical order –Metal atom/ion is named last oxidation state given in Roman numerals follows in parentheses oxidation state given in Roman numerals follows in parentheses –Use no spaces in complex name

Naming Coordination Compounds

Names of Some Common Metallate Anions

Names of Some Common Ligands

Examples of Complexes with Various Coordination Numbers

[Co(NН 3 ) 6 ]Cl 3, hexaamminecobalt (III) chloride. [Co(NН 3 ) 6 ]Cl 3, hexaamminecobalt (III) chloride. K 2 [PtCl 6 ], potassium hexachloroplatinate (IV). K 2 [PtCl 6 ], potassium hexachloroplatinate (IV). [Co(NO 2 )(NH 3 ) 3 ], triamminetrinitrocobalt (III) [Co(NO 2 )(NH 3 ) 3 ], triamminetrinitrocobalt (III) [PtCl 4 (NH 3 ) 2 ], diamminetetrachloroplatinum (IV). [PtCl 4 (NH 3 ) 2 ], diamminetetrachloroplatinum (IV).

Types of complexes. (i) А complex in which the complex ion carries а net positive charge is called cationic complex: [Co(NН 3 )] 3+, [Ni(NH 3 ) 6 ] 2+ (i) А complex in which the complex ion carries а net positive charge is called cationic complex: [Co(NН 3 )] 3+, [Ni(NH 3 ) 6 ] 2+ (ii) А complex in which the complex ion carries а net negative charge is called anionic complex: [Ag(CN) 2 ] -, [Fe (CN) 6 ] 4- (ii) А complex in which the complex ion carries а net negative charge is called anionic complex: [Ag(CN) 2 ] -, [Fe (CN) 6 ] 4- (iii) А complex carrying no net charge is called а neutral complex or simply а complex: (iii) А complex carrying no net charge is called а neutral complex or simply а complex: [Ni(CO) 4 ], [CoCl 3 (NН 3 ) 3 ] [Ni(CO) 4 ], [CoCl 3 (NН 3 ) 3 ]

1. With one central atom Ammonia complex [Cu(NH 3 ) 4 ]SO 4 Aqua complex[Al(H 2 O) 6 ]Cl 3 acidic complex K 2 [PtCl 4 ] complex with difference ligands K[Pt(NH 3 )Cl 3 ] cyclic (chelates) Polycentral compoynds Chain [Cr(NH 3 ) 5 – OH – (NH 3 )Cr]Cl 3 chelaes (CO) 5 Mn – Mn(Co) 5 Main types of complex compounds Me O O O O C C NH 2 CH 2 C O N N H2CH2C HOOC COOH CH 2 Me H2CH2C CH 2 C O O O

Isomerism Isomers Isomers –compounds that have the same composition but a different arrangement of atoms Major Types Major Types –structural isomers –stereoisomers

Structural Isomers Structural Isomers Structural Isomers –isomers that have different bonds Coordination-sphere isomers Coordination-sphere isomers –differ in a ligand bonded to the metal in the complex, as opposed to being outside the coordination-sphere Example Example [Co(NH 3 ) 5 Cl]Br vs. [Co(NH 3 ) 5 Br]Cl

Coordination-Sphere Isomers Example Example [Co(NH 3 ) 5 Cl]Br vs. [Co(NH 3 ) 5 Br]Cl Consider ionization in water Consider ionization in water [Co(NH 3 ) 5 Cl]Br  [Co(NH 3 ) 5 Cl] + + Br - [Co(NH 3 ) 5 Cl]Br  [Co(NH 3 ) 5 Cl] + + Br - [Co(NH 3 ) 5 Br]Cl  [Co(NH 3 ) 5 Br] + + Cl - [Co(NH 3 ) 5 Br]Cl  [Co(NH 3 ) 5 Br] + + Cl -

Coordination-Sphere Isomers Example Example [Co(NH 3 ) 5 Cl]Br vs. [Co(NH 3 ) 5 Br]Cl Consider precipitation Consider precipitation [Co(NH 3 ) 5 Cl]Br(aq) + AgNO 3 (aq)  [Co(NH 3 ) 5 Cl]NO 3 (aq) + AgBr(s) [Co(NH 3 ) 5 Br]Cl(aq) + AgNO 3 (aq)  [Co(NH 3 ) 5 Br]NO 3 (aq) + AgCl(aq)

Structural Isomers Linkage isomers Linkage isomers –differ in the atom of a ligand bonded to the metal in the complex Example Example –[Co(NH 3 ) 5 (ONO)] 2+ vs. [Co(NH 3 ) 5 (NO 2 )] 2+

Linkage Isomers

Stereoisomers –Isomers that have the same bonds, but different spatial arrangements Geometric isomers Geometric isomers –Differ in the spatial arrangements of the ligands –Have different chemical/physical properties different colors, melting points, polarities, solubilities, reactivities, etc. different colors, melting points, polarities, solubilities, reactivities, etc.

cis isomertrans isomer Pt(NH 3 ) 2 Cl 2 Geometric Isomers

cis isomer trans isomer [Co(H 2 O) 4 Cl 2 ] + Geometric Isomers

Stereoisomers Optical isomers Optical isomers –isomers that are nonsuperimposable mirror images said to be “chiral” (handed) said to be “chiral” (handed) referred to as enantiomers referred to as enantiomers –A substance is “chiral” if it does not have a “plane of symmetry”

mirror plane cis-[Co(en) 2 Cl 2 ] + Example 1

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