Coordination compounds

Transcription

1 Coordination compounds Compounds those contain one or more coordination bond (donor-acceptor bound) are named coordination compounds, complex compounds or complexes. Artūras Kašauskas 1

2 Covalent bond N 2 + 3H 2 2NH 3 Artūras Kašauskas 2

3 Coordination bond It occurs when interacting atoms donate different numbers of electrons for the formation of covalent bond: H + H +.. H.. + : N:.. H H: N:.. H H H There is no dislocation of charge in coordination bonds. Artūras Kašauskas 3

4 Coordination compounds NH 3 + HCl = [NH 4 ]Cl AgCl + 2NH 3 = [Ag(NH 3 ) 2 ]Cl Fe() 2 + K() 4 = K 4 [Fe() 6 ] CrCl 3 + 6H 2 O = [Cr(H 2 O) 6 ]Cl 3 Artūras Kašauskas 4

5 Structure of coordination compounds Coordination compounds consist of inner sphere (coordination sphere) and outer (second) sphere. Coordination sphere consist of central atom and ligands. There are coordination bonds between central atom and ligands. Outer sphere consists of usual ions. There are ionic bounds between inner and outer sphere. Artūras Kašauskas 5

6 Structure of coordination compounds (2) Central atom Ag + Fe 2+ Cr 3+ Ligand NH 3 - H 2 O Inner sphere [Ag(NH 3 ) 2 ] + [Fe() 6 ] 4- Cr(H 2 O) 6 ] 3+ Outer sphere Cl - K + Cl - Coordination compound [Ag(NH 3 ) 2 ]Cl K 4 [Fe() 6 ] Cr(H 2 O) 6 ]Cl 3 Artūras Kašauskas 6

7 Coordination number Coordination number is a number of ligands surrounding the central atom. It depends on ionic charge of central atom Central atoms Coordination number Coordination compounds Ag +, Cu + 2 [Ag(NH 3 ) 2 ]Cl Cu 2+, Fe 2+ 4 (rarely 6) K 4 [Fe() 6 ] Fe 3+, Cr 3+, 6 (rarely 4) [Cr(H 2 O) 6 ]Cl 3 Sn 4+, Pt 4+ 6 (rarely 8) Na 2 [Sn(OH) 6 ] Artūras Kašauskas 7

8 Valence-bond method Formation of coordination compounds could be explained using a valence-bond method. According to this method a central atom (acceptor of electrons) provides empty orbitals, and ligands(donor of electrons) provide lone pairs of electrons. These orbitals and electrons form donor-acceptor bonds (coordination bonds). Artūras Kašauskas 8

9 Valence-bond method Fe Fe 2+ [Fe() 6 ] 4- Artūras Kašauskas 9

10 Central atoms and ligands Central atoms 1. Cations: Ag +, Fe 2+, Cr Atoms of metals: Ni, Fe. 3. Positive charge possessing nonmetals: (Si 4+, S 6+ ). Ligands 1. Anions: -, Cl -, OH Polar molecules: H 2 O, NH 3, CO, NO. 3. Nonpolar molecules: I 2. Artūras Kašauskas 10

11 Formation of coordinational compounds Compound containing coordination cation: Ag + + 2NH 3 = [Ag(NH 3 ) 2 ] + [Ag(NH 3 ) 2 ] + + Cl - = [Ag(NH 3 ) 2 ]Cl Compound containing coordination anion: Fe = [Fe() 6 ] 4- [Fe() 6 ] K + = K 4 [Fe() 6 ] Artūras Kašauskas 11

12 Dissociation of coordination compounds Inner and outer spheres separate rapidly and almost completely as the coordination compound dissolves: K 4 [Fe() 6 ] 4K + + [Fe() 6 ] 4- M=368 g/mol Coordination ions dissociate insignificantly. Dissociation of coordination ions is reversible. Equilibrium constant of dissociation of coordination ion is named instability constant (Kin): [Fe() 6 ] 4- Fe , K in C C Fe C [ Fe( ) 6 6 ] 4 1, Artūras Kašauskas 12

13 Dissociation of coordination ion Dissociation of coordination ion is reversible and gradual: Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe )] ( [ )] ( [ ] ) ( [ ] ) ( [ ] ) ( [ ] ) ( [ ] ) ( [ ] ) ( [ ] ) ( [ ] ) ( [ ] ) ( [ Artūras Kašauskas 13

14 Instability constants of different coordination ions Ion Kin Ion Kin [NH 4 ] + 5, [Ag() 2 ] - 8, [Ag(NH 3 ) 2 ] + 9, [Ca EDTA] 2-1, [Zn(OH) 4 ] 2-3, [Cu EDTA] 2-1, [Fe() 6 ] 4-1, [Hg EDTA] 2-1, Artūras Kašauskas 14

15 Classification of coordination compounds Cationic coordination compounds - [Ag(NH 3 ) 2 ]Cl Anionic coordination compounds - K 4 [Fe() 6 ] Coordination salts - [Ag(NH 3 ) 2 ]Cl, Na 2 [Ag() 2 ] Coordination acids - H 2 [SnCl 6 ] Coordination bases - [Cu(NH 3 ) 4 ](OH) 2 Aqua-coordination compounds - [Cr(H 2 O) 6 ]Cl 3 Hydroxo-coordination compounds - Na 2 [Sn(OH) 6 ] Ammine-salts - [Ag(NH 3 ) 2 ]Cl Artūras Kašauskas 15

16 Chelate compounds (chelates) Formation of chelate occurrs when a ligand forms more than one coordination bound with central atom (polydentate ligand).ethylene diamine is a bidentate ligand. Chela - claw. The ligands lie around the central atom like the claws of a lobster. Artūras Kašauskas 16

17 Complexones (chelating agents) Some amino-polycarbonic acids and their salts can form stable polydentate coordination compounds with most of the cations. These compounds are named complexones. Complexones and central atom form coordination and ionic bonds. Artūras Kašauskas 17

18 Complexones (chelating agents) Ethylenediaminetetraacetic acid (EDTA) EDTA disodium salt (Na 2 EDTA) Artūras Kašauskas 18

19 Complexonometry (chelatometry) The method of quantitive analysis which is based on recations between complexones and ions of metals. Most often the disodium salt of EDTA is used. It is entitled trilon B. This compound reacts with the divalent ions forming a rather stable colourless coordination compound. Na 2 [EDTA] + Ca 2+ = Na 2 [CaEDTA] + 2H + Artūras Kašauskas 19

20 Na 2 [CaEDTA] Kin([CaEDTA] 2- ) = 1, , Kin([CuEDTA] 2- ) = 1, , Kin([HgEDTA] 2- ) = 1, Artūras Kašauskas 20

21 Na 2 [CaEDTA] Artūras Kašauskas 21

22 Hydroxylapatite (Hydroxyapatite) Hydroxylapatite (hydroxyapatite) is a naturally occurring mineral with the formula Ca 10 (PO 4 ) 6 (OH) 2. The OH - ion can be replaced by fluoride or carbonate producing fluorapatite or carbonateapatite. Hydroxyapatite and fluorapatite are the main minerals of which dental enamel and dentin are comprised. Artūras Kašauskas 22

23 Magnesium ATP Artūras Kašauskas 23

24 Porphyne Pirolas Porfinas Artūras Kašauskas 24

25 Chlorophyll Artūras Kašauskas 25

26 Haeme Artūras Kašauskas 26

27 Oxyhaemoglobin Proksimalinis His F8 Distalinis His F8 Artūras Kašauskas 27

28 Cyanocobalamin Artūras Kašauskas 28

29 The active site of metaloenzyme Artūras Kašauskas 29

30 The toxic effect of heavy metals Heavy metals (Pb 2+, Hg 2+, Cd 2+, Cu 2+ ) replace metal atom in the active site of metaloenzyme and affect functions of enzyme. Artūras Kašauskas 30