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Review on Chemistry of Coordination Compounds

Review on Chemistry of Coordination Compounds. Inner sphere. Coordination atom. Outer sphere ions. Central atom. ligand. Coordination number. Coordination Compounds. Constitution. [Co(NH 3 ) 5 Cl](NO 3 ) 2. H 2 O, NH 3 , Cl – , CN – , CO, SCN – , OH –

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Review on Chemistry of Coordination Compounds

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  1. Review on Chemistry of Coordination Compounds

  2. Inner sphere Coordination atom Outer sphere ions Centralatom ligand Coordination number Coordination Compounds • Constitution [Co(NH3)5Cl](NO3)2

  3. H2O, NH3, Cl–, CN–, CO, SCN–, OH– CO32-, NH2CH2CH2NH2 (ethylenediamine, en), C2O42– (oxalate ion) EDTA4- (ethylenediaminetetraacetate ion) is a hexadentate ligand.

  4. Polydentate ligands are also known as chelating agents

  5. Naming Coordination Compounds • The name of a complex is one word, with no space between the ligand names and no space between the names of the last ligand and the metal.

  6. Naming Coordination Compounds • a salt, name the cation first • Name the ligands, in alphabetical order, before the metal. • Note: in anionic ligand endings from -ide to -o , and -ate to -ato. -ite to -ito • the names of the ligands differ slightly from their chemical names • in the chemical formula, the metal atom or ion is written before the ligands

  7. Naming Coordination Compounds • If the complex contains more than one ligand of a particular type • Use Greek prefixes (di-, tri-, tetra-, etc.), or bis- (2), tris-(3), tetrakis-(4), and so forth, and put the ligand name in parentheses for the later. • The ligands are listed in alphabetical order, and the prefixes are ignored in determining the order.

  8. Naming Coordination Compounds • A Roman numeral in parentheses follows the name of the metal to indicate the metal's oxidation state • To name the metal • use the ending -ate if the metal is in an anionic complex, or the Latin names for some • -ium ending for Cationic coordination sphere, or same as the element

  9. Isomers 异构体 Compounds with the same formula but a different arrangement of atoms are called isomers. Isomers Linkage isomers Diastereoisomers Stereoisomers Constitution isomers Ionization Isomer Enantiomers

  10. NH3 NH3 H3N NH3 H3N NH3 Co Co NH3 H3N H3N NH3 N O O N nitro O nitrito O

  11. Coordination Isomerism • [Co(NH3)6][Cr(CN)6] and [Cr(NH3)6][Co(CN)6] • [Pt(NH3)4][PtCl6] and [Pt(NH3)4Cl2][PtCl4] • [Pt(NH3)4][PtCl4] and [Pt(NH3)4Cl2][PtCl4]

  12. Aquo Isomer • CrCl3·6H2O • [Cr(H2O)5Cl]Cl2·H2O • [Cr(H2O)4Cl2]Cl·2H2O • [Cr(H2O)6]Cl3 Green Green Violet

  13. Ionization isomers电离异构体

  14. Stereoisomers立体异构体 • two kinds of stereoisomers: • diastereoisomers非对映异构体 • enantiomers对映异构体 cis trans isomer

  15. X X L L X X M M X L L L L X Facial Fac- Meridional Meri-

  16. O O N M N O O

  17. Optical Isomerism光学异构现象 • enantiomers • chiral 手性的 • achiral 非手性的 • The [Co(en)3]3+ cation is chiral and exists in two nonidentical mirror-image forms. • propertiesidentical except for • their reactions with other chiral substances • their effect on plane-polarized light: Optical Activity

  18. N N N N N N Co Co N N N N N N

  19. The labels • d: dextrorotatory右旋 • l: levorotatory左旋 • used to indicate the direction of rotation. • racemic 外消旋 • A 50:50 mixture of both isomers • produces no net optical rotation.

  20. Valence Bond Theory Occupied ligand hybrid atomic orbital Vacant metal hybrid atomic orbital Coordinate covalent bond

  21. Valence Bond Theory • The hybrid orbitals used by the metal are determined by the geometry of the complex. • The number of d electrons in the metal is determined by the oxidation state of the metal ion. • The orbitals used to construct the hybrid orbitals for bonding must be vacant on the metal.

  22. Valence Bond Theory • For octahedral complexes it may be necessary to pair some electrons already in d orbitals to get vacant orbitals required for hybridization. This leads to a low spin complex . • Contrast this with the use of higher energy vacant d orbitals. This leads to more unpaired d electrons and a high spin complex.

  23. Valence Bond Theory • Knowing whether a complex is paramagnetic or diamagnetic can help determine which d orbitals to use. It can also help determine whether a complex is square planar or tetrahedral Spectrochemical series 光化学序列 Weak field ligandsStrong field ligands I– <   Br– <   Cl– <   F– < H2O     < NH3  <  en < CN–

  24. Hybrid Orbitals • A unsuccessful example: • Cu(NH3)42+ • A square planar complex • Hybrid form: dsp2 Cu2+ [Ar] dsp2

  25. Crystal Field Theory • This explains the color and magnetic properties of the transition metal complexes. • Bonding in complexes is viewed as entirely ionic and as arising from electrostatic interactions between the d electrons of the metal and the ligand electrons.

  26. Crystal Field Theory • It considers the effect of the ligand charges on the energies of the metal ion d orbitals. • The d orbitals are raised in energy and are separated in energy based on the geometry of the complex. • The energy separation is called the crystal field splitting, represented by the symbol Δ.

  27. Crystal Field Theory • In octahedral complexes the dx2 - y2 and the dz2 orbitals are higher tin energy than the dxy, the dxz, and the dyz because the negative charge of the electrons from the ligands point directly at the negative charges of the electrons in the d orbitals that lie on the x,y, and z axes.

  28. Crystal Field Theory • The color of the complexes is due to electronic transitions from one set of d orbitals to another. • Visible light can supply enough energy to promote an electron from the lower enegy to the higher energy orbitals. • Light at a particular wavelength is absorbed and the complementary color is seen.

  29. The angular distribution of d orbitals

  30. dx2-y2, dz2 Crystal Field Splitting eg +6 Dq Spheric field o -4 Dq t2g dxy, dyz, dxz o = 10 Dq Free atom Octahedral field

  31. CFSE: Crystal Field Stabilization Energy晶体场稳定化能 Pairing Energy 成对能 P

  32. Tetrahedral Field

  33. Splitting in Tetrahedral Field dxy, dyz, dxz Spheric field t2 t e dx2-y2, dz2 Tetrahedral field Free atom t= 4/9o = 10 Dq

  34. Color • Complementary colors: • R-G • O-B • Y-V

  35. An absorbance spectrum • It plots the absorbance (amount of light absorbed by a substance) as a function of wavelength [Ti(H2O)6]3+

  36. Spectrochemical series 光化学序列 Weak field ligandsStrong field ligands I– <   Br– <   Cl– <   F– < H2O     < NH3  <  en < CN–

  37. Back-bonding 反馈键

  38. Magnetism • Paramagnetic: unpaired electron • Diamagnetic: no unpaired electron Co3+: Oh t2geg d6 [Co(NH3)6]3+: diamagnetic t2g6 eg0 paramagnetic t2g4 eg2 [CoF6]3-

  39. Jahn-Teller Effects • For a non-linear molecule that is in an electronically degenerate state, distortion must occur to lower the symmetry, remove the degeneracy, and lower the energy. • Jahn-Teller effects do not predict which distortion will occur other than that the center of symmetry will remain. • The distortion by the unsymmetrical distribution of electrons in eg orbital is stronger than that of t2g.

  40. Stability Constant Cu2+ + 4NH3 [Cu(NH3)4]2+ [Cu(NH3)42+ ] Kstability = [NH3]4 [Cu2+ ] Overall Stability Constant Stepwise stability constants: K1, K2, …, K4 Overall stability constants: 1, 2, 3, 4 1 = K1 2 = K1 K2 3 = K1 K2 K3 4 = K1 K2 K3K4

  41. Factors That Determine The Stability Of Coordination Compounds 1. metal ions: charge, radius and electronic configuration; 2. ligand: basicity, chelate effects. Chelate Effects 螯合效应: entropy effect. [Cu(H2O)4]2+ (aq) + 2 NH3 (aq) → [Cu(NH3)2(H2O)2]2+ (aq) lg2 = 7.65 [Cu(H2O)4]2+ (aq) + en (aq) → [Cu(en)(H2O)2]2+ (aq) lg1 = 10.64 Entropy-driven reaction (process)

  42. Example 1 Calculate the molar solubility of AgCl in a 6 M NH3 solution Solution: Step 1: AgCl(s) = Ag+ + Cl- Ksp = [Ag+][Cl-] = 1.6 × 10-10 Step 2: Ag+ + 2NH3 = Ag(NH3)2+ [Ag(NH3)2+] = 1.5 × 107 2 = [Ag+][NH3]2

  43. Example 1 (continue) (s)(s) K = (6 – 2s) Overall reaction 0.1 AgCl(s) + 2NH3 = Ag(NH3)2++ Cl- [Ag(NH3)2+] [Cl-] K = s = 0.016 M [NH3]2 (1.5 × 107) = Ksp2 = (1.6 × 10-10) 0.045 = 2.4 × 10-3 Step 3 AgCl(s) + 2NH3 = Ag(NH3)2++ Cl- 6.0 0.0 0.0 Initial (M): -2s +s +s Change (M): 6 - 2s s s Equi (M):

  44. Example 2 Calculate the equilibrium concentration of every relevant species of a 0.1 M Ag(NH3)2+ solution. [Ag(NH3)+] With only a few exceptions, there is generally a slowly descending progression in the values of the Ki’s in any particular system. K1 = 2.2 × 103 = [Ag+][NH3] [Ag(NH3)2+] K2 = 5.1 × 103 = [Ag(NH3)+][NH3] [Ag(NH3)2+] 2 = = 1.5 × 107 [Ag+][NH3]2

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