Chapter 9 Coordination Chemistry Structures and...
Transcript of Chapter 9 Coordination Chemistry Structures and...
Chapter 9 Coordination Chemistry Structures and Isomers
What is Coordination Chemistry
• Cooordination Complex
– Central atom usually a d-block metal or ion
– Attach to the central atom are ligands –
– Metal = Lewis acid
– Ligand = Lewis Base
– Cu2+ + 4 :NH3 [Cu(NH3)4]2+
Lewis Lewis Coordination Complex
Acid Base
History
• Old compounds
– Prussian Blue – KFe[Fe(CN) 6]
– Aureolin – K3 [Co(NO2) 6]
– Alizarin red dye Ca2+ Al3+ salt of
– Teraamminecopper(II) ion [Cu(NH3)4(H2O)2]2+
Werner – Modern coordination theory
– Solve the bonding of [Co(NH3)6]Cl3
– Co is 3+ . How are the ammonias bonded?
– Bloomstrand = chain theory
– Werner = Coordination theory
Werner synthesized Isomers with no counterparts in chain theory.
Optically active D3 point group coordination complex
[Co(oxalate)3]3-
Werner’s optical D3 compound with no carbon atoms
Possible isomers of [Co(NH3)4Cl2]+ for various geometries
Four coordinate geometries of a Platinum complex
Skip Nomenclature 9.2
• Next few tables are common ligands
9.3 Isomerism
• Many types
• Stereoisomers – all bonds between same atoms. Different arrangements in space
• Structural or constitutional isomer – Some bonds are between different atoms.
• Diagram on next slide categorizes the types of compounds.
Stereoisomers – have same bonds but different arrangements in space.
• Four cordinate – Four coordinate MA2B2 square planar – cis and trans like cis-Platin and its isomer:
• Four coordinate MA2B2- square planar – cis and trans
• cis trans
Chirality
• Reminder: an object is chiral if it is not superimposible on its mirror image.
• Criteria – chiral object only have pure rotatations.
• Objects with improper rotations including i or σ or Sn are not chiral
Tetrahehral geometry
• Chiral for Mabcd (a,b,c, and d are monodentate ligand) similar to chiral carbon atoms
• Can be chiral with unsymmetric chelating rings
Such a a------b a and b are different donor atoms like HO-CH2-CH2-NH2
Square Planar Geometry can be chiral with asymmetrical chelates
Six coordinate complexes • Some isomers of the following compositions
may be chiral (a,b,c,d,e,f are monodentate ligands. Not all isomers of these composition are chiral
– [Ma2b2c2]
– [Mabc2d2]
– [Mabcd3]
– [Mabcde2]
– [Mabcdef]
Six coordinate complexes geometric isomers of [Ma3b3] and two tridentate ligands
Isomers for tetradentate ligands
Example Ma3bcd Total 5 isomer with one pair of enatiomers
• The 3 a ligands can be mer or fac .
• The mer configuration can have each of the 3 other ligands trans to the middle a ligand. This is three unique isomers. None of these are chiral because the plane containing a b c d in a plane of symmetry as shown in the first structure.
The other two isomers are enatiomers with the a ligands in the fac configuration this is a pair of emtiomers
Skip Sections 9.3.5, 9.3.6
Constitutional Isomers
• Have different bonded atoms
– Hydrate isomerism – Water is a ligand in one compound and an included solvent molecule in another. Ex. Isomers of CrCl3·6H2O
– (violet) [Cr(H2O)6]Cl3·
– (blue-green) [CrCl(H2O)5]Cl2·H2O
– (dark green) [CrCl2 (H2O)4]Cl3·2H2O
– (yellow-green)[CrCl3 (H2O)3]
Constitutional isomers (continued)
• Coordination isomers – ligands are bound to different metals
• Ex. [Co(en)3] [Cr(CN)6] and [Cr(en)3] [Co(CN)6]
or
[Pt(NH3)4] [PtCl6] and [Pt(NH3)4Cl2] [PtCl4]
Constitutional isomers (continued)
• Linkage isomerism – a ligand binds through two different atoms to a metal.
• Examples SCN- S bonding or N binding
• NO2- - N binding or O binding
• CN- - C binding or N binding
• Examples in Figures on next page:
Skip section 9.3.8
9.4 a survey of coordination numbers and structure
• Coordination number – number of ligands bound to the central atom
• Factors determining shape
– Coordination number
– VSEPR – main group mostly
– d electron occupancy (Chapter 10)
– Steric effects
– Crystal packing
Coordination number 1
• Rare, only with bulky ligands
Coordination number 2
• Rare, usually bulky ligands
• Some simple d10 complexes (see right side of figure) :
Coordination number 3
• Rare, usually bulky ligands or d10 like Au(I) or Cu(I).
Coordination number 3 (cont)
Coordination number 4
• Common, tetrahedral and square planar
• Tetrahedral is usually d10
Square Planar
• Usually d8 such as Ni(II), Pd(II), Pt(II) or Au(III)
Square Planar (cont)
Square planar (cont) This complex is square planar at 25 °C an tetrahedral at 80 °C
Coordination number = 5
• Less common than 4 or 6, but not rare.
• Trigonal bipyramid of square pyramidal. Energy difference often small
• Fe(CO)5 PF5 and have one NMR peak
• Some structure in the next few slides
Coordination number = 5
Coordination number = 5
Coordination number 6
• Very common, mostly octahedral some trigonal prismatic
• Octahedral may be elongated or compressed with certain d electron counts
Coordination number 6
(a) Trigonal prismatic (b) octahedral
Coordination number 6
Coordination number 6
Coordination number 7 and higher
• Less common
• 7 – pentagonal pyramid, capped trigonal prism, or capped octahedron,
•
Coordination number = 8
Coordination number 8
Coordination number 8
Coordination number greater than 8