PART 3 Theory of Coordination Compounds and Werner

PART 3 Theory of Coordination Compounds and Werner Theory

Werner Theory Alfred Werner – He received the Nobel Prize in 1913 [Co (NH 3)5 Cl ] Cl 2 Central atom Secondary valency Primary valency: ionisable valency Secondary valency: nonionisable valency

Major Assumptions of Werner's Theory 1. There are two types of valence in the elements. a. Primary valence (Ionizable valence) b. Secondary valence (non-ionizable valence) 2. An element can yield new compounds with a covalence even if the principal valence is the same. K 3 [Co (CN) 6] K 3 [Co (Cl) 6] 3. Each element has a certain number of secondary valences. This is called the coordination number of that element. 4. While the primary valences are saturated by the positive and negative groups, the secondary (auxiliary) valences are saturated by both negative and neutral groups. 5. The secondary (auxiliary) valences are oriented towards the axes and form various geometric shapes.

Jorgensen Werner Before formula Co. Cl 3. 6 NH 3 sarı Co. Cl 3. 5 NH 3 mor Co. Cl 3. 4 NH 3 yeşil Co. Cl 3. 3 NH 3 Werner Formula [Co(NH 3)6]Cl 3 [Co(NH 3)5 Cl]Cl 2 [Co(NH 3)4 Cl 2]Cl [Co(NH 3)3 Cl 3] Werner 3 mol Ag. Cl precipitated 2 mol Ag. Cl precipitated 1 mol Ag. Cl precipitated With Ag. NO 3 no precipitated

Werner rejected the formally pentavalent nitrogen in Blomstrands chain formulas and abandoned Kekuls concept of the fixed valency of a chemical element. Instead he introduced the concept of the coordination number as the number of groups around the central metal atom and assumed that ligands could be replaced by other groups. The most frequent coordination numbers were six (octahedral, for example, Co(III) and four (square-planar, for example, Pt(II). With his remarkable stereochemical perception, he realized immediately that this arrangement must lead to stereoisomers. Like vant Hoff, Werner used the method of isomer counting in order to predict new compounds. Consequently, he interpreted the croceo and violeo salts as cis and trans isomers of an octahedral complex. His new model explained the observation that the neutral [Co(NH 3)3 Cl 3] complex did not form a precipitate upon treatment with silver ions

Charge on the complexes n+/ligands X+/n Metal ion Counter ion Central metal ion surrounded by ligands Ligants donate two electrons to the d-orbital of the metal ion form a coordinated covalent bond

[Co(NH 3)6]Cl 3 [Co(NH 3)5 Cl]Cl 2 3+ [Co(NH 3)4 Cl 2]Cl 2+ +

Representaion of valencies Primary valency, secondary valency [Mn(OH 2)5(SO 4)] [Mn(OH 2)6][SO 4] Primary valency SO 42 - H 2 O Mn 2+ OH 2 H 2 O ligand H 2 O OSO 3 H 2 O Mn 2+ OH 2 O

Lewis model of Complex Formation "Lewis base example [Co(NH 3)6]3+ 3+ NH 3 N 6 N H H NH 3 + Co 3+ H 3 N H NH 3 "Lewis acid" NH 3

Colours of transition metal complexes Ruby (yakut) Korundum Al 2 O 3 ile Cr 3+ safsızlığı Sapphire (safir) Korundum Al 2 O 3 ile Fe 2+ ve Ti 4 impruty Emerald (zümrüt) Beril Al. Si. O 3 ile Be ve Cr 3+ impruty octahedral coordination number 6

LİGANDS

Ligands They are Lewis bases, attached to the central atom by electron donor atoms. Electron donor atom types - P atom fosfins - N atomu amines, nitro, piridin(py) -O atom aqua, OR-S atom SR-, SOx -organic compounds aromatics, olefinler, alkyls etc. Classification of Ligands ● according to the dent Monodentate Bidentate Tridentate Multidentate Chelating ligands: Ligands that can bind to the central atom with multiple donor atoms

Ethyilenediamine (en) acetilacetonato(acac) oxalato (ox)

• By type of donor-acceptor • donor (only) • En > NH 3 • alkyls (methyl, propyl etc. ) – donor (filled p orbitals) • H 2 O > F- > RCO 2 - > OH- > Cl- > Br- > I– acceptor • CO, CN- > phen > NO 2 - > NCS • According to their electronic structure - one electron donor H , methyl, propyl - two electron donorrici NH 3, H 2 O, CO, ethylene, py - three electron donor NO, allyl (H 2 C=CH-CH 2 ) - four electron donor bütadien - five electron donor cyclopentadienyl (Cp)

LIGAND TYPES Have one or more electron pairs 1. 2. Those without empty orbitals to get electrons from metal F-, H 2 O Those with empty or evacuable d orbitals that can receive electrons from metal PR 3 3. which can both give electrons to metal and receive electrons from metal, is CN-, CO, Chelated ligands (two, three, four , …with dent)