9-4 Coordination Numbers and Structure

Transcription

1 Chapter 9 Coordination Chemistry I: Structure and Isomers 9-1 History 9-2 Nomenclature 9-3 Isomerism 9-4 Coordination Numbers and Structure

2 History What is coordination compound? Coordniantion compounds include compound composed of a metal atom or ion and one or more ligands that formally donate electrons to the metal. More specifically, a transition metal surrounded by neutral molecules or anions with a definite geometry. What is ligand? Ligand can be a atom, ion, and molecules.

3 History russian blue (German: Preußischblau or Berliner Blau, in English Berlin lue) is a dark blue What pigment is coordination used paints and compound? formerly in blueprints. Prussian ue was Coordination discovered complexes by accident were by painter known Heinrich - although Diesbach not understood in Berlin in 04-5, in which any sense is why - it since is also the known beginning as Berlin of chemistry, blue. (Diesbach e.g. Prussian was attempting create blue, a paint Aureolin, with a and red copper hue.) It vitriol. has several different chemical names, these ing iron(iii) ferrocyanide, ferric ferrocyanide, iron(iii) hexacyanoferrate(ii), d ferric The hexacyanoferrate. key breakthrough Commonly occurred when and conveniently Alfred Werner it is proposed, simply called "PB inter alia, that Co(III) bears six ligands in an octahedral geometry. ureolin (sometimes called Cobalt Yellow) is a pigment used in oil and atercolor painting. Its color index name is PY40 (40th entry on list of yellow gments). It was first made in 1851 and its chemical composition is potassium baltinitrite. opper(ii) sulfate ("sulphate" in most Commonwealth nations) is the chemical mpound with the formula CuSO 4. This salt exists as a series of compounds at differ in their degree of hydration. The anhydrous form is a pale green or ay-white powder, while the pentahydrate, the most commonly encountered lt, is bright blue. This hydrated copper sulfate occurs in nature as the minera lled chalcanthite. The archaic name for copper(ii) sulfate is "blue vitriol"

4 Alfred Werner Nobel Prize for Chemistry 1913 or complexes with more than one type of ligand, Werner succeeded in plaining 1893, Werner the number was the of first isomers to propose observed. correct For structures exemple, he for explained coordination the istence mpounds of containing two isomers complex of "Co(NH ions, in which a central transition metal atom is 3 ) 4 Cl 3 ", one green and one purple. Werner oposed rrounded that by these neutral are or two anionic geometric ligands. isomers of formula [Co(NH 3 ) 4 Cl 2 ]Cl, with or e example, Cl - ion dissociated it was known as confirmed that cobalt by forms conductivity a "complex" measurements. with formula The Co ocl om 3 is 6NH surrounded 3, but the by nature four NH of the association indicated by the dot was 3 and two Cl ligands the vertices of an ysterious. tahedron. Werner The green proposed isomer the is "trans" structure with [Co(NH the two 3 ) 6 Cl ]Clligands 3, with the at opposite Co 3+ ion rtices, rrounded and by the six purple NH 3 at is the "cis" vertices with the of two an octahedron. Cl at adjacent The vertices. three Cl- are ssociated as free ions, which he confirmed by measuring the electrical nductivity of the compound in aqueous solution.

5 History What is coordination compound? Coordination complexes were known - although not understood in any sense - since the beginning of chemistry, e.g. Prussian blue, Aureolin, and copper vitriol. The key breakthrough occurred when Alfred Werner proposed, inter alia, that Co(III) bears six ligands in an octahedral geometry. The theory allows one to understand the difference between coordinated and ionic chloride in the cobalt ammine chlorides and to explain many of the previously inexplicable isomers. He resolved the first coordination complex into optical isomers, overthrowing the theory that chirality was necessarily associated with carbon compounds.

6 History What is ligand? In chemistry, a ligand is an atom, ion, or molecule that generally donates one or more of its electrons through a coordinate covalent bond to one or more central atoms or ions (these ligands act as a Lewis base). The ligands that are directly bonded to the metal (that is, share electrons), are called "inner sphere" ligands. If the inner-sphere ligands do not balance the charge of the central atom, this may be done by simple ionic bonding with another set of counter ions (the "outer-sphere" ligands). The complex of the metal with the inner sphere ligands is then called a complex ion (which can be either cationic or anionic). The complex, along with its counter ions, is called a coordination compound. The size of a ligand is indicated by its cone angle.

7 History Organometallic Compound Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Organometallic chemistry combines aspects of inorganic chemistry and organic chemistry. Organometallic compounds find practical use in stoichiometric and catalytically active compounds. Electron counting is key in understanding organometallic chemistry. The 18-electron rule is helpful in predicting the stabilities of organometallic compounds. Organometallic compounds which have 18 electrons (filled s, p, and d orbitals) are relatively stable. This suggests the compound is isolable, but it can result in the compound being inert.

8 Nomenclature Common Monodentate Ligands Classical (or "Werner Complexes"): Ligands in classical coordination chemistry bind to metals. Organometallic: Ligands are organic (alkenes, alkynes, alkyls) as well as "organic-like" ligands such as phosphines, hydride, and CO. Bioinorganic: Ligands are those provided by nature, especially including the side chains of amino acids, and many cofactors such as porphyrins. Example: hemoglobin Cluster: Ligands are all of the above but also include other metals as ligands. Example Ru 3 (CO) 12

9 Ambidentate Ligand Nomenclature Common Monodentate Ligands

10 Nomenclature Common Chelating Amines Monodentate, bidentate, tri-, tetra-, penta-, hexadentate

11 Nomenclature Common Multidentate (chelating) Ligand

12 Nomenclature Bridging Ligands M M N N N R N R R R N N N -O 2 C CO 2 - -O 2 C CO 2 -

13 Nomenclature Modern Ligands (Porphyrin) Porphyrin Porphyrin coordinated to magnesium: chlorophyll Porphyrin coordinated to iron: heme Photodynamic Therapy(PDT)

14 Nomenclature Modern Ligands (Porphyrin) Photodynamic Therapy(PDT) Shown is close up of surgeons' hands in an operating room with a "beam of light" traveling along fiber optics for photodynamic therapy. A patient would be given a photo sensitive drug (photofrin) containing cancer killing substances which are absorbed by cancer cells. During the surgery, the light beam is positioned at the tumor site, which then activates the drug that kills the cancer cells, thus photodynamic therapy (PDT).

15 Nomenclature Modern Ligands Salen Grubbs' Catalyst 2 nd Generation Me Me Jacobsen epoxidation Me N N Me Cl Me Ru Me Cl P(Cy) 3 Ph

16 Mirkin s Weak-Link Nomenclature Modern Ligands (Weak-Link Approach)

17 Nomenclature Nomenclature Rules 1. Cation comes first, followed by anion 2. The inner coordination sphere is enclosed in square brackets in the formula. Nomenclature: Ligand Metal Formula: Metal Ligand 3. Prefixe

18 Nomenclature Nomenclature Rules 4. Ligands are named in alphabetical order. (not prefix) 5. Anionic ligands are given an o suffix. Neutral ligands retain their name. Water is called aqua. Ammonia is called amine. 6. Designating charge or oxidation number Stock system: oxidation number of the metal as a Roman nummeral in parentheses. Ewing-Bassett system: charge on the coordination sphere in parentheses

19 Nomenclature Nomenclature Rules 7. The prefixs cis- and trans- designate adjacent and opposite 8. Bridging ligands between metal ions have the prefix μ. 9. When the complexes is negatively chared.

20 Nomenclature Nomenclature Rules Na 2 [NiCl 4 ] sodium tetrachloronickelate(ii) Pt(NH 3 ) 2 Cl 4 diamminetetrachloroplatinum(iv) Fe(CO) 5 pentacarbonyliron(0) (NH 4 ) 2 [Ni(C 2 O 4 ) 2 (H 2 O) 2 ] ammonium diaquabis(oxalato)nickelate(ii) [Ag(NH 3 ) 2 ][Ag(CN) 2 ] diamminesilver(i) dicyanoargentate(i)

21 Isomerism

22 Isomerism Are the bonds between the same atoms? Yes No Stereo or configurational isomers Are the molecule has a mirror plane? Structural or constitutional isomers Yes Diastereomers or geometric isomers No Enantiommers or optical isomers Ionization isomers, Linkage isomers, Coordination isomers, Hydrate isomers

23 4 CN ; Square planar Cis and trans Chiral isomers 4 CN ; Tetrahedral Only one structure

24 Isomerism - Stereoisomers 4 CN ; Square planar Cis and trans Antitumor agent: cisplatin Chelate can induce the cis structure Cisplatin, cisplatinum or cisdiamminedichloroplatinum(ii) (CDDP) is a platinum-based chemotherapy drug used to treat various types of cancers, It was the first member of its class, which now also includes carboplatin and oxaliplatin.

25 Isomerism - Stereoisomers 4 CN ; Tetrahedral Only one structure With four different ligands or with unsymmetrical chelating ligands Three?

26 Isomerism - Stereoisomers 6 CN ; Octahedron H 2 N H N NH 2 diethylenetriamine facial and meridional

27 Isomerism - Stereoisomers 6 CN ; Octahedron, Triethylentetraamine H 2 N H N N H NH 2 No coplanar rings Two coplanar rings Three coplanar rings

28 Isomerism - Stereoisomers Number of possible Isomers

29 Isomerism - Stereoisomers Number of possible Isomers Ma 3 bcd a facial d a c a b no mirror plane meridional a a a a a b d c a d a d a b a b a c c a b d a c

30 Isomerism - Stereoisomers Number of possible Isomers

31 Isomerism - Stereoisomers 1. Number of possible Steroisomers & Enantiomers Ma 2 b 2 cd 2. Identify the or Λ chirality of the rings [Co(dien) 2 ] 3+, using all unconnected pairs. N N N Co N N N 3+

32 Isomerism Stereoisomers: Combination of Chelate Rings (, ) Handedness of chelate Rings Lambda Delta

33 Isomerism Stereoisomers: Combination of Chelate Rings (, ) [Co(en) 3 ] 3+

34 Isomerism Stereoisomers: Combination of Chelate Rings (, ) Procedure for Determining Handedness

35 Isomerism Stereoisomers: Combination of Chelate Rings (, ) CoEDTA - Not coplanar, not connected at the same atom X X R1: R2, R3, R4, R5 X X X R2: R1, R3, R4, R5

36 Isomerism Stereoisomers: Lignad Ring Conformation 6 CN ; Octahedron, Triethylentetraamine H 2 N H N N H NH 2 S S S S R R R R

37 Isomerism Stereoisomers: Lignad Ring Conformation Chelate Ring Conformation (λ, δ)

38 Isomerism Stereoisomers: Lignad Ring Conformation 6 CN ; Octahedron, Triethylentetraamine Chelate Ring Conformation (λ, δ)

39 Isomerism Constitutional Isomers: Hydrate Isomers Hydrate Isomers: having water as either a ligand or an added part of the crystal structure

40 Isomerism Constitutional Isomers: Ionization Isomerism Ionization Isomers: Exchange of ions between inside and outside coordination sphere

41 Isomerism Constitutional Isomers: Coordination Isomerism Coordination Isomers: require at least two metal

42 Isomerism Constitutional Isomers: Linkage (ambidentate) Isomerism Linkage Isomers: Compounds containing ambidentate ligand thiocyanate thiocyano isothiocyano nitrite nitro nitrito

43 Isomerism Separation and Identification of Isomers Separation Fractional Crystalization packing, solubility, size, charge Chiral Isomers Resolution chiral counterions Identification X-ray crystallography Optical rotatory dispersion (ORD) Circular dichroism (CD)

44 Coordination Numbers and Structures Structures vs Properties. actors for Structures. Number of Bonds Bond formation is usually exothermic. So stability. VSEPR. Occupancy of d orbitals Square-planar vs Tetrahedral. Steric Effects. Crystal Packing Effects Crystalline Lattice vs Solution hat is common thing? hich one is a dominant factor? CN Geometries Rare Linear Trigonal-plane Tetrahedron, Square-plane Trigonal bipyramid, Square pyramid Octahedron, Trigonal prosm Pentagonal bipyramid, Capped trigonal prism Capped octahedron Known up to 16 CN

45 Coordination Numbers and Structures Oxidation States of Transition Metals

46 Coordination Numbers and Structures CN = 1,2, and 3 CN = 1, Rare

47 Coordination Numbers and Structures CN = 1,2, and 3 CN = 2, Rare, Linear (D h ) Mostly d 10 metals, Ag(I), Cu(I), Au(I), Hg(II) d 5, d 6, d 7 Examples of CN = 2

48 Coordination Numbers and Structures CN = 1,2, and 3 CN = 3, Rare, Trigonal planar (D 3h ) Mostly d 10, PPh 3, N(SiMe 3 ) 2, Bulky enough, Steric effect vs Electroic structure

49 Coordination Numbers and Structures CN = 4 CN = 4, Tetrahedral (T d ) Squre-planar(D 4h ) Tetrahedral (T d ) ; very common,

50 Coordination Numbers and Structures CN = 4 CN = 4, Tetrahedral (T d ) Squre-planar(D 4h ) Squre-planar(D 4h ) ; mostly d 8 (Pd(II), Pt(II), Ni(II), Ag(III), Ir(I) Rh(I)) Tetrahedral vs Square-planar Counterion, Crystal Packing Cl Cl Cu Cl Cl 2Cs

51 Coordination Numbers and Structures CN = 4 CN = 4, Tetrahedral (T d ) Squre-planar(D 4h ) Squre-planar(D 4h ) ; mostly d 8 (Pd(II), Pt(II), Ni(II), Ag(III), Ir(I) Rh(I)) Tetrahedral vs Square-planar Counterion, Crystal Packing E is not big.

52 Coordination Numbers and Structures CN = 5 CN = 5, Trigonal bipyramid (D 3h ), Square pyramid (C 4v ) Fluxional behavior.

53 Coordination Numbers and Structures CN = 6 CN = 6, Octahedral (O h ) most common O h to D 4h

54 Coordination Numbers and Structures CN = 6 CN = 6, Octahedral (O h ) to Trigonal Prism (D 3h ) Usually with three bidentate ligands

55 Coordination Numbers and Structures CN = 7 CN = 7, Pentagonal bipyramid (O h ), Capped trigonal prism, Capped octahedron Capped trigonal prism Pentagonal bipyramid Capped octahedron Different counterion, steric requirment

56 Coordination Numbers and Structures CN = 8 CN = 8, Square antiprism, Dodecahedron Eight coordination is rare in the first row transition metals Square antiprism Why? Central ion must be large in order to accommodate eightcoordination Dodecahedron

57 Coordination Numbers and Structures CN 8 CN 8, known up to 16, not common

58 Multimetallic Compexes Without direct M-M bond With direct M-Mm bond

59 Homework Exercise 9-1~9-6 Problem 1, 4, 6, 8b, 8d, 8f, 16, 17.