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

4 Alfred Werner Nobel Prize for Chemistry 1913 For complexes with more than one type of ligand, Werner succeeded in 1893, explaining Werner the was number the first of isomers to propose observed. correct For structures exemple, for he coordination explained mpounds the existence containing of two complex isomers of ions, "Co(NH in which a central transition metal atom is 3 ) 4 Cl 3 ", one green and one purple. rrounded Werner proposed by neutral that or anionic these are ligands. two geometric isomers of formula or [Co(NH example, it was known that cobalt forms a "complex" with formula 3 ) 4 Cl 2 ]Cl, with one Cl - ion dissociated as confirmed by conductivity ocl measurements. 3 6NH 3, but the The nature Co atom of the is association surrounded indicated by four NH by the dot was 3 and two Cl ysterious. ligands at Werner the vertices proposed of an the octahedron. structure [Co(NH The green 3 ) 6 ]Cl isomer 3, with is the "trans" Co 3+ with ion rrounded the two Cl by ligands six NHat 3 at opposite the vertices vertices, of an and octahedron. the purple The is "cis" three with Cl-the are two ssociated Cl adjacent as free vertices. 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. Factors for Structures 1. Number of Bonds Bond formation is usually exothermic. So stability 2. VSEPR 3. Occupancy of d orbitals Square-planar vs Tetrahedral 4. Steric Effects 5. Crystal Packing Effects Crystalline Lattice vs Solution What is common thing? Which 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 Structures vs Properties.

46 Coordination Numbers and Structures Oxidation States of Transition Metals

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

48 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 Large Ligands can induce a linear arrangement

49 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

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

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 Cl Cl Cu Cl Cl 2Cs

52 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.

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

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

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

56 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

57 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 Compressed Square antiprism

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

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