Presentation is loading. Please wait.

Presentation is loading. Please wait.

Metal Complexes -- Chapter 24 Metal Complex -- consists of a set of ligands that are bonded to a central metal ion by coordinate covalent bonds. e.g. Cu.

Similar presentations


Presentation on theme: "Metal Complexes -- Chapter 24 Metal Complex -- consists of a set of ligands that are bonded to a central metal ion by coordinate covalent bonds. e.g. Cu."— Presentation transcript:

1 Metal Complexes -- Chapter 24 Metal Complex -- consists of a set of ligands that are bonded to a central metal ion by coordinate covalent bonds. e.g. Cu L --> [CuL 4 ] 2+ ( L = NH 3, H 2 O, etc) Ligands are Lewis Bases and can be: –monodentate -- one donor atom e.g. H 2 O, NH 3, Cl –, OH –, etc. –bidentate -- two donor atoms e.g. ethylenediamine, NH 2 –CH 2 –CH 2 –NH 2 en

2 Polydentate ligands –polydentate -- more than two donor atoms e.g. EDTA -- ethylenediaminetetraacetic acid (6 donor atoms) = EDTA 4–

3 Chelate Effect Chelate effect -- complexes with bi- or polydentate ligands are more stable than those with similar monodentate ligands e.g. [Ni(en) 3 ] 3+ is more stable than [Ni(NH 3 ) 6 ] 3+ Know Table 24.2!

4 Writing Formulas of Complex Ions Metal ion first, then ligands. Charge outside brackets. total charge = sum of metal ion + ligands e.g. metal ion ligand complex Cu 2+ H 2 O [Cu(H 2 O)] 2+ Co 3+ NH 3 [Co(NH 3 ) 6 ] 3+ Fe 3+ CN – [Fe(CN) 6 ] 3–

5 Nomenclature 1. Name the ligands, put in alphabetical order. 2. Add prefixes for ligands that appear more than once. 3. Name the metal –Cationic complex; metal name –Anionic complex; metal prefix + ate 4. Add oxidation state in roman numerals 5. As separate word, write ion if not neutral, or list counterions (positive first, negative second). Examples: ComplexName [Ni(CN) 4 ] 2– tetracyanonickelate(II) ion [CoCl 6 ] 3– hexachlorocobaltate(III) ion [CoCl 2 (NH 3 ) 4 ] + tetraaminedichlorocobalt(III) ion Na 3 [Co(NO 2 ) 6 ]sodium hexanitrocobaltate(III) [CrCl 2 (en) 2 ] 2 SO 4 dichlorobis(ethylenediamine)chromium(III) sulfate

6 Coordination Number and Structure Coordination # -- number of donor atoms attached to the metal center (a) Two-Coordinate Complexes -- linear structures Rare except for Ag + e.g. [Ag(NH 3 ) 2 ] + and [Ag(CN) 2 ] – (b) Four-Coordinate Complexes -- two structural types Tetrahedral structures -- common for ions with filled d subshells, e.g. Zn 2+ as in [Zn(OH) 4 ] 2–

7 More Coordination Number and Structure (b) Four-Coordinate Complexes -- two structural types square planar structures -- common for d 8 metal ions (Ni 2+, Pd 2+, Pt 2+ ) and for Cu 2+ e.g. (c) Six-Coordinate Complexes -- the most common! always octahedral structures, e.g.

8 Sample Problem 1. Give the name or formula, as required. Draw the structure of each complex. a) [AgI 2 ] – b) [Co(en) 3 ] 3+ c) cis-dichlorobis(ethylenediamine)cobalt(III) chloride d) sodium tetracyanonickelate(II)

9 Answer 1. a) diiodoargentate(I) ion [IAgI] – b) tris(ethylenediamine)cobalt(III) ion c) cis-[CoCl 2 (en) 2 ]Cl c) Na 2 [Ni(CN) 4 ]

10 Structural Isomers of Coordination Complexes Linkage isomers Coordination isomers pentaamminenitrocobalt(II) ionpentaamminenitritocobalt(II) ion pentaamminechlorocobalt(II) bromidepentaamminebromocobalt(II) chloride

11 11 Isomerism; Overview

12 Stereoisomers of Coordination Complexes (a) Geometrical Isomers cis trans fac mer (b) Enantiomers Three common ways to get enantiomers: --chiral ligand --tetrahedral complex with 4 different groups --octahedral complexes with chelating ligands (and no mirror plane)

13 Sample Questions Draw a clear, 3-dimensional structure of the geometrical isomer of Co(en)(NH 3 ) 2 Cl 2 that is optically active. (define any abbreviations) Excess silver nitrate is added to a solution containing mol of [Co(NH 3 ) 4 Cl 2 ]Cl. How many g of AgCl (FW = 143.3) will precipitate?

14 Sample Questions Draw a clear, 3-dimensional structure of the geometrical isomer of Co(en)(NH 3 ) 2 Cl 2 that is optically active. (define any abbreviations) Excess silver nitrate is added to a solution containing mol of [Co(NH 3 ) 4 Cl 2 ]Cl. How many g of AgCl (FW = 143.3) will precipitate? 7.48 g

15 Crystal Field Theory (Bonding in Transition Metal Complexes) Metal complexes are usually highly colored and are often paramagnetic -- such facts can be explained by a d-orbital splitting diagram energy d orbitals of the free metal ion d z2 d x2-y2 egeg = crystal field splitting energy d xy d xz d yz t 2g d orbitals of the metal ion in an octahedral field of ligands

16 Shape and Directionality of the d Orbitals egeg t 2g

17 Crystal Field Strength The size of depends on… The nature of the ligand (ligand-metal bond strength!) spectrochemical series -- decreases: CN – > NO 2 – > en > NH 3 > H 2 O > OH – > F – > Cl – > Br – strong field ligands weak field ligands The oxidation state of the metal (charge!) is greater for M 3+ than for M 2+ The row of the metal in the periodic table (size!) for a given ligand and oxidation state of the metal, increases going down in a group e.g. is greater in Ru(NH 3 ) 6 3+ than in Fe(NH 3 ) 6 3+ Colors of metal complexes are due to electronic transition between the t 2g and e g energy levels

18 d Orbital Splitting Diagrams for Octahedral Complexes egeg t 2g egeg d x2 d x2–y2 d xy d xz d yz d x2 d x2–y2 d xy d xz d yz small high spin large low spin Fe(H 2 O) 6 2+ Fe(CN) 6 4–

19 High Spin vs. Low Spin CN – is a stronger field ligand than is H 2 O which leads to a greater value (i.e. a greater d orbital splitting) As a result, Fe(H 2 O) 6 2+ is a high spin complex and is paramagnetic (4 unpaired electrons) while, Fe(CN) 6 4– is a low spin complex and is diamagnetic (no unpaired electrons) The CN – complex with the larger value absorbs light of higher energy (i.e. higher frequency but shorter wavelength) OMIT … d orbital splitting diagrams for other geometries (i.e. tetrahedral and square planar)

20 Sample Questions A complex [CoA 6 ] 3+ is red. The complex [CoB 6 ] 3+ is green. a) Which ligand, A or B, produces the larger crystal field splitting ? b) If the two ligands are ammonia and water, which is A and which is B? c) Draw the d orbital diagram of either complex, assuming it is high spin. How many unpaired electrons will it have? Give the order of increase of in the following sets: a) Cr(NH 3 ) 6 3+, CrCl 6 3–, Cr(CN) 6 3– b) Co(H 2 O) 6 2+, Co(H 2 O) 6 3+, Rh(H 2 O) 6 3+

21 Sample Questions A complex [CoA 6 ] 3+ is red. The complex [CoB 6 ] 3+ is green. a) Which ligand, A or B, produces the larger crystal field splitting ? b) If the two ligands are ammonia and water, which is A and which is B? c) Draw the d orbital diagram of either complex, assuming it is high spin. How many unpaired electrons will it have? a) A b) A = NH 3, B = H 2 O c) 4 unpaired electrons Give the order of increase of in the following sets: a) Cr(NH 3 ) 6 3+, CrCl 6 3–, Cr(CN) 6 3– b) Co(H 2 O) 6 2+, Co(H 2 O) 6 3+, Rh(H 2 O) 6 3+ a) Cr(CN) 6 3– > Cr(NH 3 ) 6 3+ > CrCl 6 3– b) Rh(H 2 O) 6 3+ > Co(H 2 O) 6 3+ > Co(H 2 O) 6 2+ d z2 d x2-y2 egeg d xy d xz d yz t 2g


Download ppt "Metal Complexes -- Chapter 24 Metal Complex -- consists of a set of ligands that are bonded to a central metal ion by coordinate covalent bonds. e.g. Cu."

Similar presentations


Ads by Google