Print version Updated: 9 March 2020 Lecture #28 Coordination - - PowerPoint PPT Presentation

Lecture #28 Coordination Chemistry: Hydrolysis and Simple Complexes

(Stumm & Morgan, Chapt.6: pg.281-289)

Benjamin; Chapter 8.1-8.6

David Reckhow CEE 680 #28 1

Updated: 9 March 2020

Print version

 Martell & Smith,1977:

Critical Stability Constants

 Vol. 1: Amino Acids  Vol. 2: Amines  Vol. 3: Other Organic

Ligands

 Vol. 4: Inorganic

Complexes

 Vol. 5: Supplement

David Reckhow CEE 680 #28 2

Stability Constants

David Reckhow CEE 680 #28 3

Sources: Stumm & Morgan, 3rd Ed.

 Pg. 326

 From Morel & Hering, 1993

David Reckhow CEE 680 #28 4

Sources: Stumm & Morgan, 2nd Ed.

 Pg. 242

David Reckhow CEE 680 #28 5

Reconciling the constants: Al(OH)3

 S&M:3rd Edition

 AlL3 s 1033.5

 S&M:2nd Edition

 α-Al(OH)3(s) + 3H+ =

Al+3 + 3 H2O



*Kso

8.5

David Reckhow CEE 680 #28 6

5 . 33 3 3

10 ) ( =

• L

Al s AlL pH Al H Al H Al 3 5 . 8 ] log[ ] [ 10 ] [ ] [ ] [ 10

3 3 5 . 8 3 3 3 5 . 8

− = = =

+ + + + +

pH Al H Al H K Al OH Al

w

3 5 . 8 ] log[ ] [ ) 10 ( 10 ] [ ] [ ] [ ] ][ [ 10

3 3 3 14 5 . 33 3 3 3 3 3 3 5 . 33

− = = = =

+ + − − + + + − + −

Metal Hydrolysis

 Case for iron

David Reckhow CEE 680 #28 7

Fe(H2O)6

+3

FeOH(H2O)5

+2

Fe(OH)2(H2O)4

+

Fe(OH)3(H2O)3 Fe(OH)4(H2O)2

• + H+

+ 2H+ + 3H+ + 4H+

Fe(OH)3 (s)

FeOH(H2O)5

+2

David Reckhow CEE 680 #28 8

Fe O H

Fe(OH)2(H2O)4

+

David Reckhow CEE 680 #28 9

H O Fe O H

Dimer

David Reckhow CEE 680 #28 10

Fe Fe O O H H

Metals and acidity

 Metals increase the acidity of water  Greater as:

 Metal charge increases  Metal radius decreases

 As acidity increases, the predominant species

progresses down the list

 Aquo ion  Hydroxo complex  Hydroxy-oxo complex  Oxo complex

David Reckhow CEE 680 #28 11

David Reckhow CEE 680 #28 12

15

Fig 6.4a Pg.262

*K1

 A measure of the extent/strength of hydrolysis

 The first hydrolysis constant pK1 of an aqua metal ion is

dependent on the ionic charge and radius of the metal ion. The pK1 values of the aqua metal ions, studied here at 25°C follow, the order:

 Pb (7.8) ~ Cu (8.0) < Zn (8.96) < Co (9.85) < Ni (9.86) < Ag (11.1)

David Reckhow CEE 680 #28 13

Fig 6.4c Pg.262

[ ][ ]

] [ ) (

2 1 * + + +

= Zn H OH Zn K Barauh et al., 2014 [J. Geochem] Stumm & Morgan

Complexation of hydroxide?

 Pb (7.8) ~ Cu (8.0) > Zn (8.96) > Co (9.85) > Ni (9.86) > Ag (11.1)

David Reckhow CEE 680 #2 14

As pK1 goes up strength of OH complex goes down

Stability Constants

 Addition of a Ligand

David Reckhow CEE 680 #28 15

n K i K K K

ML ML ML ML M

n i

→  →  →  →     

2

2 1

β1 β2 βi βn L L L L

] ][ [ ] [

) 1 (

L ML ML K

i i i −

=

i i i

L M ML ] ][ [ ] [ = β

Stability Constants

 Addition of protonated Ligands

David Reckhow CEE 680 #28 16

n K i K K K

ML ML ML ML M

n i

→  →  →  →     

2

2 1

β1 β2 βi βn HL HL HL HL

] ][ [ ] ][ [

) 1 (

HL ML H ML K

i i i − +

=

i i i i

HL M H ML ] ][ [ ] ][ [

+

= β

EDTA

 Hexadentate Ligand

 Ethylenediamine Tetraacetic Acid

 Free form  Complexed with a metal  Interest to Env. Eng.

 Used in pollutant analysis  Model for NOM  Used for controlling scale  Huang et al., 2000 [JEED 126:10:919] David Reckhow CEE 680 #28 17

From: Butler, 1964

 Ni-hexammine  Tris(ethylene) diamine

nickel (II)

David Reckhow CEE 680 #28 18

Butler, 1964; pg.374

David Reckhow CEE 680 #28 19

From: Morel & Hering, 1993

Development of alpha

 Recall:  So:

David Reckhow CEE 680 #28 20

[ ]

2 2 2 2 1 2

] ][ [ ) (

− +

= = OH Zn OH Zn K K β

i i i

L M ML ] ][ [ ] [ = β

2 2 2 2 2 2

] [ ] [ ] [ ] ][ [ ] [ L M ML L M ML β β = =

3 3 3 3 3 3

] [ ] [ ] [ ] ][ [ ] [ L M ML L M ML β β = =

and Etc.

Alpha (cont.)

 Now let’s define, and alpha value

 And inverting the right hand side:

David Reckhow CEE 680 #28 21

] [ ] [ ] [ ] [ ] [ ] [

2 n M

ML ML ML M M C M + + + + = ≡  α

( )

1 2 2 1 1 2 1 2

] [ ] [ ] [ 1 ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [

− − −

+ + + + =         + + + + =         + + + + = ≡

n n n n M

L L L M ML M ML M ML M M M ML ML ML M C M β β β α   

2 2 2 2 2 2

] [ ] [ ] [ ] ][ [ ] [ L M ML L M ML β β = =

Alpha (cont.)

 Now other alpha’s can be determined

 And  So in general

David Reckhow CEE 680 #28 22

] [ ] [ ] [ ] [ ] [

1 1

L M ML C M C ML

M M

β α α = = ≡ ] [ ] [ ] [ ] ][ [ ] [

1 1

L M ML L M ML β β = =

2 2 2 2 2 2

] [ ] [ ] [ ] ][ [ ] [ L M ML L M ML β β = =

2 2 2 2 2

] [ ] [ ] [ ] [ ] [ L M ML C M C ML

M M

β α α = = ≡

n n M n n

L C ML ] [ ] [

0β

α α = ≡

Summary

 In summary:

 So if we know [L] and the β’s we can determine the

entire speciation of the metal

 This is analogous to the α’s of the acid/base systems

 Where if you know [H+] and the α’s , you can determine the

entire acid/base speciation

David Reckhow CEE 680 #28 23

( )

1 2 2 1

] [ ] [ ] [ 1 ] [

−

+ + + + = ≡

n n M

L L L C M β β β α 

n n M n n

L C ML ] [ ] [

0β

α α = ≡

To next lecture

David Reckhow CEE 680 #28 24

David Reckhow CEE 680 #28 25

Fig 6.4b Pg.262