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

Print version Updated: 9 March 2020 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

Stability Constants  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

David Reckhow CEE 680 #28 3

Sources: Stumm & Morgan, 3 rd Ed.  Pg. 326  From Morel & Hering, 1993 David Reckhow CEE 680 #28 4

Sources: Stumm & Morgan, 2 nd Ed.  Pg. 242 David Reckhow CEE 680 #28 5

Reconciling the constants: Al(OH) 3  S&M:3 rd Edition  S&M:2 nd Edition  α -Al(OH) 3 (s) + 3H + =  AlL 3 s 10 33.5 Al +3 + 3 H 2 O AlL ( s ) = 33 . 5 3 10 * K so 8.5 • L 3  Al + 3 [ Al ] 3 K = 8 . 5 10 − = + − = + 33 . 5 3 3 3 10 [ Al ][ OH ] [ Al ] w + 3 + [ H ] 3 [ H ] + + = + = − − + 3 8 . 5 3 3 33 . 5 14 3 3 [ Al ] 10 [ H ] [ Al ] 10 ( 10 ) [ H ] + + = − 3 = − 3 log[ Al ] 8 . 5 3 pH log[ Al ] 8 . 5 3 pH David Reckhow CEE 680 #28 6

Metal Hydrolysis  Case for iron + 2H + + H + Fe(H 2 O) 6 +3 FeOH(H 2 O) 5 +2 Fe(OH) 2 (H 2 O) 4 + + 3H + + 4H + Fe(OH) 3 (H 2 O) 3 Fe(OH) 4 (H 2 O) 2 - Fe(OH) 3 (s) David Reckhow CEE 680 #28 7

+2 FeOH(H 2 O) 5 Fe O H David Reckhow CEE 680 #28 8

+ Fe(OH) 2 (H 2 O) 4 H O Fe O H David Reckhow CEE 680 #28 9

Dimer H O Fe Fe O H David Reckhow CEE 680 #28 10

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

Fig 6.4a 15 Pg.262 David Reckhow CEE 680 #28 12

[ ][ ] + + Zn ( OH ) H *K 1 * = K 1 + 2 [ Zn ]  A measure of the extent/strength of hydrolysis  The first hydrolysis constant pK 1 of an aqua metal ion is dependent on the ionic charge and radius of the metal ion. The pK 1 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) Barauh et al., 2014 [J. Geochem] Fig 6.4c Stumm & Morgan Pg.262 David Reckhow CEE 680 #28 13

As pK 1 goes up strength of OH complex goes down 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

Stability Constants  Addition of a Ligand L L L L  →  →  →  → K K K K M ML ML ML ML     1 2 i n 2 i n β 1 β 2 β i β n [ ML ] [ ML ] = β = K i i i i i [ ML ][ L ] [ M ][ L ] − ( i 1 ) David Reckhow CEE 680 #28 15

Stability Constants  Addition of protonated Ligands HL HL HL HL  →  →  →  → K K K K M ML ML ML ML     1 2 i n 2 i n β 1 β 2 β i β n + + i [ ML ][ H ] [ ML ][ H ] = β = K i i i i i [ ML ][ HL ] [ M ][ HL ] − ( i 1 ) David Reckhow CEE 680 #28 16

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] From: Butler, 1964 David Reckhow CEE 680 #28 17

 Ni-hexammine  Tris(ethylene) diamine nickel (II) Butler, 1964; pg.374 David Reckhow CEE 680 #28 18

From: Morel & Hering, 1993 David Reckhow CEE 680 #28 19

Development of alpha  Recall: [ ] [ ML ] Zn ( OH ) β = i β = = 2 K K i i [ M ][ L ] 2 1 2 + − 2 2 [ Zn ][ OH ]  So: [ ML ] [ ML ] β = β = 3 2 3 2 3 2 [ M ][ L ] [ M ][ L ] Etc. and [ ML ] [ ML ] = β 3 = β 2 3 [ L ] 2 [ L ] 3 2 [ M ] [ M ] David Reckhow CEE 680 #28 20

Alpha (cont.)  Now let’s define, and alpha value [ M ] [ M ] α ≡ =  And inverting the right hand side: 0 + + + + C [ M ] [ ML ] [ ML ] [ ML ]  M 2 n − 1   + + + + [ M ] [ M ] [ ML ] [ ML ] [ ML ]  α ≡ =   2 n   0 C [ M ]   M − 1   [ M ] [ ML ] [ ML ] [ ML ] =  + + + +  2 n    [ M ] [ M ] [ M ] [ M ]   ( ) − 1 [ ML ] = + β + β + + β 2 n 1 [ L ] [ L ] [ L ]  β = 2 1 2 n 2 2 [ M ][ L ] [ ML ] = β 2 2 [ L ] 2 David Reckhow CEE 680 #28 [ M ] 21

Alpha (cont.)  Now other alpha’s can be determined [ ML ] [ M ] [ ML ] [ ML ] α ≡ = β = 1 1 C C [ M ] [ M ][ L ] M M = α β [ ML ] [ L ]  And = β [ L ] 0 1 1 [ M ] [ ML ] [ M ] [ ML ] α ≡ = 2 2 2 C C [ M ] [ ML ] M M β = 2 2 2 = α β 2 [ M ][ L ] [ L ] 0 2  So in general [ ML ] = β 2 2 [ L ] 2 [ M ] [ ML ] α ≡ = α 0 β n n [ L ] n n C M David Reckhow CEE 680 #28 22

Summary  In summary: ( ) [ M ] − 1 α ≡ = + β + β + + β 2 n 1 [ L ] [ L ] [ L ]  0 1 2 n C M [ ML ] α ≡ = α 0 β n n [ L ] n n C M  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

 To next lecture David Reckhow CEE 680 #28 24

Fig 6.4b Pg.262 David Reckhow CEE 680 #28 25