Transcript Metal Complexes

Metal Complexes
• metal cation is attached to a group of
surrounding molecules or ions (ligands) by
coordinate covalent bonds
– coordinate => ligand donates both electrons
• each ligand makes at least one coordinate
covalent bond to the metal cation
– any atom (from a ligand) that is directly bound to the
metal cation is called a donor atom
• coordination number (C.N.) = the total number
of donor atoms surrounding a metal cation (=
total number of coordinate covalent bonds)
TM I-Intro to Complexes 1
Lewis definition of acids and bases
• Base: e- - pair donor
• Acid: e- - pair acceptor
• In metal complexes, the ligand is always a Lewis
base (makes a coordinate covalent bond) and
the metal cation is a Lewis acid (accepts the
lone pair from ligand).
• Note: definition applies to things other than
metal complexes (e.g., NH3-BF3)
TM I-Intro to Complexes 2
Examples of Metal Complexes
Ni(H2O)62+
Six H2O ligands bound
to a Ni2+ cation
http://www.3dchem.com/3dinorgmolecule.asp?ID=490
Co(NH3)4Cl2+
Four NH3 ligands and two Clligands bound to a Co3+ cation
http://www.3dchem.com/3dinorgmolecule.asp?ID=196
TM I-Intro to Complexes 3
More Examples
Ni(H2O)4SO4
Four H2O ligands and one SO42ligand bound to a Ni2+ cation
http://www.3dchem.com/3dinorgmolecule.asp?ID=440
Ni(CN)42Four CN- ligands bound
to a Ni2+ cation
http://www.3dchem.com/3dinorgmolecule.asp?ID=500
TM I-Intro to Complexes 4
Charge on complex vs. charge on cation
• charge on complex = sum of the charges of the metal
cation (oxidation #) plus charges on all ligands bound
– don’t mix up charge on cation with charge on the (whole)
complex! **charge on complex appears as right superscript**
• Examples
– Co(NH3)4Cl2+
• Charge on Co is +3
• Charge of each NH3 is 0
• Charge of each Cl- is -1
– Ni(CN)42• Charge on Ni is +2
• Charge of each CN- is -1
 Charge of complex is
+3 + 4(0) + 2(-1) = +1
 Charge of complex is
+2 + 4(-1) = -2
TM I-Intro to Complexes 5
Coordination Compounds are Neutral
**The species inside the brackets is always a
complex ion (metal cation + ligands); the
part(s) outside of brackets are counterions.**
• if charge on complex is
– neutral, the complex itself is a coordination compound
• e.g., Pt(NH3)2Cl2
– Charge on Pt = +2
– Charge on NH3 = 0
– Charge on Cl- = -1
 Charge of complex is
+2 + 2(0) + 2(-1) = 0
– not neutral, complex plus counterions can form a
neutral salt, also called a coordination compound
• e.g., [Ni(NH3)6]Cl2 ; complex is a cation; Cl-’s are counterions
– In water, it dissociates into Ni(NH3)62+ and two Cl- ions:
– [Ni(NH3)6]Cl2  Ni(NH3)62+ + 2 Cl-
• e.g., (NH4)4[Fe(CN)6] ; complex an anion; NH4+’s, counterions
– (NH4)4[Fe(CN)6]  4 NH4+ + Fe(CN)64-
TM I-Intro to Complexes 6
Example
• e.g., [Co(NH3)4Cl2]Cl
– inside brackets = metal complex
– outside= counter ion(s)
– # ligands = 6 (four neutral NH3’s; two Cl-’s)
– # counterions = 1 (Cl-)
• Note! anions can sometimes be ligands and
sometimes be counterions!
• neutral ligands can never be counterions!
– # donor atoms = 6 (four N’s from NH3’s;
two Cl’s from Cl-’s)  CN = 6
TM I-Intro to Complexes 7
Common C.N.’s and their
Geometries
C.N.: 2
4
4
6
TM I-Intro to Complexes 8
Example of a tetrahedral metal complex
Ni(CO)42+
Four CO ligands bound
to a Ni2+ cation
http://www.3dchem.com/3dinorgmolecule.asp?ID=489
TM I-Intro to Complexes 9
Ligand Types
(See Table 24.3 in Tro [next slide])
• Ligands that bind to a metal cation via:
– one donor atom are called monodentate
ligands
• Cl-, NH3, CN-, H2O (donor atoms are,
respectively, Cl, N, C (or N!), O
– more than one donor atom are called
polydentate ligands
• two atoms per ligand – bidentate (en, ox2-, bpy)
• three atoms, tridentate
• etc
TM I-Intro to Complexes 10
NOTE: All donor atoms
must have at least one
lone pair
____________,
which it
uses to make a bond to
the metal cation.
Monodentate
(donor atom circled)
Monodentate
(but two possible donor
atoms [only one can
bond at a time])
Learn the
abbreviations for these
two (ox and en)
Bidentate
(two donor atoms; both
bond to the same metal
cation at the same time)
11
NOTE: Some
ligands are…
neutral
And some ligands
are…
negatively charged
12
Ligand Types
(Table 20.13, McMurry & Fay; Similar to Tro, 24.2)
TM I-Intro to Complexes 13
Ligand Types
(Tables 20.13 (McMurry) and 24.2 (Tro), continued)
TM I-Intro to Complexes 14
Example – ethylenediamine (en)
• en = NH2CH2CH2NH2
– each N in one en ligand can
bind to a metal cation!
• Co(en)2Cl2+
– # ligands = 4 (two en’s, two Cl-’s)
– C.N. = 6 (not 4!) because each en ligand
makes two coordinate covalent bonds to the
Co3+ using two different N atoms per ligand
TM I-Intro to Complexes 15