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) 1 TM I-Intro to 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 - PowerPoint PPT Presentation
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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)
1TM I-Intro to Complexes
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)
2TM I-Intro to Complexes
Examples of Metal Complexes
Ni(H2O)62+ Co(NH3)4Cl2+
Six H2O ligands bound to a Ni2+ cation
Four NH3 ligands and two Cl- ligands bound to a Co3+ cation
ligand bound to a Ni2+ cationhttp://www.3dchem.com/3dinorgmolecule.asp?ID=440
Ni(CN)42-
Four CN- ligands bound to a Ni2+ cation
http://www.3dchem.com/3dinorgmolecule.asp?ID=500
4TM I-Intro to Complexes
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
Charge of complex is +3 + 4(0) + 2(-1) = +1
– Ni(CN)42-
• Charge on Ni is +2• Charge of each CN- is -1
Charge of complex is +2 + 4(-1) = -2
5TM I-Intro to Complexes
Coordination Compounds are Neutral
• 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
– 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)6
2+ and two Cl- ions:– [Ni(NH3)6]Cl2 Ni(NH3)6
2+ + 2 Cl-
• e.g., (NH4)4[Fe(CN)6] ; complex an anion; NH4+’s, counterions
– (NH4)4[Fe(CN)6] 4 NH4+ + Fe(CN)6
4-
Charge of complex is +2 + 2(0) + 2(-1) = 0
6TM I-Intro to Complexes
**The species inside the brackets is always a complex ion (metal cation + ligands); the part(s) outside of brackets are counterions.**