TM I-Intro to Complexes CHM 122 Week 12, I&II 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

Lewis definition of acids and bases CHM 122 Week 12, I&II 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

Examples of Metal Complexes CHM 122 Week 12, I&II 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 http://www.3dchem.com/3dinorgmolecule.asp?ID=490 http://www.3dchem.com/3dinorgmolecule.asp?ID=196 TM I-Intro to Complexes

More Examples Ni(H2O)4SO4 Ni(CN)42- CHM 122 Week 12, I&II More Examples Ni(H2O)4SO4 Ni(CN)42- Four H2O ligands and one SO42- ligand bound to a Ni2+ cation Four CN- ligands bound to a Ni2+ cation http://www.3dchem.com/3dinorgmolecule.asp?ID=440 http://www.3dchem.com/3dinorgmolecule.asp?ID=500 TM I-Intro to Complexes

Charge on complex vs. charge on cation CHM 122 Week 12, I&II 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 TM I-Intro to Complexes

Coordination Compounds are Neutral CHM 122 Week 12, I&II 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 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- Charge of complex is +2 + 2(0) + 2(-1) = 0 TM I-Intro to Complexes

TM I-Intro to Complexes CHM 122 Week 12, I&II 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

Common C.N.’s and their Geometries CHM 122 Week 12, I&II Common C.N.’s and their Geometries C.N.: 2 4 4 6 TM I-Intro to Complexes

Example of a tetrahedral metal complex CHM 122 Week 12, I&II 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

Ligand Types (See Table 24.3 in Tro [next slide]) CHM 122 Week 12, I&II 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

Learn the abbreviations for these two (ox and en) Bidentate CHM 122 Week 12, I&II NOTE: All donor atoms must have at least one ____________, which it uses to make a bond to the metal cation. Monodentate (donor atom circled) lone pair 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)

NOTE: Some ligands are… CHM 122 Week 12, I&II NOTE: Some ligands are… neutral And some ligands are… negatively charged

Ligand Types (Table 20.13, McMurry & Fay; Similar to Tro, 24.2) CHM 122 Week 12, I&II Ligand Types (Table 20.13, McMurry & Fay; Similar to Tro, 24.2) TM I-Intro to Complexes

Ligand Types (Tables 20.13 (McMurry) and 24.2 (Tro), continued) CHM 122 Week 12, I&II Ligand Types (Tables 20.13 (McMurry) and 24.2 (Tro), continued) TM I-Intro to Complexes

Example – ethylenediamine (en) CHM 122 Week 12, I&II 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