2A-1
d-block elements: definitions
consider a “typical” molecule containing a d-block element
This is a “coordination complex”. Also known as a “(transition) metal complex”
ligand:
Coordination, Coordinate bond: A M-L bond is a Lewis acid-base interaction
H&S 7.11
2A-2
coordination number:
Inner coordination sphere
outer coordination sphere
d-block elements: definitions
H&S 7.11
Ligands
2A-3
Common ligands survey (Table 7.7 H&S for partial list)
Neutral ligands generally classified as “L,” anionic is “X” (X-) in molecular formulas
e.g. ML2X3 has two neutral ligands and three anionic ligands.
The metal ligand bond is nearly always polarized towards the ligand:
M +L-
M +X-
H&S 7.11
2A-4
Ligands – group 17 elements
H&S 7.11
Group 17: anionic (X): halide anions F-, Cl-, Br-, I-
Halides (and other ligands with an “extra” lone pair) can alternatively bind to two metals at
the same time – this is a “bridging ligand”. The normal mode is “terminal”
2A-5
Ligands – group 16
H&S 7.11
Group 16: neutral (L): H2O (water), alcohols (ROH), ethers (ROR)
anionic (X): OH- (hydroxide), OR- (alkoxide), O2- (“oxo”)
Metal-aquo
complex
Metalhydroxide
Metal-Oxo
(also known as “oxide”)
Alcohol
(e.g. CH3OH)
ether
e.g. diethyl
ether,
CH3CH2OCH2CH3
2A-6
Ligands - aquo
The acidity of aquo ligands goes up when bound to metals compare to water itself.
pKa considerations can be important!
e.g. suppose you wanted to make Cr(NH3)6]3+. Ammonia can substitute water. But….
H&S 7.11
2A-7
Ligands – group 15
Nitrogen donors
Ammonia
Ammine complex
Amide anion
Amide complex
Pyridine (an L type ligand)
H&S 7.11
H&S 7.11
Ligands-group 15
2A-8
Phosphines:
phosphine
trimethylphosphine Tri-isopropylphosphine
Triphenylphosphine
A phosphine complex
2A-9
Ligands – group 14
H&S 7.11
Complexes with metal-carbon bonds are commonly called organometallic compounds
Carbon monoxide (L) A metal-carbonyl
complex
Cyanide (X)
Methane
A metal-cyanide
complex
Methyl anion
A metal-methyl complex