Download Cu(NH3)4 - Granite Bay High School / Granite Bay High School

COORDINATION COMPOUNDS (In A Nutshell)
Cation or
Anion
Central
Metal
Ion
Coordination
Compound
(as needed)
Ligands
Complex Ion
[ Cu2+ + 4 NH3 ]2+ + SO42- =
[Cu(NH3)4]SO4
central ion: usually a transition metal with partially filled d orbitals
•small size + high charge = high charge density
•always has unoccupied orbitals into which electron pairs may be placed
complex ion: a cluster of a central metal ion bonded to ligands
•charge may be positive, negative or neutral (complexes are famous for bright identifiable colors)
•colors arise from electron transitions between split d orbitals (Cu2+is lt blue, Cu(NH3)42+is dk blue)
•no unpaired é’s (diamagnetic, repelled by magnet); unpaired é’s (paramagnetic, attracted)
ligands: molecules or anions bonded to central metal ion (most common are water and ammonia)
•hydrated salts have water molecules around the central metal ion
•ligands have unshared pair of electrons which they may donate to the central ion
•ligands with more than one bond to metal ion are called chelating agents (2 or more unshared é prs)
coordination number: number of ligands around the central positive ion (use sp, sp3, dsp3, or d2sp3orbitals)
•the most common are:
6 (octahedral); 4 (square planar or tetrahedral); 2 (always linear)
coordination compound: a complex ion plus the cation or anion needed to yield zero charge
•commonly used in bringing water-insoluble species into solution
•found in hemoglobin (Fe2+), chlorophyll (Mg2+), vitamin B12 (Co2+), EDTA, and qualitative analysis
coordinate covalent compound: covalent bonds in which both electrons in shared pair come from same atom
NOMENCLATURE:
(1) ligands are named first, negative ones are named before molecular ligands, in order shown below going left to right:
OH- (hydroxo)
Br- (bromo)
Cl- (chloro)
F- (fluoro)
I- (iodo)
S2- (thio)
CN- (cyano)
22SCN (thiocyano) S2O3 (thiosulfato) C2O4 (oxalato) H2O (aquo)
NH3 (ammine)
CO (carbonyl)
NO (nitrosyl)
(2) a prefix must precede ligand names designating the number of molecules or ions present (di-, tri-, tetra-, penta-, etc.)
(3) central atom is named second (Latin stems used for many of the metals)
copper (cuprate)
gold (aurate)
iron (ferrate)
lead (plumbate)
silver (argentate)
tin (stannate)
(4) name of the complex ion ends in -ate if the complex as a whole possesses a negative charge (otherwise name is unchanged)
(5) a roman numeral in parentheses must follow the metal ion name if the central atom has more than one oxidation state
(6) name of complex ion is written as one word
(7) add name of balancing ion to the complex ion name, if there is one
EXAMPLE:
The compound shown at top of the page, [Cu(NH3)4]SO4
PRACTICE:
Ag3[Fe(CN)6]
SiF62-
PtCl62-
GeF62-
= tetramminecopper(II) sulfate
[Ni(NH3)6]Br2
Na2[Sn(OH)6]
Co(NH3)4(H2O)Cl2+
COMPLEX ION FORMATION
Coord.
No.
Metal
Ion
Angles
Hybrid.
Orbitals
Shape
Example
2
Cu+
180º
sp
linear
Cu(NH3)2+
light blue
diamminecopper(I)
dia
linear
Ag(NH3)2
+
colorless
diamminesilver
dia
linear
–
dicyanoaurate(I)
2–
tetracyanonickelate (II)
dia
tetramminecopper(II)
dia
least common
Ag
Au
4
mostly d8
transition
metals
Ni
+
+
2+
Cu
Pd
2+
2+
2+
Pt
4
Al
180º
180º
90º
d sp
3
90º
2
d sp
3
90º
2
d sp
3
90º
2
3
109.5º
most common
2+
Co
109.5º
of coord. no. 4,
Ni2+
109.5º
especially the
nontransition
metals
+
2+
Zn
Cd
2+
Au
6
+
sp
2
3+
Cu
sp
109.5º
109.5º
109.5º
109.5º
d sp
square planar
square planar
square planar
square planar
Color
Au(CN)2
Ni(CN)4
Cu(NH3)4
PdI4
2+
deep blue
2–
Pt(NH3)4
2+
sp
3
tetrahedral
sp
3
tetrahedral
sp
3
tetrahedral
sp
3
tetrahedral
sp
3
tetrahedral
Zn(NH3)42+
sp
3
tetrahedral
2+
sp
3
AlCl4
CoCl4
NiCl4
–
Systematic
Name
Other Facts
tetraiodopalladate(II)
inert
tetrammineplatinum (II)
inert; always a 4
tetrachloroaluminum
2–
blue
2–
Cd(NH3)4
tetrachlorocobaltate(II)
tetrachloronickelate(II)
para
colorless
tetraamminezinc
dia
colorless
tetramminecadmium
dia
always a 6
para
inert; nonpoisonous
dia
tetrahedral
90º
d sp
3
octahedral
AlF63-
Cr3+
90º
d2sp3
octahedral
Cr(NH3)63+
yellow
Fe2+
90º
d2sp3
octahedral
Fe(CN)64–
yellow
hexafluoroaluminum
hexamminechromium
(III)
hexacyanoferrate(II)
octahedral
3–
red
hexacyanoferrate(III)
labile; poisonous
yellow
Al
3+
Fe
3+
2+
Co
3+
Co
Ni
2+
Cu
2+
4+
Pt
2
90º
2
d sp
3
90º
2
d sp
3
90º
2
d sp
3
90º
2
d sp
3
octahedral
90º
2
d sp
3
octahedral
90º
2
3
octahedral
d sp
Magnetism
octahedral
octahedral
Fe(CN)6
Co(NH3)6
2+
hexamminecobaltate(II)
always a 6
Co(NH3)6
3+
yell-orange hexamminecobaltate(III)
always a 6
2+
blue-violet
Ni(NH3)6
PtCl62–
hexamminenickel(II)
hexachloroplatinate(IV)
inert
MORE COMPLEX FACTS:
(1) most commonly complexed are those metals to the right side of the transition metals (Cr thru Zn)
(2) both electrons must be donated by ligand; total no. of prs donated = coord. no.
(3) "ligands" come from the Latin word "ligare, meaning to bind
(4) there are no outer s electrons in a transition metal cation (electrons beyond preceding noble gas are located
in an inner d sublevel; example: Cr atom: 3d54s1 while Cr3+ ion has 3d3)
(5) diamagnetic means there are no unpaired electrons (weakly repelled by a magnetic field)
(6) paramagnetic means there are unpaired electrons (very attracted to a mag. field)
(7) most metal cations (except Groups 1 and 2) are weak acids because they are hydrated
Example:
Zn(H2O)42+(aq) ↔ H+(aq) + Zn(H2O)3(OH)+(aq)
(8) chelates are complexes formed by polydentate ligands; "chelate" comes from Greek for crab's claw
(9) complexes used in sensitive qualitative tests to detect presence of ions in parts per million (ppm) range
(10) hydrated ionic salts have water molecules as ligands and are thus complex ions/coordination compounds
(11) as ligands get larger, fewer can surround central ion; coord. no. may go from 6 to 4, etc.
(12) many complexes form brilliant colors or dissolve insoluble compounds such as AgCl
(13) inert complexes undergo ligand exchange very slowly and last long eneough to be carefully studied
(14) labile complexes exchange ligands almost instantaneously (labile actually means "unstable")
(15) 1 hemoglobin (Hgb) molecule = 4 hemes = 4[Fe2+ + 4-N-of a porphyrin + 1 globin + 1 H2O] = octahedral = blue color
(16) when water ligand in each heme is replaced with O2, the color goes to bright red (arterial blood)
(17) 280 million Hgb molecules per RBC; each carries 4 molecules O2; loads/unloads 2x/minute
(18) carbon monoxide molecule is similar in size to O2 and combines 200x more readily than O2 with hemoglobin (silent killer)
(19) Hgb will replace water with cyanide (CN-) which has almost same geometry as CO;
(20) cyanide denatures respiratory enzymes causing death in 2-3 minutes (almond odor breath?)
(21) the Pb2+ ion is poisonous because it deactivates the enzyme that forms heme
(22) EDTA is a preservative (chelates unwanted metals that spoil foods) and is used as an antitumor agent in chemotherapy