Chemistry 223 Chapter 26 Coordination Complexes d-block elements
Chemistry 223 Chapter 26 Coordination Complexes d-block elements a.k.a. transition metals d-block elements are: all metals all have partially filled d subshells
exhibit horizontal & vertical similarities alloys & compounds are important components of materials in modern world most first-row transition metals are essential for life General Trends among Transition Metals
General Trends among Transition Metals 4th row Horizontal Periodic Trends General Trends among Transition Metals
Going across row from left to right , e-s are added to 3d subshell to neutralize increase in (+) charge of nucleus as atomic # increases. General Trends among Transition Metals
3d subshell fill based on aufbau principle & Hunds rule with two important exceptions: Reactivity: Size of neutral atoms of d-block elements
gradually decreases left to right across a row. Why? Due to increase in Zeff with increasing atomic # Atomic radius increases going down a column. Why?
Transition metals become less reactive (more Noble) going from left to right across a row Trends in Transition Metal Oxidation States: Transition metals form cations by initial loss of ns e-s, even though ns orbital is lower in energy
than (n1)d subshell in the neutral atom. d-electron configuration for di-cations of 1st row of transition metals Trends in Transition Metal Oxidation States: Small E difference btwn ns and (n-1)d plus screening effect means
less E losing ns e-s before (n-1)d e-s All transition-metal cations possess dn valence e- configurations for 2+ ions of 1st row. Trends in Transition Metal Oxidation States: Electronegativities of first-row transition metals
increase (somewhat) smoothly from Sc to Cu Sc Ti V Cr Mn Fe Co Ni Cu 1.36 1.54 1.63 1.66 1.55
Zn 1.83 1.88 1.91
1.90 1.65 Trends in Transition Metal Oxidation States:
max oxid states for 2nd & 3rd row transition metals in Groups 3 thru 8 increase from +3 for Y and La to +8 for Ru and Os Trends in Transition Metal Oxidation States:
Going farther to right, maximum oxidation state decreases, reaching +2 for elements of Group 12, Descriptive Chemistry of 3d Transition Metals: Scandium Titanium
+2, +3 Ores are hematite, magnetite, and pyrite (fools gold), steel, hemoglobin, blast furnace, magnetic Cobalt Nickel
Copper [Ar]4s23d7 [Ar]4s23d8 [Ar]4s13d10 +2, +3
+2 +1, +2 Blue cobalt glass, , AlNiCo, magnetic Coins, AlNiCo, Monel, magnetic Coins, brass, bronze, Statue of Liberty, patina, electric wires, ores are chalcocite, chalcopyrite and
malachite, unreactive w/ HCl and H 2SO4 but very reactive w/HNO3 Zinc [Ar]4s23d10
+2 Coins, brass, biochemistry, RA Gold [Xe]6s14f145d10
+1, +3 Coins, jewelry, soft as pure metal, alloys are harder, CN used to extract Au from ores Silver
[Kr]5s14d10 +1 Coins, jewelry, most electrically conductive of all metals
Mercury [Xe]6s24f145d10 +1, +2
Quicksilver, poisonous, mad as a hatter, Minimata Strong, light, corrosion-resistant, steel alloys, white pigments, ore is rutile Compounds of Mn in +2 to +7 oxidation states
Different # of d electrons = different colors Why is that? Coordination Compounds Metallic elements act as Lewis acids form complexes with various Lewis bases.
Metal complex: Coordination Compounds Central metal atom (or ion) bonded to one or more ligands. Ligands:
Ligands Coordination Compounds metal & ligand complexes as ions: Coordination Compounds Coordination compounds & complexes are
distinct chemical species properties & behavior diff from metal atom / ion or the ligands History of Coordination Compounds Coordination compounds used since
ancient times, but chemical nature unclear. Werner: modern theory of coordination chemistry - based on studies of several series of metal halide complexes with ammonia History of Coordination Compounds
Werner postulated that metal ions have 2 different kinds of valence: 1. primary valence (oxidation state) = 2. secondary valence (coordination #) Alfred Werner
(1866-1919) Same chemical composition, same # of groups of same types attached to same metal. What made the two different colors? More on this later!
Structures of Metal Complexes Coordination #s of metal ions in metal complexes can range from 2 to 9. Differences in E btwn
different arrangements of ligands greatest for complexes w/ low coordination #s & decrease as coordination # increases. Structures of Metal Complexes Only one or two structures possible for complexes w/ low coordination #s.
Several different energetically = structures are possible for complexes with high coordination #s (n > 6) Structures of Metal Complexes Coordination # 2 = linear
Rare for most metals; common for d10 metal ions, especially: Cu+, Ag+, Au+, and Hg2+ Coordination # 4 Two common structures: tetrahedral & square planar
Tetrahedral: all 4-coordinate complexes of non-transition metals & d10 ions and first-row transition metals, Coordination # 4 Two common structures: tetrahedral & square planar Square planar: 4-coordinate complexes of
2nd & 3rd row transition metals with d8 e- configurations, e.g. Rh+ , Pt2+ and Pd2+, also encountered in some Ni2+ & Cu2+ complexes. Structures of Metal Complexes
Coordination # 6 Most common: six ligands at vertices of an octahedron or a distorted octahedron. We will focus primarily on octahedral Other Structures of Metal Complexes Possible:
Coordination # 3 Encountered with d10 metal ions e.g.Cu+ & Hg2+ trigonal planar structure Coordination # 5 geometries
and 2nd & 3rd row transition metals 7, 8 & 9 coordination #s, give other geometries: Metal-ligand interaction is an example of
Lewis acid-base interaction. Lewis acid Lewis base Lewis bases Must have Transition metal ions tend to form
coordination complexes which we encountered back in Chapter 22. e.g. AgCl is more soluble in 0.10 M NH3 than it is in pure water because Ag+ forms a complex with NH3 with a very large formation constant: Ag+ + 2NH3 Ag(NH3)2+
The complex ion Ag(NH3)2+ that forms is called diamminesilver(I) (review rules on pp. 1055-1056). Why does it form? It forms because each NH3 is a Lewis base and forms a coordinate covalent bond
with the silver ion, Ag+, in solution The complex has a linear geometry. to purify the Ag(NH3)2+ complex ion & store it in a bottle it would need an anion to neutralize the charge
e.g. diamminesilver(I) chloride, [Ag(NH3)2+]Cl or diamminesilver(I) nitrate: [Ag(NH3)2+]NO3. [Ag(NH3)2+]Cl or
[Ag(NH3)2+]NO3. In these compounds, silver is ____________ NH3 is ______________ and Cl or NO3 is ____________________. Ligands are attached by ___________ bonds
Counterions are attached by _______ bonds! Another complex formation reaction is: Co3+ + 6 NH3 Co(NH3)63+ Kf = [Co(NH3)63+] = 2.3 x 1033 [Co3+][NH3]6 This complex ion is called:
This complex has an octahedral geometry. Another example is: Cu2+ + 4 CN Cu(CN)42 Kf = [Cu(CN)42] = 1.0 x 1025 [Cu2+][CN]4
This complex ion is called This complex has a tetrahedral geometry. When a bidentate ligand binds to a metal, A polydentate ligand is a chelating agent,
of polydentate ligands are more stable than complexes of chemically similar monodentate
ligands. Nomenclature (IUPAC) rules for Naming coordination compounds: Cation named before anion (as usual); but, transition metal atom in the complex is named last
with oxidation state in roman numerals in parentheses Nomenclature (IUPAC) rules for Naming coordination compounds: Cation named before anion (as usual), no D; anion ending for transition metal will be ate
e.g. Cobalt anion = [Ni(NH3)6] (NO3)2 cation complex K3 [Co(Cl)6] anion complex Anionic complex metal ending: Scandium = Scandate
Special names for some transition metals in an anion complex Nomenclature (IUPAC) rules for Naming complexes: Ligands named 1st (alphabetically) Greek prefixes for counting
di, tri, tetra, penta, hexa, etc. Nomenclature (IUPAC) rules for Naming anionic ligands: Use suffix o if ending in ide (e.g. chloride chloro; cyanide cyano hydroxide hydroxo; oxide oxo)
Use suffix ito if ending in ite (e.g. nitrite nitrito) Use suffix ato if ending in ate (e.g. oxalate oxalato; sulfate sulfato carbonate carbonato Neutral ligands:
Usual name: e.g. ethylenediamine Exceptions: Nitrite, NO2: Which atom on the ligand donates its lone pair Ds the name
Give the chemical formula for Hexaaquanickel(ll) diaquatetrabromochromate(lll) Give the chemical formula for Give the name for [Co(NH3)6][CoCl6]
Practice naming some complex compounds: [Pt(Cl2)(NH3)2] K2[PtCl4] Practice naming some complex compounds:
[Pt(NH3)4]Cl2 [Pt(NH3)3Cl]Cl Na[CoCl4(NH3)2] Practice writing the complex compound formulas: hexaaquochromium(III) chloride
diaquodichloroaurate(III) chloride potassium hexacyanoferrate(II) potassium hexacyanoferrate (III) Clicker Qstn: the correct name for the complex
Na2[Ni(CN)4] A. Disodium tetranickelcyanide B. Sodium tetracyanidenickel(l) C. Disodium tetracyanonickelo(lV) D. Natrium tetranickel(Vl)cyanide E. Sodium tetracyanonickelate(lll)
Constitutional (Structural) Isomers 1. Ionization isomers 2. Linkage isomers Geometrical isomers of Complexes Differ only in arrangement of ligands around metal ion. Metal complexes that differ only in which ligands are
adjacent to one another (cis) or directly across from one another (trans). Cis-platin isomer fights cancer, Trans-platin doesnt
Geometrical isomers are most important for square planar & octahedral complexes. Square planar complexes: all vertices of a square are equivalent, it does not matter which vertex is occupied by ligand B
in a square planar MA3B complex. Only one geometrical isomer is possible Only one isomer when theres one B ligand. With two, there are other possible arrangements. Symmetrical bidentate ligands
also only have one structure Isomers of Metal Complexes Octahedral complexes: Only one structure possible for octahedral complexes (if only one ligand is different from other five):
(MA5B) since all six vertices of an octahedron are equivalent. Isomers of Metal Complexes Octahedral complexes: If two ligands in an octahedral complex
are different from other four (MA4B2), two isomers are possible: two B ligands can be _____________________. Chelating agents (chelate = ________) Bidentate (2 teeth):
Bidentate (2 teeth): e.g. ethylenediamine (en) Octahedral isomer complexes: Replacing another A ligand by B gives an MA3B3 complex for which there are two isomers:
Octahedral isomer complexes: Fac: 3 ligands of each kind occupy opposite triangular faces of the octahedron Mer: 3 ligands of each kind lie on the meridian
(cut across flat mid-plane) (cut across flat mid-plane) Some coordination complexes with mixed ligands have optical isomers and are said to be chiral. A complex is chiral if its mirror images
are different molecules. Anything thats linear is not chiral (achiral), i.e. mirror image is always same as original. Anything thats square planar is not chiral (achiral),
i.e. mirror image is always same as original. Anything thats tetrahedral is chiral only if all four groups are different. octahedral is chiral with monodentate groups only if: (a) all six groups are different (ABCDEF) or
(b) two groups are the same and cis (AABCDE) or (c) three groups are the same and fac, i.e. none trans (AAABCD) or (d) there are two pairs of identical groups and both are cis (AABBCD) OR
some possibilities with bidentate ligands, cis-dichlorobisethylenediaminecobalt(III) If any pair of identical groups is trans, there is no chirality! any octahedral molecule with a mirror plane is achiral. (any single pair of identical trans ligands
guarantees a mirror plane) Crystal Field Theory Crystal Field Theory Bonding model explaining many important properties of
transition-metal complexes: Crystal Field Theory Central assumption of CFT: metal-ligand connections are electrostatic interactions btwn a central metal ion
and a set of negatively charged ligands (or ligand dipoles) arranged around metal ion. d-Orbital Splittings five d orbitals are initially degenerate (same energy).
When the 6 (-) charges are distributed uniformly over surface of a sphere, d orbitals remain degenerate. d-Orbital Splittings But!
Their energy will be higher due to d-Orbital Splittings If the 6 (-) charges are placed at vertices of an octahedron, avg energy of d orbitals
does not change. d-Orbital Splittings But! It does remove their degeneracy and the 5 d orbitals split into two groups
d-Orbital Splittings The dx2 y2 and dz2 orbitals (eg orbitals) point directly at the six (-) charges, which increase their Energy compared with a spherical distribution of negative charge. The dxy, dxz, & dyz (t2g orbitals)
are all oriented at a 45 angle to the coordinate axes and point between the 6 (-) charges, which decreases their Energy compared with a spherical distribution of charge As LPs onAs ligands approach
along x, y, and z axes. d-Orbital Splittings Difference in E btwn the two sets of d orbitals is crystal field splitting energy.
d-Orbital Splittings Magnitude of the splitting depends on: Splitting of d orbitals in a crystal field does not D total energy of the five d orbitals
Electronic Structures of Metal Complexes Using d-orbital energy-level diagram: electronic structures & some properties of transition-metal complexes can be predicted. Start with Ti3+ ion,
(contains a single d electron), proceed across first row of transition metals by adding a single e- at a time. Additional e-s placed in lowest-E orbital available while keeping their spins parallel
For d1-d3 systems, e-s successively occupy the 3 degenerate t2g orbitals with their spins parallel (paramagnetic) giving one, two, and three unpaired electrons. Electronic Structures of Metal Complexes d4 configuration: two possible choices for 4th e-:
enter one of the empty eg orbitals or enter one of the singly occupied t2g orbitals D
Spin Pairing Energy (P) is an increase in Energy (due to electrostatic repulsions) when an e- is put into an occupied orbital. If Do is < P, then lowest-energy arrangement has 4th ein an empty eg orbital.
Electronic Structures of Metal Complexes If Do is > P, lowest-energy arrangement has 4th ein one of the occupied t2g orbitals, Metal ions with d4, d5, d6, or d7 e- configurations can be either high spin or low spin,
depending on magnitude of Do magnitude of Do Large Do = Smaller Do = Only one arrangement of d electrons is possible
for metal ions with d8d10 e- configurations Factors That Affect the Magnitude of Do magnitude of Do dictates whether a complex with 4, 5, 6, or 7 d e-s is high spin or low spin:
1. Large values of Do yield a low-spin complex 2. Small values of Do a high-spin complex Which affects its: Magnetic properties Structure Reactivity
Factors That Affect the Magnitude of Do Nature of the ligands For a series of chem similar ligands, magnitude of Do decreases as size of donor atom increases
because smaller, more localized charges interact Factors That Affect the Magnitude of Do Nature of the ligands
Nature of the ligands experimentally observed order of the crystal field splitting energies produced by different ligands is called: the spectrochemical series Nature of the ligands
1. Strong-field ligands interact strongly with d orbitals of metal ions and give a large Do 2. Weak-field ligands interact more weakly and give a smaller Do The Spectrochemical Series
splitting of d orbitals in crystal field model not only depends on geometry of the complex also depends on nature of the metal ion, charge on this ion, and the ligands that surround the metal. The Spectrochemical Series
When geometry and ligands are held constant, this splitting decreases in the following order: Pt4+ > Ir3+ > Rh3+ > Co3+ > strong-field ions
Cr3+ > Fe3+ > Fe2+ > Co2+ >
Ni2+ > Mn2+ weak-field ions Metal ions at one end are called strong-field ions, because splitting due to crystal field is unusually strong.
Ions at other end are known as weak-field ions. The Spectrochemical Series When geometry & the metal are held constant, splitting of d orbitals decreases in the following order: CO
weak-field ligands Strong Field Ligands: (strongest) CN, CO > NO2 > en > NH3 Weak Field Ligands: H2O > ox > OH > F > SCN, Cl > Br > I (weakest)
tetrahedral crystal field: imagine 3 ligands lying at alternating corners of a cube The dx2-y2 & dz2 orbitals on metal ion at center of the cube lie between the ligands, and dxy, dxz, & dyz orbitals point toward the ligands.
Tetrahedral Complexes Splitting of energies of orbitals in tetrahedral complex, Do, is smaller than in an octahedral complex for two reasons: 1. d orbitals interact less strongly with ligands in a tetrahedral arrangement.
2. Only four negative charges rather than six, which decreases electrostatic interactions tetrahedral crystal field: the splitting observed in a tetrahedral crystal field is opposite of splitting in octahedral complex.
With square planar splittings, energy level for the x2-y2 orbital is very high so this is an especially good geometry for d8 complexes, e.g. Pt(II), Ni(II), Pd(II), Au(III) Factors That Affect the Magnitude of Do
Charge on the metal ion Increasing charge on a metal ion has 2 effects: 1. Radius of metal ion decreases 2. Neg charged ligands are more strongly attracted to it. Both factors decrease metal-ligand distance, which causes (-) charged ligands
to interact more strongly with the d orbitals. magnitude of Do increases as charge on metal ion increases Factors That Affect the Magnitude of Do Principal quantum # of the metal
For a series of complexes of metals from same group in periodic table with same charge and same ligands: magnitude of Do increases with increasing quantum #: Factors That Affect the Magnitude of Do
Principal quantum # of the metal Do (3d) << Do (4d) < Do (5d) Increase in Do w/ increasing principal quantum # is due to: larger radius of valence orbitals going down a column. Repulsive ligand-ligand interactions
are important for smaller metal ions, which results in shorter ML distances and stronger d-orbital-ligand interactions Colors of Transition-Metal Complexes Striking colors exhibited by transition-metal complexes are caused by the excitation of an e- from
a lower-lying d orbital to a higher-energy d orbital, which is called a d-d transition For a photon to affect the d-d transition, its E must be = to the
difference in E btwn the two d orbitals, which depends on the magnitude of Do which depends on the structure of the complex.
The energy of a photon of light is inversely proportional to its wavelength E = hc = hu l Colors of Transition Metal Complexes
CFT helps explain diff colors observed for complexes A transition metal complex absorbs specific l of light Color observed is complimentary to what was absorbed
Observed color is due to transmitted or reflected light that is complementary in color to light that is absorbed Rubies & Emeralds both contain Cr3+ impurities in octahedral 6-oxide environment.
Host lattice causes differences in distances of d-orbital-to-ligand lengths. Applications: Chelating Agents: EDTA used to treat victims of heavy metal poisoning
Chemical Analysis: Dimethylglyoxime turns red in presence of Ni(II) and yellow in the presence of Pd(II). Thiocyanate blood-red in presence of Fe(III) and blue in the presence of Co(II). Applications:
Coloring Agents: e.g. Iron blue - found in ink, paint, cosmetics (eye shadow) and blueprints. mixture of hexacyano complexes of Fe(II) & Fe(III). Drug Therapy: Cisplatin is a cancer
chemotherapeutic agent - the two chlorine ligands get replaced by donor atoms on the DNA double helix. Biomolecules: Hemoglobin and cytochrome c contain Fe-heme complexes.
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