Instructor: Dr. Upali Siriwardane - PowerPoint Presentation

Instructor: Dr. Upali Siriwardanee-mail: upali@latech.eduOffice: CTH 311 Phone 257-4941Office Hours: M,W 8:00-9:00 & 11:00-12:00 am; Tu,Th, F 9:30 - 11:30 a.m. April 7 , 2015: Test 1 (Chapters 1,  2, 3) April 30, 2015: Test 2 (Chapters  6 & 7) May 19, 2015: Test 3 (Chapters. 19 & 20) May 19, Make Up: Comprehensive covering all Chapters Chemistry 481(01) Spring 2015

Instructor: Dr. Upali Siriwardanee-mail: upali@latech.eduOffice: CTH 311 Phone 257-4941Office Hours: M,W 8:00-9:00 & 11:00-12:00 am; Tu,Th, F 9:30 - 11:30 a.m. April 5 , 2016: Test 1 (Chapters 1, 2, 3, 4) April 28, 2016: Test 2 (Chapters  (6 & 7) May 17, 2016: Test 3 (Chapters. 19 & 20) May 18, Make Up: Comprehensive covering all Chapters Chemistry 481(01) Spring 2016

Chapter 7. An introduction to coordination compounds The language of coordination chemistry 7.1 Representative ligands 7.2 Nomenclature Constitution and geometry 7.3 Low coordination numbers 7.4 Intermediate coordination numbers 7.53Higher coordination numbers 7.6 Polymetallic complexes Isomerism and chirality 7.7 Square-planar complexes 7.8 Tetrahedral complexes 7.9 Trigonal-bipyrmidal and square-pyramidal complexes7.10 Octahedral complexes7.11 Ligand chirality

Chapter 7. An introduction to coordination compounds Thermodynamics of complex formation 7.12 Formation constants 7.13 Trends in successive formation constants7.14 Chelate and macrocyclic effects 7.15 Steric effects and electron delocalization

Coordination compoundA compound formed from a Lewis acid and Lewis base.A metal or metal ion acting Lewis acid (being an electron pair acceptor) and a atom or group of atoms with lone electron pairs Lewis base electron pair donor forms an adduct with dative or coordinative covalent bonds. Ni(ClO4)2 (aq)+ 6NH3 → [Ni(NH3)6](ClO4)2 (aq) The Lewis bases attached to the metal ion in such compounds are called ligands.

The coordination number (CN) CN of a metal ion in a complex is defined as the number of ligand donor atoms to which the metal is directly bonded. [Co(NH3)5Cl]2+ CN is 6, 1 chloride and 5 ammonia ligands each donating an electron pair. For organometallic compounds. An alternative definition of CN would be the number of electron pairs arising from the ligand donor atoms to which the metal is directly bonded.

1) What is a coordination compound?

Coordination sphereCoordination sphere - the sphere around the central ion made up of the ligands directly attached to it. Primary and secondary coordination sphere.

Preparation of ComplexesThe figure at left shows cyanide ions (in the form of KCN), being added to an aq. solution of FeSO4. Since water is a Lewis base, the Fe2+ ions were originally in the complex [Fe(H2O)6]2+ The CN- ions are driving out the H2O molecules in this substitution reaction that form the hexacyanoferrate(II) ion, [Fe(CN)6]4- . [Fe(H2 O) 6 ] 2+ + 6 CN - [ Fe(CN) 6 ] 4- + 6 H 2 O

Various Colors of d-Metal ComplexesThe color of the complex depends on the identity of the ligands as well as of the metal.. Impressive changes of color often accompany substitution reactions.

Structures and symmetriesSix-coordinate complexes are almost all octahedral (a). Four-coordinate complexes can be tetrahedral (b) or square planar (c).(Square planar usually occurs with d8 electron configurations, such as in Pt2+ and Au3+.)

Representing Octahedral ShapesInstead of a perspective drawing (a), we can represent octahedral complexes by a simplified drawing that emphasizes the geometry of the bonds (b).

LigandsThe Brønsted bases or Lewis base attached to the metal ion in such compounds are called ligands.These may be Simple ions such as Cl–, CN–Small molecules such as H2O or NH3,Larger molecules such as H2NCH2CH2NH2 N(CH2CH2NH2)3Macromolecules, EDTA and biological molecules such as proteins.

Representative Ligands and NomenclatureBidentate LigandsPolydentate LigandsSome ligands can simultaneously occupy more than one binding site.Ethylenediamine (above) has a nitrogen lone pair at each end, making it bidentate. It is widely used and abbreviated “en”, as in [Co(en)3]3+.

Ethylenediaminetetraacetate Ion (EDTA)EDTA4- is another example of a chelating agent. It is hexadentate. This ligand forms complexes with many metal ions, including Pb2+, and is used to treat lead poisoning. Unfortunately, it also removes Ca2+ and Fe2+ along with the lead. Chelating agents are common in nature.

Porphyrins and phthalocyanins

ChelatesThe metal ion in [Co(en)3]3+ lies at the center of the three ligands as though pinched by three molecular claws. It is an example of a chelate, A complex containing one or more ligands that form a ring of atoms that includes the central metal atom.

Naming Transition Metal ComplexesCation name first then anion name.List first the ligands, then the central atomThe ligand names are made to end in -O if negativeAnion part of the complex ends in -ateEg. Cu(CN)64- is called the hexacyanocuprate(II) ionThe ligands are named in alphabetic orderNumber of each kind of ligand by Greek prefixThe oxidation state of the central metal atom shown in parenthesis after metal nameBriding is shown with  ( -oxo)

Some Common Ligand Names

Names of Ligands (continued)

Coordination Sphere NomenclatureCationic coordination sphere-ium endingAnionic coordination sphere-ate ending

Examples[Co(NH3)4Cl2]Cl: dichlorotetramminecobalt(III) chloride[Pt(NH3)3Cl]2[PtCl4]: di(monochlorotriammineplatinum(II)) tetrachloroplatinate(II).K3[Fe(ox)(ONO)4] :potassium tetranitritooxalatoferrate(III)

Use bis and tris for di and trifor chelating ligands[Co(en)3](NO3)2 :tris(ethylenediamine)cobalt(II) nitrate [Ir(H2O)2(en)2]Cl3 bis(ethylenediamine)diaquairidium(III) chloride [Ni(en)3]3[MnO4] :Tris(ethylenediamine)nickel(II) tetraoxomanganate(II)

Naming[Cu(NH3)4]SO4 tetraaminecopper(II) sulfate[Ti(H2O)6][CoCl6] hexaaquatitanium(III) hexachlorocobaltate(III) K3[Fe(CN)6]potassium hexacyanoferrate(III)

2) Give the formula of following coordination compoundsa)Dichlorobis(ethylenediammine)nickle b) Potasium trichloro(ethylene)platinate(1-)

c) Tetrakis(pyridine)platinum(2+) tetrachloroplatinate(2-)d) Tetraamminebis(ethylenediamine)--hydroxo- -amidodicobalt(4+) chloride

3) Give the names of following coordination compoundsa)       [Co(NH3)6]Cl3; b)       trans-[Cr(NH3)4(NO2)2]+ ; c)       K[Cu(CN)2] ; d)       cis-[PtCl2(NH3)2] ; e)       fac-[Co(NO2)3(NH3)3]Cl3

The Eta(h) System of NomenclatureFor for p bonded ligands number of atoms attached to the metal atom is shown by hn(h5 -cyclopentadienyl) tricarbonyl manganesetetracarbonyl (h3-allyl) manganese, Mn(C3H5)(CO)4

IsomersBoth structural and stereoisomers are found.The two ions shown below differ only in the positions of the Cl- ligand, but they are distinct species, with different physical and chemical properties.

4)       What is the geometry and coordination number of compounds in the problem above?a)       [Co(NH3)6]Cl3; b)       trans-[Cr(NH3)4(NO2)2]+ ; c)       K[Cu(CN)2] ; d)       cis-[PtCl2(NH3)2] ; e)       fac-[Co(NO2)3(NH3)3]Cl3

5)  Draw the formula and find the BITE of following ligands.a)       2,2'-bipyridine (bipy) ; b)       terpy; c)       cyclam; d)       edta;

Ionization IsomersThese differ by the exchange of a ligand with an anion (or neutral molecule) outside the coordination sphere. [CoSO4(NH3)5]Br has the Br- as an accompanying anion (not a ligand) and [CoBr(NH3)5]SO4 has Br - as a ligand and SO42-as accompanying anion.

Ionization IsomersThe red-violet solution of [Co(NH3)5Br]SO4 (left) has no rxn w/ Ag+ ions, but forms a ppt. when Ba2+ ions are added. The dark red solution of [CoSO4(NH3)5]Br (right) forms a ppt. w/ Ag+ ions, but does not react w/ Ba2+ ions.

Hydrate IsomersThese differ by an ex-change between an H2O molecule and another ligand in the coordination sphere. The solid, CrCl3. 6H2O, may be any of three compounds.[Cr(H2O)6]Cl3 (violet) CrCl(H2O)5]Cl2.H2O (blue-green) CrCl2 (H2O)4Cl.2H2O (green)Primary and secondary coordination spheres

Linkage IsomersThe triatomic ligand is the isothiocyanato, NCS-. In (b) it is the thiocyanato, SCN-. Other ligands capable or forming linkage isomers are NO2- vs. ONO - CN - vs. NC - .(a) NSC- ligand (the N is closest to the center); (b) SCN- ligand (S is closest the center)

Coordination IsomersThese occur when one or more ligands are exchanged between a cationic complex and an anionic complex. An example is the pair [Cr(NH3)6][Fe(CN)6] and[Fe(NH3)6][Cr(CN)6].

StereoisomersIonization, hydrate, linkage, and coordination isomers are all structural isomers. In stereoisomers, the formulas are the same. The atoms have the same partners in the coordination sphere, but the arrangement of the ligands in space differs. The cis- and trans- geometric isomers shown in next slide differ only in the way the ligands are arranged in space.There can be geometric isomers for octahedral and square planar complexes, but not for tetrahedral complexes.

Square Planar ComplexesGeometric IsomersProperties of geometric isomers can vary greatly. The cis- isomer below is pale orange-yellow, has a solubility of 0.252 g/100 g water, and is used for chemotherapy treatment. The trans- isomer is dark yellow, has a solu-bility of 0.037 g/100 g water, and shows no hemotherapeutic effect.

6)  Describe the geometrical isomerism in following compounds:a)       [Co(NH3)4Cl2]+ ; b)       [IrCl3(PPh3)3] ; c)       [Cr(en)2Cl2] ;

cis and trans-PtCl2(NH3)2

Trans Effect & Influence

Preparation Geometrical Isomers

Optical IsomerismThe two complexes at left are mirror images. (The gray rectangle represents a mirror, through which we see somewhat darkly.) No matter how the complexes are rotated, neither can be superimposed on the other. Note only four of the six ligands are different.

Combined Stereoisomerisms Both geometrical and optical isomerism can occur in the same complex, as below. The trans- isomer is green. The two cis- isomers, which are optical isomers of each other, are violet.

Identifying Optical IsomerismIf a molecule or ion belong to a point group with a Sn axis is not optically active

Molecular Polarity and Chirality Polarity Polarity:Only molecules belonging to the point groups Cn, Cnv and Cs are polar. The dipole moment lies along the symmetry axis formolecules belonging to the point groups Cn and Cnv. Any of D groups, T, O and I groups will not be polar

ChiralityOnly molecules lacking a Sn axis can be chiral.This includes mirror planesand a center of inversion as S2=s , S1=I and Dn groups.Not Chiral: Dnh, Dnd,Td and Oh.

Optical Activity

Reactions of Metal ComplexesFormation constants– the chelate effect– Irving William Series– Lability

7) Pick the chiral compounds among the following: a)       [Co(en)3]3+ ; b)       cis-[Cr(en)2Cl2] ; c)       c) trans-[Cr(en)2Cl2] ;

Formation of Coordination Complexestypically coordination compounds are more labile or fluxional than other molecules X is leaving group and Y is entering group MX + Y MY + XOne example is the competition of a ligand, L for a coordination site with a solvent molecule such as H2O [Co(OH2)6]2+ + Cl- [Co(OH2)5Cl]+ + H2O

Formation ConstantsConsider formation as a series of formation equilibria:Summarized as:

Typically: Kn>Kn+1Expected statistically, fewer coordination sitesavailable to form MLn+1eg sequential formation of Ni(NH3)n(OH2)6-n 2+ Values of Kn

Breaking the RulesOrder is reversed when some electronic or chemical change drives formationFe(bipy)2(OH2)22+ + bipy Fe(bipy)32+jump from a high spin to low spin complexFe(bipy)2(OH2)2 t2g4eg2 high spinFe(bipy)3 t2g6 low spin

Irving William SeriesValues of log Kf for 2+ ions including transition metal species Lewis acidity (acceptance of e-) increases across the per. table, thus forming more and more stable complexes for the same ligand systemKf series for transition metals: Mn2+< Fe2+ < Co2+ < Ni2+ < Cu2+ >Zn2+

Irving William Series

Bonding and electronic structureBonding Theories of Transition Metal ComplexesValance Bond TheoryCrystal Field TheoryLigand Field Theory or Molecular Orbital Theory

Valance Bond Theory”Outer orbital" (sp3d2) and ”Inner orbital" (d2sp3)[CoF6]3- - Co3+ : d6[Co(NH3)6]3+ - Co3+ : d6

Spectrochemical Series for LigandsIt is possible to arrange representative ligands in an order of increasing field strength called the spectrochemical series:I¯ < Br¯ < -SCN¯ < Cl¯ < F¯ < OH¯ < C2O42¯ < H2O < -NCS¯ < py < NH3 < en < bipy < o-phen < NO2¯ < CN¯ < CO

8) Use valence bond theory (VBT) to predict the electron configurations, the type of bonding (Inner and outer orbital) and number of unpaired electrons in following compounds: a)       [Co(CN)6]3- ;b)       [CoCl6]3-; c)       [Fe(NH3)6]3+;

Crystal Field TheoryIn the electrical fields created by ligandsThe orbitals are split into two groups: a set consisting of dxy, dxz, and dyz stabilized by 2/5Do, known by their symmetry classification as the t2g set, and a set consisting of the dx2-y2 and dz2, known as the eg set, destabilized by 3/5Do where Do is the gap between the two sets.

Crystal Field Splitting of d Orbitals

Octahedral Crystal Field Splitting

9)  What are the symmetry labels of s,p, and d orbitals in tetrahedral (NiCO)4) and square-planar ([PtCl4]2-) and octahedral (Cr(CO)6) compounds.

10)    Explain the effect of ligands on the d orbitals in octahedral, tetrahedral, trigonal-bipyramid and square-planar coordination compounds using Crystal Field Theory.  Octahedral, Tetrahedral, Trigonal-bipyramid Square-planar

11)  [Ti(H2O)6]3+ shows a absorption at 20300 cm-1. Absorption values for similar coordination compounds of Ti3+ with different ligands are given below. Based on their absorption values arrange the following ligands in a Spectrochemical Series. Absorption(cm-1)Ligand H2O CN- PPh3 F- NH3 20300 20500 20455 20100 20400

Crystal Field Stabilization Energy Crystal Field stabilization parameter Do

Crystal Field Stabilization Energyd7 case. Weak field caseThe configurations would be written t2g5 eg2 5(-2/5Do) + 2(+3/5Do) = -4/5DoStrong field caseThe configurations would be written t2g6 eg16(-2/5Do) + 1(+3/5Do) = -9/5Do

CFSE & Paring Energy[Fe(H2O)6]2+. Iron has a d6 configuration, the value of Do is 10,400 cm-1 and the pairing energy is 17600cm-1. (1 kJ mol-1 = 349.76 cm-1.) We must compare the total of the CFSE and the pairing energy for the two possible configurations.

high spin (more stable)CFSE = 4 x -2/5 x 10400 + 2 x 3/5 x 10400 = -4160cm-1 (-11.89 kJ mol-1)Pairing energy (1 pair) = 1 x 17600 = 17600 cm-1 (50.32 kJ mol-1Total = +13440 cm-1 (38.43 kJ mol-1)low spinCFSE = 6 x -2/5 x 10400= -24960 cm-1 (-71.36 kJ mol-1)Pairing energy (3 pairs) = 3 x 17600 = 52800 (151.0 kJ mol-1)Total = +27840 cm-1 (79.60 kJ mole-1)

Tetrahedral complexesSplitting order or reversed. eg is now lower energy and t2g is hgher energyBecause a tetrahedral complex has fewer ligands, the magnitude of the splitting is smaller. The difference between the energies of the t2g and eg orbitals in a tetrahedral complex (t) is slightly less than half as large as the splitting in analogous octahedral complexes (o) Dt = 4/9Do

Tetrahedral Ligand ArrangementDt = 4/9DoMostly forms high spin complxes

Octahedral Crystal Field Splitting

Square-planar Complexes-D4h

Generalizations about Crystal Field SplittingsThe actual value of D depends on both the metal ion and the nature of the ligands:The splitting increases with the metal ion oxidation state. For example, it roughtly doubles going from II to III.The splitting increases by 30 - 50% per period down a group.Tetrahedral splitting would be 4/9 of the octahedral value if the ligands and metal ion were the same.

Spectrochemical Series for LigandsIt is possible to arrange representative ligands in an order of increasing field strength called the spectrochemical series:I¯ < Br¯ < -SCN¯ < Cl¯ < F¯ < OH¯ < C2O42¯ < H2O < -NCS¯ < py < NH3 < en < bipy < o-phen < NO2¯ < CN¯ < CO

Spectrochemical Series for MetalsIt is possible to arrange the metals according to a spectrochemical series as well. The approximate order isMn2+ < Ni2+ < Co2+ < Fe 2+ < V2+ < Fe3+ < Co3+ < Mn3+ < Mo3 + < Rh3 + < Ru3 + < Pd4+ < Ir3+ < Pt 3+

Spectrum of [Ti(H2O)6]3+.d1: t2g1eg0 –> t2g0eg1

Hydration Enthalpy.M2+(g) + 6 H2O(l) = [M(O2H)6]2+(aq)

Irving-Williams Series

Ligand Field Splitting and Metalsthe transition metal also impacts Do increases with increasing oxidation numberDo increases as you move down a group (i.e. with increasing principal quantum number n)

MO forML6 diagram Molecules0

Ligand Field Stabilization Energies LFSE is a function of Doweighted average of the splitting due to thefact that they are split into groups of 3 (t2g)and 2 (eg)

Weak Field vs. Strong Fieldnow that d orbitals are not degenerate how do we know what an electronic ground state for a d metal complex is? need to determine the relative energies of pairing vs. Do

Splitting vs. Pairingwhen you have more than 3 but fewer than 8 delectrons you need to think about the relative meritspairing vs. Do• high-spin complex – one with maximum number of unpaired electrons• low-spin complex – one with fewer unpaired electrons

Rules of Thumb for Splitting vs Pairingdepends on both the metal and the ligands• high-spin complexes occur when o is small Do is small when:• n is small (3 rather than 4 or 5)– high spin only really for 3d metals• oxidation state is low– i.e. for oxidation state of zero or 2+• ligands is low in spectrochemical series– eg halogens

Four Coordinate Complexes: TetrahedralSame approach but different set of orbitals with different ligand field• Arrangement of tetrahedral field of point charges results in splitting of energy where dxy, dzx, dyz are repelled more by Td field of negative charges• So the still have a split of the d orbitals into triply degenerate (t2) and double degenerate (e) pair but now e is lower energy and t2 is higher.

Tetrahedral Crystal Field Splitting

Ligand Field Splitting: Dt describes the separation between reviouslydegenerate d orbitals • Same idea as Do but Dt < 0.5 Do for comparable systems• So …Almost Exclusively Weak Field

Electron configurations in octahedral fields Weak field and strong fieled cases

Tetragonal ComplexesStart with octahedral geometry and follow theenergy as you tetragonally distort the octahedronTetragonal distortion: extension along z andcompression on x and yOrbitals with xy components increase inenergy, z components decrease in energyResults in further breakdown of degeneracy– t2g set of orbitals into dyz, dxz and dxy– eg set of orbitals into dz2 and dx2-y2

Tetragonal Complexes

Square Planar Complexesextreme form of tetragonal distortionLigand repulsion is completely removed fromz axisCommon for 4d8 and5d8 complexes:Rh(I), Ir(I)Pt(II), Pd(II)

Jahn Teller Distortiongeometric distortion may occur in systemsbased on their electronic degeneracyThis is called the Jahn Teller Effect:If the ground electronic configuration of anonlinear complex is orbitally degenerate, thecomplex will distort to remove the degeneracyand lower its energy.

Jahn Teller DistortionsOrbital degeneracy: for octahedral geometrythese are:– t2g3eg1 eg. Cr(II), Mn(III) High spin complexes– t2g6eg1 eg. Co(II), Ni(II)– t2g6eg3 eg. Cu(II)basically, when the electron has a choice between one of the two degenerate eg orbitals, the geometry will distort to lower the energy of the orbital that is occupied. Result is some form of tetragonal distortion

Ligand Field TheoryCrystal field theory: simple ionic model, does not accurately describe why the orbitals are raised or lowered in energy upon covalent bonding.• LFT uses Molecular Orbital Theory to derive the ordering of orbitals within metal complexes• Same as previous use of MO theory, build ligand group orbitals, combine them with metal atomic orbitals of matching symmetry to form MO’s

LFT for Octahedral ComplexesConsider metal orbitals and ligand group orbitalsUnder Oh symmetry, metal atomic orbitals transform as:Degeneracy Mulliken Label Atomic Orbital 2 eg dx2-y2, dz2 3 t2g dxy, dyz, dzx 3 t1u px, py, pz 1 a1g s

Sigma Bonding: Ligand Group Orbitals

Combinationsof Metal andLigand SALC’s

Molecular Orbital Energy Level Diagram: Oh

PI Bondingpi interactions alter theMOELD that results fromsigma bonding• interactions occur betweenfrontier metal orbitals and thepi orbitals of L• two types depends on the ligand–pi acid - back bonding accepts e- density from M–pi base -additional e- density donation to the M• type of bonding depends on relative energy levelof pi orbitals on the ligand and the metal orbitals

: PI Bases and the MOELD Ohpi base ligandscontribute moreelectron density tothe metal• t2g is split to form abonding andantibonding pair oforbitalsDo is decreased• halogens are goodpi donors

PI Acids and the MOELD: Oh• pi acids accept electrondensity back from themetal• t2g is split to form abonding and antibondingpair of orbitals• the occupied bondingset of orbitals goesdown in energy so ..• Do increases• typical for phosphineand carbonyl ligands

Magnetic Properties of Atoms a) Diamagnetism? Repelled by a magnetic field due to paired electrons. b)Paramagnetism?attracted to magnetic field due to un-paired electrons. c) Ferromagnetism? attracted very strongly to magnetic field due to un-paired electrons. d)Anti-ferromagnetic?Complete cancelling of unpaired electrons in magnetic domains

Magnetic Suceptibility Vs Temperature

Types of magnetism

Magnetic PropertiesA paramagnetic substance is characterised experimentally by its (molar) magnetic susceptibility, cm. This is measured bysuspending a sample of the compound under a sensitive balance between the poles of a powerful electro-magnet,

Number of Unparied ElectronsThe magnetic moment of the substance is given by the Curie Law: m = 2.54(cmT)½ (in units of Bohr magnetons) The formula used to calculate the spin-only magnetic moment can be written in two forms m= n(n+2) B.M.

Magnetic Properties of Atoms Paramagnetism?Ferromagnetism?Diamagnetism? Gouvy Balance

Octahedral Complexes

Tetrahedral Complexes