Camp 1 - Tech

Camp 1 - Tech

Chemistry 481(01) Spring 2015 Instructor: Dr. Upali Siriwardane e-mail: [email protected] Office: CTH 311 Phone 257-4941 Office 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, Spring 2016.5, LA Tech Chapter 7-1 Chemistry 481(01) Spring 2016 Instructor: Dr. Upali Siriwardane e-mail: [email protected] Office: CTH 311 Phone 257-4941 Office 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, Spring 2016.5, LA Tech Chapter 7-2 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 complexes 7.10 Octahedral complexes 7.11 Ligand chirality

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-3 Chapter 7. An introduction to coordination compounds Thermodynamics of complex formation 7.12 Formation constants 7.13 Trends in successive formation constants 7.14 Chelate and macrocyclic effects 7.15 Steric effects and electron delocalization

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-4 Coordination compound A 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. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-5 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. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-6 1) What is a coordination compound? Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-7 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-8 Coordination sphere Coordination sphere - the sphere around the central ion made up of the ligands directly attached to it. Primary and secondary coordination sphere.

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-9 Preparation of Complexes [Fe(H2O)6] 2+ + 6 CN -

[Fe(CN)6] 4- + 6 H2O The 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- . Chemistry 481, Spring 2016.5, LA Tech Chapter 7-10 Various Colors of d-Metal Complexes The 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.

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-11 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-12 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-13 Structures and symmetries

Six-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+.) Chemistry 481, Spring 2016.5, LA Tech Chapter 7-14 Representing Octahedral Shapes

Instead of a perspective drawing (a), we can represent octahedral complexes by a simplified drawing that emphasizes the geometry of the bonds (b). Chemistry 481, Spring 2016.5, LA Tech Chapter 7-15 Ligands The Brnsted 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)3 Macromolecules, EDTA and biological molecules such as proteins. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-16 Representative Ligands and Nomenclature Bidentate Ligands

Polydentate Ligands Some 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+. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-17 Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-18 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. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-19 Porphyrins and phthalocyanins Chemistry 481, Spring 2016.5, LA Tech Chapter 7-20

Chelates The 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. Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-21 Naming Transition Metal Complexes Cation name first then anion name. List first the ligands, then the central atom The ligand names are made to end in -O if negative Anion part of the complex ends in -ate Eg. Cu(CN)64- is called the hexacyanocuprate(II) ion The ligands are named in alphabetic order Number of each kind of ligand by Greek prefix The oxidation state of the central metal atom

shown in parenthesis after metal name Briding is shown with ( -oxo) Chemistry 481, Spring 2016.5, LA Tech Chapter 7-22 Some Common Ligand Names Chemistry 481, Spring 2016.5, LA Tech Chapter 7-23

Names of Ligands (continued) Chemistry 481, Spring 2016.5, LA Tech Chapter 7-24 Coordination Sphere Nomenclature Cationic coordination sphere -ium ending Anionic coordination sphere -ate ending

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-25 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)

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-26 Use bis and tris for di and tri for 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) Chemistry 481, Spring 2016.5, LA Tech Chapter 7-27 Naming [Cu(NH3)4]SO4 tetraaminecopper(II) sulfate [Ti(H2O)6][CoCl6] hexaaquatitanium(III)

hexachlorocobaltate(III) K3[Fe(CN)6] potassium hexacyanoferrate(III) Chemistry 481, Spring 2016.5, LA Tech Chapter 7-28 2) Give the formula of following coordination compounds a)Dichlorobis(ethylenediammine)nickle b) Potasium trichloro(ethylene)platinate(1-)

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-29 c) Tetrakis(pyridine)platinum(2+) tetrachloroplatinate(2-) d) Tetraamminebis(ethylenediamine) --hydroxo- -amidodicobalt(4+) chloride Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-30 3) Give the names of following coordination compounds 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 Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-31 The Eta(h) System of Nomenclature For for p bonded ligands number of atoms attached to the metal atom is shown by hn 5 (h -cyclopentadienyl) tricarbonyl manganese 3 tetracarbonyl (h -allyl) manganese, Mn(C3H5)(CO)4 Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-32 Isomers Both 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. Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-33 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

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-34 5) Draw the formula and find the BITE of following ligands. a) 2,2'-bipyridine (bipy) ; b)

terpy; c) cyclam; d) edta; Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-35 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-36 Ionization Isomers These differ by the exchange of a ligand with an anion (or neutral molecule) outside the coordination sphere. [CoSO4(NH3)5]Br has the Bras an accompanying anion (not a ligand) and [CoBr(NH3)5]SO4 has Br - as a ligand and SO42-as

accompanying anion. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-37 Ionization Isomers The red-violet solution of [Co(NH3)5Br]SO4 n + (left) has no rx w/ Ag ions, but forms a ppt. 2+ when Ba ions are added.

The dark red solution of [CoSO4(NH3)5]Br + (right) forms a ppt. w/ Ag ions, but does not 2+ react w/ Ba ions. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-38 Hydrate Isomers These 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 Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-39 Linkage Isomers The triatomic ligand is the isothiocyanato, NCS-. In (b) it is the thiocyanato, SCN-. Other ligands capable or forming linkage isomers are NO vs.

ONO (a) NSC ligand (the N is closest to the center); 2 (b) SCN- ligand (S is closest the center) CN - vs. NC - . Chemistry 481, Spring 2016.5, LA Tech Chapter 7-40 Coordination Isomers These 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]. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-41 Stereoisomers Ionization, 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. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-42

Square Planar Complexes Geometric Isomers Properties 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. Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-43 6) Describe the geometrical isomerism in following compounds: a) [Co(NH3)4Cl2]+ ; b) [IrCl3(PPh3)3] ;

c) [Cr(en)2Cl2] ; Chemistry 481, Spring 2016.5, LA Tech Chapter 7-44 cis and trans-PtCl2(NH3)2 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-45

Trans Effect & Influence Chemistry 481, Spring 2016.5, LA Tech Chapter 7-46 Preparation Geometrical Isomers Chemistry 481, Spring 2016.5, LA Tech Chapter 7-47

Optical Isomerism The 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. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-48 Combined Stereoisomerisms

Both geometrical and optical isomerism can occur in the same complex, as below. The transisomer is green. The two cis- isomers, which are optical isomers of each other, are violet. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-49 Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-50 Identifying Optical Isomerism If a molecule or ion belong to a point group with a Sn axis is not optically active Chemistry 481, Spring 2016.5, LA Tech Chapter 7-51 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-52

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 Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-53 Chirality Only molecules lacking a Sn axis can be chiral. This includes mirror planes and a center of inversion as S2=s , S1=I and Dn groups.

Not Chiral: Dnh, Dnd,Td and Oh. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-54 Optical Activity Chemistry 481, Spring 2016.5, LA Tech Chapter 7-55

Reactions of Metal Complexes Formation constants the chelate effect Irving William Series Lability Chemistry 481, Spring 2016.5, LA Tech Chapter 7-56 7) Pick the chiral compounds among the following:

a) [Co(en)3]3+ ; b) cis-[Cr(en)2Cl2] ; c) c) trans-[Cr(en)2Cl2] ; Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-57 Formation of Coordination Complexes typically coordination compounds are more labile or fluxional than other molecules X is leaving group and Y is entering group MX + Y MY + X One example is the competition of a ligand, L for a coordination site with a solvent molecule such as H2O [Co(OH2)6]2+ + Cl-

Chemistry 481, Spring 2016.5, LA Tech [Co(OH2)5Cl]+ + H2O Chapter 7-58 Formation Constants Consider formation as a series of formation equilibria: Summarized as:

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-59 Values of Kn Typically: Kn>Kn+1 Expected statistically, fewer coordination sites available to form MLn+1 eg sequential formation of Ni(NH3)n(OH2)6-n 2+ Chemistry 481, Spring 2016.5, LA Tech Chapter 7-60

Breaking the Rules Order is reversed when some electronic or chemical change drives formation Fe(bipy)2(OH2)22+ + bipy Fe(bipy)32+ jump from a high spin to low spin complex Fe(bipy)2(OH2)2 t2g4eg2 high spin Fe(bipy)3 Chemistry 481, Spring 2016.5, LA Tech

t2g6 low spin Chapter 7-61 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-62 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-63

Irving William Series Values 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 system Kf series for transition metals: Mn2+< Fe2+ < Co2+ < Ni2+ < Cu2+ >Zn2+ Chemistry 481, Spring 2016.5, LA Tech Chapter 7-64

Irving William Series Chemistry 481, Spring 2016.5, LA Tech Chapter 7-65 Bonding and electronic structure Bonding Theories of Transition Metal Complexes Valance Bond Theory Crystal Field Theory Ligand Field Theory or Molecular Orbital Theory

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-66 Valance Bond Theory Outer orbital" (sp3d2) and Inner orbital" (d2sp3) [CoF6]3- - Co3+ : d6 [Co(NH3)6]3+ - Co3+ : d6 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-67

Spectrochemical Series for Ligands It 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 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-68

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+; Chemistry 481, Spring 2016.5, LA Tech Chapter 7-69 Crystal Field Theory In the electrical fields created by ligands The 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. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-70 Crystal Field Splitting of d Orbitals Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-71 Octahedral Crystal Field Splitting Chemistry 481, Spring 2016.5, LA Tech Chapter 7-72 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. Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-73 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 Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-74 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 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-75 Crystal Field Stabilization Energy Crystal Field stabilization parameter Do Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-76 Crystal Field Stabilization Energy d7 case. Weak field case The configurations would be written t2g5 eg2 5(-2/5Do) + 2(+3/5Do) = -4/5Do Strong field case The configurations would be written t2g6 eg1 6(-2/5Do) + 1(+3/5Do) = -9/5Do Chemistry 481, Spring 2016.5, LA Tech Chapter 7-77

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 kJ mol-1 = 349.76 cm-1.) We must compare the 1 total of the CFSE and the pairing energy for the two possible configurations. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-78

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-1 Total = +13440 cm-1 (38.43 kJ mol-1) low spin CFSE = 6 x -2/5 x 10400= -24960 cm-1 (-71.36 kJ mol1 ) Pairing energy (3 pairs) = 3 x 17600 = 52800 (151.0 kJ mol-1)

Total = +27840 cm-1 (79.60 kJ mole-1) Chemistry 481, Spring 2016.5, LA Tech Chapter 7-79 Tetrahedral complexes Splitting order or reversed. eg is now lower energy and t2g is hgher energy Because 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 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-80 Tetrahedral Ligand Arrangement

Dt = 4/9Do Mostly forms high spin complxes Chemistry 481, Spring 2016.5, LA Tech Chapter 7-81 Octahedral Crystal Field Splitting Chemistry 481, Spring 2016.5, LA Tech Chapter 7-82

Square-planar Complexes-D4h Chemistry 481, Spring 2016.5, LA Tech Chapter 7-83 Generalizations about Crystal Field Splittings The 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. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-84 Spectrochemical Series for Ligands It 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 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-85 Spectrochemical Series for Metals It is possible to arrange the metals according to a spectrochemical series as well. The approximate order is

Mn2+ < Ni2+ < Co2+ < Fe 2+ < V2+ < Fe3+ < Co3+ < Mn3+ < Mo3 + < Rh3 + < Ru3 + < Pd4+ < Ir3+ < Pt 3+ Chemistry 481, Spring 2016.5, LA Tech Chapter 7-86 Spectrum of [Ti(H2O)6]3+. 1 1 0 0 1 d : t2g eg > t2g eg

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-87 Hydration Enthalpy. M2+(g) + 6 H2O(l) = [M(O2H)6]2+(aq) Chemistry 481, Spring 2016.5, LA Tech Chapter 7-88 Irving-Williams Series

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-89 Ligand Field Splitting and Metals the transition metal also impacts Do increases with increasing oxidation number Do increases as you move down a group (i.e. with increasing principal quantum number n) Chemistry 481, Spring 2016.5, LA Tech Chapter 7-90

MO forML6 diagram Molecules D0 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-91 Ligand Field Stabilization Energies LFSE is a function of Do weighted average

of the splitting due to the fact that they are split into groups of 3 (t2g) and 2 (eg) Chemistry 481, Spring 2016.5, LA Tech Chapter 7-92 Weak Field vs. Strong Field now 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 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-93 Splitting vs. Pairing when you have more than 3 but fewer than 8 d electrons you need to think about the relative merits pairing vs. Do high-spin complex one with maximum number of

unpaired electrons low-spin complex one with fewer unpaired electrons Chemistry 481, Spring 2016.5, LA Tech Chapter 7-94 Rules of Thumb for Splitting vs Pairing depends 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 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-95 Four Coordinate Complexes: Tetrahedral Same 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. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-96 Tetrahedral Crystal Field Splitting

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-97 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 Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-98 Electron configurations in octahedral fields Weak field and strong fieled cases Chemistry 481, Spring 2016.5, LA Tech Chapter 7-99 Tetragonal Complexes Start with octahedral geometry and follow the energy as you tetragonally distort the octahedron

Tetragonal distortion: extension along z and compression on x and y Orbitals with xy components increase in energy, z components decrease in energy Results in further breakdown of degeneracy t2g set of orbitals into dyz, dxz and dxy eg set of orbitals into dz2 and dx2-y2 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-100 Tetragonal Complexes

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-101 Square Planar Complexes extreme form of tetragonal distortion Ligand repulsion is completely removed from z axis Common for 4d 8

and 8 5d complexes: Rh(I), Ir(I) Pt(II), Pd(II) Chemistry 481, Spring 2016.5, LA Tech Chapter 7-102 Jahn Teller Distortion geometric distortion may occur in systems

based on their electronic degeneracy This is called the Jahn Teller Effect: If the ground electronic configuration of a nonlinear complex is orbitally degenerate, the complex will distort to remove the degeneracy and lower its energy. Chemistry 481, Spring 2016.5, LA Tech Chapter 7-103 Jahn Teller Distortions Orbital degeneracy: for octahedral geometry

these 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 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-104

Ligand Field Theory Crystal 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 MOs Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-105 LFT for Octahedral Complexes Consider metal orbitals and ligand group orbitals Under Oh symmetry, metal atomic orbitals transform as: Degeneracy Mulliken Label Atomic Orbital 2 eg dx2-y2, dz2

3 t2g 3 t1u 1 a1g Chemistry 481, Spring 2016.5, LA Tech

dxy, dyz, dzx px, py, pz s Chapter 7-106 Sigma Bonding: Ligand Group Orbitals Chemistry 481, Spring 2016.5, LA Tech Chapter 7-107

Combinationsof Metal andLigand SALCs Chemistry 481, Spring 2016.5, LA Tech Chapter 7-108 Molecular Orbital Energy Level Diagram: Oh Chemistry 481, Spring 2016.5, LA Tech Chapter 7-109 PI Bonding

pi interactions alter the MOELD that results from sigma bonding interactions occur between frontier metal orbitals and the pi 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 level of pi orbitals on the ligand and the metal orbitals Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-110 : PI Bases and the MOELD Oh pi base ligands contribute more electron density to the metal t2g is split to form a bonding and antibonding pair of orbitals Do is decreased halogens are good

pi donors Chemistry 481, Spring 2016.5, LA Tech Chapter 7-111 PI Acids and the MOELD: Oh pi acids accept electron density back from the metal t2g is split to form a bonding and antibonding

pair of orbitals the occupied bonding set of orbitals goes down in energy so .. Do increases typical for phosphine and carbonyl ligands Chemistry 481, Spring 2016.5, LA Tech Chapter 7-112 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 Chemistry 481, Spring 2016.5, LA Tech Chapter 7-113 Magnetic Suceptibility Vs Temperature Chemistry 481, Spring 2016.5, LA Tech Chapter 7-114 Types of magnetism

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-115 Magnetic Properties A paramagnetic substance is characterised experimentally by its (molar) magnetic susceptibility, cm. This is measured by suspending a sample of the compound under a sensitive balance between the poles of a powerful electro-magnet, Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-116 Number of Unparied Electrons The magnetic moment of the substance is given by the Curie Law: = 2.54(cmT) (in units of Bohr magnetons) The formula used to calculate the spin-only magnetic moment can be written in two forms = n(n+2) B.M. Chemistry 481, Spring 2016.5, LA Tech

Chapter 7-117 Magnetic Properties of Atoms Paramagnetism? Ferromagnetism? Diamagnetism? Gouvy Balance Chemistry 481, Spring 2016.5, LA Tech Chapter 7-118 Octahedral Complexes

Chemistry 481, Spring 2016.5, LA Tech Chapter 7-119 Tetrahedral Complexes Chemistry 481, Spring 2016.5, LA Tech Chapter 7-120

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