DOCSLIB.ORG

Crystal Field Theory (CFT)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Crystal Field Theory (CFT) The bonding of transition metal complexes can be explained by two approaches: crystal field theory and molecular orbital theory. Molecular orbital theory takes a covalent approach, and considers the overlap of d-orbitals with orbitals on the ligands to form molecular orbitals; this is not covered on this site. Crystal field theory takes the ionic approach and considers the ligands as point charges around a central metal positive ion, ignoring any covalent interactions. The negative charge on the ligands is repelled by electrons in the d-orbitals of the metal. The orientation of the d orbitals with respect to the ligands around the central metal ion is important, and can be used to explain why the five d-orbitals are not degenerate (= at the same energy). Whether the d orbitals point along or in between the cartesian axes determines how the orbitals are split into groups of different energies. Why is it required? The valence bond approach could not explain the Electronic spectra, Magnetic moments, Reaction mechanisms of the complexes. Assumptions of CFT: 1. The central Metal cation is surrounded by ligand which contain one or more lone pair of electrons. 2. The ionic ligand (F-, Cl- etc.) are regarded as point charges and neutral molecules (H2O, NH3 etc.) as point dipoles. 3. The electrons of ligand does not enter metal orbital. Thus there is no orbital overlap takes place. 4. The bonding between metal and ligand is purely electrostatic i.e. only ionic interaction. The approach taken uses classical potential energy equations that take into account the attractive and repulsive interactions between charged particles (that is, Coulomb's Law interactions). Description of d-Orbitals: To understand CFT, one must understand the description of the lobes: dxy : lobes lie in-between the x and the y axes. dyz : lobes lie in-between the y and the z axes. dxz : lobes lie in-between the x and the z axes. dx2-y2 : lobes lie on the x and y axes. dz2 : there are two lobes on the z axes and there is a doughnut shape ring that lies on the xy plane around the other two lobes. The Octahedral Crystal Field: Consider a molecule with octahedral geometry. The lone pair of electrons on each of the six ligands is treated as a negative point charge. The ligands are cantered on the cartesian axes. There are two forces: electrostatic attraction between each of the ligands and the positive metal ion and electrostatic repulsion between the ligands and electrons in the d-orbitals. Figure : Octahedral complex ML6 In octahedral geometry, ligands approach the metal ion along the x, y , and z axes. Therefore, the electrons in the dz2 and dx2-y2 orbitals (which lie along these axes) experience greater repulsion. This causes a splitting in the energy levels of the d-orbitals. This is known as crystal field splitting. For octahedral complexes, crystal field splitting is denoted by Δo(or Δoct ). The energies of the and orbitals increase due to greater interactions with the ligands. The dxy , dxz , and dyz orbitals decrease with respect to this normal energy level and become more stable. The two sets of orbitals are labelled eg and t2g and the separation between these two sets is called the ligand field splitting parameter, Δo (10 Dq) .The subscript o is used to signify an octahedral crystal field. Degenerate orbitals means orbitals having same energy. "e" refers to doubly degenerate orbitals. It consists of two d-orbitals. "t" refers to triply degenerate levels orbitals. It consists of three d-orbitals. They derive from group theory. The "g" tells you that the orbitals are gerade (german for even) - they have the same symmetry with respect to the inversion centre. The overall stabilization of one set of orbitals equals the overall destabilization of the other set. In the octahedral crystal field the overall stabilization of the t2g set equals the overall destabilization of the eg set. If the eg set is raised by two units, the t2g set is lowered by three units to achieve this energy balance. Therefore, the eg set is raised by 0.6Δo and the t2g set is lowered by 0.4Δo Some texts will use 10Dq instead of Δo, these are equivalent. Factors affecting the magnitude of splitting Many experiments have shown that the magnitude of splitting is depending upon both metal and ligands. Jorgenson’s Relation : Δ o = f . g where f = metal parameter and g = ligand parameter Metal factors: For complexes having same geometry and same ligands the crystal field splitting : 1. Charge on the metal ion. It increases with the increase in charge on the ion (Same number of d - electrons) 2. Number of d- electrons. It decreases with increasing number of d -electrons (Same charge on the ion) 3. Principle quantum number of the metal d electron (With increasing n value the splitting increases) Ligand factor: The strength of the ligands determine splitting; the stronger the ligand, the larger the splitting. Ligands are classified as strong or weak based on the spectrochemical series: ─ ─ ─ 4─ ─ CN = CO = C2H4 > PR3 > NO2 = phen > bipy > SO32 > en = py = NH3 > edta > NCS > H2O > C2O42─ > ONO2- > OSO32─ > OH─ = ONO─ > F─ > Cl─ = SCN─ > Br─ > I─ ─ ─ Note that SCN and NO2 ligands are represented twice in the above spectrochemical series since there are two different Lewis base sites (e.g., free electron pairs to share) on each ligand (e.g., for the SCN ligand, the electron pair on the sulfur or the nitrogen can form the coordinate covalent bond to a metal). The specific atom that binds in such ligands is underlined. Electronic distribution in splitted d orbitals : According to the Aufbau principle, electrons are filled from lower to higher energy orbitals. For the octahedral case above, this corresponds to the dxy , dxz , and dyz orbitals. Following Hund's rule, electrons are filled in order to have the highest number of unpaired electrons. For example, if one had a d3 complex, there would be three unpaired electrons. If one were to add an electron, however, it has the ability to fill a higher energy orbital (dz² or dx²-y² ) or pair with an electron residing in the dxy , dxz or dyz orbitals. This pairing of the electrons requires energy (spin pairing energy). If the pairing energy is less than the crystal field splitting energy, ∆0, then the next electron will go into the dxy , dxz or dyz orbitals due to stability. This situation allows for the least amount of unpaired electrons, and is known as low spin. If the pairing energy is greater than ∆0, then the next electron will go into the dz² or dx²-y² orbitals as an unpaired electron. This situation allows for the most number of unpaired electrons, and is known as high spin. Ligands that cause a transition metal to have a small crystal field splitting, which leads to high spin, are called weak-field ligands. Ligands that produce a large crystal field splitting, which leads to low spin, are called strong field ligands. Hence: The strong field ligand form a low spin complex, while the weak field ligand form a high spin complex. 3d metals are generally high spin complexes except with strong ligands or higher oxidation state. 4d & 5d metals generally have a larger value of Δo than for 3d metals. As a result, complexes are typically low spin. Tetrahedral complex: Consider a tetrahedral arrangement of ligands around the central metal ion. The best way to picture this arrangement is to have the ligands at opposite corners of a cube. As with octahedral complexes there is an electrostatic attraction between each of the ligands and the positive metal ion, and there is electrostatic repulsion between the ligands and electrons in the d orbitals. None of the d-orbitals point directly at the ligands as they did with the octahedral geometry. However some orbitals come closer to the ligands than others. We can now construct the d orbital splitting diagram for a tetrahedral complex. The d-orbital splitting diagram is the inverse of that for an octahedral complex. Note, here not t2g or eg it is only t2 or e as there is not centre of symmetry in tetrahedral complex. (g stands for gerade) The difference in the splitting energy is tetrahedral splitting constant (∆t), which less than (∆0) for the same ligands as number of ligands are less and the ligands not directly facing the orbitals. The relationship between them is : ∆t = 4/9Δ0 Consequentially, is typically smaller than the spin pairing energy, so tetrahedral complexes are usually high spin. Crystal Field Stabilization Energy (CFSE): The Crystal Field Stabilization Energy is defined as the energy of the electronic configuration in the ligand field minus the energy of the electronic configuration in the isotropic field (without ligand). CFSE =ΔE = Eligand field−Eisotropic field The CSFE will depend on multiple factors including: 1. Geometry (which 2. Number of d-electrons 5. Ligand character (via changes the d-orbital 3. Spin Pairing Energy Spectrochemical Series) splitting patterns) 4. Charge on metal ion/atom For an octahedral complex, an electron in the more stable subset t2g is treated as contributing -0.4 Δ0 whereas an electron in the higher energy subset eg contributes to a destabilization of +0.6 Δ0 . The final answer is then expressed as a multiple of the crystal field splitting parameter Δ0 . If any electrons are paired within a single orbital, then the term P is used to represent the spin pairing energy. Paring energy represents the energy required to pair up electrons within the same orbital. For a given metal ion P (pairing energy) is constant, but it does not vary with ligand and oxidation state of the metal ion).
Recommended publications
  • An Earlier Collection of These Notes in One PDF File

    An Earlier Collection of These Notes in One PDF File

    UNIVERSITY OF THE WEST INDIES MONA, JAMAICA Chemistry of the First Row Transition Metal Complexes C21J Inorganic Chemistry http://wwwchem.uwimona.edu.jm/courses/index.html Prof. R. J. Lancashire September 2005 Chemistry of the First Row Transition Metal Complexes. C21J Inorganic Chemistry 24 Lectures 2005/2006 1. Review of Crystal Field Theory. Crystal Field Stabilisation Energies: origin and effects on structures and thermodynamic properties. Introduction to Absorption Spectroscopy and Magnetism. The d1 case. Ligand Field Theory and evidence for the interaction of ligand orbitals with metal orbitals. 2. Spectroscopic properties of first row transition metal complexes. a) Electronic states of partly filled quantum levels. l, ml and s quantum numbers. Selection rules for electronic transitions. b) Splitting of the free ion energy levels in Octahedral and Tetrahedral complexes. Orgel and Tanabe-Sugano diagrams. c) Spectra of aquated metal ions. Factors affecting positions, intensities and shapes of absorption bands. 3. Magnetic Susceptibilities of first row transition metal complexes. a) Effect of orbital contributions arising from ground and excited states. b) Deviation from the spin-only approximation. c) Experimental determination of magnetic moments. Interpretation of data. 4. General properties (physical and chemical) of the 3d transition metals as a consequence of their electronic configuration. Periodic trends in stabilities of common oxidation states. Contrast between first-row elements and their heavier congeners. 5. A survey of the chemistry of some of the elements Ti....Cu, which will include the following topics: a) Occurrence, extraction, biological significance, reactions and uses b) Redox reactions, effects of pH on the simple aqua ions c) Simple oxides, halides and other simple binary compounds.
  • Organic Ligand Complexation Reactions On

    Organic Ligand Complexation Reactions On

    Organic ligand complexation reactions on aluminium-bearing mineral surfaces studied via in-situ Multiple Internal Reflection Infrared Spectroscopy, adsorption experiments, and surface complexation modelling A thesis submitted to the University of Manchester for the degree of Doctor of Philosophy in the Faculty of Engineering and Physical Sciences 2010 Charalambos Assos School of Earth, Atmospheric and Environmental Sciences Table of Contents LIST OF FIGURES ......................................................................................................4 LIST OF TABLES ........................................................................................................8 ABSTRACT.................................................................................................................10 DECLARATION.........................................................................................................11 COPYRIGHT STATEMENT....................................................................................12 CHAPTER 1 INTRODUCTION ...............................................................................13 AIMS AND OBJECTIVES .................................................................................................38 CHAPTER 2 THE USE OF IR SPECTROSCOPY IN THE STUDY OF ORGANIC LIGAND SURFACE COMPLEXATION............................................40 INTRODUCTION.............................................................................................................40 METHODOLOGY ...........................................................................................................44
  • Interplay Between Gating and Block of Ligand-Gated Ion Channels

    Interplay Between Gating and Block of Ligand-Gated Ion Channels

    brain sciences Review Interplay between Gating and Block of Ligand-Gated Ion Channels Matthew B. Phillips 1,2, Aparna Nigam 1 and Jon W. Johnson 1,2,* 1 Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; [email protected] (M.B.P.); [email protected] (A.N.) 2 Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA * Correspondence: [email protected]; Tel.: +1-(412)-624-4295 Received: 27 October 2020; Accepted: 26 November 2020; Published: 1 December 2020 Abstract: Drugs that inhibit ion channel function by binding in the channel and preventing current flow, known as channel blockers, can be used as powerful tools for analysis of channel properties. Channel blockers are used to probe both the sophisticated structure and basic biophysical properties of ion channels. Gating, the mechanism that controls the opening and closing of ion channels, can be profoundly influenced by channel blocking drugs. Channel block and gating are reciprocally connected; gating controls access of channel blockers to their binding sites, and channel-blocking drugs can have profound and diverse effects on the rates of gating transitions and on the stability of channel open and closed states. This review synthesizes knowledge of the inherent intertwining of block and gating of excitatory ligand-gated ion channels, with a focus on the utility of channel blockers as analytic probes of ionotropic glutamate receptor channel function. Keywords: ligand-gated ion channel; channel block; channel gating; nicotinic acetylcholine receptor; ionotropic glutamate receptor; AMPA receptor; kainate receptor; NMDA receptor 1. Introduction Neuronal information processing depends on the distribution and properties of the ion channels found in neuronal membranes.
  • Chapter 21 D-Metal Organometalloc Chemistry

    Chapter 21 D-Metal Organometalloc Chemistry

    Chapter 21 d-metal organometalloc chemistry Bonding Ligands Compounds Reactions Chapter 13 Organometallic Chemistry 13-1 Historical Background 13-2 Organic Ligands and Nomenclature 13-3 The 18-Electron Rule 13-4 Ligands in Organometallic Chemistry 13-5 Bonding Between Metal Atoms and Organic π Systems 13-6 Complexes Containing M-C, M=C, and M≡C Bonds 13-7 Spectral Analysis and Characterization of Organometallic Complexes “Inorganic Chemistry” Third Ed. Gary L. Miessler, Donald A. Tarr, 2004, Pearson Prentice Hall http://en.wikipedia.org/wiki/Expedia 13-1 Historical Background Sandwich compounds Cluster compounds 13-1 Historical Background Other examples of organometallic compounds 13-1 Historical Background Organometallic Compound Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Organometallic chemistry combines aspects of inorganic chemistry and organic chemistry. Organometallic compounds find practical use in stoichiometric and catalytically active compounds. Electron counting is key in understanding organometallic chemistry. The 18-electron rule is helpful in predicting the stabilities of organometallic compounds. Organometallic compounds which have 18 electrons (filled s, p, and d orbitals) are relatively stable. This suggests the compound is isolable, but it can result in the compound being inert. 13-1 Historical Background In attempt to synthesize fulvalene Produced an orange solid (ferrocene) Discovery of ferrocene began the era of modern organometallic chemistry. Staggered
  • Werner-Type Complexes of Uranium(III) and (IV) Judith Riedhammer, J

    Werner-Type Complexes of Uranium(III) and (IV) Judith Riedhammer, J

    pubs.acs.org/IC Article Werner-Type Complexes of Uranium(III) and (IV) Judith Riedhammer, J. Rolando Aguilar-Calderon,́ Matthias Miehlich, Dominik P. Halter, Dominik Munz, Frank W. Heinemann, Skye Fortier, Karsten Meyer,* and Daniel J. Mindiola* Cite This: Inorg. Chem. 2020, 59, 2443−2449 Read Online ACCESS Metrics & More Article Recommendations *sı Supporting Information ABSTRACT: Transmetalation of the β-diketiminate salt [M]- Me Ph + Me Ph− − [ nacnac ](M =NaorK; nacnac = {PhNC(CH3)}2CH ) with UI3(THF)4 resulted in the formation of the homoleptic, Me Ph octahedral complex [U( nacnac )3](1). Green colored 1 was fully characterized by a solid-state X-ray diffraction analysis and a combination of UV/vis/NIR, NMR, and EPR spectroscopic studies as well as solid-state SQUID magnetization studies and density functional theory calculations. Electrochemical studies of 1 revealed this species to possess two anodic waves for the U(III/IV) and U(IV/V) redox couples, with the former being chemically accessible. Using mild oxidants, such as [CoCp2][PF6]or [FeCp ][Al{OC(CF ) } ], yields the discrete salts [1][A] (A = − 2 3 −3 4 PF6 , Al{OC(CF3)3}4 ), whereas the anion exchange of [1][PF6] with NaBPh4 yields [1][BPh4]. Me Dipp μ 12 ■ INTRODUCTION UCl3(THF)] and [{( nacnac )UCl}2( 2-Cl)3]Cl. In Me Dipp− ’ some cases, disubstitution of nacnac generates the Alfred Werner s disapproval of the complex ion-chain theory Me Dipp η3 Me Dipp 13 proposed by Jørgensen and Blomstrand,1 via the introduction rearranged species [( nacnac )( - nacnac )UI], of coordination complexes and the concept of Nebenvalenz,1,2 where one ligand has changed hapticity, most likely due to fi steric constraints.
  • M.Sc. (Chemistry) M

    M.Sc. (Chemistry) M

    Regulations 2019 Curriculum and Syllabi (Amendments updated upto June 2020) M.Sc. (Chemistry) M. Sc. Chemistry Regulations 2019 REGULATIONS 2019 CURRICULUM AND SYLLABI (Amendments updated upto June 2020) M.Sc. CHEMISTRY B.S. Abdur Rahman Crescent Institute of Science and Technology 1 M. Sc. Chemistry Regulations 2019 B.S. Abdur Rahman Crescent Institute of Science and Technology 2 M. Sc. Chemistry Regulations 2019 VISION AND MISSION OF THE INSTITUTION VISION B.S.Abdur Rahman Crescent Institute of Science and Technology aspires to be a leader in Education, Training and Research in multidisciplinary areas of importance and to play a vital role in the Socio-Economic progress of the Country in a sustainable manner. MISSION To blossom into an internationally renowned Institute. To empower the youth through quality and value-based education. To promote professional leadership and entrepreneurship. To achieve excellence in all its endeavors to face global challenges. To provide excellent teaching and research ambience. To network with global Institutions of Excellence, Business, Industry and Research Organizations. To contribute to the knowledge base through Scientific enquiry, Applied Research and Innovation. B.S. Abdur Rahman Crescent Institute of Science and Technology 3 M. Sc. Chemistry Regulations 2019 B.S. Abdur Rahman Crescent Institute of Science and Technology 4 M. Sc. Chemistry Regulations 2019 DEPARTMENT OF CHEMISTRY VISION AND MISSION VISION To blossom as a department with excellence in the field of Chemical Sciences through academic and research programmes in cutting-edge areas. MISSION To provide knowledge and skill in Chemical Sciences through post graduate and doctoral programmes. To undertake research in emerging areas of Chemical Sciences and transform the findings for the benefit of the society.
  • Limitation of Crystal Field Theory the Main Drawback of the Crystal Field Theory Is That It Does Not Consider the Covalent Character in Metal-Ligand Bonding at All

    Limitation of Crystal Field Theory the Main Drawback of the Crystal Field Theory Is That It Does Not Consider the Covalent Character in Metal-Ligand Bonding at All

    CHAPTER 7 Metal-Ligand Bonding: Limitation of Crystal Field Theory The main drawback of the crystal field theory is that it does not consider the covalent character in metal-ligand bonding at all. It treats the metal-ligand interaction in a purely electrostatic framework which is pretty far from reality. All the effects which originate from covalence cannot be explained by this theory. Therefore, the main limitations of crystal field theory can be concluded only after knowing the causes and magnitude of the covalence in the metal-ligand bonds. Evidences for the Covalent Character in Metal–Ligand Bond The crystal field theory considers the metal center as well as surrounding ligands as point charges and assumes that the interaction between them is 100% ionic. However, quite strong experimental evidences have proved that there is some covalent character too which cannot be ignored. Some of those experimental evidences are as follows: 1. The nephelauxetic effect: The electrons present in the partially filled d-orbitals of the metal center repel each other to produce a number of energy levels. The placement of these levels on the energy scale depends upon the arrangement of filled electrons. The energy of these levels can be given in terms of “Racah parameters” B and C (a measure of interelectronic repulsion). The energy difference between same multiplicity states is expressed in B and Dq while between different multiplicity states is given in term of B, Dq and C. It has been observed that the complexation of metal center always results in a decrease in interelectronic repulsion parameters which in turn also advocates a decrease in the repulsion between d-electron density.
  • Searching Coordination Compounds

    Searching Coordination Compounds

    CAS ONLINEB Available on STN Internationalm The Scientific & Technical Information Network SEARCHING COORDINATION COMPOUNDS December 1986 Chemical Abstracts Service A Division of the American Chemical Society 2540 Olentangy River Road P.O. Box 3012 Columbus, OH 43210 Copyright O 1986 American Chemical Society Quoting or copying of material from this publication for educational purposes is encouraged. providing acknowledgment is made of the source of such material. SEARCHING COORDINATION COMPOUNDS prepared by Adrienne W. Kozlowski Professor of Chemistry Central Connecticut State University while on sabbatical leave as a Visiting Educator, Chemical Abstracts Service Table of Contents Topic PKEFACE ............................s.~........................ 1 CHAPTER 1: INTRODUCTION TO SEARCHING IN CAS ONLINE ............... 1 What is Substructure Searching? ............................... 1 The Basic Commands .............................................. 2 CHAPTEK 2: INTKOOUCTION TO COORDINATION COPPOUNDS ................ 5 Definitions and Terminology ..................................... 5 Ligand Characteristics.......................................... 6 Metal Characteristics .................................... ... 8 CHAPTEK 3: STKUCTUKING AND REGISTKATION POLICIES FOR COORDINATION COMPOUNDS .............................................11 Policies for Structuring Coordination Compounds ................. Ligands .................................................... Ligand Structures........................................... Metal-Ligand
  • Organometallic Chemistry BASIC PRINCIPLES, APPLICATIONS, and a FEW CASE STUDIES

    Organometallic Chemistry BASIC PRINCIPLES, APPLICATIONS, and a FEW CASE STUDIES

    Safety Moment TYLER LAB GROUP MEETING 1 Safety Moment TYLER LAB GROUP MEETING 2 Metal Hydrides: Benchtop vs. Box Hydride = :H- Hydrides are powerful Lewis bases and reducing agent ◦ Exothermically form H2 (this should scare you) ◦ Heating leads to faster reactivity ◦ H evolution leads to rapid increase in pressure2 ◦ Uncontrolled reactions easily cause runaway exotherm, class D fire, explosion, and death/unemployment LiAlH is the #1 chemical cause of fatality in chemical4 industry 3 Metal Hydrides: “I want to commit the murder I was imprisoned for†.” LiAlH4 ◦ Insanely irritating (serious safety hazard) ◦ Extremely moisture sensitive (don’t leave out for >2 minutes) ◦ Ethereal mixtures are pyrophoric! DiBuAl-H ◦ Pyrophoric – it will explode upon exposure to oxygen NaEt3BH ◦ Pyrophoric in solution LiH and NaH ◦ Can be handled on the benchtop (not >2 minutes) ◦ Parrafin oil dispersions much safer KH ◦ Pyrophoric if not in a dispersion ◦ Handle with extreme care! † Sirius Black, Harry Potter and the Prisoner of Azkaban 4 Metal Hydrides: “I want to commit the murder I was imprisoned for†.” CaH2 ◦ Very safe to handle on the benchtop Pt-H, Pd-H, Ni-H ◦ All very pyrophoric NaBH4 ◦ Very safe in general Other hydrides ◦ Treat as pyrophoric ◦ Transition metal hydrides vary in hydridic strength ◦ General rule of thumb: if it does hydrogenations, it is probably pyrophoric ◦ If they’re in organics of any kind, they are probably pyrophoric † Sirius Black, Harry Potter and the Prisoner of Azkaban 5 Organometallic Chemistry BASIC PRINCIPLES, APPLICATIONS,
  • Organometallics Study Meeting H.Mitsunuma 1

    Organometallics Study Meeting H.Mitsunuma 1

    04/21/2011 Organometallics Study Meeting H.Mitsunuma 1. Crystal field theory (CFT) and ligand field theory (LFT) CFT: interaction between positively charged metal cation and negative charge on the non-bonding electrons of the ligand LFT: molecular orbital theory (back donation...etc) Octahedral (figure 9-1a) d-electrons closer to the ligands will have a higher energy than those further away which results in the d-orbitals splitting in energy. ligand field splitting parameter ( 0): energy between eg orbital and t2g orbital 1) high oxidation state 2) 3d<4d<5d 3) spectrochemical series I-< Br-< S2-< SCN-< Cl-< N -,F-< (H N) CO, OH-< ox, O2-< H O< NCS- <C H N, NH < H NCH CH NH < bpy, phen< NO - - - - 3 2 2 2 5 5 3 2 2 2 2 2 < CH3 ,C6H5 < CN <CO cf) pairing energy: energy cost of placing an electron into an already singly occupied orbital Low spin: If 0 is large, then the lower energy orbitals(t2g) are completely filled before population of the higher orbitals(eg) High spin: If 0 is small enough then it is easier to put electrons into the higher energy orbitals than it is to put two into the same low-energy orbital, because of the repulsion resulting from matching two electrons in the same orbital 3 n ex) (t2g) (eg) (n= 1,2) Tetrahedral (figure 9-1b), Square planar (figure 9-1c) LFT (figure 9-3, 9-4) - - Cl , Br : lower 0 (figure 9-4 a) CO: higher 0 (figure 9-4 b) 2. Ligand metal complex hapticity formal chargeelectron donation metal complex hapticity formal chargeelectron donation MR alkyl 1 -1 2 6-arene 6 0 6 MH hydride 1 -1 2 M MX H 1 -1 2 halogen 1 -1 2 M M -hydride M OR alkoxide 1 -1 2 X 1 -1 4 M M -halogen O R acyl 1 -1 2 O 1 -1 4 M R M M -alkoxide O 1-alkenyl 1 -1 2 C -carbonyl 1 0 2 M M M R2 C -alkylidene 1 -2 4 1-allyl 1 -1 2 M M M O C 3-carbonyl 1 0 2 M R acetylide 1 -1 2 MMM R R C 3-alkylidine 1 -3 6 M carbene 1 0 2 MMM R R M carbene 1 -2 4 R M carbyne 1 -3 6 M CO carbonyl 1 0 2 M 2-alkene 2 0 2 M 2-alkyne 2 0 2 M 3-allyl 3 -1 4 M 4-diene 4 0 4 5 -cyclo 5 -1 6 M pentadienyl 1 3.
  • Complexation

    Complexation

    FACULTY OF PHARMACEUTICAL SCIENCES, RAMAUNIVERSITY, KANPUR B.PHARM 3rd SEM PHYSICAL PHARMACEUTICS-I BP302T MR. PEEYUSH Assistant professor Rama university, kanpur Complexation Overview Classification Introduction Metal ion complexes Organic Complexes Inclusion Complexes Methods of Analysis Method of Continuous Variation PH Titration Distribution Method Solubility Method Spectroscopy Learning Objectives 1. Define the three classes of complexes with pharmaceutically relevant examples. 2. Describe chelates, their physically properties, and what differentiates them from organic molecular complexes. 3. Describe the types of forces that hold together organic molecular complexes with examples. 4. Describe the forces in polymer–drug complexes used for drug delivery. 5. Discuss the pharmaceutical applications of cyclodextrins. 6. Describe the methods of analysis of complexes and determine their stoichiometric ratios and stability constants. Classification Introduction Metal ion complexes Organic Complexes Inclusion Complexes INTRODUCTION Complexes are compounds that result from donor–acceptor mechanisms between two or more chemical species. Complexes can be divided broadly into three classes depending the type of the acceptor substance: 1. Metal ion complexes 2. Organic molecular complexes 3. Inclusion complexes Intermolecular forces involved in the formation of complexes: 1. Van der Waals forces. 2. Hydrogen bonds (important in molecular complexes). 3. Coordinate covalence (important in metal complexes). 4. Charge transfer. 5. Hydrophobic interaction. Introduction Types of Complexes Metal Ion Complexes A. Inorganic type B. Chelates C. Olefin type D. Aromatic type II. Organic Molecular Complexes A. Quinhydrone type B. Picric acid type C. Caffeine and other drug complexes D. Polymer type III. Inclusion Compounds A. Channel lattice type B. Layer type C. Clathrates D. Monomolecular type E.
  • Physical Organic Chemistry

    Physical Organic Chemistry

    PHYSICAL ORGANIC CHEMISTRY Yu-Tai Tao (陶雨台） Tel: (02)27898580 E-mail: [email protected] Website:http://www.sinica.edu.tw/~ytt Textbook: “Perspective on Structure and Mechanism in Organic Chemistry” by F. A. Corroll, 1998, Brooks/Cole Publishing Company References: 1. “Modern Physical Organic Chemistry” by E. V. Anslyn and D. A. Dougherty, 2005, University Science Books. Grading: One midterm (45%) one final exam (45%) and 4 quizzes (10%) homeworks Chap.1 Review of Concepts in Organic Chemistry § Quantum number and atomic orbitals Atomic orbital wavefunctions are associated with four quantum numbers: principle q. n. (n=1,2,3), azimuthal q.n. (m= 0,1,2,3 or s,p,d,f,..magnetic q. n. (for p, -1, 0, 1; for d, -2, -1, 0, 1, 2. electron spin q. n. =1/2, -1/2. § Molecular dimensions Atomic radius ionic radius, ri：size of electron cloud around an ion. covalent radius, rc：half of the distance between two atoms of same element bond to each other. van der Waal radius, rvdw：the effective size of atomic cloud around a covalently bonded atoms. - Cl Cl2 CH3Cl Bond length measures the distance between nucleus (or the local centers of electron density). Bond angle measures the angle between lines connecting different nucleus. Molecular volume and surface area can be the sum of atomic volume (or group volume) and surface area. Principle of additivity (group increment) Physical basis of additivity law: the forces between atoms in the same molecule or different molecules are very “short range”. Theoretical determination of molecular size：depending on the boundary condition.