Chemistry -Theory (CYI 101) PDF

CHEMISTRY -THEORY (CYI 101) Inorganic Chemistry Instructor: Dr. R P John Department of Chemistry & Chemical Biology  Evaluation and Study Material Examination/Class tests/others  See Academic Calendar  Will be informed time to time Course Material Lecture...

CHEMISTRY -THEORY (CYI 101) Inorganic Chemistry Instructor: Dr. R P John Department of Chemistry & Chemical Biology  Evaluation and Study Material Examination/Class tests/others  See Academic Calendar  Will be informed time to time Course Material Lecture Plan: Refer to Lecture plan uploaded on MIS  What the instructor teaches!  Books: Principles of Inorganic chemistry by Puri Sharma and Kalia – Vishal Publications Inorganic chemistry: G L Meissler and D A Tarr – Pearson Education Inorganic Chemistry: Housecroft and Sharpe Shriver Atkin’s Inorganic Chemistry: Atkins, Overton, Rourke, Weller and Armstrong – Oxford University Press Color of transition metal complexes Naturally Occurring Coordination Compounds d-orbitals  Crystal Field Theory It is an electrostatic model for transition metal complexes. 1. Ligands are considered as point charges. 2. CFT does not consider any orbital overlap, or electrons from ligands are donated to vacant metal orbitals. 3. Predicts the pattern of splitting of d-orbitals. Used to explain spectroscopic and magnetic properties. Octahedral complex (Oh) Tetrahedral complex (Td) Square planer complex (Sp)  Octahedral Field Six point negative charges (Ligands) representing the ligands are placed in an octahedral array around the central metal ion. The ligand and orbitals lie on the same axes. These charges interact strongly with the central metal ion. The stability of the depends on this The electrons in different d orbitals interact attractive interaction between opposite with the ligands to different extents. charges. This differential interaction is little more than about 10 per cent of the overall metal-ligand interaction energy, it significantly affect the properties of the complex. Octahedral Field  Octahedral Field dyz dz2 dxz dx2-y2 dxy Splitting of d-orbital energies in an octahedral field of ligands. The d orbitals split into two groups. The difference in energy between these groups is called the crystal field splitting energy, symbol Δo.  Octahedral Field Barycentre The overall stabilization of the t2g orbitals equals the overall destabilization of the eg set. Thus, the two orbitals in the eg set are raised by 0.6 Δo with respect to the Barycentre while the three in the t2g set are lowered by 0.4 Δo. The magnitude of Δo is determined by the strength of the crystal field, the two extremes being called weak field and strong field. Δo (Weak field) < Δo (Strong field) Factors influencing the Magnitude of o for Octahedral complexes 1. The nature of metal cation: i) Oxidation state of the metal ion [Ru(H2O)6]3+ 28600 cm-1 [Ru(H2O)6]2+ 19800 cm-1 ii) Different charges on the cation of different metals [V(H2O)6]2+ 12400 cm-1 3d3 [Cr(H2O)6]3+ 17400 cm-1 3d3 iii) Quantum number (n) of the d- orbitals of the central metal ion. [Co(NH3)6]3+ 23000 cm-1 3d6 [Rh(NH3)6]3+ 34000 cm-1 4d6 [Ir(NH3)6]3+ 41000 cm-1 5d6 o increases about 30% to 50% from 3dn to 4dn, and by about same amount again from 4dn to 5dn. The increase down a group reflects the larger size of the 4d and 5d orbitals compared with the compact 3d orbitals and the consequent stronger interactions with the ligands.  Strong and weak ligands: Spectrochemical Series Weak Field I-  Br- S2- SCN- Cl- NO3- F-  C2O42- H2O NCS- CH3CN NH3 en  bipy phen NO2-  PPh3 CN- CO Strong Field Crystal Field Stabilization Energy In Octahedral field, configuration is: t2gx egy Net energy of the configuration relative to the average energy of the orbitals is: = (-0.4x + 0.6y)O O = 10 Dq d1 Crystal Field Stabilization Energy (CFSE) d2 Ti2+, V3+ d3 Cr3+, Mn4+,V2+ When the 4th electron is assigned it will either go into the higher energy eg orbital at an energy cost of o or be paired at an energy cost of P, the pairing energy. d4 Strong field = Weak field = Low spin High spin (2 unpaired) (4 unpaired) P < o P > o Crystal Field Stabilization Energy (CFSE) [Mn(H2O)6]3+ Weak Field Complex the total spin (S) is 4  ½ = 2 High Spin Complex Weak field d4 [Mn(CN)6]3- Strong field Complex total spin (S) is 2  ½ = 1 Low Spin Complex Strong field d4  Placing electrons in d orbitals d5 d6 d7 1 u.e. 5 u.e. 0 u.e. 4 u.e. 1 u.e. 3 u.e. d8 d9 d10 2 u.e. 2 u.e. 1 u.e. 1 u.e. 0 u.e. 0 u.e. What is the CFSE of [Fe(CN)6]3-? CN- = S.F.L. C.N. = 6  Oh Fe(III)  d5 H.S. L.S. CN 3- eg eg CN NC Fe + 0.6 oct NC CN - 0.4 oct CN t2g t2g CFSE = 5 x - 0.4 oct + 2P = - 2.0 oct + 2P If the CFSE of [Co(H2O)6]2+ is -0.8 o, what spin state is it in? C.N. = 6  Oh Co(II)  d7 H.S. L.S. 2+ eg eg OH2 + 0.6 oct H 2O OH2 Co - 0.4 oct H2O OH2 t2g t2g OH2 CFSE = (5 x - 0.4 oct) CFSE = (6 x - 0.4 oct) + (2 x 0.6 oct) = - 0.8 oct + (0.6 oct) + P= - 1.8 oct + P  Crystal Field Stabilization Energy (CFSE) Q1: Determine whether Co2+ forms High spin or low spin complexes with chloride ions if the Dq value for its octahedral complex is 480 cm-1 and pairing energy is 22, 500cm-1. Determine the Crystal Field Stabilisation Energy for the octahedral and Tetrahedral complexes in cm-1.