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Advanced Inorganic Chemistry ADVANCED INORGANIC CHEMISTRY Diagrams Orgel a Splitting of the Weak Field Dn Ground State Terms in an Octahedral Ligand Field DVANCED

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Advanced Inorganic Chemistry ADVANCED INORGANIC CHEMISTRY Diagrams Orgel a Splitting of the Weak Field Dn Ground State Terms in an Octahedral Ligand Field DVANCED Advanced Inorganic Chemistry ADVANCED INORGANIC CHEMISTRY Diagrams Orgel A Splitting of the weak field dn ground state terms in an octahedral ligand field DVANCED Correlation of spectroscopic terms for dn configuration in O complexes I h NORGANIC om c um er Terms in O At i N b h Term of states Symmetry S 1 A1g P 3 T 1g D 5 T2g + Eg C HEMISTRY F 7 T1g + T2g + A2g Ground state determined by inspection of degeneracy of terms for given dn ADVANCED INORGANIC CHEMISTRY A Orgel Diagrams DVANCED 3 T1g(P) 4 T1g(P) I 3P 3A 4P NORGANIC 2 2g 5 Eg 4 T2g T1g 3 T2g 2 3 4 4 5 D F F T2g D C 2 3 5 HEMISTRY T2g T1g Eg 1 3 ∆o 4 ∆o 2 ∆ d 4 d ∆ d d o A2g o 2 2 T2g E 3 3 g T1g T2g 3 3 T1g A2g 3 3 T1g T1g(P) Ti3+ V2+ Cr3+ Mn3+ A DVANCED The d-d bands of the d2 ion [V(H O) ]3+ 2 6 I NORGANIC C HEMISTRY The Tanabe-Sugano diagram ADVANCED INORGANIC CHEMISTRY A DVANCED Correlation diagrams between energies of atomic and molecular terms can drawn as so-called I NORGANIC Tanabe-Sugano diagrams for each electron configuration of free ions. C HEMISTRY Y. Tanabe, s. Sugano; J. Phys. Soc, Jap., 9, 753 (1954) Energy values in a Tanabe-Sugano diagram are only given relative to the ground state (x-axis). A DVANCED The simple correlation diagram had multiples of B (the Racah parameter) on the energy axis to denote the relative energies of the atomic terms. In the I Tanabe-Sugano diagrams, the energy axis has units of E/B. The x-axis has NORGANIC units of ”o/B. Each Tanabe-Sugano diagram is given for only one specific B/C ratio (the best value). For example, the Tanabe-Sugano diagram for d3 C complexes is given for C=4.5 B. HEMISTRY non-crossing rule: Terms of the same symmetry cannot cross and will ‘repel’ each other. A DVANCED Racah Inter-electronic Repulsion Parameters (B, C) 1 S I NORGANIC 1G 3P E(3P) = A+7B C HEMISTRY 1D E(1D) = A - 3B + 2C 3F E(3F) = A - 8B d2 3 F 3P = 15B 3F 1D = 5B + 2C Evidence for covalent bonding in metal-ligand interactions A DVANCED The Nephelauxetic Effect (“cloud expansion”) Reduction in electron-electron repulsion upon complex formation I NORGANIC Racah Parameter, B: electron-elctronic repulsion parameter B is the inter- electronic repulsion in the gaseous Mn+ ion. o C n+ HEMISTRY B is the inter- electronic repulsion in the complexed MLx ion. The smaller values for B in the complex compared to free gaseous ion is taken as evidence of smaller inter-electronic repulsion in the complex due to a larger “molecular orbital” on account of overlap of ligand and metal orbital, i.e. evidence of covalency (cloud expansion”). Nephelauxetic Ratio, β = B Bo N A EPHELAUXETIC DVANCED I Nephelauxetic Ligand Series NORGANIC E 2- FFECT I < Br < CN < Cl < NCS < C2O4 < en < NH3 < H2O < F Small β Large β Covalent Ionic C HEMISTRY Nephelauxetic Metal Series Pt4+ < Co3+ < Rh3+~Ir3+ < Fe3+ < Cr3+ < Ni2+ < V4+< Pt2+~ Mn2+ Small β Large β Large overlap Small overlap Covalent Ionic A DVANCED Empirical Racah parameters, h, k β = 1– [h(ligand) x k(metal)] I NORGANIC 3+ Cr(NH3)6 β = 1 –hk β = 1 –(1.4)(0.21) = 0.706 C HEMISTRY 3- Cr(CN)6 β = 1 –hk β = 1 –(2.0)(0.21) = 0.580 Bo - B = hligands x kmetal ion Bo A DVANCED I NORGANIC Typical ” o and »max values for octahedral (ML6) d-block metal complexes __________________________________________________________________ -1 -1 Complex ” o cm ~ »max (nm) Complex ” o cm »max (nm) ___________________________________________________________________________________ [Ti(H O) ]3+ 20,300 493 [Fe(H O) ]2+ 9,400 1064 2 6 2 6 C 3+ 3+ [V(H2O)6] 20,300 493 [Fe(H2O)6] 13,700 730 HEMISTRY 2+ 3- [V(H2O)6] 12,400 806 [Fe(CN)6] 35,000 286 3- 4- [CrF6] 15,000 667 [Fe(CN)6] 33,800 296 3+ 3- [Co(H2O)6] , l.s. 20,700 483 [Fe(C2O4)3] 14,100 709 2+ 3- [Cr(H2O)6] 14,100 709 [Co(CN)6] l.s. 34,800 287 3+ 3+ [Cr(H2O)6] 17,400 575 [Co(NH3)6] l.s. 22,900 437 3+ 2+ [Cr(NH3)6] 21,600 463 [Ni(H2O)6] 8,500 1176 3+ 2+ [Cr(en)3] 21,900 457 [Ni(NH3)6] 10,800 926 3- 2+ [Cr(CN)6] 26,600 376 [Ni(en)3] 11,500 870 ___________________________________________________________________________________ Example of the use of Tanabe-Sugano Diagrams For the use of Tanabe-Sugano diagrams we will be using Tables 17.1 and 17.2 (see the resources for Test 3). 10 Dqo = f x g. Let us consider the complex 2+ Co(NH3)6 . The oxidation state of the cobalt is +2, so the the metal isconsidered 7 a d . To figure out 10 Dqo (also known as delta octahedral), from Table 17.1 we multiply f from the ligand column by g from the metal ion column. This gives -1 1.25 x 9000 = 11,250 cm which is the size of 10 Dqo. The next step is to determine the reduced Racah parameter for the complex. The reduced Racah parameter is called beta. beta=(Bcomplex)/(B free ion) = 1 - h k The quantities h and k can also be found in Table 17.1 for many ligands and metal centers. For the current example . beta=(Bcomplex)/(B free ion) = 1 - h k = 1 - (1.4)(0.09) = 0.874 From this it easy to rearrange things to get Bcomplex and use the value of Bfree ion for Co2+ from Table 17.2 -1 -1 (beta)(Bfree ion) = Bcomplex = (0.874)(971 cm ) = 849 cm To use a Tanabe-Sugano diagram, you mustdivide the value of 10 Dqo by Bcomplex. -1 -1> (10 Dqo)/Bcomplex = 11,250 cm /849 cm = 13.25 This is the value that will be read on the x-axis of the Tanabe-Sugano diagram. Using the correct Tanabe-Sugano diagram (d7 in this case) is critical. Looking at the Tanabe- Sugano diagram quickly reveals that the term symbol for a free Co2+ ion is 4F. Also looking at the Tanabe Sugano diagram, we notice that the value of 13.25 is to the left of the point of inflection. This means that the 2+ complex Co(NH3)6 is a high spin complex (if the value was to the left of the inflection point, it would be a low spin complex). Spin allowed ttransitions from the ground state will therefore all be from quadruplet to quadruplet. The allowed transitions are: 4 4 4 4 4 4 T1g -----> T2g T1g -----> T1g T1g -----> A2g Reading straight up from 13.25 on the x-axis until it crosses the line corresponding to the other quadruplet states will give us E/Bcomplex on the y- axis. 4 4 T1g -----> T2g E/Bcomplex =12.4 4 4 T1g -----> T1g E/Bcomplex = 25.6 4 4 T1g -----> A2g E/Bcomplex = 25.6 To get the energy of the transitions in cm-1, each of these must be multiplied by Bcomplex 4 4 -1 -1 T1g -----> T2g E/Bcomplex =12.4 ; 12.4 x 849 cm = 10,528 cm 4 4 -1 -1 T1g -----> T1g E/Bcomplex = 25.6; 25.6 x 849 cm = 21,734 cm 4 4 -1 -1 T1g -----> A2g E/Bcomplex = 25.6, 25.6 x 849 cm = 21,734 cm The last step is to convert the wave number (reciprocal centimeters, cm-1) to namometers 4 4 -1 -1 -5 -5 T1g -----> T2g 10,528 cm ; 1/(10,528 cm ) = 9.50 x 10 cm; (9.50 x 10 cm)(107 nm/cm) = 950 nm 4 4 -1 -1 -5 -5 T1g -----> T1g 21,734 cm ; 1/(21,734 cm ) = 4.60 x 10 cm; (4.60 x 10 cm)(107 nm/cm) = 460 nm 4 4 -1 -1 -5 -5 T1g -----> A2g 21,734 cm ; 1/(21,734 cm ) = 4.60 x 10 cm; (4.60 x 10 cm)(107 nm/cm) = 460 nm All of these transitions are d-d transitions. The first transition at 950 nm is in the near IR just above the red portion of the visible spectrum. The two transitions at 460 nm correspond to an absorbance of blue (very slightly shaded to green) light in the visible spectrum. A Use of Tanabe-Sugano Diagrams for Interpretation DVANCED of UV/Visible Absorption Spectra of Complexes I NORGANIC C d3 HEMISTRY ADVANCED INORGANIC CHEMISTRY ADVANCED INORGANIC CHEMISTRY ADVANCED INORGANIC CHEMISTRY ADVANCED INORGANIC CHEMISTRY ADVANCED INORGANIC CHEMISTRY 5 . 26 ADVANCED INORGANIC CHEMISTRY 5 . 26 ADVANCED INORGANIC CHEMISTRY Transfer Spectra Transfer - Charge Charge Transfer Transitions A DVANCED • As well as ‘d-d’ transitions, the electronic spectra of transition metal I complexes may 3 others types of electronic transition: NORGANIC Ligand to metal charge transfer (LMCT) Metal to ligand charge transfer (MLCT) C Intervalence transitions (IVT) HEMISTRY • All complexes show LMCT transitions, some show MLCT, a few show IVT Ligand to Metal Charge Transfer A DVANCED • These involve excitation of an electron from a ligand-based orbital into a d- orbital I NORGANIC O O visible light M O M O C O O HEMISTRY O O • This is always possible but LMCT transitions are usually in the ultraviolet • They occur in the visible or near-ultraviolet if metal is easily reduced (for example metal in high oxidation state) ligand is easily oxidized If they occur in the visible or near-ultraviolet, they are much more intense than ‘d-d’ bands and the latter will not be seen Ligand to Metal Charge Transfer A DVANCED •They occur in the visible or near-ultraviolet if I NORGANIC metal is easily reduced (for example metal in high oxidation state) C 3- 2- - HEMISTRY TiO2 VO4 CrO4 MnO4 Ti4+ V5+ Cr6+ Mn7+ d0 in far UV ~39500 cm-1 ~22200 cm-1 ~19000 cm-1 white white yellow purple more easily reduced Metal to Ligand Charge Transfer A DVANCED • They occur in the visible or near-ultraviolet if I NORGANIC metal is easily oxidized and ligand has low lying empty orbitals C N HEMISTRY N N N M N N N N N N M = Fe2+, Ru2+, Os2+ 2+ 6 • Sunlight excites electron from M (t2g) into empty ligand π* orbital method of capturing and storing solar energy Intervalence Transitions A DVANCED • Complexes containing metals in two oxidation states can be coloured due to excitation of an electron from one metal to another I NORGANIC C HEMISTRY “Prussian blue” contains Fe2+ and Fe3+ • Colour arises from excitation of an electron from Fe2+ to Fe3+ 3) Charge transfer bands A DVANCED • Similar to d-d transitions, charge-transfer (CT) transitions also involve the metal d-orbitals.
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